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Metal Stamping and Design Considerations, Part 1: Blanking and Shaving

stamping-1A

Blanking:
Material – CRS Rockwell 59 B Scale
Material Thickness = 0 .70 mm
Punch Diameter = 4.70 mm

Punch to die clearance
(% of material thickness per side)

5% 9%
Rollover length 0.34 0.25
Rollover depth 0.07 0.09
Burnish depth 0.53 0.38
Burnish diameter 4.76 4.76
Burr height 0.01 0.01

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, 0.25 mm 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 1.50 mm thick, make note that Unspecified sharp corner radii equal to 0.25 mm max.f

stamping-1B

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 0.10 mm x 0.05 mm 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. (mm) Smallest R (mm) EDM Time
0.25 0.15 8 hrs.
0.15 0.10 18 hrs.
0.10 0.08 24 hrs.

stamping-1C

By changing three radii from 0.08 to 0.25 – 0.38 mm, the cost of the tooling component would be reduced by 120 hours.

stamping-1D

Consider blanking an undercut when a sharp corner is required. Tooling is less expensive and the larger, full radius will last longer in production.

stamping-1E

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.

stamping-1F

For 1.52 mm of the hole depth, the held tolerance is +0/-0.02 mm. The remaining depth will be held to ±0.04 mm.