Sheet Metal Forming

Punch Rigidity during Impact
Long, slender punches are more prone to 
damage during impact. The shock waves under 
impact must be transmitted vertically to the 
punch body instead of laterally within the more 
fragile points. If the punch is long enough and is 
not guided well, this may lead to buckling/
bending or even breakage.
Punch Point Geometry
Some point geometries experience lower 
stresses than others, as discussed earlier. The 
lower the tool stress, the lower the wear and the 
longer the tool life. This results in better part 
quality and longer periods before resharpening. 
Effect of Lubrication on Punch Wear
(Ref 1.9) 
Punch wear changes with the amount of lu-
brication during blanking. Results of a test con-
ducted with varying amounts of lubricants and 
measuring the punch wear volume are shown in 
Fig. 1.15. Copper alloy of 0.254 mm (0.010 in.) 
thickness was blanked with a cylindrical punch 
of 3.7 µm diameter. Wear volume of the punch 
was measured by subjecting a blanking tool to 
selective activation (on a particular area of the 
punch) by a beam of irradiating particles and 
calibrating the energy output to wear volume. 
Fig. 1.13
 
Punch stagger method to reduce instantaneous 
shock. Adapted from Ref 1.3
Fig. 1.14
 
Jektole punch with side vent hole. Source: Ref 1.3 

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Chapter 1: Blanking / 9
Figure 1.15 shows that the wear volume of the 
punch does not increase much when lubrication 
is increased by 40% of the standard lubrication 
condition. 
Stripper Plate (Ref 1.3) 
Stripper plate plays three important roles in 
blanking: 
•
The