توالی عملیات و انتخاب ابزار در سیستم های تولید انعطاف پذیر تحت تخصیص ابزار پویا

In order to adapt to a rapid changes of manufacturing orders, flexible manufacturing systems (FMS) advances into the direction that machines become further versatile functionally and that tools are controlled by fast tool delivery device. Versatile machine can perform a variety of operations when it is supplied with the required tools. Tool management is among the essential elements in the successful operation of the FMS studied in this research. In this research, we propose an integrated model that performs operation sequence and tool selection simultaneously into the direction that minimizes tool waiting time when the tool is absent. The effectiveness of the model is demonstrated through a series of simulation experiments, and interpretations of the results are also presented

To cope with manufacturing orders which are characterized by varieties of products, high quality and short production lead time, a recent trend in flexible manufacturing systems (FMS) is to utilize versatile machines with fast tool delivery devices. Because versatile machine can perform a variety of operations when it is supplied with the required tools, tool management is critical for smooth flow of tools in this FMS (Amoko et al., 1992, Koo, 1996 and Lee et al., 1999). Also, one important tool-related issue that has not been adequately addressed in FMS literature is planning for the tool's availability (Chung, 1991). The tool allocation for FMS can be divided into two categories: static (Cuppan, 1986, Hankins and Rovito, 1984 and Mason, 1986) and dynamic (Gaalman et al., 1987 and Zeleny, 1981). In the static tool allocation, tools are assigned to the machines at the beginning of a planning horizon or a production batch, and the assigned tools remain unchanged during the period or the processing of the batch. With a dynamic tool allocation, the assignment of tools is not necessary at the beginning since tools are delivered when they are needed, and therefore, parts remain on the same machine until the required machining is completed. This strategy is possible when the system is equipped with fast tool delivery devices and an efficient tool control model.

In this paper, we have addressed operation sequence and tool selection problems in FMS under dynamic tool allocation strategy. Because in FMS of this type tool management is critical, this paper proposed the integrated model that performs operation sequence and tool selection simultaneously into the direction that minimizes tool waiting time. The real asset of this study is the way of finding the best operation sequence that minimizes tool waiting time in real-time. As expected at the beginning, this study has shown the number of tools in the system is critical for the performance of FMS. It seems that the enhancement in the performance by the proposed model is sufficient to deserve attention when a system has only a limited number of tools. The experimental results presented in this study show the effectiveness of the model for the limited cases. Thus, in order for this model to be used in real applications, further extensive work is required. To be practical, we will extend tool requirement planning which predicts the number of tool copies required for tool types.