Product Lifecycle Management (PLM) System for

Shipbuilding Industry Automation of the process of conversion of Engineering BOM to Manufacturing BOM

S.Abhilash Sharma

Final year Dual Degree student,

Dept of Ocean Engineering and

Naval Architecture,

IIT Kharagpur,

Kharagpur, India

O.P.Sha

Professor,

Dept of Ocean Engineering and

Naval Architecture,

IIT Kharagpur,

Kharagpur, India

Rajiv Sharma

Assistant Professor,

Dept of Ocean Engineering,

IIT Madras,

Chennai, India

Abstract— PLM (product life-cycle management) has become

something like „a magic wand‟ for various industries because of

its capability to integrate different product modules via online

network through the product‟s complete life-cycle, and hence

providing one window access; thereby making the whole

processes of product conception, design and manufacturing,

delivery, maintenance and disposal integrated with a reduction in

product development time and cost. However, heavy industries

(i.e. shipbuilding) are different from consumer product industries

because of high customisation in design process, and engineering

software, widely varying scales of operations and less

compatibility between different design and production processes,

e.g. ship production is planned in activity driven network

scheduling system in general, and is assumed more as a

construction process or assembling process rather than a

production process.

One of the key elements of PLM is the Product Data Model

(PDM), which is also termed as the Bill of Material in many

shipyards. Bill of Material is a list of all the materials used to

make the product. Different requirements will require different

BOMs to be made by different departments. In shipbuilding

industry a major problem is developing the manufacturing BOM

(M-BOM) from the engineering BOM (E-BOM). This is because

the E-BOM is structured in a “systems based” manner to suit the

designer, whereas the M-BOM has to follow a “block/zone” based

hierarchy as the shipbuilding process is an assembly of

intermediate products. At present the conversion of E-BOM to

M-BOM is done manually by utilizing the experience of shipyard

personnel. Automation of this process will lead to considerable

decrease in the design process time and hence in overall delivery

time too.

In this paper we present the development and the basic building

concepts for a PLM system for shipbuilding industry and a case

study in “Automation of Conversion of E-BOM to M-BOM”

Keywords; Engineering BOM (E-BOM); Manufacturing BOM (M-

BOM); BOM conversion; PLM Module; E-BOM to M-BOM

I. INTRODUCTION

In the present era where the demand for new ships is on the

rise, shipyards need to be competitive. To maintain their

competitive edge over the others, shipyards are continuously

trying to produce more economical ships within less period of

time. In this endeavour, most of the shipyards are now relying

on product life-cycle management (PLM) systems.

A PLM system has been in existence for a long time, in

most of the manufacturing sectors and primarily acts as the

common platform between the various software resources

being used by the industry and allows for easy exchange of

data across these systems.

Designing is primarily a decision-making process in which

the designer decides the various aspects and attributes of the

product. Integrating the various processes and managing the

resources of an industry across a common platform in real

time helps the designer make more informed decisions and

thus leads to an effective design in lower time.

But in light of the shipbuilding industry, PLM has more

requirements than a general manufacturing industry. This

difference arises primarily due to the nature of the

shipbuilding industry, which is quite different from a general

manufacturing industry. Unlike an assembly line production

prevalent in most of the manufacturing segments, shipbuilding

industry, owing to its high level of customization is forced to

follow a unit assembly production. Thus the PLM system for

the shipbuilding industry should be able to integrate the

processes and resources of different product types.

Similarly, the design work in the shipbuilding industry is

iterative where most of the work needs to be repeated to get a

detailed design. Because of this nature of iterative work, the

design process of the ship takes a lot of time. At present, many

of the shipyards are trying to use the data of the previous

vessels built to reduce the iterative work of design. This is also

one of the fundamental requirements of the PLM system from

the shipbuilding industry's perspective.

PLM system collects the information regarding a product

throughout its lifecycle for future use. Lifecycle of a product

refers to the lifetime of the product which starts from the

conception of the design and ends at the dismantling or reuse

of the product. At every stage, the information regarding the

product is stored into the PLM system. The system should be

effective in extracting the required and relevant information

from the existing information of the previous vessels built so

that the iterative work of the design spiral is reduced.

The overall objective of a PLM system is to streamline the

design and production processes and to achieve economic

designs within lesser time. Thus any bottleneck in the present

design and production processes needs to be dealt by the PLM

system, in order to achieve the competitive edge.

Figure 1 puts together all the functional requirements of a

PLM system for the shipbuilding industry. Thus the

fundamental requirements of a PLM system to be applicable to

shipbuilding industry are:

1. Collecting and storing the ship data in a specific

format which can be used in future.

2. Reuse of previous ship design data to reduce the

iterative work.

3. Sharing information in real time from various

software systems in the shipyard to a common

platform to help the designer make more informed

decisions.

Figure 1: A PLM system for the shipbuilding industry

Figure 2: System Based Hierarchy of an Engineering BOM

4. Provide a scheduling and planning system which can

account for the various lead time offsets in the

shipbuilding processes and make amends to the

schedule.

5. Streamlining of the bottleneck processes to achieve a

lower lead time.

At present most of the shipyards are looking into the

different approaches to achieve the integration between the

various resources and processes of a shipyard. But the major

bottleneck is still in dealing with the Bill of Material. Bill of

Material (BOM) is a hierarchical list of all the constituent

components and materials of a ship. The hierarchy of the

BOM differs across the various departments of the shipyard.

The design department requires a BOM based on a system

based hierarchy, whereas the manufacturing department

requires BOM based on product oriented hierarchy. A ship is

composed of many systems, like the hull structure, outfitting

equipment, ballast water systems, fresh water systems,

electrical cables, HVAC, piping equipment, etc. The design

department divides the ship design work into the designing of

each of the above systems. Thus a group of designers will

always be working on any one particular system of the ship.

Hence it is necessary that the BOM for a designer be

organized in a system based hierarchy.

A typical system based hierarchy is shown in Figure 2.

The second level of the hierarchy in Fig. 2 represents the

division of work of a particular system design among

designers.

The manufacturing department, on the other hand does

not assemble the vessel in a system based manner. Instead, it

adopts a product/block/zone oriented approach to assembly.

The ship as a whole is divided into many interim products like

grand blocks, which are further divided into blocks,

assemblies, subassemblies and finally into the components.

The assembly process starts with assembling the components

to form subassemblies, assemblies and blocks. The blocks are

assembled together to form grand blocks, which are then

assembled to form the entire ship. A typical hierarchy of a

manufacturing BOM is shown in Figure 3. A manufacturer if

provided with a BOM which is organized in a system based

hierarchy would not be able to use the information efficiently.

This is because any particular interim product, like a block

would include components across various systems and would

not provide a complete list of all the components required to

assemble the block.

Thus, there is a necessity to convert the bill of material

developed during the design phase to a form suitable for the

manufacturing department. The design bill of material, also

known as the engineering BOM (E-BOM) needs to be

converted into manufacturing BOM (M-BOM). At present, in

most of the shipyards, this conversion of engineering BOM

into manufacturing BOM is done manually by experienced

manufacturing personnel. To build more ships, economically

and within a less period of time it is imperative that this

conversion process be automated.

Figure 3: Product/Block Oriented Hierarchy

In this paper, a solution for the automatic conversion of

engineering BOM to manufacturing BOM has been suggested.

Section II discusses more about the structure and architecture

of a Shipbuilding PLM system. Section III is a case study

about the automatic conversion of E-BOM to M-BOM and

discusses more about the problem statement and the approach

being used by this paper to solve the problem. Section IV

provides an illustrative example of a sample data on which

this approach has been used. Section V highlights the

conclusions and proposed future works.

II. PLM FOR SHIPBUILDING INDUSTRY

A Product Lifecycle Management (PLM) is a process of

managing the product information over its entire lifecycle. The

lifecycle is a timeline which starts with the conception of the

product (in this case the ship), includes its design, planning,

manufacturing, operation, maintenance and dismantling. It

centers on the ship rather than the shipyard which builds the

ship. A general idea of a PLM system for shipbuilding

industry has been presented in this paper. More information

regarding this architecture and system modules are available

in the works of Kim [3]

.

A PLM system may be thought to be composed of two

major sub-systems, viz. BOM management system and the

process engine.

The BOM management system is composed of two

components:

1. Resource tier data

2. BOM template

The resource tier data is a database storing the BOM data

and its attributes. The data may include components,

drawings, material planning schedule, drawing schedule,

assemblies, blocks, grand blocks, etc. These attributes could

be dimensions of the part or assembly or block, its weight,

volume, etc. Table 1 demonstrates a hypothetical example of

the fields of a database and the data stored therein. B13 and

B21 are blocks while the A11 is an assembly product. As can

be seen, the resource tier data does not have any hierarchical

information. Both block and assembly information is stored in

the same database. The resource tier data may also include

scheduling information, drawing plans, components, etc.

Table 1: Example of the fields of Resource Tier Data

Data

ID

Length in

meters

Breadth in

meters

Depth in

meters

Weight in

tonnes

B13 20 10 10 50

A11 5 5 7 12

B21 22 12 10 65

The hierarchy information is stored in the BOM template.

The BOM template stores the entire hierarchy of the ship

components. A schematic is shown in Figure 4. The BOM

template stores only the hierarchy and does not have any

information about the data associated with the hierarchy. So it

is possible that two sister ships share the same hierarchy but

the data associated with the hierarchy would be different.

When the construction of a new ship commences, a search

of the previous ship data is run to find a reference ship which

is close to the new ship design particulars. These particulars

could be ship type, dimensions, deadweight, speed, block

coefficient, etc. Once the reference ship is decided the

Figure 4: The hierarchy information which is stored in BOM Template

integrated BOM database of this ship is copied and refined to

suit the requirements of the new vessel. So the design process

involves adding new data to replace the old ship data wherever

required. This refinement of the data of the database continues

till the end of the manufacturing design. At the end of the

design, the final integrated BOM for the new ship is obtained

which can further be used while designing more ships in the

future.

The various other functions of the BOM management

system are:

1. Estimation of material demand (amount of material)

2. Preparing exact manufacturing schedule (time)

3. Deciding enough margin for placing Purchase Order

Requisition (POR)

4. Helping designer generate exact design data

5. Effective collaboration in design and manufacturing

Material demand, manufacturing schedule and placing a

POR are all a part of planning and scheduling process.

Planning process is composed of three stages:

1. Main event date

2. Mid-term schedule

3. Daily schedule

The main events are Contract signing, Keel laying,

Launching and Delivery. They are shown in a timeline below

in Figure 5.

Once the main events are decided the mid-term scheduling

is done. In the mid-term scheduling, all the activities related to

manufacturing of the ship are planned. At the end of the mid-

term scheduling the knowledge of how much material would

be required and at what time it would be needed is known.

Mid-term scheduling is shown in the Figure 6. The arrows

indicate the position on the timeline when new material and

equipment would be needed by the production people.

The mid-term schedule is quite important from the design

perspective. The next step is to develop the material plan

(MP). The MP provides the details of the ordering plan i.e.

when to order for the material and equipment. From the MP,

the drawing plan (DP) is generated. Drawing plan is the

schedule of completion dates of different drawings of a ship.

The planning process time line for design and manufacturing

side are shown in Figure 7 and Figure 8 respectively.

The POR is the process through which the order for

material and equipment is placed in a shipyard. This is

basically a designer‟s work. But the information for placing a

POR follows from the Material Plan (MP). Only after the MP

has been finalized can the POR for the steel plates or stiffener

be placed.

Figure 5: Main Events Timeline

Figure 6: Mid-term Scheduling

The POR data gives an estimate of the amount of material

ordered and their expected date of arrival. The POR is placed

on the basis of an “estimate” of how much material would be

needed. But the actual usage of the material is, in most cases,

different from the estimated value.

Figure 9: Project Management Module

Figure 7: Time Line of Planning Process from Manufacturing perspective

Figure 8: Time Line of Planning Process from Design perspective

Shipyards are continuously trying to achieve an estimation

of material which is very close to the actual usage. If a

shipyard overestimates, then it is forced to bear the excess cost

of the extra material. On the other hand if the shipyard

underestimates their material demand, the production process

would be halted temporarily. This will lead to delay in

schedule. Thus it is very important for the shipyard to be able

to estimate the exact material demand.

At present the estimations during contract stages are up to

80% accurate. Mid-term schedule estimates have higher

accuracy rates of around 90-95%. By using the design process

requirements of similar previous ships the PLM system

provides an accurate estimate of the material demand at

different phases of the manufacturing.

Another important aspect is the judging of the margin time

for each POR. There might be some delays in the delivery of

the material and equipment, which would lead to increased

delays in production. Thus the PLM system keeps a record of

the previous delays in order delivery of various suppliers to

assist the designer place the PORs at appropriate times. The

system also keeps track of the difference in the delivery times

of different components to aid the designer in placing a POR

at the right time.

Similarly, a designer preparing a drawing does not have the

complete information regarding the item under consideration.

Consider an example where Designer A is making the drawing

for Block E13. Suppose this drawing requires some input from

the E/R outfit drawings. But say Designer B making the E/R

outfit drawings has not yet completed his work. In this case

Designer A has incomplete information. A PLM system helps

the designer by providing him some previous ship reference

data. Since shipyards produce many ships per year, it is not

possible for the designer to search for the reference data on his

own as the manual search takes a long time. The PLM system

helps in automating this search and thus saves on design time.

Figure 10: Task representation in Project Management Module

Block E11

Block Z

Block X Block Y

Figure 11: Adjoining Blocks of Block E11

Figure 12: Definition of Activities in Process Management Module

To be able to effectively handle the planning and extracting

information the PLM systems are equipped with a process

engine. This process engine is a part of the PLM system and is

composed of two parts:

1. Project management module

2. Process management module

The Project Management Module consists of projects. A

project is a set of all the tasks related to one or a series of

ships. Each of these projects is composed of various tasks or

works. A task or work refers to a single drawing of a particular

ship component or a POR for one part or to a specific design

task. The Project Management Module maps all the tasks on a

timeline and defines the relations between the tasks.

Figure 9 represents a particular scenario of the Project

Management Module. In this figure each of the blue boxes

represents a task or a work. The horizontal axis is the time

line. These tasks are taken from the mid-term schedule and

represented in the above form. The Project Management

Module establishes the relationships between these tasks. It

does not define the nature of relationship but only defines the

existence of a relationship between two tasks.

The Process Management Module extends the definition of

tasks to the next level. All the tasks listed in the Project

Management Module are defined in the Process Management

Module. In the Project Management Module each of the tasks

is a process which was represented as a single unit. But each

task is also a set of activities which need to be performed

sequentially. The Process management module defines these

processes and the activities of a task. Consider the example

shown in Figure 10 which shows the task of preparing the

drawings of Block E21. The definition of the activities and

processes is shown in Figure 12.

The Process Management Module also consists of the

workflow engine which executes the activities and processes

defined in a particular task. Consider the example given in

Figure 12 where the processes and activities of preparing the

drawings of Block E21 have been mentioned. The first step is

the extraction of the relevant reference data from the existing

resources and providing it to the designer. The various

reference documents to be extracted might be Building

specifications, Block division, General Arrangement,

Machinery Arrangement, Engine Room outfitting drawings,

Drawings of the Blocks E81, B51, B12 (adjacent blocks –

Figure 11), Other documents (as per requirement) etc.

Thus when a designer logs into his system the PLM system

provides him with the requisite reference data. The next

activity is the initiation of the CAD program where the

designer would prepare E11 block diagram, E11 nesting plan,

E11 hole plan, E11 outfitting etc. Once the designer has

submitted the drawings, the PLM system would automatically

direct the drawings for inspection which would verify the

drawings. Once the inspection is over the final drawings need

to be updated in the product data model. This updating the

product data model is an automatic process and needs no

manual intervention. Thus the next process calling upon the

data for Block E21 would also include the drawings of Block

E21.

Thus the Process Management Module not only defines a

task but also assigns the processes of a task, controls the

product data and defines the logic of the processes involved.

The BOM management system and Process Engine

together constitute the PLM system which effectively helps in

reducing the design time as well as design cost. The next

section proposes a module for PLM system which would

streamline the process of conversion of E-BOM to M-BOM

which is presently done manually by experienced personnel of

a shipyard.

III. AUTOMATION OF CONVERSION OF ENGINEERING BOM

TO MANUFACTURING BOM

A. Problem Statement

Shipbuilding is primarily an assembly activity which

involves the assembly of various components to form interim

products and the assembly of these interim products yields the

final ship. The production is therefore product oriented or in

other words focuses specifically on a particular interim

product at all times. Hence the manufacturing personnel need

a BOM which is structured in a product oriented hierarchy.

On the other hand the design involves breaking up the ship

into its constituent systems and designing each of these

systems and their components individually. A designer at all

times would be working on a specific system of a ship viz.

hull, outfitting, piping, ballast water systems, fresh water

systems, electrical cables, HVAC etc. Therefore, a designer

requires the BOM to be oriented in a system based hierarchy.

In terms of the data, both the engineering BOM and the

manufacturing BOM share the same components at the lowest

levels of hierarchy. Essentially a plate or a stiffener is a part of

the hull structure from a designer‟s point of view. At the same

time it is a part of a particular block too. Thus, the components

in both the BOMs are same with the difference only in the

grouping of these components and their hierarchy. Thus

conversion of engineering BOM to manufacturing BOM is

essentially re-grouping the components in the engineering

BOM into interim products keeping in mind the assembly

process. Thus the problem statement of automation of the

conversion of engineering BOM to manufacturing BOM is

primarily a re-grouping problem.

Automation of this conversion process will ensure lesser

design time as compared to the manual process which takes a

long time. It will also lead to lesser cost as this process saves

on the manpower being utilized for the designing process.

B. Solution Approach

As already mentioned before, the solution lies in providing

an algorithm which can efficiently re-group the components of

the engineering BOM into the groups of the manufacturing

BOM. The algorithm must however decide on how to group

the various constituents and how many groups are to be

formed. A solution to a similar problem in a manufacturing

sector was proposed by Wang and Li [4] [5]

. They developed an

algorithm to decide the assembly groups of a product on the

basis of assembly sequence.

Consider a product which has eleven components, each

numbered from 1 to 11. The physical connectivity between

each of these 11 components is shown in Figure 13. This

figure is known as the connectivity graph of the product.

Each of the nodes represents a component and the link

between two components denotes the “physical” connectivity

between the two components. Thus, from the figure we can

see that component 5 and 6 are connected to each other

physically but component 1 and 10 are not connected to each

other, even though all the 11 components are a part of the

same product.

Once the connectivity graph has been obtained, a

connectivity matrix for the same is defined. The connectivity

matrix will always be a symmetric matrix, with all the

diagonal elements as zeros. This is because no component is

assumed to be connected to itself. Connectivity between two

nodes is represented by 1 while the absence of connectivity is

represented by 0. Each node necessarily must have a

connection to at least one other node in the graph i.e. the

matrix cannot have any row or column with only zeros.

Let the connectivity matrix be represented by M. If there

are n nodes in the connectivity graph, the size of M would be

n x n. For representing the connectivity between node 5 and

node 6 the value of M (5, 6) and M (6, 5) are both set to 1.

(5 , 6 ) (6 , 5 ) 1M M (1)

Since there is no connectivity between node 1 and node 10,

the corresponding matrix values are set to 0.

(1,1 0 ) (1 0 ,1) 0M M (2)

The connectivity matrix for the connectivity graph shown

in Figure 13 would be:

(3)

The next step is the decomposition of the assembly into

sub-assembly groups. This process starts by finding the

articulation points in the connectivity graph.

An articulation point of a graph is defined as the node

which when removed will fragment the graph into two

separate sub-graphs. For example, consider the node 1 to be

removed from the graph and all the links with node 1 to be

broken. This will lead to two separate sub-graphs {5, 6} and

{2, 3, 4, 7, 8, 9, 10, 11} which do not have any common

nodes. Thus node 1 is an articulation point.

On the hand if node 2 is removed from the graph. It can be

seen that the connectivity throughout the graph still exists and

there are no sub-graphs. Thus node 2 is not an articulation

point.

In the given example there are four articulation points {1 4

7 8}. Based on the articulation points, the 11 components are

grouped to form sub-graphs of the original connectivity graph.

Each of the groups formed represents a sub graph of the

original connectivity graph and none of these groups can be

further decomposed further i.e. there are no articulation points

within the sub-graph. The sub-groups formed are:

Figure 13: Connectivity Graph

Group 1 = {1 5 6}

Group 2 = {1 2 3 4}

Group 3 = {4 7 8}

Group 4 = {7 10 11}

Group 5 = {8 9}

The hierarchy is shown in Figure 14. This division results

in the formation of a 3 level product hierarchy which is

product oriented.

In the actual manufacturing process, the product is divided

into smaller interim products on the basis of ease of division.

An interim product must have minimum connections to other

interim products to make it suitable for independent

concurrent assembly. A block which has a large number of

connections to other blocks would be difficult to assemble

independently as it shares many connections and managing

each of them is difficult. On the other hand if a block is

connected to only one other block, it is possible to assemble it

independently without much consideration for its connectivity

to other blocks. Since the articulation points in a graph are

single elements connecting two sub-graphs, the groups formed

by the algorithm share the same concept of least connections

to other sub-graphs. Thus, the groups formed by the algorithm

are similar to those formed on the basis of ease of division.

There is a minor difference which needs to be accounted for

while adopting this model for the Hull Block Construction

Method (HBCM). The connectivity in case of HBCM does not

indicate physical connectivity. Instead it indicates a structural

connectivity. The method described above finds the

articulation points in the connectivity graph where the

structure can be divided into separate parts. In case of the

structural components of a ship, the division into blocks is

done at a structural joint so that the assembly of these blocks

does not cause a structural weakness at the joint. For this

reason it is necessary that for the HBCM only the structural

connectivity be considered. The algorithm when applied to

structural members provides accurate results only for a

structural connectivity matrix. An example to differentiate the

Product

Group 3 Group 4 Group 5 Group 1 Group 2

1

5

6

1

2

3

4

7

8

7

10

11

8

9

4

Figure 14: Initial Product Oriented BOM

Figure 15: Panels of a typical bulk carrier

structural and physical connectivity has been provided in the

next section.

The structural connectivity is relevant only in the case of

HBCM. For other components such as the piping, outfitting,

HVAC ducts etc a physical connectivity is sufficient to

provide the product oriented hierarchy. This is because the

aim of the breaking up the piping and outfitting structures into

smaller zones does not have any structural issues related to it.

The next section provides an illustration where the present

model has been applied to relevant data for shipbuilding.

IV. ILLUSTRATIVE EXAMPLE

Consider the cargo hold of a typical bulk carrier shown in Figure 15. The problem is to find the different groups into which the components must be grouped as per the above approach and compare its closeness to the actual grouping done in the shipyards.

The typical grouping adopted by a shipyard is shown below in Table 2.

Table 2: Typical grouping from shipbuilding point of view

Sl. No. Group No. Component Elements

1 1 1, 2, 3, 4

2 2 4, 5, 7

3 3 6, 7, 8

4 4 8, 9, 10, 11, 12, 13

5 5 13, 14, 15

6 6 14, 16, 19

7 7 17, 18, 19, 20

For the sake of simplicity and limiting the BOM to only two levels, the assembly groups are assumed to be individual components. The individual assembly groups are numbered as shown in the Figure 15. There are 20 panels defined for this cargo hold. A uniform longitudinal extent is assumed for each of the panels shown. Similarly the floors connecting the various panels have not been included in the calculations as they would not be articulation points and would only be extra nodes connecting different panels.

The various panels under consideration have been listed in Table 3. To apply the approach suggested above, the first step

18 17

20

19 16 14

15

13

12 11

9 10

8

6

7 5

2 3

4

1

Articulation Point

Not an Articulation Point

Figure 16: Connectivity Graph for the cargo hold of the bulk carrier

is to define a connectivity graph between all the panels. Each of the panels would be a node in the connectivity graph. As already mentioned in the previous section, connectivity between these nodes is defined by a structural connectivity instead of physical connectivity. Thus there would not be any connectivity between panel 7 and panel 9 even though there is weld line connectivity between the two. On the other hand, panel 8 and 9 share a structural continuity and are considered to be connected in the connectivity graph. The final connectivity graph is shown in Figure 16.

On the basis of this connectivity graph the articulation points are evaluated. The violet nodes are the articulation points in Figure 16 and the green nodes are not the articulation points. On the basis of these articulation points the groups are formed. The various groups obtained by the application of the algorithm are listed in Table 4.

Table 3: List of panels of cargo hold under consideration

Sl. No. Panel No. Panel Description/ Location

1 1,20 Deck

2 2, 18 Upper Hooper Tank Side Shell

3 3, 17 Inner Upper Hooper Tank

4 4, 19 Tween

5 5, 16 Side Shell

6 6, 15 Lower Hooper Tank Side Shell

7 7, 14 Inner Lower Hooper Tank

8 8, 13 Longitudinal Girder Double Bottom

9 9, 11 Tank Top

10 10, 12 Bottom Shell

It can be seen that the groups generated by the algorithm (listed in Table 4) and the groups decided by a typical shipyard (listed in Table 2) are much in agreement. This shows that the algorithm is quite successful in generating most of the groups.

Table 4: The groups generated from the algorithm.

Sl. No. Group No. Group Elements

1 1 1, 2, 3, 4

2 2 4, 5

3 3 5, 7

4 4 6, 7, 8

5 5 8, 9, 10, 11, 12, 13

6 6 13, 14, 15

7 7 14, 16

8 8 16, 19

9 9 17, 18, 19, 20

V. CONCLUSION AND FUTURE WORKS

This method does not consider the assembly lead time into the grouping methodology. Thus even though the initial Manufacturing BOM has a product oriented hierarchy, it is not clear that this BOM will result in the minimum assembly lead time.

To overcome this problem one can try to perform a critical path analysis with the initial groups formed by the algorithm. Based on this analysis, decision can be taken to merge one or more groups to improve the assembly lead time of the product.

Similarly this method can be applied only to the lower most level of the BOM, because the assembly groups produced after the application of the Wang and Li algorithm cannot be further divided into smaller sub-assembly groups

An approach to overcome this problem might be in trying to apply the same method repeatedly over the groups formed. Thus once the initial groups have been formed out of the components, a similar process is repeated with the group as a whole being considered as a component for the next level. This way a hierarchy can be continued in a bottom to top approach till the final hierarchy has the entire ship in a single group.

Application of these developments would result into a manufacturing BOM which would provide the entire hierarchy and be efficient from the product assembly lead time perspective.

VI. REFERENCES

[1] M. Grieves (2005), „Product Lifecycle Management: Driving the Next Generation of Lean Thinking’ McGraw-Hill, 1st Edition, Oct 2005, pp 141-143

[2] HHI (2009), „Hyundai Heavy Industries Shipbuilding Division Selects Siemens PLM Software Technology to Implement Innovative Digital Shipyard‟, Siemens PLM Software News and Press Release

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