architecture of the structural design system for holes on plates and deals with the process for constructing the holes design with the help of library feature in detail. Section 4 demonstrates the hole designing of a progressive die for the motor core using the proposed system. Conclusions are given in Section 5.

2 Hole classification and the descriptive model for progressive dies

The structure of a progress die usually consists of an upper die shoe, a lower die shoe, a punch holder plate, upper backing plates, a lower plate, a punch backing plate, a die backing plate, and other die structure components required by each process station such as punches, dies, strip guide pins, lifters, guide posts and bushings, et al., as shown in Fig. 1. Figure 1 shows the structure of a typical progressive die. There are a lot of holes on the main parts such as upper die shoe, lower die shoe, punch holder plate, upper backing plates, die holder plate, punch backing plate, die backing plate, etc., which are used for connecting, locating, and installing. The holes are different in structure, function, tolerance, and fit. Meanwhile, holes on different plates have complex correlated relations for

different kinds of correlating parts or assembles, such as punches, dies, screws, pilot pin assembles, lifter pin assembles, etc. When the parameters or location is changed for the correlating parts, the size or the location must also change to fit, which cannot be defined and achieved by functions provided by general 3D CAD software. Hence, the relationship among the holes, the correlating parts (or assembles), and the correlated plates must be studied on the basis of relevance. So in this paper, we first give classification for holes on plates by structure then analyze the relationship between the plate holes and associated parts and present a descriptive model. 2.1 Hole classification by structure

By studying the structure of the progressive dies, six types of holes are summarized according to their structure. They are through hole, step hole, blind hole, screw hole, figure hole, and combined hole. The characters of the different kinds of holes are listed below in detail. 2.1.1 Through hole

The hole goes through the plate. The assemble of guideposts and bushes which are employed for aligning the die set associates with the upper die shoe, the stripper holding plate,

and the bottom die shoe, as shown in Fig. 2. The holes on the stripper holding plate and the bottom die shoe are through holes. 2.1.2 Step hole

The hole has one or two steps. As shown in Fig. 3, when screws and pins are employed to connect and locate two plates, the step holes are usually adopted. In Fig. 1, the hole on upper die shoe is also a step hole for amounting the guide seat and the housing plate. 2.1.3 Blind hole

The hole is blind. Figure 4 shows that a slot punch is amounted on the punch holding plate by a supporting plate and a screw. A blind hole must be constructed on the stripper holding plate below in order to avoid colliding when the upper die set moves down to shear. 2.1.4 Screw hole

The screw hole is mainly used for screw. As shown in Fig. 3, a screw hole is constructed on the connected plate. 2.1.5 Figure hole

The figure hole is mainly for noncircular punches and dies. As shown in Fig. 4, the slot punch which is formed by wire electrical discharge machining goes through punch holding plate, stripper holding plate, and stripper plate. The contour

of figure holes on the three plates is as same as that of slot punch, while the fits and tolerance are different. In addition, when the outside contour of the die inserts is noncircular, the hole on die holding plate is also regarded as figure hole, as shown in Fig. 5. 2.1.6 Composite hole

The composite hole means that the geometric structure of the hole is complex and can be viewed as the combination Int J Adv Manuf Technol (2010) 49:1–12 3 (a) A set of progressive die (b) Holes on bottom die shoe Hole for pilot pin components Upper die shoe Hole for guideposts and bushes Stripper backing plate Stoppers Bottom die shoe Hook screw Holes for