A long-time industry “rule of thumb“ used by die makers for the clearance between the punch and die button is 5% of the stock thickness per side. However, extensive research and testing have shown that a significant increase in punch-to-die-clearance up to 9 - 20 % can reduce burr height and improves the life of the punch by far. Even though, there is a risk that the slug is pulled up when retracting the punch. By using an ejector pin, this pulling up can be eliminated.
The clearance per side is the distance between the cutting edges of the punch and matrix. It runs evenly around the entire perimeter. Due to the circumferential clearance, the total clearance is twice the clearance per side. The total clearance is also called as total punch-to-die clearance.
Engineered clearance 10 % with 1,0 mm thick material (clearance = 0,10 mm):
|Total punch-to-die clearance (= clearance per side * 2)||0,20 mm|
|Punch Point Size||12,80 mm|
|Matrix Hole Size||13,00 mm|
The characteristics of a perforated hole are dependent on the selected die clearance. A larger die clearance reduces the frictional forces and wear, resulting in longer life of the punch.
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