Simulation study of coordinating layout change and quality improvement for adapting job shop manufacturing to CONWIP control

Abstract

Constant work-in-process (CONWIP) has been highlighted for its superiority over kanban for application in job shop environments. Smooth operation of CONWIP yet depends on some critical practices, including: layout change (from functional to cellular), quality improvement (QI) and set-up time reduction induced by layout change (STR). Simulation modelling was employed in this study to investigate the coordination of these conditions. QI was experimented with the mean magnitude and probability of occurrence for step shifts (MMSS and POSS, respectively); it has major effects on flow time variability only. If STR is below 60%, a functional layout with push control was found favourable while QI is not effective. STR needs to reach 60% to justify layout change; POSS and MMSS reductions are effective for cellular layouts with CONWIP and push control, respectively. At this stage, promotion of improvement activities should be the major concern for replacing push control with CONWIP. The performance of CONWIP is superior if a 70% or larger STR is achieved. In this case, it enables greater delivery performance upgrade via strengthening the effectiveness of QI in reducing flow time variability. Essential guidelines were ultimately derived for reforming traditional job shop practices, progressing through layout change, towards the realisation of CONWIP.