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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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FIGURE 7.3 Strips used to notch out the external profiles of a workpiece. (a) Strips generated by projecting edges<br />

vertically. Thin strips of web are provided at both sides of strip for carrying the workpiece, (b) strips generated by<br />

project edges horizontally.<br />

A ‘‘Strip’’ Approach for Punch Shape Decomposition<br />

One of the key tasks in operations planning for progressive dies is to select an optimum combination of<br />

punches to notch out the external profile of the workpiece progressively. This is achieved by decomposing<br />

the scrap areas between successive workpieces into smaller areas. This simplifies the punch construction<br />

and makes it easier to remove the resulting smaller scrap pieces from the die.<br />

A strip approach can be used to achieve this objective. This is done by projecting strips from each<br />

edge of one workpiece either horizontally or vertically to the edge of another workpiece or to the edge<br />

of the strip (Figure 7.3). The following rules can be used to control the development of the strips:<br />

• When projecting strips vertically from the edge of the workpiece to the edge of the strip, the punch<br />

will overlap the edge by the overlap allowance if a center web carrier is used. Otherwise, it will<br />

leave a thin strip of web at the side to carry the workpiece through the die.<br />

• Punches to notch away concave features on the external profile of the workpiece are selected first.<br />

Thereafter, these concave features are closed for the generation of strips.<br />

• Filleted corners are not used for strip generation. Instead they are tagged and temporarily ignored.<br />

The new corner of the edge used for projection is redefined as the meeting point of the projections

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