Metal Stamping Process: The Elements of Designing a Part
Precision metal stamping is an economical process capable of producing large quantities of precision parts out of sheet or strip metals at high production rates, usually from dedicated tooling. The precision stamping industry produces components and assemblies that are involved in our everyday lives, from electronics to transportation. Your cell phone has tiny stamped metal contact pins to send power and signals throughout your phone. The structural element of the car you drove to work this morning was built from precision metal stamped parts and assemblies.
The essence of the metal stamping process involves driving a flat-faced, sharp-edged tool steel punch through sheet or strip material into a mating die cavity to pierce, trim, and blank the material. This process can be used to yield perforations, trimmed edges, and finished sheet metal parts of all shapes and sizes.
When designing a metal stamped part—metal maintains the consistent wall thickness throughout. It’s a given that whatever feature is incorporated into a part is going to have the same wall thickness. What happens when we punch holes in it? What should you expect when creating trimmed edges?
The Anatomy of a Hole
Cutting clearances between the punch and die are closely defined and specified, and the process produces a very predictable edge condition on the finished part. Basically, the punch starts out by trying to compress the material, producing a rolled or radiused top edge. As the sharp punch begins to cut through, it shears the material, producing a straight, burnished wall, usually 1/4 to 1/3 of the material thickness. As forces build up beyond the strength of the material, it yields and breaks away at an angle equal to the punch and die cutting clearance, resulting in a burr around the bottom edge.
Burrs, like parting lines in plastics or flash on castings, are normal by-products of the metal stamping process. Blanking burrs are usually somewhat ragged, and sharp. They can vary in height as punch and die edges become dull, but generally, up to 10% of material thickness can be expected. When required, burrs can be dulled or removed by mass finishing processes or secondary operations, depending on the application.
Hole Dimensioning and Tolerancing
Since punch and die clearances are normally around 8 to 10% of material thickness per side, the bottom portion of the hole or trim will be tapered the amount of die clearance. Therefore, inside dimensions are normally measured at the shear, or smallest portion, disregarding the breakaway. If this breakaway cannot be tolerated in a particular application, geometry should be specified, and non-standard methods can be employed. For most applications, normal piercing and blanking operations are extremely repeatable and very close tolerances can be achieved.
With the use of dedicated, custom-built tooling and properly-sized press equipment, high volumes of precision components can be produced over the life of the product run. In most cases, tooling changes can be easily and affordably made to accommodate changes as product is revised and improved.
Larson Tool works with our customers from the earliest stages of design to optimize your part design for the metal stamping process and determine the best materials, tooling, and process solutions for your product. We’ll leverage our 90-plus years of experience as a valued supplier of metal stampings and assemblies to help you with all your metal stamping needs. Download our Stamping Design Guide to get started with your next successful part production.