Investigating the efficacy of Investigating the efficacy of exercising JIT practices to exercising JIT practices to support pull production support pull production

control in a job shop control in a job shop environmentenvironment

Author: Jing-Wen LiAuthor: Jing-Wen LiAccepted March 2004Accepted March 2004

Presented by: Kelly LaylandPresented by: Kelly Layland11-26-200711-26-2007

PurposePurpose

Use a simulation experiment to Use a simulation experiment to investigate the schemes for investigate the schemes for coordinating Just in Time (JIT) coordinating Just in Time (JIT) practicespractices

Job Shop environmentJob Shop environment Pull SystemPull System

Push vs. PullPush vs. Pull

PushPush Parts produced Parts produced

according to according to schedule/forecastschedule/forecast

Once part is done at a Once part is done at a workstation it is workstation it is “pushed” to the next“pushed” to the next

Long lead timesLong lead times Large amounts of WIPLarge amounts of WIP Large WIP impedes Large WIP impedes

continuous continuous improvementimprovement

PullPull Parts are authorized by Parts are authorized by

visual signals – helps visual signals – helps reveal disturbances in reveal disturbances in the manufacturing the manufacturing processesprocesses

When a signal is sent a When a signal is sent a part is “pulled” from part is “pulled” from the previous the previous workstationworkstation

Shorter lead times Shorter lead times Controls the amount of Controls the amount of

WIPWIP

ParametersParameters Production Control SystemProduction Control System

– PushPush– PullPull

Shop Layout (SL)Shop Layout (SL)– Cellular Manufacturing (CM)Cellular Manufacturing (CM)– Functional Layout (FL)Functional Layout (FL)

FlowFlow– BatchesBatches– Operations Overlap – one piece flow (OPOVR)Operations Overlap – one piece flow (OPOVR)

Set-up Time Reduction (STR)Set-up Time Reduction (STR) Coefficient of Variability (CV)Coefficient of Variability (CV)

– Setup Variability (S)Setup Variability (S)– Process Variability (P)Process Variability (P)

Literature ReviewLiterature Review Most past literature found faults with Most past literature found faults with

implementing pull JIT systems in job shopsimplementing pull JIT systems in job shops These papers were limited:These papers were limited:

– Size of job shop investigatedSize of job shop investigated– Lack of analysis for interactions of factorsLack of analysis for interactions of factors– Excluded CM technology Excluded CM technology

However practical experience has shownHowever practical experience has shown– 66% reduction in cycle time66% reduction in cycle time– 80% reduction in WIP80% reduction in WIP

Design Of ExperimentDesign Of Experiment

Set-up Time Improvement (STI)Set-up Time Improvement (STI) Inter-cellular Movement (ICM)Inter-cellular Movement (ICM) Full Factorial Design (3x6x4) Full Factorial Design (3x6x4)

– 72 simulation runs72 simulation runs

Design of ExperimentDesign of Experiment

Mean set-up time 2 hours per batchMean set-up time 2 hours per batch Mean processing time 0.1 hours per Mean processing time 0.1 hours per

partpart

Simulation ModelSimulation Model

Used SIMSCRIPT II.5Used SIMSCRIPT II.5 Shop ConfigurationsShop Configurations Production ControlProduction Control Job ProcessingJob Processing Job SequencingJob Sequencing SimulationSimulation

STRCSTRC

STRC – Set-up time reduction due to STRC – Set-up time reduction due to CMCM

STRC = (Minor Setup Change)/(Major Setup STRC = (Minor Setup Change)/(Major Setup

ChangeChange))

ResultsResults

ResultsResults

ResultsResults

ResultsResults

ResultsResults

ConclusionsConclusions

Traditional push systems and FL result Traditional push systems and FL result in poor production performance in poor production performance

CM – substantial STR effected by CM is CM – substantial STR effected by CM is neededneeded

OPOVR – not recommendedOPOVR – not recommended CV reduction – Depends on level of STICV reduction – Depends on level of STI STR – critical for delivery, cost and STR – critical for delivery, cost and

qualityquality

ConclusionsConclusions

FL recommended if S/P =< 8FL recommended if S/P =< 8 STRC of 50% needed to implement CMSTRC of 50% needed to implement CM STRC of 80% needed to implement STRC of 80% needed to implement

OPOVROPOVR Variability reduction is critical to Variability reduction is critical to

implementing JITimplementing JIT If variability can be reduced and set-up If variability can be reduced and set-up

time can be reduced JIT can lead to time can be reduced JIT can lead to “remarkable performance “remarkable performance improvement”improvement”

ReferencesReferences