Time Weighted Petri Nets for Optimization of a Refrigerator Manufacturing Plant

Abstract

In a flexible manufacturing plant handling systems, transportation vehicles, manufacturing stations, and workpieces in process have to be coordinated well in order to guarantee the desired output of the manufacturing plant. Especially, using driverless transportation vehicles in a complex manufacturing area the optimization of the manufacturing structure has to be supported by simulation of the manufacturing process prior to the implementation of expensive hardware. Therefore, a program module has been developed for the flexible simulation of any time weighted petri net structure.

The efficiency of the optimization tool will be demonstrated for a manufacturing plant in home appliance industry. The manufacturing plant consists of up to 12 manufacturing stations, a station for the foaming of the appliance housing, two manufacturing stations which combine the necessary components for the proceeding processes, and several stations for the plastification of the foam under definite temperature and time conditions. Each workpiece has to be machined in three stations.

By calculating the necessary operating frequency the optimal number of stations for the foam plastification is determined. Next, the optimized number of driverless transportation vehicles is computed and evaluated. Simulations prove that the number of workpieces in process has a relevant effect on the output of the manufacturing plant. Finally, the number of workpieces in process is optimized to reach a high performance of the manufacturing plant.

As a result of previous optimization a considerable reduction of manufacturing stations and driverless transportation vehicles was possible and the output of the manufacturing plant could be further increased.