Bridge hitting reduces tool wear
By alternating hits when performing shearing/slitting operations, forces upon the tool remain balanced from side to side and end to end. As a result, the punch operates square to the material and die. Over the long run, this will reduce the frequency of sharpening and generally longer tool service. This practice is called “bridge” hitting because the full hits leave a “bridge” of material between them that is removed by the next sequence of hits.

If punches overheat:

• Use a lubricant. This will decrease friction.
• Use more than one punch of the same size in the sequence. By alternating the punches, there will be a longer time for each punch to cool down before it is used again.
• Simply give the tool a rest. Program tool changes to interrupt long repeated operations.
• Slow the press down.
• Use Maxima™ coating.

What do your slugs tell you?
The slug is essentially a mirror image of the hole, with the same parts in reverse order. By examining your slugs you can tell if punch-to-die clearance is correct. If clearance is too large, the slug will show a rough fracture plane and a small burnish zone. The larger the clearance, the greater the angle between the fracture plane and the burnish zone. If clearance is too small, the slug will show a fracture plane with little angle, and a large burnish zone.

An ideal slug is created when the fracture planes coming from the top and the bottom of the material have the same angle and form in alignment with each other. This keeps punching force to a minimum and forms a clean hole with little burr. At this point, any extension in tool life gained by increasing clearance comes at the sacrifice of hole quality.

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