lean manufacturing application to an automotive assembly line

7/27/2019 Lean Manufacturing Application to an Automotive Assembly Line

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Paulo Peas, Elsa HenriquesLean Manufacturing Application to an Automotive Assembly Line

Proceedings of the Business Excellence I - Performance Measures, Bechmarking and Best Practices in New EconomyBraga: Escola de Engenharia da Universidade do Minho (ed. G. D. Putnik, A. Gunasekaran), p. 590-595, 2003

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LEAN MANUFACTURING APPLICATION TO AN AUTOMOTIVE ASSEMBLY LINE

Duarte Trindade*, Pedro Leal*, Paulo Peas**, Elsa Henriques***AgilTec-Engenharia e Tecnologia para a Produo Eco-Eficiente

Estrada do Pao do Lumiar Campus do INETI, Edf. M6; 1649-038 Lisboa, [email protected];[email protected],

**Instituto Superior Tcnico, Seco de Tecnologia MecnicaAv. Rovisco Pais 1049-001 Lisboa, Portugal

[email protected]; [email protected]

Abstract

Portuguese automotive industry began at sixties of last century, mainly based on CKD (ComponentsKnock Down) assembly plants. Since then a long process of technological, engineering and organizationaldevelopment has taken place and, nowadays, automotive components industry can be considered astandard of manufacturing excellence in the national and even sometimes in the global context.Nevertheless, we can still find companies in the automotive sector based on the initial CKD conceptneeding logistics, organizational and agility improvements to sustain their competitiveness in particularmarket niches.

In this paper a diagnosis of a small-scale assembly line of small trucks is presented, focusing on theorganizational and work methods, internal logistics and lean manufacturing procedures. The fullmanufacturing system characterisation and the identification of waste generation and productionbottlenecks, created the framework to develop a set of actions both on an organizational/structural basisand on internal logistics, whose implementation allow a huge advance on productivity.

Keywords: assembly_line; lean_manufacturing, automotive_industry, manufacturing_excellence.

INTRODUCTION

Since the beginning of the last century, theautomobile has performed true small revolutions inquite a few levels, starting with the ones emergedfrom the common user expectations, until thosestrictly related to improvement of the technical andeconomical industrial environment. The hugeautomotive value chain justifies the natural trendof our industry in undertaking an active andrelevant position in the sector at several levels andwithin a diversity of competences [1]. Throughoutalmost a century, several efforts have beendeveloped to achieve a position of automotiveconstructors and/or at least to reach as relevantsuppliers of the big constructors. The unsuccessfulof these efforts is mainly due to the lack of asustainable strategy that focuses the criticalfactors of competitiveness and their dynamicbehaviour.

Nowadays the national scenario of theautomotive industry (with a national decision

centre) can be resumed basically to the auto partsmanufacturing. This capacity is mainly used tosupply the OEMs (Original EquipmentManufacturers) with assembly facilities in Portugal,

although in the last decade a considerable growthof exportations had occurred [1].

Therefore, the aim of this paper is tocontribute to the demystification of some conceptsrelated with the improvement of manufacturingsystems, like lean manufacturing and morerecently the agile production that would appear tobe the blueprints for future manufacturing [2].

In a broad concept the aim of leanmanufacturing consists on keeping production

steady and predictable and minimize cost andwaste in a world of business that is increasinglyvolatile and unsteady [3]. Lean Manufacturing hascaptivated the imagination of manufacturingpeople in many countries and its implementation isnow a commonplace for large companies [4].Although, as regards to SME their lack ofadvanced competencies and their typical focus onday to day production problems have been anobstacle to lean manufacturing expanding.

Normally the SME companies look at this sortof concepts as they have a mysterious theory

behind or something completely exoteric andunintelligible [3]. However, if they look closer, theywill perceive that when we are talking about leanmanufacturing we are simply talking about


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manufacturing without waste. The waste, which isbroadly considered as any type of consumption ofresources without a correspondent added-value inthe product or service, can take manyconfigurations [2]. As examples we can refer

material and time wastes, idle equipment andinventory. Several authors refer that mostcompanies waste between 70% and 90% of theiravailable resources and even the best leanmanufacturers probably waste about 30% [3].These figures constitute themselves a tremendousopportunity towards the progress of productivityand industrial competitiveness and embody alarge field for the improvement of the materialshandling, inventory reduction, quality assurance,scheduling and layout configuration, personnelempowerment and, of course the final goal,customer satisfaction.

In short, lean manufacturing embraces theentire manufacturing system. Starting with thecustomer and including the product and processengineering, the production management, the finalassembling and all tiers of the supply chain, leanmanufacturing is essentially a systematicapproach to identify the wastes, to evaluateimprovement potentials, to propose and designbest solutions and finally to implement thesesolutions in a controlled way[2][3]. We have nodoubt that any truly lean system is highlydependent on the demands of its customers and

on the reliability of its suppliers. The success oflean manufacturing relies on effective analysis andplanning including the entire enterprise [4].

One thing is certain: there is no recipe bookfor lean manufacturing. While certain principlesmay be immutable, their application is not. Eachcompany has its own unique set of products,processes, people, culture and history. We have togive heed to the company particularities in theirinvolving and consider lean manufacturingimplementation as an individual process.

SYSTEM PRESENTATION

The work presented in this paper wasperformed in a company that among otheractivities, like metalworking and industrial partspainting, runs a production line in which mediumand light-duty trucks are assembled. Thisassembly line has a layout strongly characterizedby a product-oriented structure. So, like in mostautomotive facilities, all the necessarytechnologies and resources are strictly dedicatedto the product assembly requirements.

In Fig. 1 is presented the general layout of themanufacturing plant, with the CKD (CompleteKnock Down), pre-assembly areas, the fourassembling workstations (WP) and a final control

area. The production starts at the CKD area,where all components and modules areunpackaged, checked and distributed in severalconveyors and trays depending on their futureuse. Some of these materials are pre-assembled,

before its introduction in the assembly line, namelythe transmission shaft, the brake light supportsand some components of the engine.

Fig. 1. Assembly line layout and materials flow

As referred above, four workstations, aproduct certification area and the final qualitycontrol area compose the assembly line. In thefirst workstation the operations related with theheavy mechanics of the vehicle are performed, so

here within are handle the components with largedimensions/weight. In the second workstation theoperations related with the trimming of the chassisare made, namely in what regards the electricalsystem, the vacuum system and the brakingsystem (all the cable- systems). The thirdworkstation is basically characterized by theoperations related to the coupling of the cabin andengine. In the fourth workstation the finaloperations are carried out, such as the final fillingup as well as the final small assemblies at theinterior and exteriors levels. Finally the vehicle isturned on to assess its functioning. In the product

certification area the wheels calibration and ageneral inspection are performed. Finally, in thecontrol area some tests and controls are made toevaluate the quality of the product in a systematicand rigorous way.

SYSTEM ANALYSIS

To take the maximum advantage of theapplication of lean manufacturing principles thefirst step should be the identification of criticalareas/problems. Afterwards, it is necessary toselect a methodology and a technique to analyseand quantify them. Finally, new procedures shouldbe designed and tested to evaluate their potentialsuccess. Considering the evaluation, through


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technological/economical indicators, theimplementation phase, with a close control ofmethods engineering, will take place until itscomplete validation.

The system diagnosis began with the directobservation of the operators and workflow. In fact,only through a simple visual analysis and throughinformal brainstorming emerged from a set ofwhys several simple solutions withoutimplementation cost and with an evident benefitthat were conceived and applied. An example ofthose promptly improvements was a new layoutfor the location of some manual tools, in order toreduce the waste of time in the movement ofoperators inside each workstation. However thebenefits of these simple improved solutions aredistant from the limit gains in productivity. A further

analysis was required to achieve a completediagnosis of the assembly line.

Some of the critical points identified wererelated with the main pillars of a manufacturingsystem, namely, global layout and the assemblyline balance. Consequently, it was necessary toquantify the real impact of these critical points tobe able to justify any modification, which at thislevel always imply a strong impact on themanufacturing system.

After the direct observation, the production linewas evaluated using the methods-study and time-

study techniques. This analysis has as mainobjective the establishment and the normalizationof procedures to allow a maximum effectivenessand quality in the assembly process. It will beaccomplished through the improvement of someprocesses and procedures and through thesuitability of the workstations resources(operators, equipment and tools) to the nature ofthe operations.

For each workstation, a list of operations wasprepared and to each operation its responsibleand the resources required were identified.

Moreover, a layout of each workstation wascreated to completely understand if thearrangement of the materials and tools wasoptimised and also if the operations division wasdone regarding its location in the product. Thelayout of the workstation 1 is presented in the Fig.2 as an example.

Due to the high number of operations in eachworkstation and the randomness of the operationsequence at each workstation, the analysis toolselected was a time sample method throughinstantaneous observations. Basically, this methodconsists in the observation of each workstation

status (photos of each workstation) at randominstants. Through that workstation status samplingit is possible to infer the behaviour of the assemblyline.

Fig. 2. Workstation 1 Lay-out

Due to the high volume of data generatedduring this analysis a software application wasdeveloped to assist the analysis process. This toolhas the capability to create random time sheetsand generate several graphs with relevant datatreated for each workstation or operator and forthe overall assembly line.

In the Fig.3 it is possible to observe theperformance of the three operators involved inworkstation 1. The graph presents for each

operator the time distribution through five differentoperator status.

89,4%

72,7%

81,7%

13,1%15,4%

0,5%

9,6%

0,5%1%

6,7%1,9%

7,1%

0,4%

Operator 1 Operator 2 Operator 3

Operation

Dislocation

Absence

Waiting Time

Out-WorkStation

WS 1

Fig. 3. Operators Performance, workstation 1

In the operators graph (Fig. 3) it is possible toevaluate the labour performance, observing thepercentage of effective work related to valueadded operations and compare it with others non-productive features like the percentage of theoperator time devoted to dislocations, absenceand waiting (for work, for the availability ofresources, etc), and also the percentage of timeeach operator is not at their workstation (but is at

the shop-floor). With this kind of analyse it ispossible to balance the work contents associatedto the different operators in a workstation, as wellas take some training approaches that allow a


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better posture and teamwork attitude in theirquotidian work. Finally, the analysis supports, in aquantitative way, a relevant inefficiency related tothe workstations layout. Indeed more than 10% ofthe operators time is spent in travelling in the

interior of each workstation.

The previous analysis allows the identificationof the operators time distribution. But the analysisit is not sufficient when it is necessary to deal withline balancing improvement. In fact under theoperator status operations several elementaryoperations are performed. So within eachworkstation a detail analysis of the work contentswas performed.

In the vertical axis of the graph presented inFig. 5 each number represents one elementaryoperation (with value added in the product)executed in the workstation and each letter is anon-productive operation (without value added),which are common to all the workstations, namelywaiting, absence etc. The major outputs of thisgraph are the time spent in each operation and thetotal time required to perform all the operations ina workstation. The time required for eachoperation was, when possible, decomposed inseveral tasks types: assembly, fixation,preparation and others.

Every workstation and every operator wereanalysed individually through the use of this typeof data processing and presentation.

Making a general picture of the overall

assembly line in terms of the tasks decompositionmade (Fig. 4), it is possible to conclude that about50% of the available time is not used to add valueon the product. Tasks classified as preparation orother tasks that, effectively, do not built trucks,even if in some cases they could be considered asnecessary for the process. Based on the resultsobtained, the effective nonproductive operationsrepresent almost one third of all the operationsperformed.

Fixation

14,6%Others

28,4%

Assembly

32,5%

Preparation

24,5%

Fig. 4. Time decomposition in task classes

.

Fig. 5. Operations time in Workstation 1 (medium time, tm = 95 min

With the information gathered it was possibleto generate another analysis in terms of theoverall time currently spent in the differentworkstations, in order to evaluate their

equilibrium in terms of work content andoperators distribution all along the assemblyline. A graphic presentation of the results of thisanalysis is shown in Fig. 6.

1,3% - 1,2 min.

2,9% - 2,7 min.

2,9% - 2,7 min.

11,7% - 11,1 min.

3,1% - 3 min.

1,2% - 1,1 min.

3,1% - 3 min.

1% - 1 min.

0,5% - 0,5 min.

0,7% - 0,6 min.

3,3% - 3,1 min.

9,5% - 9 min.

5,9% - 5,6 min.

1,8% - 1,7 min.

3% - 2,8 min.

1,6% - 1,5 min.

2,5% - 2,3 min.

2,6% - 2,5 min.

0,3% - 0,2 min.

4,2% - 4 min.

4,9% - 4,7 min.

5,6% - 5,3 min.

8,7% - 8,3 min.

3,5% - 3,3 min.

7,9% - 7,5 min.

2,3% - 2,2 min.

4,2% - 4 min.

Fixation

19,4%

Preparation

24,6%Assembly

26,8%

Others

29,2%

WS1

tm= 95

12

3

4

5

67

8

910

11

12

1314

15

16

1718

19

2021

a

bc

d

e

f


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RECOMMENDATIONS

In this section the major achievements of theintervention, as regards to the suggestedimprovements and their potential benefits, will be

presented.

Observing the graph in the Fig. 6 severalconclusions can be drawn. The workstation 1represents the assembly line bottleneck and setsits cycle time in 95 min. The discrepancybetween the timework of the differentworkstations is notorious. Considering that weare dealing almost only with manual operationsthis reflects the lack of equilibrium in theoperation/operators division through theworkstations. The yellow horizontal line in thegraph represents the theoretical cycle time (80.6

min) obtained just by the distribution of theoperations through the workstations, withoutperform any methods of improvement insidethe workstations. This represents per se animprovement of 20%, just by changing theworkstation where some operations areperformed. Considering that the useful time ofproduction is about 7h20min/day (440 min), dueto the existing break periods in the working day(8h/day), and 4,6 vehicles is the daily capacityoutput of the assembly line. So, a 20% increase

in the cycle time is materialised in almost onemore vehicle assembled per day.

Through the graph presented in the Fig. 6 itis possible to confirm the initial intuition that the

workstations where the operations involvinglarger parts are performed, specifically theworkstation 1 and workstation 3, show a smallervariability of the average operations total time.Relatively to the workstation 2 we can see thatthe first measurement is totally in disharmonycomparatively to the remaining ones, this can beexplained by the fact that this measurementcoincides with the first vehicle in the batch,denoting the need of operators habituation tothe work content in this workstation.

The application of the methods and timestudy allowed to build a repository of informationand quantified data that permitted theestablishment of some recommendations asregards to a new operations distribution throughthe workstations, in order to get a 20% increasein productivity. Obviously this new distributionwas done regarding the active constrains like thetechnological precedence between operations,the available skills in each workstation and thecosts of the modification.

Fig. 6. Overall assembly line analysis

Unfortunately, this short analysis is notcommon in the daily activity of the company. Ifthey adopt current procedures related to the

production monitoring, the company would beable to create a set of data to support thecontinuous improvement actions and to measuretheir impact on productivity. As the data is

getting more and more consistent they would beable to track non-productivity time and thereforereduce costs.

Considering the kind of workforce presentedin the line, which is constituted by lowqualification/high experience operators, the work

102 104

8684

69

83

64

96

7573 73

9489

69

83

57

77,3

95

79,2 81,2

70,274

67

93

Posto 1 Posto 2 Posto 3 Posto 4 Posto Pr-Montagem

tc equilibrado= 80,6

Workstation 1 Workstation 2 Workstation 3 Workstation 4 Pr-Pre-Assembly

Theoretical Cycle Time =80.6 min


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developed was done in a close interaction withthe line operators. Indeed any line modificationor recommendation was previously discussedwith them. On the one hand, the experience ofthe operators has effectively a high practical

value as regards the generation of new ideasand the first validation of the proposed ones. Onthe other hand, the operators involvementfacilitates their adherence and acceptance to theprocess and enlarges their motivation towards acontinuous improvement and teamwork attitude.

It should be noted that before the lineassembly diagnosis through the methods andtime study that provided the quantitativemeasures, the line unbalancing was not obvious.In fact the initial visual observation has notshown particular waits and the line seems to beperfectly balance. One must remember that

manual work tends to extend itself through outthe available time.

As referred above, the layout was alsoanalysed and two alternatives were idealised.Relatively to this topic only some highlights willbe given because it will be the target of a futurepublication

The existing layout did not support thelinearity and smoothness of the materials flowand people displacements. So the alternativeswere created to eliminate or reduce the criticalpoints of the existing one. Once more, all theshop-floor operators were involved particularlythe ones responsible by the internal logistic. Inthis field, it was necessary to estimate thevolume of the medium and maximum stocks ofeach item (largely related to the external supplyconstrains), calculate the dimension of thewarehouses and the point of use storages.

The first alternative layout was createdregarding the minimal impact on current linefunctioning and a reduced transportation cost. Itkept the main functional areas and displaced theCKD and Pre-assembly cells near to the

assembly line. Using this simple principle it waspossible to foresee a 20% reduction in timewasted in travels. The other layout idealised is areal cut off with the existing one. The totaldistance between the unloading area and thearea where the final product is delivered isreduced. The total transportation distance isreduced by almost 50% and the result is a farmore linear and agile layout. Fig. 7 shows thetotal distance covered by a batch assembly (sixunits) in the different alternatives.

Layout A B C

Distance 5977m 4929m 3250m

Fig. 7. Layout alternatives (A - existing layout; B -

small improvements / minimal impact on currentlayout; C - radical transformation layout/great impact)

CONCLUSIONS

The study carried out generated several newprocedures and recommendations within theglobal objective of productivity increasing withincremental improvements in the manufacturingsystem. Some of these new procedures wereimplemented during the intervention and otherremained as recommendations for futuremodifications in the manufacturing system.

Although not all solutions were immediatelyimplemented, the estimated increase ofproductivity was always significant. In particular,through the application of good practices of linebalance a 20% increase in the number ofvehicles produced per day was achieved. A newlayout design foresees about 50% decrease inthe time spent in materials flow.

The main conclusion transmitted with thispaper is the demystification of the application ofseveral methods and techniques related with thelean manufacturing approach to the continuous

improvement. Lean manufacturing is mainly anattitude or a mindset and not just a collection oftechniques. Through the incorporation of a leanmanufacturing attitude it is possible to have allthe organization involved in the search ofexcellence within the existent resourcesframework.

REFERENCES

[1] Tavares, L.V., A Engenharia e a Tecnologia aoServio do Desenvolvimento de Portugal, 2000,Ed. Verbo, Portugal.

[2] Allen, J., Make Lean Manufacturing Work for You,Manufacturing Engineering, Jun, vol. 123 n7,2000, SME.

[3] Womach, J.P., Lean Thinking: where have youbeen and where are you going, ManufacturingEngineering, Sep, vol. 128 n9, 2002, SME.

[4] Drucker, P., Strategies for the 21st Century,Tooling & Production, Apr, 2000, ManufacturingCenter, Nelson Publishing, Inc.

lean manufacturing application to an automotive assembly line

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