Slug
pulling prevention
Slug
pulling during stamping process = slugs can easily pull
up for one or more of the following reasons:
 The
die cutting edges have become worn to a bell-mouth.
The
material being cut is very thin and light in weight.
The
die is running with excessive lubrication and has just been
sharpened.
The
cutting clearance is too big or has worn off.
The
slugs are not held on all sides.
Many methods
can be applied to keep slugs down.
 Adding
ejector into the punch, if space is permitted. ( Fig. 1 )
This method is most effective and most common method in the
market.
 If
the cutting punch is unable to put in any ejector due to the
space constrain. A small shear angle can be ground on the
punch face as shown in Fig. 2. Slug can be held in the die
profile when slug spring back to it original shape while punch
retract.
Another
effective method is to machine a small groove ( 0.005 - 0.01
mm ) to the die profile to creates a precise amount of interference.
The grooves were machined at an angle ( 3 - 5 deg. ) to the
die surface. ( See picture below ) The slug expands into a
series of this special grooves, pressure between the slug
and the die land occurs, preventing it from pulling back through
the top of the die and onto the work zone. The
slug is then safely cleared on the next stroke from the punching
zone
. 
Slug pulling
is a problem that can be prevented by proper design and correct
techniques,
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