The impact of sequence changes on product lead time

Abstract

In practice, sequence changes during production often occur due to material shortages, rush jobs, etc. Rescheduling, expediting and de-expediting are common practice on the shop floor, but in many cases it is less clear to which extent such control policies influence throughput times. The aim of this paper is to study the impact of sequence changes on the average throughput time and its variability. The analysis is done by means of simulation. Our basic model consists of five machines, each preceded by a buffer with infinite capacity. In a first part, we rely on the first in, first out (FIFO) priority rule, common in queuing theory. In a second part, we keep all parameters the same, except for the priority rule. In each queue, the priority is now given to the entity with the highest probability of being late. Comparing the results of our FIFO model (FIFO rule) with the results of the model with the new priority rule allows us to draw conclusions concerning the impact of sequence changes on both the average and the variance of product lead time. Although further research is necessary, the results of this study indicate that in our setting sequence changes have no significant impact on the average product lead time but do increase the variance of the lead time and thus influence customer service.