Parallel Conwip for a High-mix Multi-stage Production System with the entrance of rework

Abstract

In a complex production environment, more than one type of pull systems is often used to regulate the processes
of different products. In literature, performance studies appertaining to multiple pull systems co-existed in a
production environment are rare. The present paper evaluates the performances of parallel CONWIP (PC)
systems in a high-mix production system with the entrance of rework. The production comprises three stages of
shared-machine facilities. Reject parts produced by the first stage are to be reworked by an independent station
and later readmitted into the middle stage to undergo the remaining processes. The high- and low-runner
products are handled using a separate CONWIP system. The PC systems were differentiated in terms of the
model driver, loading rule, and rework entrance policy. The performance measures adopted are total output,
average work-in-process, flow times, and average machine utilizations. Discrete-event simulations were
conducted with an analysis enhanced by multi-factor ANOVA and response surface methodology. From the
analysis, the major finding is that optimum performances can be achieved at a specific composition of low- and
high-runner products when low-runner products are loaded first at all stages. The merging of the reworked
parts with a forthcoming similar batch is consistently superior to its counterparts.