Workload control and order release in two-level multi-stage job shops: an assessment by simulation

Abstract

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.