STUDYING THE INFLUENCE OF VARIABLE SUB-LOT SIZES ON HYBRID FLOW- SHOP WITH UNRELATED ELIGIBLE PARALLEL MACHINES

The manufacturing systems have many configurations. The hybrid flow-shop configuration is one of the most manufacturing systems that have many applications. One of these applications is the metal nails factory. This system consists of different stages and each stage has different parallel machines. The machines are unrelated parallel or multi-machines. The speed of the machines can be uniform or variable. With respect to the jobs, the stream of material flows in the same direction among the stages and the jobs can be split into batches to utilize the machines. In this paper, a system of hybrid flow-shop of machines, which are unrelated, have variable speed, and have eligibility constraints is considered. The jobs have variable sub-lot sizes. The variability of the sub-lots sizes can be achieved by splitting the sub-lots into smaller sub-lots from one stage to another. A real case for this system is solved using a non-linear mixed-integer programming model and the sub-lot size and schedule that minimize the overall make-span are achieved. The model is compared to four benchmarking cases studies. The results show the proposed model is better than the benchmarking cases studies. The relative percentage index that is used to compare the results is up to 47%.