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Most studies on the performance of workload control (WLC) order release methods assume products have simple structures. But, in practice, products are often complex and consist of a number of sub-assemblies that flow through a ‘level 1’ job shop before converging on several final assembly operations in a ‘level 2’ assembly shop. Evaluating the performance of release methods in this context – referred to as the ‘two-level multi-stage job shop’ – is an important step towards improving the alignment between WLC theory and practice. We use simulation to assess the performance of four of the best-performing WLC order release methods. Results suggest that WLC order release has the potential to limit work-in-process (WIP) while reducing the percentage of tardy jobs. It is also important to consider when and where release should be controlled. Results suggest that: (1) orders should be considered for release to level 2 when the first sub-assembly is complete, rather than only when all of the sub-assemblies that make up an assembly order are complete at level 1; and, (2) exercising control at level 2 (with or without control at level 1) leads to a greater reduction in the percentage of tardy jobs than control at level 1 only.
Thürer et al. (Tue,) studied this question.