Parallel CONWIP for a High-mix Multi-stage Production System with the Entrance of Rework

Resumé

 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.Keywords: CONWIP, mixed pull system, rework, high-mix multi-stage production, simulation analysis, response surface methodology.