Master production scheduling in capacitated sequence-dependent process industries

Traditional approaches to planning and control of manufacturing (MRPII) foc us on discrete parts manufacturing industries (e.g. automotive). The chemic al industry, however, presents unique challenges. Cross-contamination of pr oduction is a key issue among some chemical facilities. A considerable amou nt of capacity is lost as a result of changeovers which involve performing thorough clean-ups to wash away the impurities which may contaminate the ne xt product to be produced. Therefore, planning for sequence-dependent chang eovers becomes crucial and complicates the master production scheduling pro cess. This paper shows how improved master production scheduling performanc e can be obtained by using a two-level master production schedule (MPS) to focus on key plant processes, and by incorporating a scheduling heuristic w hich considers sequence-dependent changeovers and capacity constraints. Thi s approach is illustrated using actual operating data from a chemical firm typical of many process industry operations. Simulation experiments are reported that test the performance of the propos ed master scheduling method in a single-stage sequence-dependent process. T he experimental factors include both the introduction of the two-level MPS with the scheduling heuristic, and the effect of changes in the MPS batch s ize. The results demonstrate that important simultaneous improvements in pr ocess changeover time and delivery performance can be achieved using the pr oposed MPS scheduling approach against a more traditional (single-level) MP S approach which does not consider sequence-dependent changeovers. Further, we rnd that delivery performance is relatively insensitive to adjustments in the MPS batch size when using the two-level MPS approach.