Load smoothing by the planning and Order Review/Release systems: A simulation experiment

Most research studies investigating the impact of Order Review/Release (ORR) mechanisms on shop performance have focused strictly on managing the flow of orders to the shop floor once they have been generated by the planning system. This approach ignores the possibility that the manufacturing planning system may be managing the incoming work flow so that peaks and valleys in the work load have been smoothed out. This study shows, via a simple computer simulation of a random job shop, that such smoothing by the planning system can improve system performance and enhance the effects of Order Review/Release. The two ‘filtering’ mechanisms of planning system smoothing and Order Review/Release have a complementary impact on the system, with smoothing working to reduce flow time and flow time variability and ORR working to reduce work in process and work in process variability. The combination of smoothing with ORR results in shorter and more consistent lead times, lower and more stable work-in-process levels, and better delivery performance. This results in a system which is very stable and predictable. Further, the study shows that the combined effects of smoothing and ORR can improve the performance of simple shop floor dispatching rules like first come-first served to the point where they are competitive with more sophisticated, due date oriented rules. This raises the possibility of simplifying control mechanisms on the shop floor by doing a better job of work load planning and order release.