Generating a backlog list for a CONWIP production line: A simulation study

A CONWIP (CONstant Work In Process) line is a flow line in which the WIP level in the line is held constant by synchronizing releases to departures. One of the first decisions that CONWIP users must address is to generate a backlog list, which gives the sequence of orders to be introduced into the line. This study uses both two-stage (group scheduling) heuristics and single-stage heuristics to generate the backlog list, and then utilizes simulation to compare the performance of the two types of heuristics. Two-stage heuristics attempt to serially process similar orders and eliminate major set-ups required between part types. Results of the paired t-test analysis show that two-stage heuristics outperform single-stage heuristics for various measures. The superior performance of the two-stage heuristics is due to the reduction in major set-up times. The simulation results can provide guidance for schedulers in the selection of preferable heuristics for relevant CONWIP lines.