Blanking:
Material - CRS Rockwell 59 B Scale
Material Thickness = .0275
Punch Diameter = .1875
Punch to die clearance
(% of mat’l thickness per side)
5% 9%
Rollover Length .0136 .0101
Rollover Depth .0030 .0035
Burnish Depth .0210 .0150
Burnish Diameter .1875 .1877
Burr Height .0005 .0006
As the punch to die clearance decreases, the burnished
depth will increase, and the burr will generally decrease, as
will punch life.
General Rule #1:
For material greater than, or equal to, .010 thick, a normal burr
height will be approximately 10% of material thickness.
General Rule #2:
Blanked corner radii should be greater than, or equal to, material
thickness. For sharp corner radii on material less than .060 thick,
make note that “Unspecified sharp corner radii equal to
.010 max.”
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A general guideline for a
minimum blank width A is 1.5 x material thickness T. It is possible
to stamp a blank width A equal to material thickness T, however
this will contribute to increased tool downtime. The smallest
blank width that can be stamped is .004 in .002 thick material.
The smallest recommended pierce diameter is 2 x T.
The size of an inside or outside corner
radius is directly related to tool cost. Corner radii on blanking
punches and dies are cut by wire EDM. The wire diameter determines
the smallest radii that can be produced. Reducing the wire diameter
increases the cutting time.
Wire Dia. |
Smallest R |
EDM Time |
.010 |
.006 |
8 Hrs. |
.006 |
.004 |
18 Hrs. |
.004 |
.003 |
24 Hrs. |
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Consider blanking an undercut when a sharp corner
is required. Tooling is less expensive and the larger, full radius
will last longer in production.
Shaving:
A blanked hole can be shaved to increase the burnished depth and
maintain a tighter tolerance throughout the hole. The shaving
station removes a minimal amount of material with a minimum amount
of punch to die clearance. A shaving station will increase die
downtime. Keeping the shavings out of the die is usually a problem.
Tooling components tend to gall or pick up blanked material. Tool
wear is increased.
For .060 of the hole depth, the held
tolerance is +0/-.001. The remaining depth will be held to ±.0015. |
