Work-in-process analysis in a production system using a control engineering approach

There are different types of inventories in production systems including raw material, work-in-process (WIP) inventory and finished products, and each of them causes associated costs in the production system. In this paper, we analyze work-in-process inventories using a control engineering approach. We apply the Automotive Pipeline Inventory and Order Based Production and Control System (APIOBPCS) as a control system with demand updating, finished products recovery and WIP inventory adjustment as control parameters. We analytically prove that levels of WIP inventory in the system follow Little's law, where the average number of WIP inventory in the system is equal to the production quantity multiplied by production leadtime. Furthermore, we validate this result showing system responses for different inputs such as step function and sinusoidal function. The results shows that WIP behaves the same with the production quantity of the production system, and hence an analysis of WIP can be substituted by an analysis of production quantity.