Work In Process Control for a High Product Mix Manufacturing System

Abstract

This paper presents the development and application of a Work In Process (WIP) control approach to manage inventory in order to reduce manufacturing throughput time and its variation in a high product mix case study company. The approach involves a stage level regulation of WIP, which also serves as the means of sequencing production at the workstations. Its stage level regulation of WIP is similar to that of the Kanban (supermarket-based) control approach; however, its own set WIP levels are not for stock keeping, but are thresholds that the stage WIP should not exceed for each product type. Therefore, it avoids the proliferation of WIP that has been identified as a hindrance to the application of Kanban control in high product mix manufacturing environments.It is applied under the CONWIP and the Push production control mechanisms and its performance is compared against the first in first out (FIFO) rule for the prioritisation of products for processing and a sequencing rule that is based on the similarity of products, and this provides an opportunity to compare the improvements obtained from it against the company's current application of FIFO rule under the Push control.The results obtained show that the CONWIP's regulation of total system WIP reduces throughput time and facilitates the application of sequencing rules in selecting the next product for processing. In real life, this might reduce the time needed by personnel to decide and identify the next product for processing. On the other hand, the Push control delivers a higher throughput rate, but can also lead to the proliferation of WIP which in turn increases the mean and variation of the throughput time. However, the application of the WIP control approach to sequence production under the Push control is able to avoid this negative outcome of the Push control.