In a flexible manufacturing system, cylinder blocks and heads are processed in batches by four machine in line. Each part is fully processed on one machine only. During batch production the tool magazines contain the same set of tools. This paper reports on a simulation study to investigate the possibility of reducing the investment in tools by sharing the tools among the machines by means of an automated tool transporting vehicle. The performance of the system is measured by the fraction of time that machines must wait for a tool required for the next imminent operation. These waiting (i.e. idle) times, which characterize the productivity loss, will depend on the selected tool mix, that is the number of tools (<4) per tool type. The input to the simulation program consists of the process plan, tool lives, tool transport and handling times and the tool mix. Machines may break down due to tool breakages. The transport device carries one tool at a time. Special attention is given to the allocation policy of tools, which plays a central role during real-time operations. Since the process plans are fixed, the times when specific tools are required are known in advance. However, these “events” must be updated continually, due to waiting and breakdown periods. Since the lengths of these periods are not known in advance, updating takes place at the end of such periods. A “look- ahead” policy is defined based on the events. Results show that the system can be operated with considerable less investment in tools while maintaining a small fraction of machine idle times. The reduction in the tool investment out- weighs the extra investment in the tool transport device.
|Journal||Engineering Costs and Production Economics|
|Publication status||Published - 1987|