chapter 15 Group Technology and Cellular Manufacturing CHAPTER CONTENTS 15.1 Part Families 15.2 Parts Classification and Coding 15.2.1 Features of Parts Classification and Coding Systems 15.2.2 Examples of Parts Classification and Coding Systems 15.3 Production Flow Analysis 15.4 Cellular Manufacturing 15.4.1 Composite Part Concept 15.4.2 Machine Cell Design 15.5 Application Considerations in Group Technology 15.5.1 Applications of Group Technology 15.5.2 Survey of Industry Practice 15.6 Quantitative Analysis in Cellular Manufacturing 15.6.1 Grouping Parts and Machines by Rank Order Clustering 15.6.2 Arranging Machines in a GT Cell Batch manufacturing is estimated to be the most common form of production in the Unit- ed States, constituting more than 50% of total manufacturing activity. There is a growing need to make hatch manufacturing more efficient and productive. In addition, there is an increasing trend toward achieving a higher level of integration between the design and manufacturing functions in a firm. An approach directed at both of these objectives is group technology (GT). Group technology is a manufacturing philosophy in which similar parts are identified and grouped together to take advantage of their similarities in design and production. Sim- chapter 15 Group Technology and Cellular Manufacturing CHAPTER CONTENTS 15.1 Pe rt Families 15.2 Parts Classification and Coding 15.2.1 Features of Parts Classification and Coding Systems 15.2.2 Examples of Parts Classification and Coding Systems 15.3 Production Flow Analysis 15.4 Cellular Manufacturing 15.4.1 Composite Part Concept 15.4.2 Machine Cell Design 15.5 Application Considerations in Group Technology 15.5,1 Applications of Group Technology 15.5.2 Survey of Industry Practice 15.6 Quantitative Analysis in Cellular Manufacturing 15.6.1 Grouping Parts and Machines by Rank Order Clustering 15.6.2 Arranging Machines in a GT Ceil Batch manufacturing is estimated to be the most common form of production in the Unit- lanufacturing it and produi :1 of integral mfacturing functions in a firm. An approach directed at both of these objectives is tunng is ed States, constituting more than 50% of total manufacturing activity. There is a ition, thei increasing trend toward achieving a higher level of integration between the design and need (o make batch manufacturing more efficient and productive. In additii is a growing i, there is an group technology (GT). Group technology is a manufacturing philosophy in which similar parts are identi fied and grouped together to take advantage of their similarities in design and productionSim-
Transcript
chapter 15
Group Technologyand Cellular Manufacturing
CHAPTER CONTENTS
15.1 Part Families15.2 Parts Classification and Coding
15.2.1 Features of Parts Classification and Coding Systems15.2.2 Examples of Parts Classification and Coding Systems
15.3 Production Flow Analysis15.4 Cellular Manufacturing
15.4.1 Composite Part Concept15.4.2 Machine Cell Design
15.5 Application Considerations in Group Technology15.5.1 Applications of Group Technology15.5.2 Survey of Industry Practice
15.6 Quantitative Analysis in Cellular Manufacturing15.6.1 Grouping Parts and Machines by Rank Order Clustering
15.6.2 Arranging Machines in a GT Cell
Batch manufacturing is estimated to be the most common form of production in the Unit-ed States, constituting more than 50% of total manufacturing activity. There is a growingneed to make hatch manufacturing more efficient and productive. In addition, there is anincreasing trend toward achieving a higher level of integration between the design andmanufacturing functions in a firm. An approach directed at both of these objectives isgroup technology (GT).
Group technology is a manufacturing philosophy in which similar parts are identifiedand grouped together to take advantage of their similarities in design and production. Sim-
chapter 15
Group Technology
and Cellular Manufacturing
CHAPTER CONTENTS
15.1 Pert Families
15.2 Parts Classification and Coding15.2.1 Features of Parts Classification and Coding Systems15.2.2 Examples of Parts Classification and Coding Systems
15.3 Production Flow Analysis15.4 Cellular Manufacturing
15.4.1 Composite Part Concept15.4.2 Machine Cell Design
15.5 Application Considerations in Group Technology15.5,1 Applications of Group Technology15.5.2 Survey of Industry Practice
15.6 Quantitative Analysis in Cellular Manufacturing15.6.1 Grouping Parts and Machines by Rank Order Clustering15.6.2 Arranging Machines in a GT Ceil
Batch manufacturing is estimated to be the most common form of production in the Unit-lanufacturingit and produi:1 of integral
mfacturing functions in a firm. An approach directed at both of these objectives is
tunng is
ed States, constituting more than 50% of total manufacturing activity. There is aition, thei
increasing trend toward achieving a higher level of integration between the design andneed (o make batch manufacturing more efficient and productive. In additii
is a growingi, there is an
group technology (GT).Group technology is a manufacturing philosophy in which similar parts are identified
and grouped together to take advantage of their similarities in design and production. Sim-
Introduction 42'
ilar parts are arranged into part/amities. where each part family possesses similar designand/or manufacturing characteristics. for example, a plant producing 10,000 different partnumbers may be able 10 group the vast majority of these parts into 30-40 distinct familiesIt is reasonable to believe that the processing of each member of a given family is similar.and this should result in manufacturing efficiencies. The efficiencies are generally achievedhy arranging the production equipment into machine groups, or cells, to facilitate workflow. Grouping the production equipment into machine cells, where each cell specializes inthe production of a part family. is called cellular manufacturing. Cellular manufacturingis an example of mixed model production (Section 13.2.4). The origins of group technolo-gy and cellular production can be traced to around 1925 (Historical Note 15.!)
Historical Note 15.1 Grouptechnology
In 1925.R
Lamson Company that would today group technology. In 1937. A.Sokclovskiy of the Soviet Union described the essential features of group technology by propos-iJlglhalparl,()f,imilarc()nfiglirali<Jnb"pr",Jl1c~dbyastao.dardprocess sequence, thus per-milling flow line techniques to be used for work normally accomplished by batch production.In 1949.A. Koding of Sweden presented a paper (in Paris. France) on "group production."whose principles are an adaptation of production line techniques to batch manufacturingInthe paper. he describes how work is decentralized into independent grcups, each of which con-tainst~_emaehillcsandlO{}ling\Qproduce"aspecialcategoryofparts."
lnl959,researcherS.MilrofanuvoftheSovietUnionpublishedabook entitled Scten-tiftc Principles of Group Ttchnology. Thc book was widely read and is considered rcspcnsi-b1eforoverROOplantsinthcSovietUnionusillggrouptechnologybyJ965.Anotherresearchcr,H. Opitz in Gcrrnanv studied work parts manufactured by the German machine tool industryand developed the well-known parts classification and coding system for machined parts thatbears his name (Section 15.2.2).
In the United States, the first appucatton of group technology was at the Langston Drvision of Harris-Intertype in New Jersey around 1969.Traditionally a machine shop arrangedas a process type layout, the company reorganized into "family of parts" lines, each of whichspecialized III producing a given part configuration. Part families were identified by taking pho-tos of about 151;;: of the parts made in the plant and grouping them into families. When implc-merueu.me cnanges improved producnvtty by 50%and reduced lead times from ••••eeks to days
Group technology and cellular manufacturing are applicable in a wide variety ofmanufacturing situations. GT is most appropriately applied under the following conditions:
• The plant currently uses traditional batch production and a process type layout(Section 1.1.2), and this results in much material handling effort, high in-process in-ventory, lind long manufacturing lead times .
• The parts can be grouped Into part families. This is a necessary condition, Each ma-chine cell is designed to produce a given part family, or limited collection of part fam-ilies, so it must be possible to group parts made in the plant into families. However,it would be unusual to find a mid-volume production plant in which parts could nothe grouperl into part families
There are two major tasks that a company must undertake when it implements grouptechnology. These two tasks represent significant obstacles to the application of GT.
421
ilar parls are arranged into pari families, where each part family possesses similar designand'or manufacturing characteristics, t-
'
or example, a plant producing 10,000 different partnumbers may he able to group the vast majority of these parts into 30-40 distinct families.
lable to believe that the processing of each member of a given family is similar.the processing ot each member ot a given tamny isand this should result in manufacturing efficiencies.The efficiencies are generally achievedby arranging the production equipment into machine groups, or cells, to facilitate workHow. Grouping the production equipment into machine cells, where each cell specializes inthe production of a part family, is called cellular manufacturing. Cellular manufacturingis an example of mixed model production (Section 13.2.4). The origins of group technolo-gy and cellular production can be traced to around 1925 (Historical Note 15.1).
Historical Note 15.1 Group technology
In ll)25. R Flanders presented a paper in the United States before the American Society of Me-chanical Engineers in which he desenbed a way of organizing manufacturing at Jones andLamson Machine Company that would today be called group technology. In 1937, A.Sokolovskiy of the Soviet Union described the essential features of group technology by propos-ing lhaL parls of similar eon fig Lira I kin tie pruduced by a standard process sequence, thus per-mitting flow line techniques to be used for work normally accomplished by batch production.In 1949. A Korling of Sweden presented a paper (in Paris. France) on "group production."
whose principles are an adaptation of production line techniques to batch manufacturing. Inthe paper, he describes how work is decentralized into independent groups,
each of which con-
tains the machines and tooling to produce "a special category of parts."In 1959, researcher S. Milrofanuv of the Soviet Union published a book entitled Scten-
tiflc Principles of Group Technology. The book was widclv read and is considered rcsponsi-| ble for nver 800 plants in the Soviet Union using group technology by 1%5. Another researcher,j H. Opitz in Germany studied workparts manufactured by the German machine tool industry
and developed the well-known parts classification and coding system for machined parts thatbears his name (Section 15.2.2).
In (he United States, the first application of group technology was at the Langston Di-vision of Harris-lntertype in New Jersey around 1969. Traditionally a machine shop arraas a process type layout, the company reorganized into "family of parts" lines, each of \specialized in producing a given part configuration. Part families were identified by taking pho-tos of about 157r of the parts made in the plant and grouping them into families. When imple-mented, (he changes improved productivity by 50% and reduced lead times from weeks to days.
Group technology and cellular manufacturing are applicable in a wide variety ofmanufacturing situations. GT is most appropriately applied under the following conditions:
. The plant currently uses traditional batch production and a process type layout(Section 1.1.2), and this results in much material handling effort, high in-process in-ventory, and long manufacturing lead times.
. The parts can be grouped Into pan families.This is a necessary condition. Each ma-chine cell is designed to produce a given part family, or limited collection of part fam-ilies, so it must be possible to group parts made in the plant into families. However,
it would be unusual to find a mid-volume production plant in which parts could notbe grouped into part families.
There are two major tasks that a company must undertake when it implements grouptechnology. These two tasks represent significant obstacles to the application of GT.
422 Chap. 15 I Group Technology and Cellular Manufacturing
1 Identifying the part families. If the plant makes 10,000 different parts, reviewing allof the part drawings and grouping the parts into families is a substantial task thatconsumes a significant amount of time.
2. Rearranging production machines into machine cells. It is time consuming and cost-ly 10 plan and accomplish this rearrangement, and the machines are not producingduring the changeover
Group technology offers substantial benefits to companies that have the perseveranceto implement it. The benefits include:
• GT promotes standardization of tooling, fixturing. and setups.• Material handling is reduced because parts are moved within a machine cell rather
than within the entire factory.• Process planning and production scheduling are simplified• Setup times are reduced, resulting in lower manufacturing lead times.• Work-in-process is reduced.• Worker satisfaction usually improves when workers collaborate in a OT cell.• Higher quality work is accomplished using group technology.
In this chapter, we discuss group technology, cellular manufacturing, and several relatedtopics. Let us begin by defining an underlying concept of group technology: part families.
15.1 PART FAMILIES
Apart family is a collection of parts that are similar either because of geometric shape andsize or because similar processing steps are required in their manufacture. The parts with-in a family are different, but their similarities are close enough to merit their i.nclusion asmembers of the part family. Figures 15.1 and 15.2 show two different part families. The twoparts in Figure 15.1 are very similar in terms of geometric design, but quite different interms of manufacturing because of differences in tolerances, production quantities, andmaterial. The ten parts shown in Figure 15.2 constitute fl. part f<lmily in manufacturing, buttheir different geometries make them appear quite different from a design viewpoint.
One of the important manufacturing advantages of grouping workparts into fami-lies can be explained with reference to Figures 15.3 and 15.4. Figure 15.3 shows a process
Figure 15.1 Two parts of identical shape and size but different man-ufacturing requirements: (a) 1.000,OOOpc/yr, tolerance = ±O.OlOin,material = 1015 CR steel, nickel plate; and (b) 100 pc/yr, toler-ance = ±D.DO! in, material = 18 - 8 stainless steel.
422 Chap. 15 / Group Technology and Cellular Manufacturing
I. Identifying the part families, if the plant makes 10,000 different parts, reviewing all
of the part drawings and grouping the parts into families is a substantial task thatconsumes a significant amount of time.
2. Rearranging production machines into machine cells. It is time consuming and cost-
ly lo plan and accomplish this rearrangement, and the machines are not producingduring the changeover.
Group technology offers substantial benefits to companies that have the perseveranceto implement it.The benefits include:
. GT promotes standardization of tooling, fixiuring, and setups.
. Material handling is reduced because parts are moved within a machine cell ratherthan within the entire factory.
. Process planning and production scheduling are simplified.
. Setup times are reduced, resulting in lower manufacturing lead times.
. Work-in-process is reduced.
. Worker satisfaction usually improves when workers collaborate in a GT cell.
. Higher quality work is accomplished using group technology.
In this chapter, we discuss group technology, cellular manufacturing, and several relatedtopics. Let us begin by defining an underlying concept of group technology: part families.
15.1 PARTFAMILIBS
A part family is a collection of parts that are similar either because of geometric shape andsize or because similar processing steps are required in their manufacture.The parts with-in a family are different, but their similarities are close enough to merit their inclusion asmembers of the part family. Figures 15.1 and 15.2 show two different part families. The twoparts in Figure 15.1 are very similar in terms of geometric design, but quite different interms of manufacturing because of differences in tolerances, production quantities, andmaterial. The ten parts shown in Figure 15.2 constiiute a part family in mamifacturing,
but
their different geometries make them appear quite different from a design viewpoint.One of the important manufacturing advantages of grouping workparts into fami-
lies can be explained with reference to Figures 15.3 and 15.4. Figure 15.3 shows a process
Figure 15.1 Two parts of identical shape and size but different man-ufactuiing requirements: (a) 1.000,000 pc/yr, tolerance = ±0.010 in,material = 1015 CR steel
, nickel plate; and (b) 100 pc/yr, toler-ance = ±0.001 in
, materia] =18-8 stainless steel.
Sec. 15.1 I Part Families 423
Figure 15.2 A family of parts with similar manufacturing processrequirements but different design attributes. All parts are machinedfrom cylindrical stock by turning; some parts require drilling and/ornulling.
Figure 15.3 Process type plant layout. (Key: "Thm" = turning,"Mill" = milling,"Drll" = drilling,"Gmd" = grinding,"Asby" = as-sembly, "Man" == manual operation; arrows indicate work flowthrough plant, dashed lines indicate separation of machines intodepartrnerrts.}
Shipping andrece,vl1lg
Sec. 15-1 / Part Families 423
c
Figure 15.2 A family of parts with similar manufacturing processrequirements but different design altributes. All parts are machinedfrom cylindrical stock by turning; some parts require drilling and/ormilling.
Turn
Man
Turn Mill
Man
Mill Mill Urll Urll
Man
Turn
Man
Mill Mill Mill Drll Drll
Man
Turn rum
Man
Mill
Gmd Gmd
2 Mai
GmdMan
Figure 15.3 Process type plant layout. (Key: '"Rim" = turning,
rll" = drilling," Gmc" = manual open
through plant, dashed lines indicate separation of machines intodepartments.)
"
Mill" = milling,"Drll" = drilling,
" Gmd" - grinding, "Asby" = asembly,
"Man" = manual operation; arrows indicate work flow
424 Chap. 15 I Group Technology and Cellular ManufacturIng
Figure 15.4 Group technology layout. (Key: "Turn" = turning,"Mill" = milling,"Drll" = drillingrGmd" = grindmg.-Asby'' = as--sembly, "Man" = manual operation; arrows indicate work flow in rna-chine cella}
type plant layout for batch production in a machine shop. The various machine tools arearranged by function. There is a lathe department, milling machine department, drillpress department, and so all. To machine a given part, the workpiece must be transport-ed between departments, with perhaps the same department being visited several times.This results in a significant amount of material handling, large in-process inventory, manymachine setups, long manufacturing lead times, and high cost. Figure 15.4 shows a pro-duction shop of equivalent capacity, but the machines are arranged into cells. Each cellis organizt;:d to specialize in thc production of a particular part family. Advantages of reoduced workpiece handling yield lower setup times, fewer setups (in some cases, no setupchanges are necessary), less in-process inventory, and shorter lead times.
The biggest single obstacle in changing over to group technology from a conven-tional production shop is the problem of grouping the parts into families. There are threegeneral methods for solving this problem. All three are time consuming and involve theanalysis of much data by properly trained personnel. The three methods are; (1) visual in-spection, (2) parts classification and COding, and (3) production flow analysis. Let us pro-vide a brief description of the visual inspection method and then examine the second andthird methods in more detail.
The visual inspection method is the least sophisticated and least expensive method.It involves the classification of parts into families by looking at either the physical parts ortheir photographs and arranging them into groups having similar features. Although thismethod is generally considered to be the least accurate of the three. one of the first major-success stories of GT in the United States made the changeover using the visual inspection
Chap. 15 / Group Technology and Cellular Manufacturing
« Man
Mill
Man
Drll
Mar
r,
"
'"'*J Mill
Dtll
Man *1 ManGrad
Man
3nid
Man
Mill Urll
Man
Figure 15.4 Group technology layout. (Key: "Turn" = turning,"Mill" = milling, "Drll" = drilling, "Gmd" = grinding "Asby" = as-sembly,"Man" = manual operation; arrows indicate work flow in ma-chine cells.)
type plant layout for batch production in a machine Sihop. The various machine tools arearranged by function. There is a lalhe department, milling machine department, drillpress department, and so on. To machine a given part, the workpiece must be transport-ed between departments, with perhaps the same department being visited several times.This results in a significant amount of material handling, large in-process inventory, manymachine setups, long manufacturing lead times, and high cost. Figure 15.4 shows a pduction shop of equivalent cafis organised to specialize in thiduced workpiece handling yield lower setup limes, fewer setups (in some cases, no setup
ups, long manutactunng lead times, and high cost. Figure 15.4 shows a pro-duction shop of equivalent capacity, but the machines are arranged into cells. Each cell
organised to specialize in the production of a particular part family.iced workpiece handling yield lo\
Hze in the production of a particular part family. Advantages of re-
changes are necessary), less in-process tnvenlory, and shorter lead times.The biggest single obstacle in changing over to group technology from a conven-
tional production shop is the problem of grouping the parts into families. There are threegeneral methods for solving this problem. All three are time consuming and involve theanalysis of much data by properly trained personnel. The three methods are: (1) visual in-spection, (2) parts classification and coding, and (3) production flow analysis. Let us pro-vide a brief description of the visual inspection method and then examine the second andthird methods in more detail.
The visual inspection method is the least sophisticated and least expensive method.>sificat
s generally considered to be the least accurate of the three, one of the first major:ories of GT in the United States made the changeover using the visual inspeciion
It involves the classification of parts into families by looking at either the physical parts ortheir photographs and arranging them into groups having similar features. Although thismethod is generally considered to be the least accurate of the three
, one of the first major
iy looking at (s having simil'ing similar features. Although this
Sec. 15.2 / Parts Classification and Coding 425
method. This was the Langston Division of Harris Intertype in Cherry Hill, New Jersey[18] [HistoricalNote rs.u
15.2 PARTS CLASSIFICATION AND CODING
lhis is the most time consuming of the three methods. In parts classification and coding,similarities among parts are identified, and these similarities are related in a coding system.Two categories of part similarities can be distinguished: (1) design attributes, which arcconcerned with part characteristics such as geometry, size, and material; and (2) manufae--turing attributes, which consider the sequence of processing steps required to make a part.While the design and manufacturing attributes of a part are usually correlated, the corre-tauon is less than perfect. Accordingly, classification and coding systems are devised to in-clude both a part's design attributes and its manufacturing attributes. Reasons for using acoding scheme include:
• Design retrieval. A designer faced with the task of developing a new part can usea design retrieval system to determine if a similar part already exists. A simplechange in an existing part would take much less time than designing a whole newpart from scratch.
• Automated process planning. The part code for a new part can be used to search forprocess plans for existing parts with identical or similar codes
• Machine cell design. The part codes can be used to design machine cells capable ofproducing all members of a particular part family, using the composite part concept(Section 15.4.1).
To accomplish parts classification and coding requires examination and analysis of thedesign and/or manufacturing attributes of each part. The examination is sometimes doneby looking in tables to match the subject part against the features described and dia-grammed in the tables. An alternative and more-productive approach involves interactionwith a computerized classification and coding system, in which the user responds to ques-tions asked by the computer. On the basis of the responses, the computer assigns the codenumber to the part. Whichever method is used, the classification results in a code numberthat uniquely identifies the part's attributes.
The classification and coding procedure may be carried out on the entire list of ac-tive parts produced by the finn, or some sort of sampling procedure may be used to establishpart families. For example, parts produced in the shop during a certain time period couldbe examined to identify part family categories. The trouble with any sampling procedureis the risk that the sample may be unrepresentative of the population.
A number of classification and coding systems are described in the literature [13], [16],[31], and there are a number of commercially available coding packages. However, noneof the systems has been universally adopted. One of the reasons for this is that a classifi-cation and coding system should be customized for it given company or industry. A systemthat is best for one company may not be best for another company.
Sec. 15.2 / Parts Classification and Coding
method. This was the Langston Division of Harris Inlertype in Cherry Hill, New Jersey[18] (Historical Note 15.1).
75.2 PARTS CLASSIFICATION AND CODING
This is the most time consuming of the three methods. Inports classification and coding,similarities among parts are identified, and these similarities are related in a coding systi-Two categories of part similarities can be distinguished: (1) design attributes, which areconcerned with pan characteristics such as geometry, size, and material; and (2) manufac-turing attributes, which consider the sequence of processing steps required to make a part.While the design and manufacturing attributes of a part are usually correlated, the corre-lation is less than perfect. Accordingly, classification and coding systems are devised to in-clude both a part's design attributes and its manufacturing attributes. Reasons for using acoding scheme include;
. Design retrieval. A designer faced with !he task of developing a new part can usea design retrieval system to determine if a similar part already exists. A simplechange in an existing part would take much less time than designing a whole newpart from scratch.
. Automated process planning. The part code for a new part can be used to search forprocess plans for existing parts with identical or similar codes.
. Machine cell design. The part codes can be used to design machine cells capable ofproducing all members of a particular part family, using the composite part concept(Section 15.4.1).
To accomplish parts classification and coding requires examination and analysis of thedesign and/or manufacturing attributes of each part.
The examination is sometimes done
by looking in tables to match the subject part against the features described and dia-grammed in Ihe tables. An alternative and mure-pruiiuclive approach involves interactionwith a computerized classification and coding system, in which the user responds to ques-tions asked by the computer. On the basis of the responses, the computer assigns the codenumber to the part. Whichever method is used,
the classification results in a code number
that uniquely identifies the part's attributes.The classification and coding procedure may be carried out on the entire list of ac-
tive parts produced by the firm, or some sort of sampling proceduremay be used to establishpart families For example, parts produced in the shop during a certain time period couldbe examined to identify part family categories. The trouble with any sampling procedureis the risk that the sample may be unrepresentative of the population.
A number of classification and coding systems are described in the literature [13], [16],[31], and there are a number of commercially available coding packages. However,
none
of the systems has been universally adopted. One of the reasons for this is that a classifi-
cation and coding system should be customized for a given company or industry. A systithat is best for one company may not be best for another company.
426 Chap. 1S f Group Technology and Cellular Manufacturing
15.2.1 Features of Parts Classification and Coding Systems
The principal functional areas that utilize a parts classification and coding system are designand manufacturing. Accordingly. parts classification systems fall into one of three categorie,;
1. systems based on part design attributes2. systems based on part manufacturing attributes3. systems based on both design ond manufocturing attributes
Table 15.1 presents a list of the common design and manufacturing attributes typically in-cluded in classification schemes. A certain amount of overlap exists between design andmanufacturing attributes, since a part's geometry is largely determined by the sequence ofmanufacturing processes performed on it.
In terms of the meaning of the symbols in the code, there are three structures usedin classification and coding schemes:
1. hierarchicalstructure, also known as a monaeode, in which the interpretation of eachsuccessive symbol depends on the value of the preceding symbols
2. dO;'I.type structUN!,also known as a polyoode, in which the interpretation of eachsymbol in the sequence is always the same; it does not depend on the value of pre-ceding symbols
3. mixed-mode structure. which is a hybrid of the two previous codes
To distinguish the hierarchical and chain-type structures, consider a two-digit code num-ber for a part, such as 15 or 25. Suppose the first digit stands for the general shape of thepart: 1 means the part is cylindrical (rotational), and 2 means the geometry is rectangular.In a hierarchical structure, the interpretation of the second digit depends on the value ofthe first digit. If preceded by 1, the 5 might indicate a length-to-diameter ratio; and if pre-ceded by 2, the 5 indicates an aspect ratio between the length and width dimensions of thepart. In the chain-type structure, the symbol 5 would have the same meaning whether pre-ceded by 1 or 2. For example, it might indicate the overall length of the part. The advan-tage of the hierarchical structure is that in general. more information can he included in a
Part Design Attributes
TABLE 15.1 Design and Manufacturing Attributes Typically Included in a GroupTechnology Classification and Coding System
Part Manufacturing Attributes
Basic external shapeBasic internal shapeRotational or rectangular shapeLangth-to-diameter ratio (rotational parts)Aspect ratio (rectangularpartslMaterial typePart functionMajor dimensionsMinor dimensionsTolerancesSurface finish
426 Chap. 15 / GroupTechnology and Cellular MamifBcturing
15.2.1 Features of Parts Classification and Coding Systems
The principal functional areas that utilize a parts classification and coding system are designand manufacturing. Accordingly.parts classification systems fall into one of three categories;
1. systems based on part design attributes
2. systems based on part manufacturing attributes
3. systems based on both design and manufacturing attributes
Table 15.1 presents a list of the common design and manufacturing attributes typically in-cluded in classification schemes. A certain amount of overlap exists between design andmanufacturing attributes, since a part
's geometry is largely determined by the sequence ofmanufacturing processes performed on it.
In terms of the meaning of the symbols in the code, there are three structures usiedin classification and coding scheme
1. hierarchical structure, also known as a ntonocode, in which the interpretation of each
successive symbol depends on the value of the preceding symbols7
. chain-type structure, also known as a polycode, in which the interpretation of eachsymbol in the sequence is always the same; it does not depend on the value of pre-ceding symbols
3. mixed-mode structure, which is a hybrid of the two previous codes
To distinguish the hierarchical and chain-type structures, consider a two-digit code nber for a part, such as 15 or 25. Suppose the first digit stands for the general shape of thepart: 1 means the part is cylindrical (rotational), and 2 means the geometry is rectangular.In a hierarchical structure, the interpretation of the second digit depends on the value ofthe first digit.If preceded by l.the 5 might indicate a length-to-dtameter ratio; and if pre-ceded by 2, Ihe 5 indicates an aspect ratio between the length and width dimensions of thepart. In the chain-type structure, (he symbol 5 would have the same meaning whether pre-ceded by 1 or 2. For example, it might indicate the overall length of the part. The advan-tage of the hierarchical structure is that in general, more information can he included in a
TABLE 15.1 Design and Manufacturing Attributes Typically Included in a GroupTechnology Classification and Coding System
Pan Design Attributes Part Manufacturing Attributes
Basic external shape Major processesBasic internal shape Minor operationsRotational or rectangular shape Operation sequerLength-to-diameter ratio (rotational parts) Major dimensionAspect ratio (rectangular parts) Surface finishMaterial type Machine tool
m cycle timePart function ProductioiMajor dimensions Batch sizeMinor dimensions Annual productionTolerances Fixtures requiredSurfj
ranees Fixtures requirfFace finish Cutting tools
427
is the most common structure
The number of digits in the code can range from 6 to 30. Coding schemes that con-tain only design data require fewer digits. perhaps 12 or fewer. Most modem classification;lntl cntlin!!-~)'~If'm"include hnth rlecign and manufacturing data, and this usually requires20-30 digits. This might seem like too many digits fur a human reader to easily comprehend,but it must be remembered that most of the data processing of the codes is accomplishedby computer. for which a large number of digits is of minor concern
15.2.2 Examples of Parts Classification and Coding Systems
Some of the important systems (with emphasis on those in the United States) include: {heOpitz classification system, which is nonproprietary; the Brisch Sy,tem (Brtsoh-Birn, Inc.);CODE (Manufacturing Data Systems. lnc.]: CUTPLAN (Metcut Associates); DCLASS(Brigham Young University): MultiClass (OIR: Organization for Industrial Research);andPart Analog System (Lovelace. Lawrence & Co., Inc.). Reviews of these systems and oth-ers can be found in [161 and [23J.
In the following. we discuss two classification and coding systems: the Opitz Systemand MultiClass. The Opitz system is 0' interest because it was one of the first published clas-sification and coding schemes for mechanical parts [31] (Historical Note 15.1) and is stillwidely used. MultiClass is acommercial product offered by the Organization for Industri-a! Research (OIR)
Opitz Classification System. This system was developed by H. Opitz of the Uni-versity of Aachen in Germany. It represents one of the pioneering efforts in group tech-nology and is probably the best known, if not the most frequently used, of the partsclassification and coding systems. It is intended for machined parts. The Opitz codingscheme uses thc following digit sequence:
12345 6789 ABCD
The basic code consists of mne digits, which can be extended by adding four more digits.The first nine arc intended to convey both design and manufacturing data. The interpre-tation of the first nine digits is defined in Figure 15.5. The first five digits, 12345, are calledthc/onn code. It describes the primary design attributes of the part, such as external shape(e.g., rotational vs. rectangular) and machined features (e.g., holes, threads, gear teeth, etc.].The next four digits, 6789, constitute the supplementary code, which indicates some of theattributes that would be of use in manufacturing (e.g., dimensions, work material, startingshape, and accuracy). The extra four digits,ABCD, are referred to as the secondary codeand are intended to identify the production operation type and sequence. The secondarycode can be designed by the user firm to serve its own particular needs.
The complete coding system is too complex to provide a comprehensive descriptionhere. Opitz wrote an entire book on his system [31]. However, to obtain a general idea ofhow it works, let us examine the form code consisting of the first five digits. defined gen-erally in Figure 15.5. The first digit identifies whether the part is rotational or nonrota-tional.1t also describes the general shape and proportions of the part. We limit our surveyhere to rotational parts possessing no unusual features, those with first digit values ofO, 1,
Sec. 15.2 I Parts Classification and CodingSec. 15.2 / Parts Classification and Coding 427
code of a given number of tligiis.The mixed-mode classification and coding systemcombination o! hierarchical and chain-type structures. It is the most common s
""
found in GT pans classification and coding systems.The number of digits in the code can range from 6 to 30. Coding schemes that con-
lain only design data require fewer digits, perhaps 12 or fewer. Most modem classificationand i-nHin}i -.yMems include both design and manufacturing data, and this usually requires20-30 digits, this might seem like too many digils tor a human reader to easily comprehend,but it must be remembered that most of the data processing of the codes is accomplishedby computer, for which a large number of digits is of mil
15.2.2 Examples of Parts Classification and Coding Systems
Some of the important systems (with emphasis on those in the United States) include: (heOpitz classification system, which is nonproprietary; the Brisch System (Brisch-Bimjnc);CODE (Manufacluring Data Systems. Inc.); CUTPLAN (Mctcut Associates); DCLASS(Brigham Young University); MulliClass (OIR: Organization for Industrial Research};andPart Analog System (Lovelace. Lawrence & Co., Inc.). Reviews of these systems and oth-ers can be found in [ I6| and |23J.
In ihe following, we discuss two classification and coding systems: the Opitz Systemand MulliClass. The Opitz system is or
"
interest because it was one of the first published clas-sification and coding schemes for mechanical parts [31] (Historical Note 15.1) and is stillwidely used, MulliClass is a commercial product offered by the Organization for Industri-al Research (OIR).
Opitz Classification System. This system was developed by H. Opitz of the Uni-versity of Aachen in Germany. It repicsents one of the pioneering efforts in group tech-nology and is probably the best know-classification and coding systemscheme uses the following digit sequence:
y. It repicsents one of the pioneering efforts in group tech-iest known, if not the most frequently used, of the partslems. 11 is intended for machined parts. The Opitz coding
12345 6789 ABCD
The basic code consists of nine digits, which can be extended by adding four more digits.The first nine arc intended to convey both design and manufacturing data. The interpre-tation of the first nine digits is defined in Figure 15.5. The first five digits, 12345, are calledihcform code. It describes the primary design attributes of the part, such as external shape(e.g., rotational vs. rectangular) and machined features (e.g., holes, threads, gear teeth, etc.).The next four digits, 6789, constitute the supplementary code,
which indicates some of the
attributes that would be of use in manufacturing (e.g., dimensions, work material, startingshape, and accuracy). The extra four digits, ABCD, are referred to as the secondary codeand are intended lo identify the production operation type and sequence.The secondarycode can be designed by the user firm to serve its own particular needs.
The complete coding system is too complex to provide a comprehensive descriptiie an entire book on his system [31]. However,
to obti
sisting of therally in Figure 15.5. The first digit identifies whether the part is rotational or
here, Opitz wrote an entire book on his system [31]. However, to obtain a general idea ofhow it works, let us examine the form code consisting of the first five digits, defined gen-
der, to ol
ie first fi
if the pahere to rotational parts possessing no unusual features, those with first digit values ofO, 1,tional.Ilalso describes the general shape and proportions of the part. We limit our survey
ossessing no unusual features, those with first
428 Chap. 15 I Group Technology and Cellular Manufacturing
I)Lgl12
supp~~~m.ry
Figu1'f'15.5 Basic structure of the Opitz system of parts classificationand coding.
or2. For this etas, of work parts, the coding of the first five digits is defined in Figure 15,6.Consider the following example to demonstrate the coding of a given part.
EXAMPLE 15.1 Opitz Part Coding System
Given the rotational part design in Figure 15.7, determine the form code in theOpitz parts classification and coding system
Solution: With reference to Figure 15.6, the five-digit code is developed as follows:
Length-to-diameter ratio, LID = 1.5 Digit 1 = 1
External shape: stepped on both ends with screw thread on one end Digit 2 = 5
Internal shape: part contains a through-hole Digit 3 == 1
MultiClass. MultiClass is a classification and coding system developed by the Or-ganization for Industrial Research (OIR). The system is relatively flexible, allowing theuser company to customize the classification and COlling scheme 10 a large extent to fit itsown products and applications. Multi Class can be used for a variety of different types ofmanufactured items, including machined and sheer metal parts, tooling, electronics, pur-
Rotot;onRI PI."e,urfa<e Addll;onalhobmachLn"'g machlmn. l••lh and fo,mlllg
~~:.~,L:~;:~R
428 Chap. 15 / Group Technology and Cellular Manufacturing
Supplimentary
1
Digit J
Mam shapt
D,£.i3
Rotational
rD,Ki,4
Plane surfau
DtgitS Dipt
I3
5
Figure
d coding.
or2. For this class, of workparts, the coding of the first five digits is defined in Figure 15.6.
iart design in Figure 15.7, determine the form code in theion and coding system,
jure 15.5 Basic structure of the Opitz system of parts classification
rts, the coding of the first five digits is defined inConsider the following example to demonstrate the coding of a given part.
EXAMPLE 15.1 Opilz Part Coding Syslei
Given the rotational pzOpitz parts dassificatk
Solution: With reference to Figure 15.6, the five-digit code is developed as follows:
Length-to-diameter ratio, L/D - 1.5 Digit 1 = 1
Esternal shape: stepped on both ends with screw thread on one end Digit 2 = 5
Internal shape, part contains a through-hole Digit 3 = 1
Plane surface machining: none Digit 4 = 0
Auxiliary holes.gearteeth,etc.:none Digits = 0
The form code in the Opitz system is 15100,
MultiClass. MultiClass is a classification and coding system developed by the Or-ganization for industrial Research (OIRJ. The system is relatively flexible, allowing theuser company to customize the classification and coding scheme to a large extent to fit itsown products and applications. MultiClass can be used for a variety of different types ofmanufactured items, including machined and sheet metal parts, tooling, eleclronics, pur-
Figure 15.6 Form code (digits 1-5) for rotational parts in the Opitzcoding system. The first digit of the code is limited to the value 0,1.0r2.
fJ13.'C~000 __ . _ -----r-- --.l I
1-g~=I~TL5(XI---J
Figure 15.7 Part design for Example 15.1.
Sec. 15.2 / Parts Classification and Coding
71
I
4
J
as;
Opcranng thread
i
Digit 3
nt rnal ihapc.is! shape tk-mtnIS
No hole.
Digit 4
No shap
Plane surface
Surface plane.I cuived in one
I diieciion. tslemiil
:}-
J
-
i
Nf'hape
l nctional
groove
Functional cone
Operating thread
External plane surface
E-ssr
Digit 5
!I4
imernal spline(polygon)
[ntemaland
6
9
.1
No auiiiUary hole
Spur gear
Figure 15.6 Form codecoding 5'l,or2.
le (digits 1-5) for rotational parts in the Opit/lystem. The first digit of the Code is limited to the value 0,
.1X10
-O.SOO-H
0.875 -
- 0.250 0.750
Figure 15.7 Part design for Example 15.1
.
430 Chap. 15 I Group Technology and Cellular Manufacturing
chased pam, assemblies and subassemblies, machine tools, and other elements. Up to ninedifferent types of components can be included within a single MultiClass software structure
Multif.lass uses a hierarchical or decision-tree coding structure in which the suc-ceeding digits depend on values of the previous digits. In the application of the system, aseries of menus, pick lists, tables, and other interactive prompting routines are used to codethe part. This helps to organize and provide discipline to the coding procedure.
The coding structure consists of up to 30 digits. These are divided into two regions,one provided by GIR, and the second designed by the user to meet specific needs and re-quirements. A prefix precedes the code number and is used to identify the type of part(e.g., a prefix value of 1 indicates machined and sheet metal parts). For a machined part,the coding for the first 18 digit positions (after the prefix) is summarized in Table 15.2.
TABLE 15.2 First 18 digits of the Murtretess Classificationand Coding System
Digit Function
o Code system preflx1 Main shape category
2,3 External and internal configuration4 Machinedsecondary ••lernents
5,6 Functional descriptors7-12 Dimensional data !length, diameter, etc.)
13 Tolerances14,15 Material chemistry
16 Raw material shape17 Production quantity18 Machined element orientation
EXAMPLE 15.2 MuitiClass Coding System
Given the rotational part design in Figure 15.8, determine the IS-digit code inIhe MultiClass parts coding system
Fig~lre 15.8 Workpart of Example 15.2. (Courtesy of OIR, Organi-zeuon for Industnal Research.)
Chap. 15 / Group Technology and Cellular Manufacturing
chased pans, assemblies and subassemblies, machine lools, and other elements. U|include
series of menus, pick lists, lables, and other ii
Upton,different types (if components can be included within a single MuitiClass software structu
MultiClass uses a hierarchical or decision-tree coding structure in whichceeding digits depend on values of the previous digits In the application of the system, a
quin
(e.g.,the
active prompting routines are used to code
region:and re
of pared pari
ig for the first 18 digit positions (after the prefix) is summarized in Table 15.2.
ve promplthe part This helps to organize and provide discipline to the coding procedure.
The coding structure consists of up to 30 digits. These are divideiby OIR, and the second designed by the user to meet spe prefix precedes the code number and is used to identify the type c
;., a prefix value of 1 indicates machined and sheet metal parts). For a machined part,
le provided by OIR, and the secondlirements. A prefix
consists of up to 30 digits. These are divided into two regions,"
designed by the user to meet specific ne:edes the code number and is used to identify the type of part
>cific needs and re-
TABLE 15.2 First 18 digits of the Multiclass Classificationand Coding Systam
Digit Function
0
2,
3
5,
6
7-12
13
14, 15
16
18
Code system prefixMain shape categoryExternal and internal configurationMachined secondary ulementsFunctional descriptorsDimensional data llength, diameter, etc.)Tolerances
Material chemistryRaw material shapeProduction quantityMachined element orientation
EXAMPLE 1S.2 MuitiClass Coding System
Given the rotational pthe MuitiClass parts ciGiven the rotational part design in Figure 15.
8, determine the 18-digit code in
~
:oding system.
5/16-18UNC2A (2)
-1@ AO.OIOdia |Umax (2)
0 °mi-j-
JR 1 l,02»»-
0.352 ± 0.003 dia
@ AO.MST.I.R. |
- o.oi5 _0;ml>R.B)
-0.080
- 0.030 x 45° |2)
Figure 15.8 Workpart of Example 15.2
. (Courtesy of OIR, Organi-zation for Industrial Research
.)
Sec. 15.3 ! Production Flow Analysis 43'
lJu"l(l~ataIl1~lcrrange0251-D.J7Iin
a groove
Figun: 15.9 MultrClass code number determined for part in Exam-ple 15.2. (Courtesy of OIR, Organization for Industrial Research.]
Solution: The Multi'Class code number for the given part is developed in Figure 15.9.
15.3 PRODUCTION FLOW ANALYSIS
This is an approach to part family identification and machine cell formation that was pic-necred by J. Burbidge [6]-[R].Productionflow analysis (PFA) isa method for identifyingpart families and associated machine groupings that uses the information contained 011production route sheets rather than on part drawings. Work parts with identical or similarroutings are classified into part families. These families can then be used to form logical ma-chine cells in a group technology layout. Since PFA uses manufacturing data rather thandesign data to identify part families, it can overcome two possible anomalies that can occurin parts classification and coding. First, parts whose basic geometries are quite different maynevertheless require similar or even identical process routings. Second, parts whose georne.tries are quite similar may nevertheless require process routings that are quite different.
The procedure in production flow analysis must begin by defining the scope of thestudy, which means deciding on the population of parts to be analyzed. Should all of theparts in the snop be Included in the study, or should a representative sample be selectedfor analysis! Once this decision is made, then the procedure in PFA consists of the fol-lowing steps:
Sec. 15.3 / Production FlowAnalvsis
miufacBinnj;
Code
Dimcnuons
sccomlarv
L-lemcnls (holes, j
visible lYom . inside L-
p-
1
Materia!
18 19 20
5
Ts,r
Thread
Figurtpie 15
15.9 MultiClass code number determined for part in Exam-15.2. (Courtesy of OIR, Organization for Industrial Research.)
Solution: The MultiClass code number for the given part is developed in Figure 15.9.
75.3 PRODUCTION FLOW ANALYSIS
This is anis an approach to part tamily identification and machine cell tormation that was pio-sd by J. Burbidge [6]-[8\. Production flow analysis (PFA) is a method for identifyingfamilies and associated machine groupings that uses the information contained oniction route sheets rather than on part drawings. Workparts with identical or similarigs are classified into part families. These families can then be used to form logical ma-cells in a group technology layout. Since PFA uses manufacturing data rather thani data to identify part families, it can overcome two possible anomalies that can occur
cation and coding. First, parts whose basic geomt:quire similar or even identical process routings.similar may nevertheless require process routii
design data lily part families, itin parts classification and coding. First, parts whose basic geometries are quite different may
lat or even identical process routings. Second, parts whly nevertheless require process routings that are quilt
The procedure in production flow analysis must begin by defining the scopewhich means deciding on ihe population of parts to be analyzed.
Should all of the
in the shop he included in the study, or should a representative sample be selected
nevertheless rei
The
lose geoi
of the
study, whicl
parts in the shop he included in the study, or should a represenfor analysis? Once this decision is made
, then the procedure in PFA consists of the fol-lowing steps:
432 Chap, 15 / Group Technology and Cellular Manufacturing
1. Data collection. The minimum data needed in the analysis are the part number andoperation sequence, which is contained in shop documents called route sheets or op-eration sheets or some similar name. Each operation is usually associated with a par-ticular machine, so determining the operation sequence also determines the machinesequence.Additional data.such as 101size, time standards, and annual demand mightbe useful for designing machine cells of the required production capacity.
2. Sonatton of process routings. In this step, the parts are arranged into groups ac-cording to the similarity of their process routings. To facilitate this step, all operationsor machines included in the shop are reduced to code numbers, such as those shownin Table 15.3. For each part, the operation codes are listed in the order in which theyare performed. A sortation procedure is then used to arrange parts into "packs,"which are groups of parts with identical routings. Some packs may contain only onepart number, indicating the uniqueness of the processing of that part. Other packs willcontain many parts, and these will constitute a part family.
3. PFA chart. The processes used for each pack are then displayed in a PFA chart, a sun.plified example of which is illustrated in Table 15.4.1 The chart is a tabulation of theprocess or machine code numbers for all of the part packs. In recent GT literature [30],the PFA chart has been referred to as part-machine incidence matrix. In this rna.trix, the entries have a value Xii = lor 0: a value of X;j = 1 indicates that the corre-sponding part i requires processing on machine j, and X'I = 0 indicates that noprocessing of component i is accomplished on machine j. For clarity of presentingthe matrix, the D's are often indicated as blank (empty) entries, as in our table.
4. Cluster analysis. From the pattern of data in the PFA chart. related groupings areidentified and rearranged into a ncw pattern that brings together packs with similarmachine sequences. One possible rearrangement of the original PFA chart is shownin Table 15.5, where different machine groupings are indicated within blocks. Theblocks might be considered as possible machine cells. It is often the case (but not inTable 15.5) that some packs do not fit into logical groupings. These parts might be an-alyzed to see if a revised process sequence can be developed that fits into one of thegroups. If not, these parts must continue to be fabricated through a conventionalprocess layout. In Section 15.6.1, we examine a systematic technique called rank orderdusterlnR that can be used to perform the cluster analysis.
TABLE 15.3 Possible Code Numbers indicatingOperations and/or Machines forSortation in Production Flow Analysis(Highly Simplified)
Operation or Machine Code
CutoffLathe
Turret latheMill
Drilf:manualNCdri/iGrind
0102030405ee07
l For clarity in the p~-machine incidence matrices and related discussion, we are identifying parts by al-phabellc cbracter and machInes by number. In practice, number, would be nsed lor both
Chap. 15 / Group Technologv and Cellular Manufacturing
1. Daia collection. The minimum data needed in the analysis are the part number and
)eration sequence, which is contained in shop documents called route sheets or op-cratii
ticulE
sequence. Additional data,such aslol size,i
be useful for designing machine cells of the required production capacity.
sheets or some similar name. Each operation is usually associated with a par-iiachine
,so determining the operation sequence also determines the machinelence. Additional data
,such as lot size, time standards,and annual demand might
are performed. A sortation procedure is then used to arrange parts into "packs,"
which are groups of parts with identical routings. Some packs may conlain only onepart number, indicating the uniqueness of the processing of that part. Other packs will
ire groups of parts with identical routings. Some packs may conlain only one
2. Sanation of process routings. In this step, the parts are arranged into groups ai
cording to the similarity of their process routings. To facilitate this step, all operatioror machines included in the shop are reduced to code numbers, such as those shownin Table 15.3. For each part, the operation codes are lisled in the order in which they
rocedur
al routings.
contain many parts, and Ihese will constitute a part family.3
. PFA chart. The processes used for each pack are then displayed in a PFA chart,plified example of which is illustrated inTable 15.4.lThe chart is a tabulalion of the
process or machine code numbers for all of the part packs. In recent GT literature [30],the PFA chart has been referred to as part-machine incidence matrix.
In this ma-
trix, the entries have 3 value x,, = 1 or 0: a value of - 1 indicates that the
spending part / requires processing on machine and - 0 indicates that noprocessing of component i is accomplished on machine For clarity of presentingthe matrix
, the 0's are often indicated as blank (empty) entries, as in our table.4
. Cluster analysis. From the pattern of data in the PFA chart, related groupings areidentified and rearranged into a new pattern that brings together packs with similarmachine sequences. One possible rearrangement of the original PFA chart is shownin Table 15.5
, where differenl machine groupings are indicated within blocks Theblocks might be considered as possible machine cells. It is often the case (but not in
packs do not fit intoed process sequenci
groups. If not, these parts must continue to be fabricated through a conventionalprocess layout. In Section 15.6.1, we examine a systematic technique called rank orderclustering that can be used to perform the cluster analysis.
TABLE 15.3 Possible Code Numbers IndicatingOperations and/or Machines forSortation in Production Flow Analysis(Highly Simplified)
is possib
Table 15.5) that some packs do not fit into logical groupings.These parts might be an-alyzed to see if a revised process sequence can be developed that fits into one of the
Operation or Machine Code
Cutoff 01Lathe 02
Turret lathe 03Mil' M
Drill: manual
NC drill
07
1 Fot clarity in the part-machine incidence matrices and related discussion, we are identifying parts by al-
phabetic character and machines by number. In practice, rambers would be used for both.
Sec. 15.3 / Production Flow Analysis 43'
TABLE 15.4 PFA Chart, Also Known as a Part-Machine Incidence Matrix
Parts
Machines
TABLE 15.5 Rearranged PFA Chart. Indicating Possible Machine Groupings
Parts
Machines A
1 , ,, ,
, 1
1 , ,, ,
, , ,, 1
The weakness of production flow analysis is that the data used in the technique arederived from existing production route sheets. In all likelihood, these route sheets havebeen prepared by different process planners, and the routings may contain operations thatare non optimal, illogical, or unnecessary. Consequently, the final machine groupings ob-tained in the analysis may be suboptimal. Notwithstanding this weakness, PFA has thevirtue of requiring less time than a completc parts classification and codmg procedure.This virtue is attractive to many firms wishing to introduce group technology into theirplant operations.
Sec. 15.3 / Production Flow Analysis
TABLE 15.4 PFA Chart, Also Known as a Part-Machine Incidence Matrix
Parts
Machines ABCDEFGHI
1
2
3
£
5
6
7
433
TABLE 15.5 Rearranged PFA Chart, Indicating Possible Machine Groupings
Parts
Machines CE IADHFGB
3
2
6
1
5
7
4
1
1 1
1 1
1
1 1 1
The weakness of production flow analysis is that the data used in the technique arederived from existing production route sheets. In all likelihood,
these route sheets have
been prepared by different process planners, and the routings may contain operations thatare nonoptimal, illogical, or unnecessary. Consequently, the final machine groupings ob-tained in the analysis may be suboptimal. Notwithstanding this weakness,
PFA has the
virtue of requiring less time than a complete parts classification and coding procedure.
This virtue is attractive to many firms wishing to introduce group technology into theirplant operations.
Chap. 15 / Group Technology and Cellular Manufacturing
15.4 CELLULAR MANUFACTURING
Whether part families have been determined by visual inspection. parts classification andcoding, or production flow analysis, there is advantage in producing those parts using grouptechnology machine cells rather than a traditional process-type machine layout. When themachines are grouped. the term cellular manufacturing is used to describe this work orga-nization. Cdlular manufacturing is an application of group technology in which dissimi-lar machines or processes have been aggregated into cells, each of which is dedicated to theproduction of a pari or product family or a limited group of families. The typical objectivesin cellular manufacturing are similar to those of group technology:
• To shorten manufacturing lead times, by reducing setup, workpart handling, waitingtimes, and batch sizes
• To reduce work-in-process inJ!enIOry. Smaller batch sizes and shorter lead times re-duce work-in-process.
• To tmprove quality. This is accomplished by allowing each cell to specialize in pro-ducing a smaller number of different parts. This reduces process variations.
• To simplify production scheduling. The similarity among parts in the family reducesthe complexity of production scheduling. Instead of scheduling parts through a se-quence of machines in a process-type shop layout, the parts are simply scheduledthough the cell.
• To reduce setup times. This is accomplished by using group tooling (cutting tools,jigs, and fixtures) that have been designed to process the part family, rather than parttooling, which is designed for an mdividual part. This reduces the number of indi-vidual tools required as well as the time to change tooling between parts.
Additional reasons for implementing cellular manufacturing are given in Table 15.7. Inthis section, we consider several aspects of cellular manufacturing and the design of ma-chineceils.
15.4.1 Composite Part Concept
Part families are defined by the fact that their members have similar design and/or manu-facturing features. The composite part concept takes this part family definition to its logi-cal conclusion. It conceives of a hypothetical part, a composite part for a given family,which includes all of the design and manufacturing attributes of the family. In general. anindividual part in the family will have some of the features that characterize the family butnot all of them. The composite part possesses all of the features.
There is always a correlation between part design features and the production op-erations required 10 generate those features. Round holes are made by drilling, cylindricalshapes are made by turning, flat surfaces by milling, and so on. A production cell designedfor the part family would include those machines required to make the composite part. Sucha cell would be capable of producing any member of the family, simply by omitting thoseoperations corresponding to features not possessed by the particular part. The cell wouldalso be designed to allow for size variations within the family as well as feature variations.
To illustrate, consider the composite part in Figure 15.1O(a).1l represents a family ofrotational parts with features defined in Figure 15.1O(b). Associated with each feature is acertain machining operation as summarized in Table 15.6. A machine cell to produce this
434 Chap. 15 / Group Technology and Cellular Manufacturing
15.4 CELLULAR MANUFACTURING
Whether part families have been determined by visual inspection, parts classification andcoding, or production flow analysis, there is advantage in producing those parts usinggrouptechnology machine cells rather than a traditional process-type machine layout. When themachines are grouped, the term cellular manufacturing is used to describe this work orga-nization. Cellular manufacturing is an application of group technology in which dissimi-lar machines or processes have been aggregated into cells, each of which is dedicated to theproduction of a pan or product family or a limited group of families The typical objectivesin cellular manufacturing are similar to those of group technology:
. To shorten manttfacturing lead limes, by reducing setup, workpart handling, waitingtimes, and batch sizes.
. To reduce work-in-process inventory. Smaller batch sizes and shorter lead times re-
duce work-in-process.. To improve quality. This is accomplished by allowing each cell to specialize in pro-
ducing a smaller number of different parts. This reduces process variations.. To simplify production scheduling.The similarity among parts in the family reduces
the complexity of production scheduling. Instead of scheduling parts through a se-quenctthough the cell.
'inplexity of production scheduling. Ilence of machines in a process-type shop layout, the parts are simply scheduled
roup toojigs, and fixtures) that have been designed to process the part family, rather than parttooling, which is designed for an individual part. This reduces the number of indi-
To reduce setup times. This is accomplished by using group tooling (cutting tools,gs, and fixDoling, wh
vidual tools required as well as the time to change tooling between parts.
Additional reasons for implementing cellular manufacturing are given in Table 15.7. Inthis section, we consider several aspects of cellular manufacturing and the design of ma-chine cells.
15.4.1 Composite Part Concept
Part families are defined by the fact that their members have similar design and/or manu-facturing features. The composite part concept takes this part family definition to its logi-cal conclusion. It conceives of a hypothetical part, a composite part for a given family,which includes all of the design and manufacturing attributes of the family. In general,
an
individual part in the family will have some of the features that characterize the family butnot all of them. The composite part possesses all of the features
There is always a correlation between part design features and the production op-erations required to generate those features. Round holes are made by drilling, cylindricalshapes are made by turning, flat surfaces by milling, and so on. A production cell designedfor the part family would include those machines required to make the composite part.
Such11 would a cell would be capable of producing any member of the family, simply by omitting those
operations corresponding to features not possessed by the particular part. The cell would
also be designed to allow for size variations within the family as well as feature variations.
To illustrate, consider the composite part in Figure 15.10(a). It represents a family ofrotational parts with features defined in Figure 15.10(b). Associated with each feature is a
Sec. 15.4 l Cellular Manufacturing 43'
;:=- Ge:U) Ibl
Figure 15.10 Composite part concept: (a) the composite part for afamily of machined rotational parts and (b) the individual featuresof the composite part. See Table 15.6 for key to individual featuresand corresponding manufacturing operations.
Label
TABLE 15.6 Design Features of the Composite Part in Figure 15.10 and theManufacturing Operations Required to Shape Those Features
part family would be designed with the capability to accomplish all seven operations re-quired to produce the composite pan (the last column in the table). To produce a specificmember of the family, operations would be included to fabricate the required features ofthe part. For parts without all seven features, unnecessary operations would simply beomitted. Machines, fixtures, and tools would be organized for efficient flow of workparlsthrough the cell,
In practice, the number of design and manufacturing attributes is greater than seven,and allowances must be madc for variations in overall size and shape of the parts in the fam-ily. Nevertheless, the composite part concept is useful for visualizing the machine cell de-sign problem.
15.4.2 Machine Cell Design
Design of the machine cell is critical in cellular manufacturing. The cell design determinesto a great degree the performance of the cell. In this subsection, we discuss types of machinecells, ceJllayouts, and the key machine concept.
Sec. 15.4 ; Cellular Manufactumg 435
ciins.fsiinj! ..if 3)1 f"
seven Sevgn :-.nJct'Mingait'iburcs
Figure 1S.10 Composite part concepl: (a) the composite part for afamily of machined rotational parts and (b) the individual featuresof the composite part. See Table 15.6 for key to individual featuresand corresponding manufacturing operations.
TABLE 15.6 Design Features of the Composite Part in Figure 15.10 and theM;inufacluring Operations Required (o Shape Those Featuree
part family would be designed with the capability to accomplish all seven operations re-quired to produce the composite part (the last column in the table). To produce a specificmember of the family, operations would be included to fabricate the required features ofthe part. For parts without all seven features, unnecessary operations would simply beomitted. Machines
, fixtures, and tools would be organized for efficient flow of workpartsthrough ihe cell.
In pracLice. the number of design and manufacturing allribules is greater than seven.
and allowances musl be made for variations in oveiall size and shape of the parts in the fam-ily. Nevertheless, the composite part concept is useful for visualizing the machine cell de-sign problem.
15.4.2 Machine Cell Design
Design of the machine cell is critical in cellular manufacturing. The cell design determinesto a great degree the performance of the cell. In this subsection, we discuss types of machinecells, cell layouts, and the key machine concept.
436 Chap. 15 / Group Technology and Cellular Manufacturing
Types of Machine Cefls and Layouts. GT manufacturing cells can be classifiedaccording to the number of machines and the degree to which the material flow is mech-anized between machines. In our classification scheme for manufacturing systems (Section13.2), all GT cells are classified as type X in terms of part or product variety (Section 13.2.4,Table 13.3). Here we identify four common GT cell configurations (with system type iden-tified in parenthesis from Section 13.2):
1. single machine cell (type I M)2. group machine cell with manual handling (type n M generally, type III M less common)3. group machine cell with semi-integrated handling (type II M generally, type III M
less common)4. flexibie manufacturing cell or flexible manufacturing system (type IT A generally,
type III A less common)
As its name indicates, the single machine cefl consists of one machine plus support-ing fixtures and tooling. This type of cell can be applied to workparts whose attributesallow them to be made on one basic type of process, such as turning or milling. For exam-ple, the composite part of Figure 15.10 could be produced on a conventional turret lathe,with the possible exception of the cylindrical grinding operation (step 4)
The group machine cell with manual handling is an arrangement of more than onemachine used collectively to produce one or more part families. There is no provision formechanized parts movement between the machines in the cell. Instead, the human opera-tors who run the cell perform the material handling function. The cell is often organizedinto a Ij-ehaped layout, as shown in Figure 15.11. This layout is considered appropriatewhen there is variation in the work flow among the parts made in the cell. It also allows themultifunctional workers in the cell to move easily between machines [29].
The group machine cell with manual handling is sometimes achieved in a conventionalprocess type layout without rearranging the equipment. This is done simply by assigningcertain machines to be included in the machine group and restricting their work to speci-fied part families. This allows many of the benefits of cellular manufacturing to be achievedwithout the expense of rearranging equipment in the shop. Obviously, the material handlingbenefits of OT are minimized with this organization.
•••
Workout•••Figure 15.11 Machine cell with manual handling between machines.Shown is a If-shaped machine layout. (Key: "Proc" 0= processingoperation (e.g., mill. turn, etc.), "Man" = manual operation; arrowsindicate work flow.)
Work in
Maaualbandlingbetween machines
3. group
less CO
436 Chap. 15 / Group Technology and Cellular Manufacturing
Types of Machine Cells and Layouts. GT manufacturing cells can be classifiedaccording to the number of machines and the degree to which the material flow is mech-anized between machines. In our classification scheme for manufacturing systems (Section13.2), all GT cells are classified as type X in terms of part or product variety (Section 13.2.4,Table 13.3). Here we identify four common GT cell configurations (with system type iden-tified in parenthesis from Section 13.2):
1. single machine cell (type 1 M)
2. group machine cell with manual handling (type TT M generally, type III M less common)
)up machine cell with semi-integrated handling (type II M generally, type III Mis common)
4, flexible manufacturing cell or flexible manufacturing system (type II A generally,
type III A less common)
As its name indicates, the single machine cell consists of one machine plus support-ing fixtures and tooling. This type of cell can be applied to workparts whose attributesallow them to be made on one basic type of process, such as turning or milling. For exam-ple, the composite part of Figure 15.10 could be produced on a conventional turret lathe,with the possible exception of the cylindrical grinding operation (step 4).
The group machine cell with manual handling is an arrangement of more than onemachine used collectively to produce one or more part families.There is no provision formechanized parts movement between the machines in the cell. Instead, the human opera-tors who run the cell perform the materia] handling function. The cell is often organizedinto a U-shaped layout, as shown in Figure 15.11. This layout is considered appropriatewhen there is variation in the work flow among the parts made in the cell. It also allows themultifunctional workers in the cell to move easily between machines [29],
The group machine cell with manual handlingis sometimes achieved in a conventionalprocess type layout without rearranging the equipment. This is done simply by assigningcertain machines to be included in the machine group and restricting their work to speci-fied part families. This allows many of the benefits of cellular manufacturing to be achievedwithout the expense of rearranging equipment in the shop. Obviously, the material handlingbenefits of GT are minimized with this organization.
Work inProc Hroc
JQ3
iiial handling f? Proceen machines & Man
Proc
ManProc
Man. 9«
Figure 15.11 Machine cell with manual handling between machines.
Shown is a U-shaped machine layout. (Key. "Proc" = processingoperation (e.g., mill, turn, etc.), "Man" = manual operation; arrowsindicate work flow.)
Sec. 15.4 / Cellular Manufacturing 437
The group machine cell with semi-integrated handling uses a mechanized handlingsystem, such as a conveyor, to move parts between machines in the cell. Theflexible man-ufacturing system (FMS) combines a fully integrated material handling system with auto-mated processing stations. The FMS is the most highly automated of the group technologymachine cells. The following chapter is devoted to this form of automation, and we deferdiscussion till then.
A variety of layouts are used in GT cells, The Ucshape, as in Figure 15.11, is a popu-lar configuration in cellular manufacturing. Other GT layouts include in-line, loop, andrectangular, shown in Figure 15.12 for the case of semi-integrated handling.
Mechanized
~ I
~"~~(oj
Wmbo AA ~w;;;:; ••• (- ...OOJ
(bj
[;ill @ill Mechanlzed
~
P'::"R:;::WO'k,,",dliO'Work in VO\I ~ \'t--... --WorkDut ~-... - ~
The group machine cell with semi-Integrated handling uses a mechanized handlingsystem, such as a conveyor, to move parts between machines in the cell.The
_/Ie«:i6/eman-
ufacturing system (FMS) combines a fully integrated material handling system with auto-mated processing stations. The FMS is the most highly automated of the group technologymachine cells. The following chapter is devoted to this form of automation, and we deferdiscussion till then.
A variety of layouts are used in GT cells, The U-shape, as in Figure 15.11, is a popu-lar configuration in cellular manufacturing. Other GT layouts include in-line, loop, and
[angular, shown in Figure 15.12 for the case of semi-integrated handling.
438 Chap. 15 I Group Technology and Cellular Manufacturing
(1) Repeal
QOP""';OP (3)8,_p.".gmo'O
"~""""~"~Man Man Man Man(I)
In-sequence
(4) Backtrackingmove
Figure 15.13 Four types of part moves in a mixed model productionsystem. The forward flow of work is from left to right.
Determining the most appropriate cell layout depends on the routings of parts pro-duced in the cell. Four types of part movement can be distinguished in a mixed model partproduction system. They are illustrated in Figure 15.13 and are defined as follows, wherethe forward direction of work flow isdefined a~heing from left to right in the figure:(l) re-peat operation, in which a consecutive operation is carried out on the same machine, so thatthe part does not actually move; (2) in-sequence move, in which the part moves from thecurrent machine to an immediate neighbor in the forward direction; (3) by-passing move,in which the part moves forward from the currenl machine to another machine that is twoor mort machines ahead; and (4) backtracking move, in which the part moves from the cur-rent machine in the backward direction to another machine.
When the application consists exclusively of in-sequence moves, then an in-line lay-out is appropriate. A V-shaped layout also works well here and has the advantage of clos-er interaction among the workers in the cell. When the application includes repeatedoperations, then multiple stations (machines) are often required. For cells requiring by-passing moves, the Li-shape layout is appropriate. When backtracking moves are needed,a loop or rectangular layout is appropriate to accommodate recirculation of parts withinthe cell. Additional factors that must be accounted for in the cell design include:
• Quantity of work to be done by the cdt. This includes the number of parts per yearand the processing (or assembly) time per part at each station. These factors deter-mine the workload that must be accomplished by the cell and therefore the numberof machines that must be included, as well as total operating cost of the cell and theinvestment that can be justified .
• Part size, shape, weight, and other physical attributes. These factors determine thesize and type of material handling and processing equipment that must be used.
Key Machine Concept. In some respects, a GT machine cell operates like a man.ual assembly line (Chapter 17), and it is desirable to spread the workload evenly among themachines in the cell as much as possible. On the other hand, there is typically a certain rna-chine in a cell (or perhaps more than one machine in a large cell) that is more expensiveto operate than the other machines or that performs certain critical operations in the plantThis machine is referred to as the key machine. It is important that the utilization of this
438 Chap. 15 / Group Technology and Cellular Manufacturing
(1)RepealOptra lion
(3) By-passing m- l iKl |!C|n-sequence
(4) Backtracking
Figure 15.13 Four types of part moves in a mixed model productionsystem. The forward flow of work is from left to right.
Determining the most appropriate cell layout depends on the routings of parts pro-duced in the cell. Four types of part movemeni can be distinguished in a mixed model partproduction system-They are illustrated in Figure 15.13 and are defined as follows, wherethe forward direction of work flow is defined as heing from left to right in the figure: (1) re-peal operation, in which a consecutive operation is carried out on the same machine, so thatthe pari does not actually move; (2) in-sequence move, in which the part moves from the-setfuen
current machine to an immediate neighbor in the forward direction; (3) by-passing mo ve,in which the part moves forward from the current machine to another machine that is twoor more machines ahead; and (4) backtracking move, in which the part moves from the cur-rent machine in the backward direction to another machine.
When the application consists exclusively of in-sequence moves, then an in-line lay-out is appropriate. A U-shaped layout also works well here and has the advantage of clos-er interaction among the workers in the cell. When the application includes repeatedoperations, then multiple stations (machines) are often required. For cells requiring by-passing moves, the U-shape layout is appropriate. When backtracking moves are needed,a loop or rectangular layout is appropriate to accommodate recirculation of parts withinthe cell. Additional factors that must be accounted for in the cell design include:
. Quantity of work to be done by the cell.This includes the number of parts per yearand the processing (or assembly) time per part at each station. These factors deter-mine the workload that must be accomplished by the eel! and therefore the numberof machines that must be included, as well as total operating cost of the cell and theinvestment that can be justified.
. Fart size, shape, weight, and other physical attributes. These factors determine thesize and type of material handling and processing equipment that must be used.
Key Machine Concept. In some respects, a GT machine cell operates like a man-ual assembly line (Chapter 17), and it is desirable to spread the workload evenly among themachines in the cell as much as possible. On the other hand, there is typically a certain ma-chine in a cell (or perhaps more than one machine in a large cell) that is more expensiveio operate than the other machines or that performs certain critical operations in the plant.
This machine is referred to as the key machine. It is important that the utilization of this
Sec, 15.5 I Application Considerations in Group Technology 439
key machine be high. even if it means that the other machines in the cell have relatively lowutilization. The other machines are referred to as.mpporting machines, and they should beorganized in the cell to keep the key machine busy. In a sense, the cell is designed so thatthe key machine becomes the bottleneck in the system.
The key machine concept is sornetnues used to plan the GT machine cell. The ap-proach i~ to decide what parts should be processed through the key machine and then de-termine what supporting machines are required to complete the processing of those parts.
There are generally two measures of utilization that are of interest in a GT cell: theutilization of the kev machine and the utilization of the overall cell. The utilization of thekey machine can be'measured using the usual definition (Section 2.4.3). The utilization ofeach of the other machines can also be evaluated similarly. The cell utilization is obtainedby taking a simple arithmetic average of all the machines in the cell. One of the exerciseproblems at the end of the chapter serves 10 illustrate the key machine concept and the de-termination of utilization
15.5 APPLICATION CONSIDERATIONS IN GROUP TECHNOLOGY
In this section, WP, ,~onsider how and where group technology is applied, and we report onthe results of a survey of industry ahout cellular manufacturing in the United States [38]
15.5.1 Applications of Group Technology
Tn our introduction to this chapter, we defined group technology as a "manufacturing phi-losophy." GT is not a particular technique, although various tools and techniques, such asparts classification and coding and production flow analysis, have been developed to helpimplement it. The group technology philosophy can be applied in a number of areas, Ourdiscussion focuses on the two main areas of manufacturing and product design.
Manufacturing Applications. The most common applications of GT are in man-ufacturing. And the most common application III manufacturing involves the formation ofcells of one klnd or another, Not all companies rearrange machines to form cells. There arethree ways in which group technology principles can be applied in manufacturing [24]:
1. Informal scheduling and routing of similar parts through selected machines. Thisapproach achieves setup advantages. but no formal part families are defined, and nophysical rearrangement of equipment is undertaken.
2. Virtual machine celkThis approach involves the creation of part families and ded-ication of equipment to the manufacture of these part families, but without the phys-ical rearrangement of machines into formal cells. The machines in the virtual cellremain in their original locations in the factory. Use of virtual cells seems to facilitatethe sharing of machines with other virtual cells producing other part families [25J.
3. Formal machine cells. This is the conventional GT approach in which a group of dis-similar machmes are physically relocated into a cell that is dedicated to the produc-tion of one or a limited set nfp:lTI families (Section 15.4.2). The machines in a formal~achine cell are located in close proximity to minimize part handling, throughputnrne.serup time, and work-in-process.
Sec. 15.5 / Application Considerations in Group Technologv
key machine be high, even il it means that the other machines in the cell have relatively lowutilization. The other machines are referred to as supporting machines, and they should be
organized in the cell to keep the key machine busy. In a sense, the cell is designed so thatthe key machine becomes the bottleneck in the system.
The key machine concept is sometimes used to plan the GT machine cell. The ap-proach i!. to decide what parts should be processed through the key machine and then de-termine what supporting machines are required to complete the processing of those parts.
There are generally two measures of utilization that are of interest in a GT cell: theutilization of the key machine and the utili/.ation of the overall cell. The utilization of thekey machine can be measured using the usual definition (Section 2.4.3). The utilization ofeach of the other machines can also be evaluated similarly. The cell utilization is obtainedby taking a simple arithmelic average of all the machines in the cell. One of the exerciseproblems at the end of the chapter serves to illustrate the key machine concept and the de-termination of utilization.
15.5 APPLICATION CONSIDERATIONS IN GROUP TECHNOLOGY
In this section, we. consider how and where group technology is applied, and we report on
the results of a survey of industry about cellular manufacturing in the United States [38],
15.5.1 Applications of Group Technology
In our introduction to this chapter, we defined group technology as a "manufacturing phi-losophy." GT is not a particular technique, although various tools and techniques, such asparts classification and coding and production flow analysis, have been developed to helpimplement it. The group technology philosophy can be applied in a number of areas. Ourdiscussion focuses on the two main areas of manufacturing and product design.
Manufacturing Applications. The most common applications of GT are in man-ufacturing, And the most common application in manufacturing involves the formation ofcells of one kind or another. Not all companies rearrange machines lo form tells. There arethree ways in which group technology principles can be applied in manufacturing [24]:
1. Informal scheduling and routing of similar parts through selected machines. This,
approach achieves setup advantages, but no formal part families are defined, and nophysical rearrangement of equipment is undertaken.
2. Virtual machine ceWs.This approach involves the creation of part families and ded-
ication of equipment to the manufacture of these part families, but without the phys-ical rearrangement of machines into formal cells.
The machines in the virtual cell
remain in their original locations in the factory. Use of virtual cells seems to facilitate
the sharing of machines with other virtual cells producing other part families [25].
3. Formal machine cetls.This is the conventional GT approach in which a group of dis-
similar machines are physically relocated into a cell that is dedicated to the produc-tion of one or a limited set of part families (Section 15.
4.2).The machines in a formal
machine cell are located in close proximity to minimize part handling, throughputtime, setup time, and work-in-process.
440 Chap. 15 / Group Technology 311d Cellular Manufacturing
Other GT applications in manufacturing include process planning (Chapter 25), fam-ily tooling, and numerical control (NC) part programs. Process planning of new parts canbe facilitated through the identification of part families. The new part is associated with anexisting part family. and generation of the process plan for the new part follows the rout-ing of the other members of the part family. This is done in a formalized way through theuse of parts classification and coding.The approach is discussed in the context of automated process planning (Section 25.2.1).
In the ideal, all members of the same part family require similar setups, tooling, andfixturing. This generally results in a reduction in the amount of tooling and fixturing need-edInstead of determining a special tool kit for each part, a tool kit is developed for eachpart family. The concept of a modular fixture can often be exploited, in which a commonbase fixture is designed and adaptations are made to switch between different parts inthe family
A similar approach can be applied in NC part programming. Called parametric pro-/lTamming. [28], it involves the preparation of a common NC program that covers the en-lire part family. The program is then adapted for individual members of the family byinserting dimensions and other parameters applicable to the particular part. Parametricprogramming reduces both programming time and setup time.
Product Design Applications. The application of group technology in productdesign is found principally in the use of design retrieval systems that reduce part prolif-eration in the firm. It has been estimated that a company's cost to release a new part de-sign ranges between $2000 and $12.000 [37]. In a survey of industry reported in [36], itwas concluded that in about 20% of new part situations, an existing part design could beused. In about 4(J% of the cases, an existing part design could be used with modifications,The remaining cases required new part designs. If the cost savings for a company gen-erating 1000 new part designs per year were 75% when an existing part design could beused (assuming that there would still be some cost oftime associated with the new partfor engineering analysis and design retrieval) and 50% when an existing design could bemodified, then the total annual savings to the company would lie between $700,000 and$4,200,000, or 35% of the company's total design expense due to part releases. The kindsof design savings described here require an efficient design retrieval procedure. Mostpart design retrieval procedures lin: based on parts classification and coding systems(Section 15.2).
Other design applications of group technology involve simplification and standard-ization of design parameters, such as tolerances inside radii on corners, chamfer sizes on out-side edges, hole sizes, thread sizes, and so forth. These measures simplify design proceduresand reduce part proliferation. Design standardization also pays dividends in manufactur-ing by reducing the required number of distinct lathe tool nose radii, drill sizes,and fastenersizes. There is also a benefit in terms of reducing the amount of data and information thatthe company must deal with. Fewer part designs, design attributes, tools, fasteners, and soon mean fewer and simpler design documents, process plans, and other data records.
15.5.2 Survey of Industry Practice
A number of surveys have been conducted to learn how industry implements cellular manufacturing [24], [36], [38J. The surveyed companies represent manufacturing industries,such as machinery, machine tools, agricultural and construction equipment, medical equip-
Chap. 15 / Group Technology and Cellular Manufacturing
Other GT applications in manufacturing include process planning (Chapter 25), fam-ily tooling, and numerical control (NC) part programs. Process planning of new parts canbe facilitated through the identification of part families.The new part is associated with anexisting part family, and generation of the process plan for the new part follows the rout-ing of the other members of the part family. This is done in a formalized way through theuse of parts classification and coding. The approach is discussed in the context of automated process planning (Section 25.2.1).
In the ideal, all members of the same part family require similar setups, tooling, and
fixturing. This generally results in a reduction in the amount of tooling and fixturing need-ed. Instead of determining a special tool kit for each part, a tool kit is developed for eachpart family.The concept of a modular fixture can often be exploited, in which a coinmonbase fixture is designed and adaptations are made to switch between different parts inthe family.
A similar approach can be applied in NC part programming. Called parametric pro-gramming, [28], it involves the preftire part family. The program is then adapted for individual members of the family bygramming, [28], it involves the preparation of a common NC program that covers the en-tire part family. The program is then adapted for individual members of the family byinserting dimensions and other parameters applicable to the particular part. Parametricprogramming reduces both programming time and setup time.
Product Design Applications. The application of group technology in productdesign is found principally in the use of design retrieval systems that reduce part prolif-eration in the firm. It has been estimated that a company's cost to release a new part de-sign ranges between $2000 and $12,000 [37], In a survey of industry reported in [36], itwas concluded thai in about 20% of new part situations, an existing part design could bewas concluded thai in about 20% of new part situations, an existing part design could beused. In about 40% of the cases, an existing pari design could be used with modificationf.The remaining cases required new part designs. If the cost savings for a company gen-
dbe
Id be
The remaining cases required new part designs. If the cost savings for a company gen-part designs per year were 75% when an existing part design could berat there would still be some cost of time associated with the new partnalysis and design retrieval) and 50% when an existing design could be
modified, then the total annual savings to the company would lie between $700,000 and
$4,200,000, or 35% of the company's total design expense due to part releases. The kinds
crating 1000 new part designs per year were 75% when an existing par'ouid still be some cost of time associated \
I design retrieval) and 50% when an existin_
modified, then the total annual savings to the company would lie between $700,000 and
$4,200,000, or 35% of the company's total design expense due to part releases. The kindsof design savings described here require an efficient design retrieval procedure.
Mosl
part design retrieval procedures are based on parts classific;(Section 15.2).
Other design applications of group technology involve simplification and standard-ization of design parameters, such as tolerances, inside radii on corners, chamfer sizes on out-
retrieval procedures are based on parts classification and coding system
ters, such
side edges, hole sizes, thread sizes, and so forth. These measures simplify design proceduresand reduce part proliferation. Design standardization also pays dividends in manufactur-ing by reducing the required number of distinct lathe tool nose radii,
drill sizes, and fastener
sizes. There is also a benefit in terms of reducing the amount of data and information thatthe company must deal with. Fewer part designs, design attributes, tools, fasteners, and s<
n fewer and simpler design documents, process plans, and othern mean fewer and simpler design documents, process plans, and other data records.
15.5.2 Survey of Industry Practice
A number of surveys have been conducted to leam how industry implements cellular n.aiiufacturing [24], [36], [38]. The surveyed companies represent manufacturing industries,such as machinery, machine tools, agricultural and construction equipment, medical equip-
Sec. 15.5 I Application Considerations in Group Technology
TABLE 15.7 Benefits of Cellular Manufacturing Reported by Companies in Survey
441
Reason for Installing Manufacturing Cells
AverageImprovement ('Yo)Rank,
2345678910
"
Reduce throughput time IManufacturing lead time)Beduce work-ln-processImprove partand/or product qualityReduce response time for customer ordersReduce rnove d.stancesIncrease manufacturing flexibilityReduce unit costsSimplify production planning and controlFacilitate employee involvementReduce setup timesReduce finished goods inventory
6'48285061
16
4439
merit. weapons systems. diesel engines. and piece parts. Processes grouped into cells in thecompanies included machining, joining and assembly, finishing, testing, and metal forming
Companies in the survey were asked to report their reasons for establishing machinecells and the benefits they enjoyed from implementing cellular manufacturing in the op-erations. Results are listed in Table 15.7. The reasons are listed in the relative order ofim-penance as indicated by the companies participating in the survey. We also list the averagepercentage improvement reported by the companies, rounded to the nearest whole per-centage point. Reasons 6, 8, and 9 are difficult to evaluate quantitatively, and no percent-age improvements are listed in these cases.
One of the questions considered in the 1989 survey [36] was: What are the approachesused by companies to form machine ccus'' The results are listed in Table 15.8. The most com-mon approach consisted of visually grouping similar parts with no consideration given toexisting routing information and no parts classification and coding. The use of a part-ma-chine incidence matrix was not widely reported, perhaps because the formal algorithmsfor reducing this matrix, such as rank order clustering (Section 15.6.1) were not widelyknown at the time of the survey
Companies also reported costs associated with implementing cellular manufacturingj3o].Thc reponed cost categories are listed in Table 15.9 together with the number of com-panies reporting the cost. No numerical estimates of actual costs are provided in the report.
Approach to Cell Formation
TABLE 15.a Approaches to Cell Formation Used in Industry
19 Section 15.1
11 Section 15.4.2~ Section 15.3, Section 15.6.1
Visual inspection to identify family ofsimilar parts
Number of CompaniesEmploying the Approach Text Reference
Sec. 15.5 / Application Considerations in Group Technology 441
TABLE 15.7 Benefits of Cellular Manufacturing Reported by Companies in Survey
AverageRank Reason for Installing Manufacturing Cells Improvement (%)
1 Reduce throughput time I Manufacturing lead time) 612 Reduce work-in-process 483 Improve part and/or product quality 284 Reduce response time for customer orders 505 Reduce move distances 61
6 Increase manufacturing flexibility7 Reduce unit costs 16
8 Simplify production planning and control9 Facilitate employee involvement10 Reduce setup times 4411 Reduce finished goods ini/entory 39
Source: Wemmerlov and Johnson [381.
men t. weapons system;,, dicseI engines, and piece parts. Processes grouped into cells in the
companies included machining, joining and assembly, finishing, testing, and metal forming.Companies in the survey were asked to report their reasons for establishing machine
cells and the benefits they enjoyed from implementing cellular manufacturing in the op-erations. Results are listed in Table 15.7. The reasons are listed in the relative order of im-
portance as indicated by the companies participating in the survey. We also list the averagepercentage improvement reported by the companies, rounded to the nearest whole per-centage point. Reasons 6,8, and 9 are difficult to evaluate quantitatively, and no percent-age improvements are listed in these cases.
One of the questions considered in the 1989 survey [36] was: What are the approachesused by companies lo form machine cells? The results are listed in Table 15.
8. The most com-
mon approach consisted of visually grouping similar parts with no consideration given toexisting routing information and no parts classification and coding. The use of a part-ma-chine incidence matrix was not widely reported, perhaps because the formal algorithmsfor reducing this matrix, such as rank order clustering (Section 15.6.1) were not widelyknown at the time of the survey.
Companies also reported costs associated with implementing cellular manufacturing[36],The reported cost categories are listed in Table 15.9 together with the number of com-panies reporting the cost. No numerical estimates of actual costs are provided in the report.
TABLE 15.8 Approaches to Cell Formation Used in Industry
Number of CompaniesApproach to Cell Formation Employing the Approach Text Reference
Visual inspection to identify family of 19 Section 15.1similar parts
Key machine concept 11 Section 15.4
.2
Use of part-machine incidence matrix 9 Section 15,3
, Section 15.6.1
Other methods |e.g.r From-to diagrams, 7simple sorting of routings)
Source: Wemmerlov and Hver (361.
Chap. 15 / Group Technology and Cellular Manufacturing
TABLE 15.9 Costs of Introducing Cellular Manufacturing Reported by Companiesin Survey
Number of CompaniesCost Reporting
1. Relocation and installation of machines 162. Feasibility studies, planning and design, and related costs 83. New equipment and duplication of equipment 64. Training 65. New tooling and fixtures 56. Programmable controllers, computers, and software 47. Material handtinq equiprnent 28. Lost production time during installation 29. Higher operator wages 1
Source-Wem.-nerlovandHyar[36]
Topping the list wa.s the expense of equipment relocation and installation. Most of thecompanies responding tu the survey had implemented cellular manufactunng by movingequipment in the factory rather than hy installing new equipment to form the cell.
15.6 QUANTITATIVE ANALYSIS IN CELLULAR MANUFACTURING
A number of quantitative techniques have been developed to deal with problem areas ingroup technology and cellular manufacturing. In this section, we consider two problemareas: (1) grouping parts and machines into families, and (2) arranging machines in a GTcell. The first problem area has been and still is an active research area, and several of themore significant research publications are listed in our references [2}, [3}, [II}, [12], [26}, [27}.The technique we describe in the current section for salving the part and machine group-ing problem is rank orderciustering [26J. The second problem area has also been the sub-ject of research, and several reports are listed in the references [1], [6], [8]. [17). In Section15.6.2. we describe two heuristic approaches introduced by Hollier II7].
15.6.1 Grouping Parts and Machines by Rank OrderClustering
The problem addressed here is to determine how machines in an existing plant should begrouped into machine cells. The problem is the same whether the cells are virtual or for-mal (Section 15.5.1 ).It is basically the problem of identifying part families. By identify-ing part families, the machines required in the cell to produce the part family can beproperly selected. As previously discussed, the three basic methods to identify part fam-ilies are (1) visual inspection, (2) parts classification and coding, and (3) production flowanalysis.
The rank order clustering technique. first proposed by King [26J, is specifically ap-plicable in production flow analysis. It is an efficient and easy-to-use algorithm for group-ing machines into celts. In a starting part-machine incidence matrix that might be compiledto document the part ruutings in a machine shop (or other job shop), the occupied locationsin the matrix are organized in a seemingly random fashion. Rank order clustering works
Chap. 15 / Group Technology and Cellular Manufacturing
TABLE 15.9 Costs of Introducing Cellular Manufacturing Reported by Companiesin Survey
Number of CcerofCompantReporting
)n, and related costsuipment
1. Relocation and installation of machines
2. Feasibility studies, planning and design,
3. New equipment and duplicatiori of equi|
4. Training 6
5. New tooling and fixtures 56, Programmable controllers, computers, and software 47
. Material handling equipment 28. Lost production time (luring installation 29
. Higher operator wages 1
lerlovand Hyer [361.
Topping the list was the expense of equipment relocation and installation. Most of (hecompanies responding to the survey had implemented cellular manufacturing by movingequipment in the factory rather than by installing new equipment to form the cell.
15.6 QUANTITATIVE ANALYSIS IN CELLULAR MANUFACTURING
group technology and cellular manufacturing. In this section, we consider two problem:s: (1) grouping parts and machines into families, and (2) arranging machines in a GT
A number of quantitative techniques have been developed to deal with problem areas inj. In this sectioi
) grouping parts and machines into ftcell. The first problem area has been and still is an active research area,
and several of the
more significant research publications are listed in our references [2], [3], [11], [12], [26], [27].The technique we describe in the current section for solving the part and machine group-ing problem is rank order clustering [26].The second problem area has also been the sub-ject of research, and several reports are listed in the references [1], [6], [8], [17]. In Section15.6.2. we describe two heuristic approaches introduced by Hollier [17].
15.6.1 Grouping Parts and Machines by Rank OrderClustering
The problem addressed here is to determine how machines in an existing plant should begrouped into machine cells. The problem is the same whether the ceils are virtual or for-mal (Section 15.5.1). It is basically the problem of identifying part families. By identify-ing part families, the machines required in the cell to produce the part family can beproperly selected. As previously discussed, the three basic methods to identify part fam-ilies are (1) visual inspection, (2) parts classification and coding, and (3) production flowanalysis.
The rank order clustering technique, first proposed by King [26], is specifically ap-plicable in production flow analysis. It is an efficient and easy-to-use algorithm for group-ing machines into celts. In a starting part-machine incidence matrix that might be compiledto document the part njutings in a machine shop {or other job shop), the occupied locationsin the matrix are organized in a seemingly random fashion. Rank order clustering works
Sec. 15.6 I Quantitative Analysis in Cellular Manufacturing 443
bv reducing the part-machine incidence matrix to a set of diagonalized blocks that repre-sent part families and associated machine groups. Starting with the initial part-machine in-cidence matrix. the algorithm consist, of the following steps:
1. In each row of the matrix. read the series of ls and G's (blank entries = D's) from leftto fight as a binary number. Rank the rows in 01 del uf decreasing value. In case of atie, rank the rows in the same order as they appear in the current matrix
2. Numbering from top to bottom, is the current order of rows the same as the rank orderdetermined in the previous step? If yes, go to step 7, If no, go to the following step.
3, Reorder the rows in the part-machine incidence matrix by listing them in decreasingrank order, starting from the top
4. In each column ot tbe matrix. read the series of I 's and O's (blank entries = (j's) fromtop to bottom as a binary number. Rank the columns in order of decreasing value, Incase of a tie. rank the columns in the same order as they appear in the current matrix.
5. Numbering Irom left to right, is the current order of columns the same as the rankorder determined in the previous step? If yes. go to step 7. If no.go to the following step.
6. Reorder the columns in the part-machine incidence matrix by li~ling them in de-creasing rank order, starting with the left column. Go to step I.
7 Stop
For readers unaccustomed to evaluating binary numbers in steps 1 and 4, it might be help-ful to convert each binary value into its decimal equivalent (e.g., the entries in the first rowof the matrix in Table 15.4 are read as 100100(10). This is converted into its decimal equiv-alent as follows: lx28 + Ox2' + Ox2b + 1x25 + Ox24 + Ox23 + Ox22 + Ix2] + Ox2° =
256 + 32 + 2 = 290. It should be mentioned that decimal conversion becomes impracti-cal for the large numbers of parts found in practice, and comparison of the binary numbersis preferred
EXAMPLE 15.3 Rank Order Cfuseering Technique
Apply the rank order clustering technique to the part-machine incidence ma-trixinTable 15.4
Solution: Step I consists 01 reading the series of 1 's and D's in each row as a binary num-ber. We have done this in Table 15.IO(a). converting the binary value for eachrow to its decimal equivalent. The values are then rank ordered in the far right-hand column. In step 2. we see that the row order is different from the startingmatrix. We therefore reorder the rows in step 3. In step 4, we read the series ofI's and D's in each column from top to bottom as a binary number (again we haveconverted to the decirnalcquivajenr], and the columns are ranked in order ofdecreasing value, as shown in Table 15.10(b).ln step 5, we see that the columnorder is different from the preceding matrix. Proceeding from step 6 back tosteps 1 and 2, we see that a reordering of the columns provides a row order thatis in descending value. and the algorithm is concluded (step 7). The final sotu-riou is shown in Table 15.10(c), A close comparison of this solution with Table15,5 reveals that they are the carne part-machine groupings,
Sec. 15.6 / Quantitative Analysis in Cellular Manufacturing
by reducing the part-machine incidence matrix to a set of diagonalized blocks that repre-sent part families and associated madiiut' groups. Starling with the initial part-machine in-
cidence matrix, the algorithm consists of the following steps:
1.
In each row of the malrix.read the series of Is andO's (blank entries = O
"s)fromleftto right as a binary number. Rank the rows in oidci of decicasing value. In case of atie, rank the rows in the same order as they appear in the current matrix.
2. Numbering from top to bottom, is ihe current order of rows the same as the rank order
determined in the previous step? If yes, go to step 7. If no, go to the following step.3
. Reorder the rows in the part-niachine incidence matrix by listing thera in decreasingrank order, starting from the top.
4. In each column ot the matrix, read the series of 1 's and O's (blank entries = (I's) from
top to bottom as a binary number. Rank the columns in order of decreasing value. Incase of a tie, rank the columns in the same order as they appear in the current matrix.
5. Numbering Irom left to right, is the current order of columns the same as the rank
order determined in the previous step? If yes, go to step 7. If no. go to the following step.
6. Reorder the columns in the part-machine, incidence matrix by listing them in de-
creasing rank order, starting with the left column. Go to step 1.
7 Stop.
For readers unaccustomed to evaluating binary numbers in steps 1 and 4, it might be help-ful to convert each binary value into its decimal equivalent (e.g., the entries in the first rowof the matrix in Table 15.4 are read as 100100010). This is converted into ils decimal equiv-alent as follows: U-28 + Oxl1 + O.rl" + 1x2s + 0x2' + 0x23 + ()x2z + 1x2' + 0x2° =256 + 32 + 2 = 290. It should be mentioned that decimal conversion becomes impracii-cal for the large numbers of parts found in practice, and comparison of the binary numbersis preferred.
EXAMPLE 15.3 Rank Order Clusiering Technique
Apply ihe rank order clusiering technique to the part-machine incidence ma-trix in Table 15.4.
Solution: Step 1 consists ol reading the series of 1 's and 0"s in each row as a binary num-ber. We have done this in Table 15.10(a), converting the binary value for eachrow to its decimal equivalent. I he values are then rank ordered in the far right-hand column. In step 2, we see that the row order is different from the startingmatrix. We therefore reorder the rows in step 3. In step 4, we read the series ofTs and O's in each column from top to bottom as a binary number (again we haveconverted to the decimal equivalent),
and the columns are ranked in order of
decreasing value, as shown in Table 15.10(b). In step 5, we see that the columnorder is different from the preceding matrix. Proceeding from step 6 back tosteps 1 and 2, we see that a reordering of (he columns provides a row order thatis in descending value, and the algorithm is concluded (step 7). The final solu-tion is shown in Table 15.10(c). A close comparison of this solution with Table15.5 reveals that they are the same part-machine groupings,
444 Chap. 15 I Group Technology and Cellular Manufacturing
TABLE 15.10{a} First Iteration {Step 1) in the Rank Order Clustering Technique Applied to Example
15.3
a a " a " "Parts Decimal
Equivalent Rank
290
17
81
13.
258
65
140
Machines
TABLE 15.101bJ Second Iteration (Steps 3 and 4) in the Rank Order Clustering Technique Appliedto Example 15.3
Parts
Machines
a
a
a
a
a
"a
Decimal 96Equivalent
64 24 16 96
Rank
Binary Values
Chap. 15 / Group Technology and Cellular Manufacturing
TABLE 15.10{al First Iteration (Step 1) in the Rank Order Clustering Technique Applied to Example15.3
Binary Values 2"
Decimal
Equivalent Rank
290 1
7
5
4
2
6
3
D
TABLE 15.10(bl Second Iteration (Steps 3 and 4) in the Rank Order Clustering Technique Appliedto Example 15.3
D G Binary Value
2"
2=
,4
2J
2U
Decimal
Equivalent
Rank 1
Sac. 15.6 " Ouantltetive Analysis in Cellular Manufacturing 445
TABLE 1S.10Ic) Solution of Example 15.3
Parts
Machines
, 1 1
1 1
1 1 1 I
, 1
1 , ,, ,1 ,
In the example problem, it was possible to divide the parts and machines into threemutually exclusive part-machine groups. This represents the ideal case because the partfamilies and associated machine cells are completely segregated. However, it is not un-common for there to be an overlap in precessing requirements between machine groupsThat is, a given part type needs to be processed by more than one machine group. Let usillustrate this case and how the rank order clustering technique deals with it in the follow-ingexampJe.
EXAMPLE 15.4 Overlapping Meehjne RequiremenfS
Consider the part-machine incidence matrix in Table 15.11. This is the same as theoriginal part-machine incidence matrix in Table 15.4 except that part B requires
TABLE 15.1' Part-Machine Incidenca Matrix for Example 15.4
Parts
Machines
Sec. 15.6 / Quantitative Analysis in Cellular Manufacturing
TABLE 15.10(c) Solution of Example 15.3
G
In the example problem, it was possible to divide the partsmutually exclusive part-machine groups. This represents the id*families and associated machine cells are completely segregate
and machines into three
ideal case because the partletely segregated. However,
it is not un-
common for there to be an overlap in processing requirements between machine groups,Thai is. a given part type needs to be processed by more than one machine group. Let usillustrate Ihis case and how the rank order clustering technique deals with il in the follow-ing example.
EXAMPLE 15.4 Overlapping Machine Requirements
Consider the part-machine incidence matrix in Table 15.ll.This is the same as theoriginal part-machine incidence matrix in Table 15.4 except that part B requires
TABLE 15.11 Part-Machine Incidence Matrix for Example 15.4
Parts
2
3
5
6
7
G
446 Chap. 15 / Group Technology and Cellular Manufacturing
processing on machines 1.4, and 7 (1 is the additional machine) and partD nowrequires processing on machines 1 and 4 (4 is the additional machine). Use therank order clustering technique to arrange parts and machine into groups.
Solution: The rank order clustering technique converges to a solution in two iterations,shown in Tables 15.12(a) and 15.l2(b), with the final solution shown inTable1.'l.12(c).
TABLE 15.12Ia) First Iteration of Rank Order Clustering Applied to Example 15.4
Machines
2" 2' 2' 2' 2' 2'
Parts Decimal
Equivalent Ran(
418
17
B1
'68
258
65
140
Binary Values 2" 2) 26
TABLE 15.12(b) Second Iteration of Rank Order Clustering Applied to Example 15.4
Parts
Machines A Binary Values
I; 2"
2'
I2'
I 2'
I
2'
2'
2'
96 68 24 96DecimalEQuivalent
Rank
Chap. 15 / Group Teclinology and Cellular Manufacturing
jrocessing on machines 1.4, and 7 (1 is the additional machine) and part D nowrequires processing on machines 1 and 4 (4 is the additional machine). Use the
rank order clustering technique to arrange parts and machine into groups.
Solution: The rank order clustering technique converges to a solution in two iterations,shown in Tables 15.12(a) and 15.12(b), with the final solution shown inTablelS. 12(c).
TABLE IS.12{a) First Iteration of Rank Order Clustering Applied to Example 15.4
Binary Values
1
2
3
5
6
7
2" 2s 23 2'
B :qu(Valert
418
65
7
5
3
2
6
4
TABLE 15.12(b) Second Iteration of Rank Order Clustering Applied to Example 15.4
Parts
Machines ABCDEHGHI Binary Values- -_ - __.
2
5
4
7
3
S
2
EqiDecimalluivalent
1
96
1
1
1
1
6
1 1
1
1
1
8
1
1
1
1
7
26
2'
23
2'
21
2°
1 3 8 4 9 5 6 2 7
Sec.15.6 Quantitative Analysis in Cellular Manufacturing 447
TABLE15.12lcl Solution of Example 15.4
Parts
"-1' I~-, ,, ,
Parts B and D could be included in either of two machine groups. Our solutionincludes them in machine group (-1.7); however, they must also be proee~s,,<J ill machinegroup i!. 5)
King [26] refers to the matrix elements Bl and Dj (parts Band D processed on ma-chine in Table 15.l2(c) as exceptional elemems, He recommends that they each he re-
an asterisk (*) and treated as zeros when applying the rank order clusteringtechnique. The effect of' this approach in our example problem would be to organize themachines exactly as we have done in our final solution in Table 15.12(c).Anotherway ofdealing with the overlap h simply to duplicate the machine that is used hy more than onepart family. In Example 15.4, this would mean that two machines of type 1 would be usedin the two censTbe result of this duplication is shown in the matrix ofJable 15.13.wherethe two machines are identified as l a and jb. Of course. there may be economic consider-ations that would inhibit the machine redundancy.
Other approaches to the problem of overlapping machines, attributed to Burbidge[26J, include: (1) change the routing so that all processing can be accomplished in the pn.mary machine group. (2) redesign the part to eliminate the processing requirement outsidethe primary machine group, and (3) purchase the part from an outside supplier.
15.6.2 Arranging Machines in 8 GT Cell
After part-machine groupings have he en identified hy rank order clustering or othermethod. the next problem is to organize the machines into the most logical arrangement.Let us describe two simple yet effective methods suggested by Hollier [17].2 Both methodsuse data contained in From-To charts (Section 10.6.1) and are intended to arrange the ma-chines in an order that maximizes the proportion of in-sequence moves within the cell
Sec. 15.6 / Quanlitaiive Analysis in Cellular Manufacturing
TABLE 15.12(c) Solution of Example 15.4
5
7
3
6
2
447
Parts B and D could be included in either of two machine groups. Our solutionincludes them in machine group (-1, 7); hnwever, :hcy must also be processed in machir.egroup il. 5).
King [26] refers to the matm elements Bl and Dl (parts B and D processed on n
'
~*
mts. He recommends that they each be re-is when applying the rank order clustering
chine I) in Table 15.12(c) as exceptional elements. He recommends that they each be re-placed with an asterisk (*) and treated atechnique. The effeci of this approach in our example problem would be to organize the
ichincs etaclly as we have done in our final solution in Table 15.12(c}. Another way ofdealing with the overlap is simply to duplicate the machine thai is used by more than opart family. In Example 15.4, this would mean that two machines of type 1 would be usedin the two cells. The result of this duplication is shown in the matrix of'fable 15.13. wherethe two machines are identified as la and lb. Of course
, there may be economic consider-alkms that would inhibit the machine redundancy.
Other approaches to the problem of overlapping machines, attributed to Burbidge[26], include: (1) change the routing so that all processing can be accomplished in themary machine group. (2) redesign the part to eliminate the processing requirement outthe primary machine group, and (3) purchase the part from an outside supplier.
: pn-
15.6.2 Arranging Machines in a GT Cell
After part-machine groupings have been identified hy rank order clustering or othermethod, the next problem is to organize the machines into the most logical arrangement,
Let us describe two simple yet effective methods suggested by Hollier [17].2 Both methods
use data contained in From-To charts (Section 10.6.1 j and are intended to arrange the ma-
~' -i-.. .
o wj in-sequence moves within the cell.chines in an order that maximizes the proportior
:H0ll,el
which we dcs«r IHollicr] inlrodnbc ih: firs; [wo
six heuristic approaches to ing the machine arrangement problem, of
448 Chap. 15 I Group Technclcgv and Cellular Manufacturing
TABLE 15.13 Solution to Example 15.4 Using Duplicate Machines of Tvpe 1 {Shown
as Machines ta and 1b in the Matrix}
Parts
Machines
" 1 1
1 1
1 1 1
1 1
1 1 1
1 1 1
1 1
1 1
lb
Hollier Method 1. The first method uses the sums of flow "From" and "To" eachmachine in the cell. The method can be outlined as follows:
L Df!1'elopthe From-To chartfrom part routing data. The data contained in the chartindicates numbers of part moves between the machines (or workstations) in the cell.Moves into and out of the cell are not included in the chart.
2. Delermine the "From" lUId "To" sums for eQch machine. This is accomplished bysumming all of the "From" trips and "To" trips for each machine (or operation). The"From" sum for a machine is determined by adding the entries in the correspondingrow, and the "To" sum is found by adding the entries in the corresponding column.
3. Assign machines to the cell hosed on minimum "From" or "To" sums. The machinehaving the smallest sum is selected. If the minimum value is a "To" sum, then the ma-chine is placed at the beginning of the sequence. If the minimum value is a "From"sum, then the machine is placed at the end of the sequence. TIe breaker rules:(a) If a tie occurs between minimum "To" sums or minimum "From" sums, then the
machine with the minimum "From/To" ratio is selected.(b) If both "To" and "From" sums are equal for a selected machine,it is passed over
and the machine with the next lowest sum is selected.(c) If a minimum "To" sum is equal to a minimum "From" sum, then both machines
are selected and placed at the beginning and end of the sequence, respectively.4. Rejrmnat the From-To chan. After each machine has been selected, restructure the
From-To chart by eliminating the row and column corresponding 10 the selected ma-chine and recalculate the "From" and "To" sums. Repeat steps 3 and 4 until all ma-chines have been assigned.
Chap. 15 / Group Technology and Cellular Manufacturing
TABLE 15.13 Solution to Example 15.4 Using Duplicate Machines of Type 1 {Shownas Machines 1a and 1b in the Matrix}
Parts
B G
la
Hollier Method 1. The first method uses the sums of flow "From" and "To" each
machine in the cell.The method can be outlined as follows:
1. Develop the From-To chart from pan routing data. The data contained in the chart
indicates numbers of part moves between the machines (or workstations) in the cell.Moves into and out of the cell are not included in the chart.
2. Determine the "From" and "To" sums for each machine. This is accomplished by
summing all of the "From" trips and "To" trips for each machine (oroperation).The"From" sum for a machine is determined by adding the entries in the correspondingrow, and the "To"
sum is found by adding the entries in the corresponding column.3
. Assign machines to the cell based on minimum "From" or "To" sums. The machinehaving the smallest sum is selected. If the minimum value is a "To" sum,
then the ma-
chine is placed at the beginning of the sequence. If the minimum value is a "From"sum, then the machine is placed at the end of the sequence. Tie breaker rules:(a) If a tie occurs between minimum "To" sums or minimum "From" sums, then the
machine with the minimum "From/To" ratio is selected.
(b) If both "To" and "From" sums are equal for a selected machine, it is passed overand the machine with the next lowest sum is selected.
(c) If a minimum "To" sum is equal to a minimum "From" sum, then both machinesare selected and placed at the beginning and end of the sequence, respectively.
4. Reformat the From-To chart. After each machine has been selected, restructure the
From-To chart by eliminating the row and column corresponding to the selected ma-chine and recalculate the "From" and 'To" sums. Repeat steps 3 and 4 until all ma-chines have been assigned.
Sec. 15.6 / Quantitative Analysis in Cellular Manufacturing 449
EXAMPLE 15.5 Group Technology Machine Sequence using HoDier Method 1
Suppose that four machines. I, 2.3, and 4 have been identified as belonging ina OT machine cell. An analysis of 50 parts processed on these machines hasbeen summarized in the From-To chart of Table 15.14. Additional informationis that '50 parts enter the machine grouping at machine 3,20 parts leave after pro-cessing at machine 1, and 30 parts leave after machine 4. Determine a logical ma-chine arrangement using Hollier Method 1.
Solution: Summing the From trips and To trips for each machine yields the "From" and"To" sums in Table 15.15(a). The minimum sum value is the "To" sum for ma-chine 3. Machine 3 is therefore placed at the beginning of the sequence. Elim-inating the row and column corresponding to machine 3 yields the revisedFrom-To chart in Table 15.15(b). The minimum sum in this chart is the "To"
TABLE 15.14 From-To Chart for Example 15.5
To:
From: 1
30
10
10
"15
40
TABLE 15.1518) From and To Sums for Example 15.5: FirstIteration
To: 2 3 4 "Fromwsum.
From: 1 0 5 0 " '0
'0 0 0 15 45
10 40 0 0 50
10 0 0 0 10
wTo"'sums 50 45 0 40 135
TABLE 15.151bJ From and To Sums for Example 15.5:Second Iteration with Machine 3 Removed
To: "'From'" Sums
From: 1
'025
15
ae45
'0
40 40NTowsums
Sec. 15.6 / Quantitative Analysis in Cellular Manufacturing 449
EXAMPLE 1S.S Group Technology Machine Sequence using Hollier Method 1
Suppose that four machines, 1,2.3
, and 4 have been identified as belonging ina GT machine cell. An analysis of 50 parts processed on these machines hasbeen summarized in the From-To chart of Table 15
.14. Additional information
is that 50 parts enter the machine grouping at machine 3,20 parts leave after pro-cessing at machine 1, and 30 parts leave after machine 4. Determine a logical ma-chine arrangement using Hollier Method 1.
Solution: Summing the From trips and To trips for each machine yields the "From" and"
To" sums in Table 15.15(a). The minimum sum value is the "To" sum for ma-chine 3. Machine 3 is therefore placed at the beginning of the sequence.
Elim-
inating the row and column corresponding lo machine 3 yields the revisedFrom-To chart in Table 15.15(b). The minimum sum in this chart is the "To"
TABLE 15.14 From-To Chart for Example 15.5
To: 12 3 4
From: 1 0 5 0 25
2 30 0 0 15
3 10 40 0 0
4 10 0 0 0
TABLE 15.151a) From and To Sums for Example 15.5: First
Iteration
To: 1 2 3 4 "From" Sums
From: 1 0 5 0 25 30
2 30 0 0 15 45
3 10 40 0 0 50
4 10 0 0 0 10
"
To" sums 50 45 0 40 135
TABLE 15.15(b) From and To Sums for Example 15.5:
Second Iteration with Machine 3 Removed
To: 1 2 4 "From" Sums
From: 1 0 5 25 30
2 30 0 15 45
4 10 0 0 10
"To'sums 40 5 40
Chap, 15 I Group Technology and Cellular Manufacturing
TABLE 15.15(cl From and To Sums for Example 15.5: ThirdIteration with Machine 2 Removed
To: 4 MFrom" Sums
10 0 10
tu 25
sum corresponding to machine 2. which is placed at the front at the sequence,immediately following machine 3. Eliminating machine 2 produces the revisedFrom-To chart in Tahle 15.15(c). The minimum sum in this chart is the "To"sum for machine I. Machine I is placed after machine 2 and finally machine 4is placed at the end of the sequence. Thus, the resulting machine sequence is
3--->2--->1--->4
Hollier Method 2. This approach is based on the use of From/Ib ratios formed bysumming the total flow from and to each machine in the cell. The method can he reducedto three steps:
1. Develop the From-To chart. This is the same step as in Hollier Method 1.
2. Determine the From/To ratio for each machine. This i~ accomplished by summingup all of the "From"trips and "To" trips for each machine (or operation). The "From"sum for a machine is determined by adding the entries in the corresponding row, andthe "To" sum is detcnnined by adding the entries in the corresponding column. Foreach machine, the From/To ratio is calculated by taking the "From" sum for each ma-chine and dividing by the respective "To" sum.
3. Arrunge machines in order of decreasing From/To ratio. Machines with II highFrom/To ratio distribute work to many machines in the cell but receive work from fewmachines. Conversely, machines with a low Fromffo ratio receive more work thanthey distribute. Therefore, machines are arranged in order of descending Prom/Ioratio. That is, machines with high ratios are placed at the beginning of the work flow,and machine, with low ratios are placed at the end of the work flow. in case of a tie,the machine with the higher "From" value is placed ahead of the machine with alower value
EXAMPLE 15.6 Group Technology Machine Sequence using Hollier Me.hod 2
Solve Example 15.5 using Hollier Method 2.
Solution: Table 15.15(a), containing the "From" and "To" sums, is repeated in Table 15.16,along with the From/To ratios given in the last column on the right. Arrangingthe machines III order of descending Prom/To ratio, the machines in the cellshould he sequenced as follows'
3--->2~1 __ 4
From'
MTo" sums
Chap. 15 / Group Technology and Cellular Manufacturing
TABLE 15.15(c) From and To Sums for Example 15.5: ThirdIteration with Machine 2 Removed
To: 1 4 "From" Sums
From- J 0 25 25
4 10 0 10
10 25
n corresponding to machine 2. which is placed at the front of the sequence,immediately following machine 3. Eliminating machine 2 produces the revisedFrom-To chart in Table 15.15(c). The minimum sum in this chart is the "To"sum for machine 1. Machine 1 is placed after machine 2 and finally machine 4is placed at the end of the sequence. Thus, the resulting machme sequence is
3 -> 2 1 -v 4
Hollier Method 2. This approach is based on the use of From/To ratios formed bysumming the total flow from and to each machine in the cell. The method can be reducedto three steps:
1. Develop the From-To eAaW.This is the same step as in Hollier Method 1.
2. Determine the From/To ratio for each machine. This is accomplished by summing
up all of the "From" trips and "To" trips for each machine (or operation). The "From"
sum for a machine is determined by adding the entries in the corresponding row, and
the "To" sum is determined by adding the entries in the corresponding column. For
each machine, the From/To ratio is calculated by taking the "From" sum for each ma-
chine and dividing by the respective "To" sum.
3. Arrange machines in order of decreasing From/To ratio. Machines with a high
From/To ratio distribute work to many machines in the cell but receive work from fewmachines. Conversely, machines with a low From/To ratio receive more work than
they distribute. Therefore, machines are arranged in order of descending From/Toratio.That is, machines with high ratios are placed at the beginning of the work flow,
and machines with low ratios are placed at the end of the work flow. In case of a tie
,
the machine with the higher "From" value is placed ahead of the machine with alower value.
EXAMPLE 15.6 Group Technology Machine Sequence using Hollier Method 2
Solve Example 15.5 using Hollier Method 2.
Solution: Table 15.15(a), containing the "From" and "To" sums, is repeated in Table 15.16,
along with the From/To ratios given in the last column on the right. Arrangingthe machines in order of descending From/To ratio,
the machines in the cellshould be sequenced as follows:
3 2 -» 1 - 4
Sec. 15.6 I Quantitative Anetvse in Cellular Manufacturing 451
TA.BLE 15.16 From-To Sums and FromfTo Ratios for Example 15.6
To: MFrom~ Sums From/To Ratio
From' 1 30 0.60
30 1.0
10 40 50
10 10
HTo" sums 50 45 40 135
This is the same solution provided by Hollier Method 1.
\() 15
~
O"'25~Om 3 2 t 4 300ul
5 10 200ul
figure 15.14 Flow diagram for machine cell in Examples 15.5 lind15.6. Flow of parts into lind out of the cells has also been included.
It is helpful to use one of the available graphical techniques, such as the flow dia-gram (Section 10.6.1), to conceptualize the work flow in the cell. The flow diagram for themachine arrangement in Examples 15.5 and 15.6 is presented in Figure 15,14. The work flowis mostly in-line; however, there is some back fluw or parts that must be considered in thedesign of any material handling system that might be used in the ceH. A powered conveyor would be appropriate for the forward flow between machines. with manual handlingfor the back flow.
For our example data in Table 1'1.14, Hollier Methods 1 and 2 provide the same so-lution. This is not always the case. The relative performance of the two methods dependson the given problem. In some problems.Method J will outperform Method 2.and in otherproblems the opposite will happen. In many problems, the twomethods yield identical so-lutions, as in Examples 15.5 and 15.0. Hollier presents a comparison of these and his otherproposed methods with a variety of problems in [17J.
Two performance measures can be defined to compare solutions to the machine se-quencing problem: (1) percentage of in-sequence moves and (2) percentage of backtrack-ing moves. The percentage of in-sequence moves is computed by adding all of the valuesrepresenting in-sequence moves and dividing by the total number of moves. The percent-age of backtracking moves is determined by summing all of the values representing back-tracking moves and dividing by the total number of moves.
EXAMPLE 15.7 Perfonnance Measures for Alternative Machine Sequence ••in II GT c{"\1
Compute (a) the percentage of in-sequence moves and (b) the percentage ofbacktracking moves for the solution in Examples 15.5 and 15.0.
Sec. 15.6 / Quantitative Analysis in Cellular Manufacturing 451
TABLE 15.16 From-To Sums and From/Jo Ratios for Example ?5.6
To. 12 3 4 "From" Sums From/To Ratio
from: I 0 5 0 25 30 0.60
2 30 0 0 15 45 1.0
3 10 40 0 0 50 oc
4 10 0 0 0 10 0.25
"To"sums 50 45 0 40 135
This is the same solution provided by Hollier Method 1.
Figure 15.14 Flow diagram for machine cell in Examples 15.5 and15.6. Flow of parts into and out of the cells has also been included.
It is helpful to use one of the available graphical techniques, such as the flow dia-
gram (Section 10.6.1), to conceptualize the work flow in the cell.The flow diagram for ihcmachine arrangement in Examples 15.5 and 15.6 is presented in Figure 15.(4. The work flowis mostly in-line; however, there is some back flow of parts that must be considered in thedesign of any material handling system that might be used in the cell. A powered convey-or would be appropriate for the forward flow between machines, with manual handlingfor the back flow.
For our example data in Table 15.14, Hollier Methods 1 and 2 provide the same so-lution.This is not always the case.The relative performance of the two methods dependson the givenproblem.lnsome problems,Method 1 will outperform Method 2.and motherproblems the opposite will happen. In many problem the two methods yield identical so-lutions, as in Examples 15,5 and 15.6. Hollier presents a comparison of these and his otherproposed methods with a variety of problems in [17].
Two performance measures can be defined to compare solutions to the machine se-quencing problem: (1) percentage of in-sequence moves and (2) percentage of backtrack-ing moves. The percentage of in-sequence moves is computed by adding all of the valuesrepresenting in-sequence moves and dividing by the total number of moves. The percent-age of backtracking moves is determined by summing all of the values representing back-tracking moves and dividing by the total number of moves.
EXAMPLE 15.7 Performance Measures for Alternative Machine Sequences in a C.T cell
Compute (a) the percentage of in-sequence moves and (b) the percentage ofbacktracking moves for the solution in Examples 15.
5 and 15.6.
452
REFERENCES
Chap. 15 / Group Technology and Cellular Manufacturing
Solution: From Figure 15.14, the number of in-sequence moves = 40 + 30 + 25 = 95,and the number of hacktracktng moves = 5 + 10 = 15. The total number ofmoves = 135 (totaling either the "From' sums or the "To" sums), Thus,
[I] A~EKE,N. A. G" and A. S. CARRIE,"A Design Technique for the Layout of Multi-ProductFlowlines," Iraernationai Journal of Production Research, Volume 24, 1986, pp 471-481.
[2] ASKIN,R. G, H. M. SELIM, and A. J. VAKHARIA. "A Methodology for Designing Flexible Cel-lular Manufacturing Systems," llE Transactions, VoL 29, 1997, pp. 599--610.
[31 BEAL'L:EU,A., A. OHARB!, and AIT-KADI, "An Algorithm for the Cell Formation and The Ma-chine Selection Problems in the Design of a Cellular Manufacturing System," InternationalJournal of Production Research, Volume 35, 1997,pp 1857-1874
[4J BLACK, 1. T., 'An Overview of Cellular Manufacturing Systems and Comparison to Conven-honal System..," I"dusllial E"gin~~ring,November 1983,pp 36--41\
[5] BLACK, J. T., The Design of the Factury With A Future, McGraw-Hill Book Company, NewYork,1990
[6J BLRBIDGE, J. L., "Production Flow Analysis." Production Engineer, Vol. 41, 1963, p 742
[7] BLRBIDGE,1. L., The Introduction of Group Technology, John Wiley & Sons, New York, 1975.
(8) BURBIDGE, 1. L., "A Manual Method of Production Flow Analysis," Production Engineer, Vol56,197i.p34.
[9J BURBIDGE,J. L., Group Technology in the Engineering Industry,Mechanical Engineering Pub-lications Ltd., London, U.K., 1979.
[10] BURBtDGE,1. L., "Change to Group Technology: Process Organization is Obsolete," InternationalJournalofProduction Research,Volume 30, 1992,pp 1209--1219.
[11 J CANTAMESSA, M., and A. 'fl:RRONI, "A Pragmatic Approach to Machine and Part Grouping inCellular Manufaetll-ring Systems Design," IntemarionalJournal of Production Research, Vol·ume35,1997,pp1031-I050.
[12] CHANDRASEKHAR,AN, M. P:, and R. RAJAUOPALAN, "ZODIAC An Algorithm for Concurrent
Formation of Part Families and Machine Cells," Inlernational Journal of Production Research,Volume 25,I987,pp 83j....850.
[13] GALLAGHER" C. C; and W. A. KNIGHT, Group Technology, Butterworth & Co, Ltd., London,1973.
[14] GROOVER, M.P.,Fwldamentals of Modern Manufacturing: Materiills,Processes:and Systems,Chapter 38, Prentice Hall, Upper Saddle River, New Jersey, 1996 (now published by John Wiley& Sons.Inc., New York)
[151 HAM, I., "Introduction to Group Technology," Technical Report MMR76-03, Soc. Manufac-turing Engineers, Dearborn, Michigan, 1976.
[16] HAM, I., K. HITOMI. and T. YOSHIDA, Group Technology:ApplicatiollS 10 Production Manage.ment, Kluwor-Nijhoff Publishing, Boston, Ma>;s., 1985
[17] HOLLIER, R. H., "The Layout of Multi-product lines," lnternationalJoumal of Production Re-search,Vol. 2,1963,pp 47-57,
REFERENCES
Chap. 15 / Group Technology and Cellular Manufacturing
Solution: From Figure 15.14, the number of in-sequence moves = 40 + 30 + 25 = 95,and the number of backtracking moves = 5 + 10 = 15. The total number ofmoves = 135 (totaling either the .'From" sums or the "To" sums). Thus,
[ 1 ] Aneke, N. A. G,. and A. S. Carrie, ''A Design Technique for the Layout of Multi-ProductFlowHnes," Inlema'ional Journal of Production R esearch. Volume 24,1986, pp 471-481.
[2] Askin.R. G.. H. M. Selim, and A.J, Vakhahia."A Methodology for Designing Flexible Cel-lular Manufacturing Systems," HE Transactions, . 29,1997, pp. 599-610,
[31 BtAULiEU.A., A. Gharbi, and Ait-Kadi, "An Algorithm for the Cell Formation andThe Ma-chine Selection Problems in the Design of a Ccllula.Journai of Production Research, Volume 35,1997, pp 1857-1874.
;Ilular Manufacturing System," International
[4] Black, J. T., ' An Overview of Cellular Manufacturing Systems and Comparison to Conven-tional Systenfs," Industriat Enginzering, November 1963, pp 36-48.
[5] Black, J. T., The Design of the Factory With A Future, McGraw-Hill Book Company, NewYork, 1990.
[fi] Blrbidge, J, L., "Production Flow Analysis," Production Engineer, Vol.41,1963, p 742.[7] BuRBmot, J. L., I he Introduction of Group Technology, John Wiley & Sons, New York, 1975.
[8] Burbidge, J. L., "A Manual Method of Production Flow Analysis," Production Engineer, Vol56,1971. p 34.
[9] Burbidge,! L., Group Technology in the Engineering Industry, Mechanical Engineering Pub-lications Ltd., London, U.K., 1979.
[10] Burbtdoe, J. L.,"Change to Group Technology: Process Organization is Obsolete," Intemationa'.Journal of Production Research, Volume 30,1992,pp 1209-1219.,1992,pp 1209-12
[11] Cantamessa, M., and A.TL'rront."A Pragmatic Approach to Machine and Part Grouping inCellular Manufaciviting System* Design," IntemationalJoumal of Production Research, Vol-ume 35,1997, pp 1031-1050.
[12] Chandrasekharan, M. P, and R. Rajauopalan,"ZODIAC: An Algorithm for ConcurrentFormation of Part Families and Machine Cells
,
" InlernationalJournal of Production Research,Volume 25,1987
, pp 835-850.
[13] Gallagher, C. C, and W, A. Knight, Group Technology, Butterworth & Co. Ltd., London,1973.
[14] Groover, M, P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,Chapter 38, Prentice Hall, Upper Saddle River, New Jersey, 1996 {now published by John Wiley& Sons,Inc, New York).
[15] Ham, I., "Introduction to Group Technology," Technical Report MMR76-03, Soc. Manufac-turing Engineers, Dearborn, Michigan, 1976.
[16] Ham, I., K. HrrOMI, and T. YoSHIDa, Group Technology: Applications to Production Manage-ment, Kluwcr-Nijhoff Publishing, Boston, Mass., 1985.ff Publishing,
Bostoi
;La
jearc/i. Vol. 2,1963, pp 4:
[17] HoLL[ER,R.H.,"The Layout of Multi-product lines," International Journal ofProduction Re-,47-57.
References
[18]
[19] HOITTZFFl. A "The Many Faces of Group Technology." American Machinist, January 1979,pp115-12o
l21J HOl II.H.L. A.. Ctassificanon and Coding. Organization for Industrial Research, Inc.,Waltham. Mass.
[22] HOUTZEEL,A., "Classification and Coding, Group Technology, Design Retneval. and Com-puter Assisted Process Planning," Organization for Industrial Research, waltham, Mass.
[23]
[24] HYER,N L.. and U.WEMMFRLOV,"Group Technology in the U.S.Manufacturing Industry:A Sur-veyof Current Practices," tmernationsl lournal of ProducrionResearch.Vol.27,1989,pp 1287-1304.
[25] IRANI,SA.. T M. CAVALlfR,andP.H.COHEl\,"Virtual ManufacturingCells:Exploiting Lay-OUiDesign and lntercell Flows for the Machine Sharing Problem," lntemationai Journal ofProduction Research,VoI.31, 1993.pp791-810
[261 KIN(j,J. R., -wecntne-componem Grouping in r-rooucuon now Analysis: an Approach Usinga Rank Order Clustering Algorithm," International Journal of Production Research, Vol. 18,1980.pp213-222
[27] KUSIAK,A.,"EXGT-S: A Knowledge Based System for Group Technology," Imemationai lour-nat of Production Research, Vol. 26, 1988,pp 1353-1367
[28] LYNCH,M., CrompurerNumerical Control for Machining, McGraw-Hill, Inc" New York, 1992[2Q1 Moxoex Y, Toyota Production System, Industrial Engineering and Mnnllg",ment Press. Insr.
Industrial Engineers. Norcross, Georgia, 1983[30J MOODIE,C, R. lJ7-S0Y,and Y YIH,Manufacturing Cell.s:A Systems Engineering View, Taylor
& Francis Ltd" London, U.K., 1995.[31] OPITZ,H__A Classification System to De.trribe workpieces, Pergamon Press, Oxford, Eng-
land,1970[32J OPITZ,H., and H. P.WIE'IDAHL,"Group Technology and Manufacturing Systems for Medium
Quantity Production." lruemanonal laumai of Production Research.Vol.9,No.l, 1971.pp 181-203[33] SINGH,N.,and D. RAJAMA:-I,Cellular Manufacturing Systems: Design. Planning, and Control.
Chapman & Hall, London, 1996.[34] SNEAD,C. S., Group Technology: Foundation for Competitive Manufacturing, Van Nostrand
Reinhold, New York, 1989[35] VAKHARIA.A. 1.,and H. .\1.Selim, "Group Technology," Handbook of Design, Manufacturing
and Automation, R. C Dorf and A. Kusiak (Editors),John Wiley & Sons, Inc., New York, 1992,pp435--460.
[36] WEMMEkLOV,0., and N. L. HYER,"Cellular Manufacturing in U.S.Industry:A Survey of Users,"International Journal of Production Resean'h, Volume 27,1989, pp 1511-1530
[37J WEM.\1t.RlOV,0.. and N. L. HYER."Group Technology," Handbook of Industrial Engineering,G. Salvendy (Editor),John Wiley & Sons, Inc., New York, 1992,pp 464-488.
138] WEMMERI.OV,LT.. ~nd D. J. JOHNSON,"Cellular Manufacturtng at ee User Plants: Implementa-non Experiences and Performance Improvements," International Journal of Production Re-search.Volurne 35, 19l17,pp 29--49.
[39J WILD.R.. Mas,1Production Management, John Wiley & Sons Ltd., London, 1972,Chapter 8.
[20J
References 453
[]8] Holtz.R. D..-'GTand CAPP Cut Work-in-proeeasTime 80%.." Assembly Engineering,Partl:Jiine 1978, pp 24-27; Pan 2: July l S, pp 16-10.
[19] HoinzFEl. A., -'The Many Faces uf Group Technology," American Machinist, January 1979,pp 115-120.
(20] HoltzeluA./'A Management Overview of Group Technology," SME Technical Paper MS82-167. Society of Manufacturing Fnginecrs, Deartiorn, Michigan, IW2.
[21] Hoi r/.hKL. A,, Classification and Coding. Organi/alion for Indusiria! Research, Inc.,Waltham. Mass.
|22] HoirrzEEL, A., "Classification and Coding, Group Technology, Design Retrieval, and Com-puter Assisted Process Planning," Organization for Industrial Research, Waltham, Mass.
[23] Hyer, N. L., and U. Wemmerlov, "Group Technology Oriented Coding Systems: Structures,Applications, and Implementalions,'' Production and Inventory Management, 2nd quarter,1983
, pp 55-78.
[24] Hyer, N. L.. and U.Wemmfrlov, "Group Technology in the U.S. Manufacluring IniiustryiA Sur-vey of Current Practices," International Journal of Producrion Research.Vo[.21,1989, pp 1287-1304.
[25] Irani, S A., T M. CAVALI .and P.H.Cohen,"Virtual Manufacturing Cells. Exploiting Lay-out Design and Intercell Flows for the Machine Sharing Problem,
" Internalional Journal of
Production Research.Vcl 31.1993.pp 791-810.
[26] Kino, J. R., " Machine-Component Grouping in Production How Analysis: an Approach Usinga Rank Order Clustering Algorithm," International Journal of Production Research, Vol. 18,1980, pp 213-222.
[27] Kusiak, A., "EXGT-S: A Knowledge Based System for GroupTfechnologyr/niernntionfliJour-nalof Produaion Research, Vol.26,1988,pp 1353-1367.
[28| Lynch, M., Computer Numerical Control for Machining, McGraw-Hill, Inc., New York, 1992.[29] Monden, Y., Toyota Production System, Industrial Engineering and Management Press, Inst.
Industrial Engineers, Norcross, Georgia, 1983.
[30] Moodje, C, R. IJzsoy, and Y. Ym, Manufacturing Cells:A Systems Engineering View, Taylor& Francis Ltd., London, U.K.,
1995.
[31] Opitz, H., A Classification System to Describe Workpieces, Pergamon Press, Oxford, Eng-land, ig o.
[32] Opir/,,H.,and H. P. Wiendahl, "Group Technology and Manufacturing Systems for MediumQuantity Production." IntemanonaUoumai of Production Research, Vol. 9,No.l, 1971, pp 181-203.
[33] Singh, N., and D. Rajamani, Cellular Manufacturing Systems: Design, Planning, and Control.Chapman & Hall, London,
19%.
[34] Snead, C. S., Group Technology: Foundation for Competitive Manufacturing, Van NostrandReinhold
, New York, 1989.
[35] Vakharia, A. J., and H. M. Selim, "Group Technology," Handbook of Design, Manufacluringand Automation, R, C. Dorf and A. Kusiak (Editors), John Wiley & Sons,Inc.,New York,;992,pp 435-160.
[36] Wemmerlov, U., and N. L. Hyer, "Cellular Manufacturing in U.S. Industry: A Survey of Users,"Imernatimal Journal of Production Researeh.Volume 27,1989
, pp 1511-1530.
[37] WEMMtaiov, U, and N. L. Hyer. "Group Technology," Handbook of Industrial Engineering,G
. Salvendy (Editor), John Wiley & Sons, Inc., New York, 1992, pp 464- 88.
138] Wemmerlov, U., and D.J. Johnson, "Cellular Manufacturing at 46 User Plants: Implementa-tion Experiences and Performance Improvements,
" International Journal of Production Re-search
, Volume 35,1997, pp 29-49.
[39] Wild. R.. Wart Production Management, John Wiley & Sons Ltd., London, 1972, Chapter 8.
454
PROBLEMS
Chap. 15 I Group Technology and Cellular Manufacturing
Parts Classification and Coding
15.1
Figure PIS.! Part for Problem 15.1.Dimensions are in millimeters.
15.2 Develop the form code (first five digits) in the Opitz System for the part illustrated in Fig-ureP15.2
Figure P15.2 Part for Problem 15.2.Dimensions are in millimeters.
15.3 Develop th.e form code (first five digits) in the Opitz System for the part illustrated in Fig-ur"P15,3
Figure P15.3 Part for Problem 15.3. Dimensions are in millimeters.
(h(llh~nd~)
SpurgellT36.0piwhdiamereT
454
PROBLEMS
Chap. 15 / Group Tecfinology and Cellular Manufacturing
Parts Classification and Coding
1S.1 Develop the form ttiJe (first five digits) in Hit Opitz System for Die part illustrated in Fig-ure P15.1.
Dimt
ireP15.1 Part for Problem 15.1.
lemions are in miilttnetcrs.
15.2 Develop me form code (first five digits) in the Opitf System for the part illustrated in Fig-ure P15
.
2.
Figui
L Dimt
ire P15.2 Part for Problem 15.2.
lenstons are in millimeters.
1SJ Develop the form code (first five digits) in the OpiU System for the part illustrated in Fig-ure P15.3.
I P=L r
43.0 -.
Figure P1SJ Part for Problem 15.3. Dimensions are in millimeters.
Problems 455
Rank Order Clustering
15.4
Pans
Machines A B,-----1
Parts
Machines A
15.6 Apply the rank order clustering technique to the part-machine incideuce matrix in thetol.lo,,;ng table to identify logical pan families and machine groups. Parts are identified by let-tersand machines are identified numerically
15.4 Apply [lie rank order clustering technique lo the part-machine incidence matrix in the fol-
:rs, and machines are identified numericallylovmig tahlc to identify logical pari families and machine groups. Parts are identified by let-
1
2
3
4
5
A
1
1
B
1
1
Parts
C
1
D
1
1
155 AppK the rank order clustering technique to the part-machine incidence matrix in the fol-lowing table to identify logical pari families and machine groups. Parts are identified by let-ters. and machines are identified numerically.
1
2
3
4
5
6
1S.6 Apply lire rank order clustering technique to the part-machine incidence matrix in the fol-
lowing tabic \a identify logical part families and imchine groups. Parts are identified by let-ters. and machines are identified numerically.
45. Chap. 15 I Group Tecbnoto qv end Cellular Manufacturing
Parts
Machines
15.7 Apply the rank order clustering technique to the part-machine incidence matrix in the fol-lowing table to identify logical part families and machine groups. Parts are identified by let-tees, and machines are identified numerically.
Parts
Machines A
15.8 The following table lists the weekly quantities and routings of ten parts that are being oon-stdered for cellular manufacturing in a machine shop. Parts are identified hylettcrs, and rna-chines are identified numerically. For the data given, (a) develop the part-machine incidencematrix.and (b) apply the Tank order clustering technique 10the part-machine incidence rna-trix to identify logical part families and machine groups.
15.7 Apply the rank order clustering technique io the part-machine incidence matrix in the fol-ig table to identify logical part families and machine groups. Parts are identified by let-
s are identifie
Apply thlowing taters, and machines are identified numerically.
Parts
Machines ABCDEFQHI
1
2
3
d
5
6
7
8
1
1
1
1
1
1
1
1
1 1
15.8 The following table lists the weekly quantilies and routings often parts thai are being con-sidered for cellular manufacturing in a machine shop.Parts are identified hy letters,
and ma-
ss are identified nurchine
p.Iters,andn
hine inciden
trii
Ltnerically. For the data given, (a) develop the parl-machinarrix.and (b) apply the rank order clustering technique to the part-machine incidence ma-in to identify logical pari families and machine groups.
Problems 457
Part Weekly Quantitv Machine RoutingP,rt Weekly Quantity Machine Routing
50 3--t2--t720 6~1
75 6~5
10 6--t5 ....•112 3--t2 ....•7...,.4
60 5 .....•,
5 3 .....•2...,.4
100 3 _ 2 _4...,.7
40 2...,. 4 ...,.7
15 5...,>6...,.1
Machine Cell Organization and Design
15.9 Four machines used to produce a family of parts are to be arranged into a GT cell. TheFrom-To data for the parts pf<)cess~dby the machine~ are shown in the table below. (a) De-terrnine the most logical sequence of machines for this data using Hollier Method I. (b) Con-struct the flow diagram for the data, showing where and how many parts enter and exit thesystem. (c) Compute the percentage of in-sequence moves and the percentage of back-tracking moves in the solution. (d) Develop a feasible layout plan for the cell
To:
From:
a 10 40o 0 0
50 0 20o 50 0
15.10 Solve Problem 15.9 except using Hollier Method 2.
15.11 In Problem 15.8. two logical machinr: groups are identified by rank order clustering. Foreach machine group, (a) determine the most logical sequence of machines for this data usingHollier Method 1. (b) Construct the flow diagram for the data. (c) Compute the percentageof in-sequence moves and the percentage of backtracking moves in the solution
15.12 Solve Problem 15.11 only using Hollier Method 2.15.13 Five machines will constitute a UT cell.The From-To data tor the machines are shown in the
table below. (a) Determine the most logical sequence of machines lor this data, according toHollier Method Land construct the flow diagram for the data.showing where and how manyparts enter and exit the system. (b) Repeat step (a) only using Hollier Method 2, (c) Com-pute the percentage of in-sequence moves and the percentage of backtracking moves in thesolution for the two methods. Which method is better.according to these measures? (d) De-velop a feasible layout plan for the cell based on the better of the two Hollier methods.
To:
From'
ooo
70o
10ooo
75
80oo
20o
o85oo
20
457
Part Weekly Quantity Machine Routing Part Weekly Quantity Machine Routing
A 50 3 2 .7 F 60 5 -» 1
8 20 6-»1 G 6 3-.2->4
C 75 6-.5 H 100 3_*2-*4-*7
D 10 6--5->1 I 40 2 4-t7
E 12 3->2--7 4 J 15 5-*6-*1
Machine Cell Organization and Design
15.9 four machines used to produce a family of parts are to be arranged into a GT cell. TheFtom-To data for the parts processed by the jnachines are shown in the table below, (a) De-termine the most logical sequence of machines for this data using Hollier Method 1. (b) Con-struct the flow diagram for the data, showing where and how many parts enter and exit thesystem, (c) Compute the percentage of in-sequence moves and the percentage of back-tracking moves in the solution, (d) Develop a feasible layout plan for the cell.
To:
12 3 4
1 0 10 0 40
2 0 0 0 03 50 0 0 204 0 50 0 0
1S.10 Solve Problem 15.9 except using Hollier Method 2.
1S.11 In Problem 15.8. two logical machine groups are identified by rank order clustering Foreach machine group, (a) determine the most logical sequence of machines for this data usingHollier Method 1. (b) Construct the flow diagram for the data, (c) Compute the percentageof in-sequence moves and the percentage of backtracking moves in the solution.
15.12 Solve Problem 15.11 only using Hollier Method 2.
15.13 Five machines will constitute a UT cell. The From- lo data for the machines are shown in the
table below, (a) Determine the most logical sequence of machines for this data, according toHollier Method Land construct the flow diagram for the data.showing where and how manyparts enter and exit the system, (b) Repeat step (a) only using Hollier Method 2. (c) Com-pute the percentage of in-sequence moves and the percentage of backtracking moves in thesolution for the two methods. Which method is better
, according to these measures? (d) De-velop a feasible layout plan for the cell based on the better of the two Hollier methods.
To:
crom: 7 2 3 4 5
1 0 10 80 0 02 0 0 0 85 03 0 0 0 0 04 70 0 20 0 0
5 0 75 0 20 0
458 Chap, 15 I Group Technology and Cellular Manufacturing
15.15 This problem is concerned with the design of a GT cell to machine the components for a f<IIII'
ily of part~ The parts come in several different sizes, and the cell will be designed to quick-ly change over from one size to the next.This will be accomplished using fast-change fixtu-esand distr;hllled numerical control (ONe) to download the NC programs from the plantcomputer to the CNC machines In the cell.The parts are rotational type, so the cell must beable to perform turning, boring. facing, drilling, and cylindrical grind ing operaticns.Ac-cordingly. there will be several machine tools in the cell, of types and numbers to be speci-fled by the designer To transfer parts between machines in the cell , the designer may electto use a belt or similar conveyor system.Any conveyor equipment of this type will be 0.4 mwide. The arrangement of the various pieces of equipment in the cell is the principal prob-lem to be considered. The raw workpans will be delivered into the m~chine cellon a bellconveyor. The finished parts must be deposited onto a conveyor that delivers them to theassembly department. The input and output conveyors are 0.4 illwide, and the designer mustspecify where they enter and exit the cell.The parts are currently machined by convention-al methods in a process-type layout. In the current production method, there are seven ma-chi[\e~ involved, but two of the machine, are duplicates. From-To data have been collectedfor the jobs that are relevant to this problem.
To:
From: 2 3 4 5 6 7 Parts Out
112 0 61 59 53 0
12 0 0 0 0 226 0 4574 0 0 35 31 0 180 0
82 0 0 0 23 5 16
73 0 0 0 23 0 14
0 0 0 C 0 0 325174 16 20 30 20 0 0 0
Parts in 25 0 300 0 0 0 75
Chap. 15 / Group Technologv and Cellular Manufacturing
15.14 A GT machine cell contains three machines. Machine 1 feeds machine 2. which is Ihe key ma-chine in the cell. Machine 2 feeds machine 3. The cell is set up to produce a family of live
pai Is (A, B. C, D, and E). The operalion limes for each part at each machine are given in thetable below. The products are to be produced in the ratios 4:3:2:2:1. respectively, (a) If 35hrs/wk arc worked, determine how many of each product will be made by the ccll.(b) Whatis the utilization of each machine in the cell?
Operation Time (min)
Part Machine 1 Machine 2 Machine 3
A 4.0 16.0 10.0
B 15.0 18.0 7.0
C 26.0 20.0 15.0
D 15.0 20.0 10.0
E 8.0 16.0 10.0
lv change over from one size lo the next.This will be accomplished using fasl-change fixturesand distributed numerical control (DNC) to download the NC programs from the plant
15.15 This problem is concerned with Ihe design of a GT cell lo machine the componenls for a fam-ily of part*. The parts come in several different sizes, and the cell will be designed to quick-
from one size lo the next.This will be accomplished using fasl-change fixturesd numerical control (DNC) to download the NC programs from the plant
computer ID the CNC machines m the cell.The parts are rolalional type, so the cell must beable to perform turning, boring, facing, drilling, and cylindrical grinding operations. Ac-cordingly. there will be several machine tools in the cell, of types and numbers to be speci-fied by the designer To transfer parts between machines in the cell, the designer may electto use a belt or similar conveyor system. Any conveyor equipment of this type will be 0.4 mwide. The arrangement of the various pieces of equipment in the cell is the principal prob-lem to be considered. The raw workparts will be delivered into the machine cell on a beltconveyor. The finished pans must be deposited onto a conveyor that delivers them to theassembly department. The input and output conveyors are 0.4 m wide, and the designer mustspecify where they enter and exit the cell.The parts are currently machined by convention-al methods in a process-type layout. In the current production method, there are seven ma-chines involved, bul two of the machines are duplicates. From-To data have been collectedfor the jobs that are relevant to this problem.
To:
From: 7 2 3 4 S 6 7 Parts Out
1 0 112 0 61 59 53 0 0
2 12 0 0 0 0 226 0 45
3 74 0 0 35 31 0 180 0
4 0 82 0 0 0 23 5 16
5 0 73 0 0 0 23 0 14
6 OO00C00 325
7 174 16 20 30 20 0 0 0
Parts in 25 0 300 0 0 0 75
Problems 459
Production RateMachine Operation (pcjhr! Machine Dimensions
Turn outside diameter 9 3.5m x 1-5m
Bore inside diameter 15 3,Om x 1.6m
Face ends 10 2.5m x 1.5m
Gnnd outside diarneter 12 3.0m x 1.5m
Grind outside diameter 12 3.0m x 1.5m
Inspect 5 Bench 1.5 m x 1.5 m
Drill 9 1.5m x 2.5m
lhc From- To data indicate the number of workparts moved betweenThe From- To data indicate the number of workparts moved between machines during atypical 40-hr week. The data refer to the parts considered in rhe case. The two categories"parts in
" and "parts out " indicate pans entering and exiting the seven-machine group. A totalof 400 parts on average are processed through the seven machines each week. However, as
red by the data, not all 400 parts are processed by every machine. Machines 4 and 5 areTdi.ntical.and assignment of parts to these machines is arbitrary.Average productionparity on .?ach of the machines for the particular distribution of this parts family is gi'the table below. Also given are ihe floor space dimensions of each machine in ractci
ic that all loading and unloading operations take place in the center of the machine.
eduction Rat
lachine Operation Ipc/hr) Machine Dimensions
1 Turn outside diameter 9 3.5 m x 1.5 m
2 Bore inside diameter 15 3.0 m x 1.6 m
3 Face ends 10 2.5 m x 1.5 m
4 Grind outside diameter 12 3.0m x 1.5m
5 Grind outside diameter 12 3.0 m x 7,5 m
6 Inspect 5 Bench 1.5 m x 1.5 m
7 Drill 9 1.5 m X 2.5 m
OperaTion 6 is currently a manual inspection operation. It is anticipated that this manualstation will be replaced by a coordinate measuring machine (CMM).This automated in-spection machine will triple througbpul rate to 15 parts/hr from 5 parts/hr for the manualmethod. The floor bpa;e dimensions of the CMM arc 2.0 m X 1.
6 m. All other machines
currently listed are to he candidates for inclusion in the new machine cell, (a) Analyze theproblem and determine the most appropriate sequence of machines in the cell using thedata contained in the from-To chart, (b) Construct the flow diagram for the cell, showing
d how many parts enter and exit the cell, (c) Determine the utiliiation and pro-duction capacity of the machines in the cell as you have designed it. (d) Prepare a layout (topview) drawing of the GT cell, showing the machines, Ihe robot(s), and any other pieces ofequipment in the cell, (c) Write a one-page (or less) desciiplion of the cell, explaining thebasis ol your design and why ihe cell is arranged as it is.
chapter 16
Flexible Manufacturing Systems
CHAPTER CONTENTS
16.1 WhallsanFMS?16.1.1 What Makes It Flexible?16.1.2 TypesofFMS
16.2 FMS Components16.2.1 Workstations16.2.2 Material Handling and Storage System16.2.3 Computer Control System16.2.4 Human Resources
16.3 FMS Applications and Benefits16.3.1 FMS Applications
16.3.2 FMSBenefits16.4 FMS Planning and Implementation Issues
16.4.1 FMS Planning and Design Issues
16.4.2 FMS Operational Issues16.5 Quantitative Analysis of Flexible Manufacturing Systems
16.5.1 Bottleneck Mode!16.5.2 Extended Bottleneck Model16.5.3SizingtheFMS16.5.4 What the Equations Tell Us
The flexible manufacturing system (FMS) was identified in the last chapter as one of themachine cell types used to implement group technology. It is the most automated and tech-nologically sophisticated of the GT cells. In our classification scheme for manufacturing sys-
chapter 16
Flexible Manufacturing Systems
CHAPTER CONTENTS
16.1 What Is an FMS?16.1.1 What Makes It Flexible?
16.1.2 Types of FMS16.2 FMS Components
16.2.1 Workstations
16.2.2 Material Handling and Storage System16.2.3 Computer Control System16.2.4 Human Resources
16.3 FMS Applications and Benefits16.3.1 FMS Applications16.3.2 FMS Benefits
16.4 FMS Planning and Implementation Issues16A1 FMS Planning and Design Issues16.4.2 FMS Operational Issues
16.5 Quantitative Analysis of Flexible Manufacturing Systi16.5.1 Bottleneck Model
16.5.2 Extended Bottleneck Model
16.5.3 SizingtheFMS16.5.4 What the Equations Tell Us
The flexible manufacturing system (FMS) was identified in the lasi chapter as one of themachine cell types used to implement group technology.lt is the most automated and tech-nologically sophisticated of the GT cells. In our classification scheme for manufacturing sys-
