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Abstract: The production process plan design and configurations of reconfigurable machine tool (RMT) interact with each other. Reasonable process plans with suitable configurations of RMT help to improve product quality and reduce production cost. Therefore, a cooperative strategy is needed to concurrently solve the above issue. In this paper, the cooperative optimization model for RMT configurations and production process plan is presented. Its objectives take into account both impacts of process and configuration. Moreover, a novel genetic algorithm is also developed to provide optimal or near-optimal solutions: firstly, its chromosome is redesigned which is composed of three parts, operations, process plan and configurations of RMTs, respectively; secondly, its new selection, crossover and mutation operators are also developed to deal with the process constraints from operation processes (OP) graph, otherwise these operators could generate illegal solutions violating the limits; eventually the optimal configurations for RMT under optimal process plan design can be obtained. At last, a manufacturing line case is applied which is composed of three RMTs. It is shown from the case that the optimal process plan and configurations of RMT are concurrently obtained, and the production cost decreases 6.28% and nonmonetary performance increases 22%. The proposed method can figure out both RMT configurations and production process, improve production capacity, functions and equipment utilization for RMT. Key words: reconfigurable manufacturing system, reconfigurable machine tool, configuration, process plan, cooperative optimization model5476
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1 Introduction
* Corresponding author. E-mail: xienan115@tongji.edu.cn This project is supported by National Natural Science Foundation of China (Grant Nos. 51005169, 50875187, 50975209), Shanghai Municipal Natural Science Foundation of China (Grant No. 10ZR1432300), International Science & Technology Cooperation Program of China (Grant No. 2012DFG72210), and Zhejiang Provincial Key International Science & Technology Cooperation Program of China (Grant No. 2011C14025) © Chinese Mechanical Engineering Society and Springer-Verlag Berlin Heidelberg 2012
Current trends in the manufacturing industry are intensified global competition, perse user needs and accelerating product upgrading. In order to adapt to the changes, KOREN, et al[1], the professors of the University of Michigan firstly presented reconfigurable manufacturing system (RMS). RMS is a kind of changeable manufacturing system that can rapidly respond to changes in market demand[2]. Some key issues of RMS design have been discussed and suggestions of RMS research have also been identified[3].RMS incorporates reconfigurable machine tools (RMTs) that are designed to machine a specific set of features for specific production times. RMTs are essential components to implement the RMS[4]. Its features are that components can be upgraded which includes structural components, the main axis, controller, software, fixture
cutting tool, and so on, and configurations can also be adjusted. Device reconfiguration and adjustment according to production process features and plan is a key issue in RMS area. On the other hand, according to changes of market demands, how to utilize the reconfigurability of RMT, and optimize simultaneously the process is one of the core issues. The personalized product demand make product designer take into accounts both modular design and inpidual differences. RMTs can be rapidly adjusted its own production capabilities and capacity according to rapid changes in product demand. RMTs can be used to quickly respond to the manufacturing process fluctuation caused by personalized product design.
The design objective of RMT is by its own reconfiguration, it can be easily converted to a new configuration according to different part process features, which aims to achieve high-precision, low-cost parts production. Characteristics of RMT are: modular, integration, customizability and convertibility. At present, there are a lot of prototype studies and projects of RMTs or variable configuration machine tools that have being carried out in the world. For example, the machine tool developed by INDEX Corporation from Germany can increase or decrease the main axis and parts of bogies to satisfy new production needs of customers. Moreover its modular building block system can provide users an accurate machine configuration to meet actual production needs. Take machine tool V160C for example, it has several different configurations according to perse needs, which are shown in Fig. 1[5]. Fig. 1. Different configurations of machine tool KATZ[6] introduced design principles for RMTs, which was applied in different fields of manufacturing. MOON[7] presented a mathematical representation scheme using the screw theory that laid the foundation for the systematic design of RMTs. MOON, et al[8], developed a design prototype of RMT, and using reservation interfaces in advance, and it could optimize resources of machine tool by adding or reducing the main component. LANDERS, et al[9], developed cooperatively a design prototype of RMT that was applied to cam-hole cut hinge cylinder. Its objective was to produce two different parts by adjustment of configurations of machine tool. LIU, et al[10], proposed a RMT design optimization using the modified fuzzy- Chebyshev programming method. Because both modular product design and personalized design should be considered in product design, how to reconfigure RMT according to the same/similar product family has become an increasingly important issue. CHEN, et al[11], presented a feature-based method for selecting an optimal set of modules to form a new configuration of RMT. SHABAKA, et al[12], presented a method to select different types of machine tools according to part process features. XU, et al[13], cooperatively considered the assembly modules and assembly line design during assembling. TANG, et al[14], designed the RMS using a virtual production line-based approach based on automaton theory. Nowadays, part process plan based process features and machining devices configuration are two relatively independent problems. Moreover, no mathematical formulation was provided.