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3.0 SHEET METAL PROCESSES
Figure 3.4 The slug.
3. The rough fracture surfaces are due to these cracks; the smooth and shiny burnished
surfaces on the hole and the slug are from the contact and rubbing of the sheared
edge against the walls of the punch and die, respectively.
4. The major processing parameters in shearing are:
a. the shape of the punch and die;
b. the speed of punching;
c. lubrication;
d. the clearance, c, between the punch and the die.
5. Fig. 3.5 (a) shows effect of the clearance, c, between punch and die on the
deformation zone in shearing.
6. As the clearance increases, the material tends to be pulled into the die rather than be
sheared. In practice, clearances usually range between 2 and 10% of the thickness
of the sheet.
7. Fig. 3.5 (b) shows micro-hardness (HV) contours for a 6.4-mm (0.25-in) thick AISI
1020 hot-rolled steel in the sheared region.
Figure 3.5 (a) Effect of the clearance. (b) Micro-hardness.
BPLK 65 DMV 20173
