Minimising total tardiness for hybrid flowshop with batch-discrete processors, setup times, and distinct job sizes

This research addresses a complex hybrid flowshop (HFS) scheduling problem confronted in a real industrial environment in a manufacturing plant which provides electro-plating services to the electronic and semiconductor industries. It is modelled as a four-stage hybrid flowshop problem with multiple batch and discrete processors at different stages. The first and the last stages consist of multiple batch processors, while the other stages consist of discrete processors. Most of the studies in flowshop assume that jobs need to visit all the stages; this research considers the flexible case where stage skipping by jobs is allowed. On top of this, the existence of sequence dependent setup time and sequence independent setup time in discrete stages has further increased the complexity of the scheduling problem