Minimizing Work-in-Process and Material Handling in the Facilities Layout Problem

Abstract

We consider the plant layout problem for a job shop environment. This problem is generally treated as a quadratic assignment problem with the objective of minimizing material handling costs. In this paper we investigate conditions under which the quadratic assignment solution also minimizes average work-in-process. To get some initial insights, we model the plant as an open queueing network and show that under a certain set of assumptions, the problem of minimizing work-in-process reduces to the quadratic assignment problem. We then investigate via simulation the robustness of this result. We found that the relationship between material handling costs and average work-in-process holds under much more general conditions than are assumed in the analytical model. For those cases where the result does not hold, we have refined the model by developing a simple secondary measure which appears to work well in practice.