The impact of worker forgetting on production scheduling

摘要

Numerous articles suggest using the Japanese manufacturing strategy of minimizing inventories by producing small lot sizes. However, few studies actually have investigated the relative advantages or disadvantages of such a strategy. Worker productivity improvements during production of a batch (learning)and the loss of productivity improvements due to the breaks between batches (forgetting)both influence the optimal lot size for a product. The results of this study indicate that worker forgetting in a batch production environment can substantially increase optimal lot sizes. Since forgetting causes a type of setup cost by penalizing breaks in production, it is intuitive to expect an increase in optimal lot size for forgetting. This study confirms the expectation. What is interesting, however, is that only a small amount of forgetting is required to substantially increase the optimal lot size. The conditions under which lot sizes need to be significantly increased are discussed and illustrated. The results also suggest that special attention must be given to eliminate forgetting due to production disruption when using just-in-time scheduling techniques to reduce lot sizes. The use of automated processes in batch production may overcome the need for large lot sizes by negating the worker forgetting cost, which is a form of setup cost. Robotic technologies or flexible manufacturing systems are types of automated processes which can diminish the forgetting effect in a batch production mode, and therefore, allow efficient production of small lot sizes.