Ask the Stamping Expert: Five essential stamping rules for component designers
Over the years I have received many requests from readers asking for suggestions and advice for particularly challenging stamping applications. Some of the issues can be addressed through creative tool design; some can’t. Some stampings by design make it virtually impossible to satisfy all the dimensional criteria.
This poor design for manufacturability can result in very high maintenance and scrap costs. Constant adjustments and service are needed in production, resulting in a very inefficient program. I can’t tell you how many times I have heard the stamping engineering and tooling staff say, “If only the person who designed this stamping was a toolmaker.”
The bottom line is that stamping designs are most robust and cost-effective when the product designer gets input from the people who will manufacture the part. When the manufacturing team and component design team work together, the result is the best design for manufacturing—and sometimes a component stamping cost savings of as much as 50 percent.
Why manufacturing and component design teams don’t collaborate on each job is inexplicable.
Following are some rules for component designers—strictly for stamping, of course.
1. Writing “No die roll allowed” on the component print doesn’t work. There will be die roll; it’s part of the process. The best you can expect on a 0.030-inch-thick stamping is 0.0030-in. rollover depth. The punch-to-die clearance will have to be decreased from optimal, so maintenance costs go up.
2. If you note “No edge break allowed” on a component print, you might be dictating a fineblanking process instead of standard, conventional stamping, and fineblanking is much more expensive. The stamping tool designers can minimize the break, but they probably will have to add shave stations to the tool, and this will at least double maintenance costs. Having to reduce the punch-to-die clearance and the resulting increased rate of tooling wear also will increase maintenance costs.
3. For material thicker than 0.010 in., the burr height usually will be 10 percent of material thickness. By writing “No burr allowed” on the component print, you are requiring a secondary deburring operation, and that’s a big cost driver. Specifying “0.001-in. burr max.” on a 0.040-in.-thick part isn’t any better. This will drive up maintenance cost by as much as four times.
4. Most component prints have callouts for forming radii, unless it is a flat blank. Bending metal involves physical laws. For instance, a 90-degree bend with a 0.020-in. inside radius on 0.010-in.-thick full hard stainless steel is doable. The same radius on 0.1-in.-thick full hard stainless is not doable. Specifying a dead sharp radius rules out stamping altogether.And please don’t add callouts on the outside radius to the component print. Stamping cannot control the outside radius. Material will stretch as it is formed. The part maker can control only the inside radius with the forming die, so when dimensioning feature locations, you must dimension from the inside radius.
5. Always make sure the corner radii on blanking are greater than or equal to material thickness. Writing “Sharp corner required” on a print will drive costs up—if the stamper can accomplish the feat in the first place. Part geometry rarely allows the formation of a sharp corner. Even if it does, stations will likely have to be added in the stamping die. A print with corner radii specified at 0.010 in. on 0.040-in.-thick material is a stamper’s maintenance nightmare. The same principle applies to holes. The minimum diameter should be material thickness or greater. A 0.020-in. hole in 0.040-in.-thick material is another stamping nightmare. These specifications can increase service requirements by four to five times.
All component designers can gain a huge market advantage by working with their stamping suppliers in the design review of their components. A thoughtful design for manufacturability, thoroughly reviewed by the component design and manufacturing teams together, will result in achieving the best-quality stamped part at the best price. And that is in everyone’s best interest!
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.