A methodology for simultaneously dealing with machine duplication and part subcontracting in cellular manufacturing systems

In this article, we present a model and a solution algorithm for dealing simultaneously with duplicating bottleneck machines and subcontracting bottleneck parts under budgetary restrictions in CM systems. Because the problem is proven NP-hard in the strong sense, a higher-level heuristic algorithm based upon a concept known as tabu search is presented. The functionality of the algorithm is demonstrated by solving an example (small) problem. Further, the small problem as well as a variant of the small problem are solved for the optimal solution, and the solutions obtained at four different budgetary levels are shown to match with those obtained with the heuristic algorithm. The applicability of the algorithm for problems encountered in industry practice to create either completely disaggregated or nearly completely disaggregated manufacturing cells is demonstrated by solving a fairly large problem that has appeared in the published literature. When parts manufacturing companies are subject to budgetary restrictions, the results obtained show that the proposed approach can be used to determine which of the following three actions should be undertaken for each bottleneck part. That is should, the bottleneck part be left as in the initial solution, all the bottleneck machines connected to it be duplicated, or the part be subcontracted?