The effect of container size on a CONWIP production line: A simulation study

A CONWIP (CONstant Work In Process) line is a flow line in which the WIP (Work In Process) level in the line is held constant by synchronizing releases to departures. Setting container sizes is one of the first decisions that CONWIP users must address. This study investigates the effect of container size on a CONWIP production line processing multiple part types. Container size and the number of containers are varied in tandem so that total WIP inventory capacity remains constant. Simulation results show that smaller container sizes generally lead to shorter average flow time and smaller average WIP. Smaller container sizes may increase average flow time or average WIP when the benefit of more frequent material handling (i.e., fewer waits for batch) offsets the cost of more total move time. The line using a container size of 20 parts performs best for average flow time and average WIP. Larger container sizes generally lead to higher average service level and smaller average tardiness. Larger container sizes may decrease average service level or increase average tardiness when the line has higher processing time variability (PTV). The line using a container size of 100 parts (PTV=low) or 50 parts (PTV=high) performs best for average service level and average tardiness.