Chapter 7
- Designing for Stamping Production
Design Guidelines for Blanked
Features
Regarding blanking, specific recommendations should be
followed to obtain the most economical and functional part design.
-Corners may be designed sharp (less
than 0.015 in. (0.4 mm) radius), but often this involves additional cost to address
increased die wear and burr formation. Generally, radii for corners should be 1Ž2 of
the material thickness or greater, with a 0.015 in. (0.4 mm) minimum radius preferred
(Figure 12).
 Figure 13. Notches in blanks should not be narrower than
1.5 times the material thickness. Notches can be extended and narrowed slightly if they
are tapered about 0.004 in. (0.1 mm) or greater--on one end.
--Notches and tabs on blanks should generally not be
narrower than 1.5 times the material thickness. With a 0.060 in. (1.5 mm) stock thickness,
a 0.090 in. (2.3 mm) wide notch or tab is readily cut.
Typically, notch and tab lengths can be up to five times the width. In
marginal cases, the metalformer can use a heavier die, punch or stripper at a slight cost
increase. Alternately, notches and tabs can be extended and narrowed slightly if they are
tapered, i.e., if they are a little narrower--about 0.004 in. (0.1 mm) or greater--on one
end (see Figure 13).
Depending on the material, hardness and shear characteristics, notches
and tabs can be de-signed with widths as small as one material thick-ness and with lengths
up to six or seven times the width--usually at additional tooling cost.
Notches and tabs should not be too close to another feature or too long
and narrow because of die weakening. If close proximity to notches is necessary, secondary
operations may be required.
Figure 14. Four ways to avoid feather edge
burrs on radiused cut-offs (A to D). Example E is not recommended.
Cutoffs. Three basic types of cutoffs apply to
blanking: straight or square cut-off; half-round or partial radius; and full radius
(Figure 14), with square being the most economical.
The full radius option is not recommended because the tangential
blending of the radius into the outside material edge creates a condition where there is
no material to be cut. This is called "feather edge" and in this condition the
material will extrude along the die edge for an unavoidable, large burr. (See Figure 14
for design solutions).
Go to the Design Guidelines Overview
Go to the Glossary
Excerpt taken from Design Guidelines for Metal Stampings and Fabrications -- 2nd Edition copyright © 1995 Precision Metalforming Association
Purchase the new Third Edition of Design Guidelines for Metal Stampings and Fabrications copyright © 2004 Precision Metalforming Association at Marketplace today!
|
