Sheet Metal Forming

part is held firmly during the blanking 
operation by the stripper.
•
The punch is guided to the blank through the 
clearance hole in the stripper.
•
The part is stripped off the end of the punch 
after blanking at withdrawal. 
There are three basic kinds of strippers: fixed, 
urethane, and spring strippers (Fig. 1.16). Fixed 
strippers do not hold the material during blank-
ing because a clearance is required for material 
movement. Hence, the part material tends to 
buckle. Fixed strippers also do not absorb im-
pact and snap-thru, which are important for 
blanking, depending on the material and thick-
ness of the part.
Urethane strippers are simple to use and are 
inexpensive. They slide over the end of the 
punch with a slight press fit. Urethane strippers 
deform easily under load and do not form a flat 
surface for holding the part material. They fa-
tigue through use and become loose on the 
punches. Spring strippers perform all three func-
tions mentioned previously. Spring strippers are 
much more effective in holding the part during 
blanking. They also prevent the part from lifting 
or hanging up on punch withdrawal. A spring 
stripper hangs below the ends of the perforat- 
ing punches. As one of the first components 
to contact the part material, it holds the part
in a fixed position throughout the cycle of the 
press.
Stripping force depends on the part material 
and thickness and the punch-die clearance. 
Strippers with the right design and force can 
have an effect on part quality. They also help in 
absorbing shock at snap-thru and reducing the 
shock felt by the tooling. 
Pilots
Pilots, as the name suggests, locate the part in 
the blanking tool (Fig. 1.17). They have nosed 
or tapered ends and usually enter an existing 
hole for guidance and move the stock strip into