The effect of push and pull lot splitting approaches on lot traceability and material handling costs in stochastic flow shop environments

This study evaluates how the procedures followed in splitting job lots on the shop floor influence both material handling and lot integrity in stochastic flow shop environments. Former work has shown that lot splitting improves flow time and customer service performance, but with an increased number of transfers along with a corresponding increase in material handling costs. Physical lot integrity, which is important to lot tracing, has not been considered in prior literature. In order to overcome these limitations and address material handling concerns better, we define a new measure of performance called the lot integrity loss exposure. We use this and other measures to show that the traditional ‘push’ approach that has been followed in modelling lot splitting complicates lot traceability in the shop and leads to an excessive number of transfers. As an alternative, we propose a ‘pull’ approach in which an order is split between any successive pair of machines only on an as-needed basis. The push and pull approaches for lot splitting are compared under a range of conditions characterized by factors such as machine utilization levels within the shop, setup-to-processing time ratios, and number of splits created in job lots. Our results indicate that relative to the push approach, pull lot splitting helps significantly in reducing the number of transfers incurred and in maintaining a greater degree of physical lot integrity. At the same time, there is no significant difference in the two approaches with respect to improvements in flow time and customer service measures. Both the degree to which lot integrity is preserved, and the extent of savings in material handling that result from using the pull approach, are shown to be most pronounced under conditions characterized by high machine utilization rates and setup-to-processing time ratios. Managerial implications of our study along with further research directions in this area are also discussed.