The method used to determine the steps necessary to make a part is called processing the part. These processing steps are critical to the success of the entire stamping operation.
The first thing to determine when processing a part is the style and type of blank that will be used to make it. The blank is the starting piece of sheet metal that will eventually be formed and cut into the desired part shape or profile.
Three basic types of blanks are used in sheet metal stamping, and all three can be used with transfer, progressive, and stage tooling.
An undeveloped blank (see Figure 1) starts off as a basic shape such as a square, rectangle, or trapezoid that can be created using straight-line cuts. The advantage to using an undeveloped blank is that you won’t have to purchase a special blanking die to cut out a special shape; you can use a simple shearing die.
Keep in mind that using an undeveloped blank is not conducive to all metal forming operations, such as deep drawing. The extra material outside of the forming punch can sometimes create a resistance to flow, resulting in part failures such as splitting. Engineers typically choose undeveloped blanks if the material has a great deal of stretchability, and limited inward flow of metal will be required to make the desired part geometry.
A semideveloped blank (see Figure 2) is shaped to use just enough material, so that little material is left to trim away later. This type of blank is popular when the trim tolerance on the part is very small. A semideveloped blank will require slightly more material to produce a piece part than a fully developed blank.
A blank also can be undeveloped in certain areas and partially developed in other areas. This allows the process engineer to hold tight tolerances in areas of the part that require it and save material and the cost of additional cutting operations in areas that have greater tolerance.
Read more: Stamping Die Essentials: Processing the part