Tooling by Design
Angular Piercing and Punching
Hole-size elongations can be calculated rather easily and precisely, too. A method for calculating the hole elongation—we’ll call this the minor-axis punch diameter—for holes punched on an angle is shown in Fig. 3. For example: Find the minor-axis punch diameter (X+Y) if the part print hole-diameter specification is 1.000 in., the material thickness is 0.060 in. and the hole is being pierced at a 15-deg. angle.
Distance “X” is equivalent to the cosine of the cutting angle (15 deg.) times the punch diameter (D).
Cos. 15 deg. = 0.9659
D = 1.000 in.
X = 0.9659 in.Sine 15 deg. = 0.2588
t = 0.060 in.
Y = 0.0155 in.
Calculation Results: Minor-Axis Diameter = 0.9659 in. + 0.0155 in. = 0.9811 in.
Final Punch Size = 0.9811 in. by 1.000 in.
The resulting hole shape is not perfectly round. Therefore, the punch and die matrix must be keyed to ensure proper alignment.
Cam-piercing operations may still require some of the punches to cut on an angle (Fig. 4). Again, keep the maximum punching angle less than 15 deg., calculate the minor-axis diameter and be sure that the punch body and die matrices are keyed. MF
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