Combining Value Stream Mapping and Discrete EventSimulation

Anthony J. DonatelliGregory A. Harris

University of Alabama in HuntsvilleHuntsville, AL 35899

donatea@uah.edu

KEYWORDS

Industrial processes, Industrialengineering, Manufacturing, Production,Documentation, Model design, Modelevaluation, Discrete simulation

ABSTRACT

This paper discusses the integration ofvalue stream mapping (VSM) anddiscrete event simulation to further thecontinuous improvement goals of leanmanufacturing.

INTRODUCTION

Models are descriptions ofsystems, and model simulation isperhaps the primary tool for studying thebehavior of large, complex systems.(IIE, 1992) Usable models should beeasily understood, yet have enoughdetail to realistically reflect theimportant characteristics of the system.Two tools used in implementing leanmanufacturing are value stream mapping(VSM) and simulation. If VSM is asnapshot, simulation is the movie. VSMand simulation complement each other,and at the end of this paper a real world

application of their combination isshown.

LEAN MANUFACTURING

Lean manufacturing is thesystematic approach to identifying andeliminating waste (non-value addedactivities) through continuousimprovement by flowing the product atthe pull of the customer in pursuit ofperfection. (NIST, 2000) For example,wastes would be things liketransportation, waiting, and inventory.

VALUE STREAM MAPPING

A value stream is all the actions(both value and non-value added)required to bring a product, or group ofproducts that use many of the sameresources in much the same way,through the main flow essential to everyproduct – from raw material to the armsof the customer. VSM is a pencil andpaper visualization tool that shows theflow of material and information as aproduct makes its way through the valuestream. (Rother and Shook, 1999) VSMserves as a starting point to helpmanagement, engineers, suppliers, andcustomers recognize waste and itssources. Value stream mapping is done

in two steps. The first step is to draw thecurrent state value stream map to take asnapshot of how things are being donenow, and the second step is to draw thefuture state map to show how thingsought to be done. Value stream mappingprovides both a picture of the currentstate of affairs as well as a vision of howwe would like to see things work.Identifying the differences in the currentand future states yields a roadmap forimprovement activities.

USE OF SIMULATION WITHVSM

Some obvious steps in VSM thatcan be helped by simulation are (1)analysis and evaluation of the currentand future states, (2) documentation ofareas to improve, and (3) assessment ofthe impact of proposed improvements.

The data collected in the act of valuestream mapping provides theinformation necessary to develop acomputer simulation of the currentprocess. The simulation can be used inanalyzing and evaluating the current andfuture states. And once a suggestion toimprove a targeted problem has beenmade, the simulation can be modified toinclude the suggestions and then run tomeasure the potential impact. Thisallows the team to make changes andobserve the effects without disruptingthe production process or causingunnecessary downtime and costs.

Both VSM and simulation take aholistic look at the system, but VSM isan efficient design tool, while simulationis an efficient analysis tool. VSM createsthe model and provides the vision,whereas simulation is used to evaluatethe model and substantiate the vision.VSM is a pencil and paper, down to

earth, and realistic representation, butsimulation is a general analysistechnique, and as such can only provideestimates of model performance. Again,the vision and the model come from thevalue stream maps, and simulation givesanalysis and flexibility.

APPLICATION OF SIMULATIONWITH VSM

Notice from Figure 1 that thecurrent process consists of 13 material

operations and 9 information operations.Notice from Figure 2 that the futureprocess consists of only 4 materialoperations and 5 information operations.Figures 3 and 4 show the obviouscorrelation between the value streammaps and the simulation models, as theyare almost identical. The modelgeneration and data collection phases ofsimulating the process were basicallyeliminated, due to value stream mappingfirst. Simulation of the VSM showproblems that might have been missedwith the value stream maps alone – forexample, extended running of thissimulation shows that the informationflow, not the material flow, is the sourceof the process problems. Due to the lackof data in this case, the onlyimprovements VSM and simulation canoffer at this time are improvements inlayout and flow.

CONCLUSIONS

The following conclusions aremade for the use of simulation withvalue stream mapping:

• VSM is an extremely valuabletool in lean manufacturing andthe continuous improvementeffort.

• Simulation adds the fourthdimension, time, to a valuestream map. After beingsimulated, the VSM is no longerjust a snapshot; it is a movingpicture, which offers insights thatmay have been missed if VSMalone had been used.

• One tenet of lean manufacturingis to not get “paralysis byanalysis,” – simulation of theVSM allows the lean team tomore quickly “just do it,” andwithout causing interruption inthe production process.

• Simulation makes not onlytesting ideas easier, cheaper, andquicker, but also gives immediateassessment of proposed changesto the system.

• The VSM process provides themodel and the data, makingsimulation easier to do.

• VSM and simulation are anatural combination and eachenhances the other’s value in thelean manufacturing effort.

REFERENCES

• [Rother and Shook, 1999] M.Rother, and J. Shook, 1999:Learning to See, The LeanEnterprise Institute, Brookline,MA.

• [IIE, 1992] IIE, Handbook ofIndustrial Engineering, WestLafayette, IN.

• [NIST, 2000] NIST-MEP Lean,Lean Certificate Series, NISTManufacturing ExtensionPartnership, Gaithersburg, MD.

ABOUT THE AUTHORS

Tony Donatelli is a Research Associateat the ATN Region 1 Center at UAH. Hehas BS in Industrial and SystemsEngineering and is currently pursuing anMS in Engineering Management fromUAH. He has experience in value streammapping, simulation, production control,line balancing and standardization,facility layout, and as a leanmanufacturing trainer.

Greg Harris is Director of the ATNRegion 1 Center at UAH and has over 20years of experience in manufacturing as

an industrial engineer, quality engineer,operations manager and plant manager.He is a certified NIST LeanManufacturing Trainer and a registeredProfessional Engineer. Mr. Harris hasBS in Industrial Engineering fromAuburn University, a MBA from St.Edwards University and is pursuing aPh.D. in Industrial Engineering at UAH.