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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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TABLE 7.1<br />

Schema for the Generation of Punch Plates<br />

Component Name: Punch plate<br />

Function: Hold and support punches<br />

Requirements: 1. Provide sufficient area to mount punches, fasteners, locators, pilots,<br />

and other components.<br />

2. Provide sufficient strength to bear stripping forces.<br />

Geometrical and Topological Features Governing Rules and Functions<br />

Plate Thickness Function of punch sizes.<br />

Plate Length and Width Spatial arrangement of punches as defined by strip layout.<br />

Location and size of fasteners, locators and pilots.<br />

Rules on minimum distance between holes.<br />

Rules on minimum distance between holes and plate edges.<br />

Plate Location Below backing plate.<br />

Rules governing size and location of retaining holes for:<br />

Punches: spatial arrangement of punches as defined by strip layout.<br />

Pilots: spatial arrangement of pilots as defined by strip layout.<br />

Dowels: rules on locators.<br />

Screws: rules on arrangement of fasteners; size is a function of stripping forces.<br />

the screws and dowels should be placed in locations so that they are sufficiently far apart to provide the<br />

fastening strength and positional accuracy required. At the same time, they cannot be too close to the<br />

other holes and pockets on the plates so as to adversely affect the strength of the plates they are holding<br />

and locating. The following steps can be used to place screws and dowels on plates:<br />

1. The envelope areas of the holes and pockets on the plate are derived. The envelope area of a hole<br />

is the circumscribing circle whose diameter is equal to the diameter of the hole enlarged by a<br />

factor to satisfy die design rules controling minimum distances between holes.<br />

2. The envelope rectangle circumscribing the envelope areas of all the holes and pockets is derived.<br />

This represents the minimum plate area required to mount the tools (on punch plate) or accommodate<br />

the holes (on die block).<br />

3. Thereafter the envelope areas of the holes to accommodate the screws and dowels are placed at<br />

the corners of the envelope rectangle according to the predefined configurations, some of which<br />

are shown in Figure 7.14.<br />

4. The arrangement in which the locators are farthest apart is the preferred solution and will be<br />

accepted immediately if it satisfies the die space constraint.<br />

5. Otherwise, the arrangement which requires the minimal die space will be accepted.<br />

6. The envelope area including the holes for the screws and dowels is derived. This represents the<br />

minimum plate area required by the punch plate.<br />

7. The actual plate size will be selected by matching the dimensions of the envelope area with the<br />

next bigger plate provided in the standard catalogue component library.<br />

8. Finally, the position of the screws and dowels is adjusted to be further away from the center of<br />

the plate to take advantage of the bigger plate area.<br />

7.12 3-D CAD Representation of the Progressive Die<br />

The MBR approach can be used to generate a complete description of the progressive die assembly in<br />

the knowledge base. This has to be translated into CAD models for visualization and manufacturing<br />

purposes. Traditionally, die designers have used 2-D drawings to represent the die assembly. However,<br />

in an automated design environment, 2-D drawings are no longer adequate or efficient. There are several

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