A heuristic algorithm for joint optimisation of MRP and scheduling in a mixed model assembly line

Abstract

This paper considers an integrated materials requirement planning (MRP) and scheduling model for a multi-period and sequence dependent mixed model assembly line with an objective of joint optimisation of MRP and production scheduling. The interdependency between procurement lot sizing 'referred here as MRP' and sequencing decisions demands the integration of MRP and scheduling. Considering the cost reduction potential of MRP and scheduling simultaneously, a cost model that integrates MRP and scheduling is developed with the objective of minimising integrated total cost (ITC), which takes account of assembly, switchover, procurement, inventory and shortage costs. The mathematical formulation of the integrated cost model belongs to the category of non-linear integer programming (NLIP) and combinatorial optimisation problem. This paper proposes a heuristic algorithm for joint optimisation of MRP and scheduling decisions in a mixed model assembly line. It provides: 1) the order of processing the batches of different models during the entire planning horizon; 2) the quantity to be produced (i.e., batch size) for each model in each planning period. The proposed heuristic algorithm is evaluated using the sequences generated with certain single period flow shop heuristic algorithms.