Toyota production system introduces the value stream mapping which is a method to evaluateand improve business functions. A value stream includes all elements both value added andnon-value added which occur to a given product from its inception through delivery to thecustomer. Value Stream Mapping (VSM) mainly deals with three steps: current state map, futurestate map and action plan. Main steps to achieve a optimized value stream consists of selectionof product family of high demand and low variety, forming a multidisciplinary team, understandingthe customer demand, mapping the process, material and information flow, calculating the Takttime, lead time and change over time. Understanding and application of mapping symbols indesigning material, process and information flow and data collection are vital parameter for thesuccess of mapping. Work presented here is aimed at applying the VSM technique for leadingseat manufacturing company. It uses foam (chemicals), frame (metal), trim (fabric or leather)and plastic parts as a raw material. There is a wide scope for process improvements throughenhancing the supply chain from supplier end to the customer end which will results in tangibleand intangible benefits such as time, cost and fatigue. Implementation of VSM tools has resultedin self examination of the present process performance against the customer demand. It alsoguides to the future state via scientific techniques like time and motion study, NVA reduction,Kaizen, 5S and focuses on root cause of the problem.
Keywords: Information flow, Inventory management, Pacemaker process, Value streammapping
INTRODUCTIONValue Stream Mapping (VSM) is anadvanced form of process mapping. It is
ISSN 2278 – 0149 www.ijmerr.comVol. 3, No. 4, October 2014
1 Sinhgad Institute of Technology, Lonavala.2 V.J.T.I., Mumbai, India.
management system which gives a vividpicture of existing status of processes in anorganization and highlights the path to
Research Paper
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achieve zero downtime, reduced number ofdefective parts, efficient working environmentand ult imately the Total ProductivityMaintenance (TPM). Basically VSM can beclassified into three fields: (1) Informationmanagement, e.g., orders processing,purchasing, (2) Physical transformation, e.g.,materials, logistics, (3) Intellectual property,e.g., improvement ideas, designs, projectmanagement.
To achieve overall productivityimprovement in any organization; valuestream mapping along with other leantechniques like 5S, Kaizen, Pokayoke actsas an important tools to reduce 7 kinds ofwastes. VSM is an excellent tool for anyenterprise that wants to become lean. Rotherand Shook (1999) defined VSM as a powerfultool that not only highlights processineff iciencies, transactional andcommunication mismatches but also guidesabout the improvement. According to Hinesand Rich (1997), Value stream is a collectionof all actions value added a well as non-valueadded that are required to bring a product ora group of products that use the sameresources through the main flows, from rawmaterial to the hands of customers. Jones andWomack (2000) explain VSM as the processof visually mapping the flow of information andmaterial as they are and preparing a futurestate map with better methods andperformance. A value stream consists ofeverything including the non-value addedactivities and provides a pictorial view of whatelements of the process the customer iswilling to pay for. Jones and Womack (2000)define VSM as ‘the simple process of directlyobserving the flows of information and
materials as they now occur, summarizingthem visually and then envisioning a futurestate with much better performance’.
Main parts of any automotive seatassembly are back assembly, cushionassembly and head-rest assembly or nap-rest assembly. Raw materials like foam, frameand trim [“A” Class] are consumed along withnumerous in-process materials like listingwires, plastic parts [“B” Class], etc., and nutbolts [“C” Class]. Cushion assembly isperformed first at the start of the line bycollection of frame and the putting on fixture.Further, foam is aligned on the frame, trim isput on the foam and hogering is done atpredefined locations. As per designspecifications, track and riser are assembledto cushion by marriage bolts. Finally, finishingis done and assembly is wrapped in apolythene bag and passed on to next station,mean while other operators perform backassembly by putting frame on the fixture,aligning foam on frame, picking and aligningtrim on foam, hogering at prescribedlocations, matching bezel holes of trim andfoam, inserting and hammering active [onright side] and passive[on left side] bezels infoam and trim, finishing the assembly bysteaming, wrapping the assembly in apolythene bag, passing the assembly to
Front Seat 504 460 964
Rear Seat 549 283 832
Jump Seat 121 73 194
Total % 52.25,65.95, 47.75,34.05, 10062.42 37.58
Table 1: Total Cycle Time Required for Seat
Seat VA Time[Sec]
NVA Time[Sec]
Total Time[Sec]
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marriage. Analysis of the previous data(Figure 1) indicates that the existing seatmanufacturing process has higherpercentage of non value added activities Thusthe objective of this paper is to map thepresent seat manufacturing process,compare it with a future state map and identifyand eliminate non value added activities,thereby streamlining work processes, cutting
lead times, reducing costs and increasingquality.
CURRENT STATE MAPFor the initial Current state mapping activity,keep data at high level or ‘overall level’ forthe process. The main purpose of the currentstate flow is to understand the current stateprocess flow, material flow, information flow
Figure 1: Value Added-Non Value Added Activities Analysis for Seat Assembly Line
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in the Value Stream and analyze to findsolution over the inhibitors to it. The stepsinvolved in the mapping the current state ofprocess are shown in Figure 2. Selectedpart should have minimum variety and highproduction volume. The obvious choice ofthe product for present study was seat familysuch as variants such as LX, EX and VXPand seats for front line Driver and Co driver;Rear seats 40%-60% each with head restassembly and Jump seats LH, RH withoutheadrest assembly. A multidisciplinary teamwas formed including production, stores andlogistics, continuous improvement, lineoperators, etc. Analysis of the demand fromcustomer was done for each product mix by
obtaining information about the product fromvarious departments including productioncontrol. Further, all the operations requiredfor completion of part was analyzed byindustrial engineering techniques. Incoordination with Stores and Logistics teamflow of material right from its inception todispatch is analyzed. Stop watch time studywas performed to calculate standard time ofeach operation Based on the observed time:Takt time, cycle time and change over timewere calculated. Off line Non value addingactivities such as material handling byoperators and other futile activities whichincur cost, time and fatigue to the operatorsare noted. Figure 3 of seat line gives vivid
Figure 2: Steps for Mapping the Process
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picture of process flow and material flow ofseat assembly. Customer demand for seatsis 65 units per day. Present manufacturingline has 16 workstations operated by 18operators per shift.
The process flow of seat manufacturingprocess is shown in Figure 4. Operationsinvolved are movement from, Driver seatcushion, Driver seat back, Track To slider andDriver seat marriage, End of line andinspection and similarly Co Driver SeatCushion, back and marriage stations. Pusharrow is shown in Figure 4 to indicate that eachstation gives its product to next using pushsystem so line will be in balanced state. Driver& Co. Driver Seat Back assembly is done onfixture suitable for ease of process flow.
One Piece Flow• Builds in quality: Every operator fixes the
problem at the station only before passingit on; problems are delectated quickly andthey can be immediately diagnosed andcorrected.
• Creates flexibility: Shorter lead times, buildto customer order, set-up time reduction.
• Creates higher productivity: Easiness tospot the idle station and calculate the valueadded work.
• Frees up floor space: Inventory reductionsaves money and space.
• Improves safety: Smaller batches meanssimpler transportation system and simplertransportation system and fewer accidents.
• Improves morale and efficiency: Peopleperform high percentage of value addedwork and can see faster results by strivingfor continuous improvements.
Non Value Added (NVA) and ItsSolution for Seat Assembly Line viaAction Plan
Top 3 Contributors to NVA Activities• Material shortage by supplier (foam, frame,
trim, and slider or): Non availability of thematerial on line results in stoppage of line-Dept. responsible Stores and Logistics.
Identify weak links in the flow and strengthenthem by taking corrective actions Visual controls Problem solving
Table 2: Strategies and Tools Used in Creating Connected Process Flow
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• Tool down time: Stoppage time due to toolmaintenance and no spare tool availableDept. responsible-Maintenance.
• Materials handling by operator (self orguiding material handler to pick right kindof material) Dept. responsible-Process.
Station-Wise NVA Activities
FUTURE STATE MAPFuture state VSM as shown in Figure 7 lies inthe continuous improvement processes likeKaizen on entire NVA’s and NNVA’s on line.Figure 7 indicates the clear picture of howfuture state VSM should be. It mainly focuseson pacemaker process which is the coreOperation on the line as in this line, Driver SeatBack is the pacemaker process since all otheroperations depend on it and it takes highercycle time than others on which the focusshould be to reduce the cycle time.
Correct product mix to be given on as perproduction schedule for the maximumefficiency and proper utilization of resources.Kanban can be used as an effective tool mainlyfor operators and material handlers so that theywill not have any confusion for picking rightmaterial from right place and operators will notbe required to monitor them, ultimately savingtheir time and reducing the fatigue.
Dept. Name Down Time hrs
Production 0.5
Quality 2.5
Stores and Logistic 15
Process 1.5
Maintenance 5
Human Resources 1
Customer Demand Fluctuation 10
Materials 7
Total hrs 42.5
Table 3: Monthly Down Time Assessmenton Seat Line
Station NVA Solution
Front Seat Assembly Line Excess material handling for ‘A’ class Raw material storage shifteditems involving 10 m distance travel near to respective Front, Reareach time and 5 min duration and Jump lines to reduce
material handling distance to2 m and time to 1 min
Front -Rear -Jump Seat Assembly Poor visibility at the workstations and Lux level increased to 2000 andmainly at inspection stations leading on inspection stations to 2500to less detect ability of defects for 100% defect identification
Driver & Co. Driver Seat Back Assembly Bending and segregation activity: Materials pick up problem:Bezel bin position is below avg. MTM clogging of back support lumberheight and mixing of active and pads occur due to fitment withpassive bezels occur one another
Driver Seat Track to Cushion Assembly Difficulty in picking up of sliders on Provision of in process bins onright hand and left hand sided due to right and left hand sided for180 degrees turning+ peeping action sliders to have mistake proofinginvolved
End of Line and Inspection Belt conveyor damage due to stud of Provision of nylon boardsliders as assembly is kept on completely covering the stationconveyor for checking, the contactpoints rapture the conveyor completely
Table 4: NVA Activities on Seat Assembly Line
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ACTION PLANFor the initial efforts in creating connectedValue Stream continuous improvements byrapid action implementations are requiredrather than long term project planning andevaluating the process. The aim should be toimprove respective employee’s workstationwith complete involvement right form operatorto manager. The actions were focused onlayout changing for assembly and rawmaterials. Assembly layout changed as shownin Figure 7 to get the output of front and rearline in single finished seats trolley. Also firewallstations and seat review area are added for100% inspection. Detailed action plan tocreate ‘one piece flow’ for a seat assemblyline is as shown in Table 4.
Kaizen Implemented
Problem/Waste
Rear Seat Line spring balancerrebounding issue [Refer Figure 8]
1. Rebounding of nut runner andPokayoke while return stroke on toMTM face.
2. Clogging of pneumatic and electriclines due to less space width.
1. Process modification wassuggested to operators to carry outassembly without breaking the nip.
2. Trials shown the results that due toinsufficient gap between frame andnip, nip slipped downside of frameand gap observed which is not asper specifications.
3. Seat got assembled, still plasticcover shown the wobbling effectdue to non conformance of partassembly process with design.
Table 5: Kaizen Implemented on Seat Assembly Line
Changes
1. Spring balancers tensionreduced.
2. Space width increased to 60 cm.
3. Electrical and pneumatic linesseparated using hooks.
4. Sliding railing shifted as per theproper positioning of nut runnerand Pokayoke.
1. Process modification wassuggested to operators to carryout assembly without breakingthe nip.
2. Trials shown the results that dueto insufficient gap between frameand nip, nip slipped downside offrame and gap observed which isnot as per specifications.
3. Seat got assembled, still plasticcover shown the wobbling effectdue to non conformance of partassembly process with design.
Results
1. Safety issue of Pokayokerebounding resolved.
2. Ease of processing theoperation.
1. No process performancedifficulty while fitment ofplastic cover to frame due tosufficient gap between frameand nip.
2. Ease of operation due to nonbraking of nip.
3. Process time reductionduring assembly due toelimination of non valueadded activity.
4. No wobbling of plastic cover,no scratch marksappearance on plastic cover.
Figure 4: Spring Balancers Improvements
Figure 5: Jump Seat Process-QualityImprovements: A) Before, and B) After
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Problem/Waste Changes Result
Jump Seat material mix up issue 1. We prepare the separate small 1. No material mixing of leg tube.[Refer Figure 10] trolley for leg tube
1. Mixed Storage in one Rack. 2. Visual identification. 2. Easiness for identification.
2. No visual identification. 3. Defined specific locations for 3. Dust Free Storage.the trolley.
3. Time loss for material handler 4. Material at its location withto pick right material. identification.
4. No any Proper location for leg tube. 5. 5S Improvement in Storage.
6. Saves material handling andissuing Time.
Table 6: 5S Improvements on Seat Assembly Line
Front Seat 504 380 964
Rear Seat 549 231 832
Jump Seat 121 35 194
Total % 56.97,70.32, 43.03,29.68, 10077.60 22.40
Table 7: Improved Cycle Time for SeatAssembly
Seat VA Time[Sec]
NVA Time[Sec]
Total Time[Sec]
Figure 7: Upgraded Value Added-NonValue Added Activities Chart
Figure 6: Jump Seat Material StorageImprovements; a) Before, b) After
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Figure 8: Process and Material Flow of Seat Assembly Line
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Table 8: Action Plan for Seat Assembly Layout Change to Create “One Piece Flow”
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Figure 10: Current State Mapping of Seat Assembly Line
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NVA ReductionNVA’s are mainly created due to lack ofmaterial handlers, non standardized work,improper layout and equipmentdysfunctionality, inappropriate line balancing,
material shortage. To reduce these standardpractices should be followed by operators withinsurance that all the processes in the planthave the necessary material, qualifiedequipment and safety.
Figure 11: Future State Mapping of Seat Assembly Line
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CONCLUSIONValue stream mapping is a continuousprocess of self examining the processperformance against the customer demandand satisfaction to the current state. It guidesto the future state via scientific techniques liketime and motion study, NVA reduction,Kaizen, 5S and focuses on root cause of theproblem. After analyzing the most problematicNVA of waste-‘Motion’ during assemblyoperation at each station; through layoutmodification as per ‘One Piece Flow’ conceptfor overall Seat assembly setup reduction inNVA percentage was achieved as per thefollowing data: (Refer Table 7, Figure 7).
Totally NVA reduction achieved by 25% allover the seat assembly line. Thus, it clearlyindicates that the systematic application ofvalue stream mapping process results insignif icant improvements in creatingconnected processes with continuous flow withreduction in non value added activities.
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