Scheduling in a production environment with multiple process plans per job

Traditional job shop scheduling problems generally assume that there is a s ingle feasible routing with which a part can be processed in a shop. In tod ay's flexible production systems, this assumption is rarely true. For most manufactured parts, it is possible to generate multiple ways to sequence th e operations required to realize the finished product. Each feasible orderi ng of the operations generates a process plan. Multiple process plans per j ob increase production flexibility, while at the same time they increase pl anning and scheduling difficulty. In this paper, the problem of scheduling multiple jobs with each having multiple process plans in a job shop environ ment is addressed. The problem is modelled and solved using a mathematical approach. Because of the high computational effort required to solve the mo del using an exact solution procedure, two algorithms were developed and co mpared against solutions obtained by an optimum finding technique. The resu lts of the test problems indicate that one of the algorithms, referred to a s the preprocessing algorithm, finds the optimal solution in all problem ca ses tested. The second algorithm, referred to as the iterative algorithm, i s also effective in finding good solutions; however, its overall performanc e is lower than that of the first algorithm.