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Nowadays, sheet metal products are some of the most frequently found parts in industry. Progressive dies have a special role in various methods of sheet metal production. The design process however, requires a considerable amount of time and expertise. Two important activities during a progressive die design are "Nesting" and "Piloting". In this paper, a software is introduced which automates the nesting of different parts according to minimum scrap strategy. The software is also capable of choosing the most suitable existing holes or designing auxiliary holes on the scrap part of the strip for piloting pur- poses.41367
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Sheet metal products are frequently used in industry. Press tool design plays a critical role in this issue. Progressive dies can be used instead of several simple dies when more than one operation is needed. Progressive dies are often compli- cated and expensive; however, combining several dies into one, results in a more reasonable cost for mass production. Progressive die design involves considerable expertise and experience and nesting in the design process has a critical effect on reducing the scrap. In sheet metal production, over 70% of the total cost is spent on material, so efforts are made to reduce the scrap in an attempt to influence the final cost. In recent decades, much work has been done on computerizing and automating progressive die designs both in academia and industry.
Shafer was one of the pioneers in the field of computer aided progressive die design. In 1971, he developed PDDC (Progres- sive Die Design by Computer) (Schaffer, 1971). In 1975, Fogg and Jaimeson considered further parameters and followed Shafer in improving the software (Fogg and Jaimeson, 1975). One of the problems with their system, however, was the interactive and time-consuming nature of the software which removed the automation aspect of it to some extent. In 1978, Nakahara developed a semi-automated software, but it was not able to analyze the design parameters and the interac- tion of a skillful designer was needed (Nakahara et al., 1978). In 1981, Shibata and Kanimoto developed a CAD/CAM sys- tem to help designers nest the parts on the strip and design the layout (Shibata and Konimoto, 1981). In 1996, Choi intro-
duced STRTDES which was developed for blanking die design of free form parts. Although it worked better than previous systems, it did not behave well where nesting, piloting and
Software structure
die components design of complex shapes were concerned (Choi et al., 1996, 1997a,b, 1998a,b; Choi and Konimoto, 2001). In 2001, Nye developed an optimized algorithm for minimiz- ing the scrap in the nesting process (Nye, 2001). However, the algorithm was very time-consuming when dealing with seg- mental shapes. Furthermore, technical limitations were not considered. In 1998, Arezoo and Sekhavat developed a soft- ware to design blanking dies (Sekhavat, in press). This work was further developed in 1999 when Arezoo and Barzegari introduced an automated system for progressive die design (Barzegari and Arezoo, 1998). In this system, nesting was car- ried out for all kind of shapes including free-form shapes and the results were acceptable. However, the system was
The software is made up of two major modules.
• Nesting module • Piloting module
The input to the system is made up of a 2D draw- ing of the part, material, accuracy, thickness, number of production and so on. The output data contains the best nesting template and pilot's position. The software was programmed using Visual Basic in Solidworks environment (Solidworks, 2005).
very time-consuming and the selection of pilots was not com- 4. Nesting
pletely automated. In 2002, Lee opened the discussion of
nesting optimization, considering the deflections caused by residual stresses (Lee et al., 2002). Finite Element analysis was used for blanking process simulation to predict the amount of deflections and spring back. The results of this simula- tion were then used to determine the operation precedence of punches in layout design. In 2003, Lin and Chen deter- mined the die center of force using a simple mathematical model (Lin and Chen, 2003). They also used the simulated