The most common issue our clients face is a design that looks great on paper, but runs into problems during manufacturing. Metal stamping is a breeding ground for inconsistencies between design ideas and manufacturing realities.
Metal stamping requires an understanding of how cutting, punching, and bending will warp the final product. Manufacturing engineers are often required to optimize a metal stamping design so it will meet consistency and quality standards.
When designing for metal stamping services, it's best to involve a manufacturing engineer during the design process. Post-design changes can be costly, difficult, and a huge time sink.
However, if you're hesitant to involve outside engineers in the project, you should still be aware of some of the major metal stamping design issues. Here are some of the basic guidelines manufacturing engineers use to keep metal stamping designs within quality standards.
Blanking is the first process of metal stamping. It's the most basic process: cutting a sheet of metal into the shapes that will produce the final product. The basic shapes are cut into the metal, but not fully separated. This makes it easy to perform additional metal stamping services in sequence.
When designing for blanking, any notches, slots, or tabs need to have a width greater than 1.5 times the thickness of the material, and a length no more than 5 times the slot or tab width. This ensures the notches and tabs will be able to withstand piercing, bending, and other stamping processes later on.
Notches and tabs that are too thin or long are difficult to create with standard stamping dies, and are easily damaged. However, this standard rule can be broken if you are willing to pay additional tooling costs.
Cut-offs separate the piece that was cut during the blanking phase from the rest of the sheet metal web. Each piece becomes an individual component.
When considering cut-offs, you should not design for a full radius cut-off. Square cut-offs are most economical, though you can also design for an angle-blended radius if necessary.
Full radius cut-offs create a feather-edge burr on the edge of the metal, which will require an additional process (deburring) to remove. Left alone, they can negatively impact later stamping processes.
When designing holes for piercing, the minimum diameter of the holes should be at least 20% (1.2 times) larger than the thickness of the material. For stainless steel and other materials with high tensile strength, the hole diameter should be twice the thickness of the material.
Forming, or bending, requires more delicacy than most other stamping processes. Done wrong, bending can deform and weaken the metal, especially if there are tabs, slots, and holes near the bending location.
To avoid distortion of pierced holes, the holes should be placed AT LEAST 2.5 times material thickness from the bend (this includes the bend radius). Otherwise, the holes can stretch out of the range of tolerances.
Drawing refers to the process of creating a basin/plateau shape out of the metal. Depending on the material, the tolerated draw depth can be very shallow or very deep. Drawing is similar to forming in that it is guaranteed to deform the product if done wrong.
When designing for draw, the punch and die radius should be a MINIMUM of 4x the material thickness. The larger the radius, the smoother the draw will be. For square draws, the radius should be at least 6x the material thickness. Other draw shapes are possible at additional tooling costs.
An experienced manufacturing engineer will be familiar with these rules and more (and there are PLENTY more to be aware of for metal stamping design). Design issues can be mitigated by remembering these tips or, if you're so inclined, spending additional money on special tooling to fit your project requirements.
If you're interested in metal stamping services & design assistance, we're happy to discuss your project!