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developed a punch machine selection expert system which was built in AutoCAD and used AutoLISP. Lin and Kuo [9] developed an integrated CAD/CAE/CAM system for stamping dies of a trunk lid outer panel. Lin et al. [10–12] utilized CAD software integrated with an empirical formula to develop the automated design system for drawing die structure for automobiles.
In a progressive die, the workpiece is produced in a number of stamping stations. At each station, one or more die operations are performed on the sheet metal strip. The finished workpiece is produced with each strike of the press. Cheok and Nee [13] developed a knowledge-based strip layout design system in AutoCAD. Chang et al. [14] established a genetic algorithm to solve the problems of ranking the working steps in progressive dies. Kim et al. [15] developed a process planning system for an electric product with bending and piercing operation. Ismail et al. [16] developed an interactive feature-based strip layout de-sign system using cheap CAD software. Ghatrehnaby and Arezoo [17] introduced a mathematical model based on set theory to optimize strip layout using a minimum number of stations and a torque equilibrium criteria. Tor et al. [18] introduced a knowledge-based blackboard framework for the stamping process planning to speed up the progressive die design process by automating the strip layout design. Jiang et al. [19] proposed a systematic representation scheme of insert design automation for progressive dies using an object-oriented, feature-based approach. Giannakakis and Vosniakos [20] developed an expert sys-tem for both process planning and die design of sheet metal cutting and piercing operations. Jia et al. [21] developed an automated plate hole design system for progressive dies. Jia et al. [22] introduced an automated structural design of punches and dies for progressive dies.
Though designing dies is a very knowledge-intensive, complex, and time-consuming process, technologies used throughout the process are mature, which makes the entire process routine. To make the design process more efficient and of higher quality, this paper introduces an automated structural design system for progressive dies with drawing, bending, and punching operations. Designers only need to input a minimum set of design information and the system will automatically accomplish the structural design of pro-gressive dies.
The outer shell of a mobile phone is fabricated by the progressive stamping process. The design of the pro-gressive stamping consists of two parts: layout design of the sheet metal strip and structural design of the pro-gressive die.
The stamping process of shells for mobile phones, as shown in Fig. 1, consists of the following nine sub-tasks: the first and second stations are for piercing the pilot holes and blanking the raw material outline. The third station is for drawing the shell shape. The fourth station is for restriking the shell shape and piercing the pilot holes. The fifth to eighth stations are for bending the earphone and charger holes, blanking the keyboard and screen holes, and side punching the earphone and charger holes. The last station is for cutting products from the strip. The progressive pro-cess includes all sub-tasks in a single die. This die is called a progressive die. Each of the processes performed within progressive dies is called a process station.
Since sheet metal strips should be fed into the progressive system continuously, the sheet metal coils will go though the decoiler, straightener, and feeder before being fed into the progressive die, where they are processed by each of the processing stations. The strips not only provide raw materials for the stamping process but also carry workpieces from one station to another. The sections used to connect workpieces from adjacent stations are called carriers, and the sections between carriers and workpieces are called bridges. The dis-tance strips move forward each time, which is called the progressive pitch. To correctly position workpieces in each of the process stations, there are a number of reference holes on both carriers and workpieces, which we call pilot holes.