By Dave Bachelier
The following is a guideline intended to capture the basic 101 design criteria for a metal stamped component. Rules are intended to be a general guideline and deviations can be implied, while understanding the design intent of the part.
Design shapes or cutouts need to be at a minimum 1-1/2 x the material thickness. As a reference the smallest opening on a 1 mm thick part needs to be 1.5 mm.
- Corners should have a minimum radius of 0.5 x material thickness or 0.4 mm (0.016in) whichever is greater. Sharper corners can be produced but at a greater die maintenance costs and more burrs.
- Slots or tabs widths should be greater than 1.5 x stock thickness.
The length can be a maximum of 5 times slot/tab width.
These rules can be violated at an increased tooling cost– width as low as 1 x thickness and length as high as 7 x thickness can be achieved.
No draft is needed or designed in to a stamped part. You will have a edge
condition with Roll, Shear, Break and Burr. The edge of a stamped part will
have a rounded top edge with a vertical shear that can vary from almost none to 95% of the thickness. The part of the edge that isn’t vertical shear will be angled and not smooth and is known as break. The amount of the angled portion is the “punch to die clearance” used to cut the edge. Generally from 5% to 20% of material thickness depending on the type of material being cut, the hardness of the material being cut and the thickness of the material being cut.
There will be a bit of a burr at the bottom edge of the break.
Inside corner radii for a cutting punch depends on type of and hardness of the material being cut. Harder materials need larger radii.
A general guideline is if the material is stainless steel or relevant then the minimum inside corner radii = material thickness. Softer materials =1/2 material thickness. Thick or soft materials =1/4 material thickness.
Bend or Form Considerations
If your part design requires bends, there are minimum inside bend radii needed as well. Generally speaking most material manufacturers will provide a minimum bend radius for the given material required for your design. Note that there is a difference in the bend direction vs the material grain.
Technical Sales Manager
Brunk Industries Inc.