Minimization of WIP inventory cost at CNC-machining centers through assignment of m serial machines and transfer batch size reduction

In the batch production, the use of a single machine for several stages of the processes will result in waiting time of production batch to be long. It will cause an increase in work in process (WIP) inventory cost. CNC-machining centre is a type of CNC machine that can carries out several stages of processes singly. In some cases, this machine is often single used to make a product through several stages of processes, from raw material to end product. One of the reasons to use a single machine is to avoid transfer from one stage (machine) to next machine. However, single use causes inventory to accumulate due to long waiting times. The objective of this research is to reduce the WIP inventory cost at the CNC-machining centre. Scheduling to minimize WIP inventory cost is done through two steps. First step, divide number of stages of processes to be assigned to m serial CNC-machining centers. Second step, determine transfer batch size is smaller than the production batch size to be transferred to the next stages. The results of this research indicate that there is a reduction in WIP inventory cost by 53.47 percent. Scheduling multi-stage batch production on m machines with small transfer batch size will reduce WIP inventory cost.