Production planning for mixed assembly/arborescent systems

The focus of this paper is that a complex manufacturing system often has arborescent or non-assembly portions in its network. In automotive assembly, a given component frequently appears in more than one subassembly in the manufactured product. Certain components are used in each of four wheels; left- and right-side body subassemblies contain common modules. The result is a mixed assembly/arborescent structure, which also merit consideration as the prototype for combined production/distribution systems. In this article, the authors consider such mixed structures by building on properties of pure assembly and pure arborescent systems. First, for a wide class of parameters and various pure assembly structures, they study several single-level lot-sizing algorithms in conjunction with the cost-parameter-revision method of Blackburn and Millen. Cost-parameter revision is a way to account for the impact at other stages, of decisions made at a given stage, in a pure assembly system. The authors also show it is better not to revise these cost parameters for a pure arborescent system. The present approach to a mixed assembly/arborescent system is thus based on identifying its ‘largest, independent pure assembly sub-graph.’ This is a significant subsystem of the original graph or network, the largest portion that is pure assembly in nature. Modification of the cost parameters there, followed by state-by-stage application throughout the whole network of the best single-stage lot-sizing method, gives lower total costs than when no cost revision is applied in the mixed system. Suggestions are then made for further research.