Performance evaluation of hybrid-CLP vs. GA: non-permutation flowshop with constrained resequencing buffers

This paper is located in the area of mixed model non-permutation flowshop production lines where jobs of more than one model are being processed on the same production line in an arbitrary sequence. Nevertheless, the majority of publications in this area are limited to solutions which determine the job sequence before the jobs enters the line and maintains it without interchanging jobs until the end of the production line, which is known as permutation flowshop. The present work considers a non-permutation flowshop. Resequencing is permitted where stations have access to intermediate or centralised resequencing buffers. The access to the buffers is restricted by the number of available buffer places and the physical size of the products. The primary objective is the minimisation of the make span, but also setup-cost and setup-time is contemplated. A hybrid approach, using constraint logic programming (CLP), is presented and compared to a genetic algorithm (GA). These solution methods are conceptually different and recommendations for their applicability are presented.