Determining Transfer Batch Sizes in Trip-Based Material Handling Systems

Trip-based material handling systems such as AGV systems or lift trucks are often designed with a given flow matrix (or from-to chart), which typically shows the number of loaded trips that the devices must perform per unit time between the workstations. A from-to chart that would result from the parts flow in a facility actually is dictated by the transfer batch size; that is, the number of parts transferred from one workstation to the next in one trip. In this paper, we present analytical and simulation results aimed at determining optimal or nearoptimal transfer batch sizes in manufacturing systems and develop an analytical relationship between the material handling capacity and the expected work in process (WIP) in a manufacturing system. Although the results apply to any discrete-parts flow, trip-based material handling system, they are particularly relevant for the electronics manufacturing industry, where parts (such as printed circuit boards or substrates for flat panel displays) typically are handled as a group (in specially designed containers such as cassettes) and the costs associated with WIP tend to he large. In such applications, the cassette size is the transfer batch size.