Abstract:
This research attempts 1) to study factors contributing to effective planning of work in process inventory; 2) to find a guideline for planning of work in process inventory with lowest cost in limited inventory area; 3) to reduce time to make a production plan starting from the initial stage to delivery process (Lead time production) for a beverage packaging manufacturer in Eastern Seaboard Industrial Estate in Rayong province. This study applied mixed methods of qualitative study including literature review, collecting four types of samplings, and focus group with representatives from production, inventory, quality check, and production planning in order to find model for operational research which is quantitative research study and the process. It came to conclusion and presentation that the data from interviews with representatives from production, inventory, quality check, and production planning in focus group can be used to improve further operational research. To reach effectiveness and best conclusion, in the last stage, conclusion in each process were proposed to administrators including factory manager, supply chain manager, financial manager, production manager, quality control manager, and system development manager continuously. The findings reveal that 1) to reach effectiveness, in production planning, there should be the right production that constantly impacted the cost of production, the cost of inventory as well as the efficiency of machine and the total effectiveness of machine at the highest level, with the lowest degree of the waste from production. The most economical production design mean the most effective design in all factors. 2) efficient production design could control the cost of inventory and reduce time of delivery. The basic factors contributing to effectiveness of production planning included the readiness of raw material and engine which is the crucial factor in factory. 3) The results from mentioned production planning can reduce the cost of inventory