Metal Stamping: Elements Of Designing Parts

  • Precision Stamping Parts is an economical process, and usually a large number of precision parts can be produced from sheet metal or strip metal with high productivity by special tools. The parts and components produced by the precision stamping industry involve our daily lives from electronics to transportation. The essence of the metal stamping process is to pass a flat, sharp tool steel punch through the plate or strip into the matching cavity to pierce, trim and punch the material. This process can be used to produce perforations of various shapes and sizes, trimmed edges, and finished sheet metal parts.

    Anatomy of a hole
    The cutting gap between the punch and die is tightly defined and specified, and this process creates very predictable edge conditions on the finished part. Basically, punching starts by trying to compress the material, creating a rolled or rounded top edge. When a sharp punch begins to cut in, it will shear the material, resulting in a flat, smooth wall, usually 1/4 to 1/3 the thickness of the material. When the force accumulates beyond the strength of the material, the angle of yield and rupture is equal to the cutting clearance of the punch and die, causing burrs around the bottom edge.

    Burrs, such as plastic parting lines or flashes on castings, are normal by-products of metal stamping processes. The burrs are usually somewhat jagged and sharp. Their height varies as the punch and die edges become dull, but it is usually expected to reach 10% of the material thickness. When needed, depending on the application, burrs can be eliminated or removed by batch finishing or secondary operations.

    Hole size and tolerance
    Since the gap between punch and die is usually 8% to 10% of the material thickness on each side, the bottom of the hole or trim will gradually reduce the amount of die clearance. Therefore, internal dimensions are usually measured at the shear force or the smallest part, ignoring fracture. If this detachment cannot be tolerated in a particular application, the geometry should be specified and non-standard methods can be used. For most applications, normal piercing and blanking operations are extremely repeatable and very small tolerances can be achieved.

    By using dedicated, customized tools and press equipment of the right size, a large number of precision parts can be produced over the life of the product. In most cases, tool changes can be made easily and economically to accommodate changes as the product is revised and improved.