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

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

Comparing Functional and Cellular Layouts: A Simulation Study Based on Standardization

In the last decade, over two dozen simulation studies have focused on comparing cellular and functional layouts. The results reported by these studies vary widely, however. This remains true even when the key performance measure is flow time. These variations reflect the disparate manufacturing and operating environments, as well as differences in parts demands, set-up economies, overall loads and other factors. This work attempts to reduce the sources of variation due to different operating assumptions while retaining the variability associated with differences in part mix and demand characteristics. Instead of focusing on a single data source, this study uses a test bed of six problems extracted from the literature and ensures they share the same operational rules. The simulation results show that conversion to CMS can reduce flow times (relative to the job shop configuration) consistently across all data sets, provided the same operating rules and ranges for key parameter are used. We investigate the reduction in flow time while controlling for the key factors of set-up reduction, overall load on the system and batch size. We also assess the benefits of using transfer batches as a further factor in reducing flow time. Our overall conclusion is that set-up reductions in cells can overcome pooling losses, even under the conservative assumptions where batch size remain unchanged and the material transport times in the job shop are assumed to be negligible

Application of Perturbation Analysis to Multiproduct Capacitated Production-Inventory Control

We consider a multiproduct periodic review system with a capacity constraint and no setup cost. Since the optimal stationary control policy for such a system is characterized by a complex switching curve that is usually computationally intractable, we propose a linear approximation to the optimal switching curve. We apply perturbation analysis in a stochastic approximation algorithm to estimate the parameters in the linear approximation. For a randomly chosen test example, we compare numerical results using the linear approximation with results using the optimal dynamic programming formulation. We find that the proposed procedure provides a very good approximation to the optimal solution in a computational time orders of magnitude faster than the dynamic programming solution