Metal Stamping Material Considerations
The choice of metal stamping materials used depends on the desired attributes of the finished piece. Stamping is not limited as a fabrication process to just metals – there are numerous materials that can be processed through stamping techniques, such as paper, leather, or rubber, but metals are by far the most commonly used.
In general, metals tend to maintain their malleability and ductility after stamping. Those used in precision stamping usually range from soft to medium hardness and carry a low coefficient of flow. Some of the customary metals and metal types fabricated through stamping include:
● Precious metals, such as silver, gold, and platinum
● Ferrous metals, especially iron-based alloys like stainless steel
● Non-ferrous metals, such as bronze, brass, and zinc
● Non-standard alloys, such as beryllium nickel and beryllium copper
Ferrous metals are commonly used in stamping operations, as their low carbon content means they are among the least expensive options available resulting in low unit production costs.
Several important factors and design considerations need to be addressed when performing metal stamping operations. Metal Stamping Material Considerations
Post-stamping production operations can include having the stamped product go through deburring, tapping, reaming, and counterboring processes. These allow for the addition of other parts to be added to a stamped piece or for the correction of imperfections in finish or removal of sharp edges that may impact safety.
Deburring involves the removal of shards of cut material that remain on the workpiece after the stamping operation has been completed. Sharp edges may require grinding to remove burrs or may need to be flanged over to produce a smoothed edge and to direct the burred edge to the inside fold where it will not cause injuries or be noticed cosmetically.
Overly narrow projections should generally be avoided in stamped products, as these may be more easily distorted and impact the perception of quality in the finished product.
Avoidance of sharp internal and external corners in stamped product designs can help reduce the potential for the development of larger burrs in these areas and sharp edges that require secondary treatment to remove. Also, a great potential for stress concentrations exists in sharp corners, which may cause cracking or subsequent failure of the part through extended use. Metal Stamping Material Considerations
Overall dimensions for the finished product are going to be limited by the available dimensions of the sheet metal sheets or blanks, and these limits need to be factored for the material consumed in folds on edges or flanges and any additional material removal or use. Very large products may need to be created in multiple steps and mechanically joined together as a second step in the production process.
For punching operations, consider both the direction of punching as well as the size of the punched feature. Generally, it is best to do punching in one direction, so that any sharp edges produced by the punch will all be on the same side of the workpiece. These edges can then be hidden for appearance purposes and kept away from general access by workers or product end-users where they might represent a hazard. Punched features should reflect the thickness of the raw material. A general rule is that punched features should be at least twice the material thickness in size.
For bends, the minimum bend radius in sheet metal is roughly the same as the material thickness. Smaller bends are more difficult to achieve and may result in points of stress concentration in the finished part that may subsequently cause issues with product quality.
When drilling or punching holes, performing these operations in the same step will help to assure their positioning, tolerance, and repeatability. As general guidelines, hole diameters should be no smaller than the material thickness, and the minimum spacing of holes should be at least twice the material thickness apart from each other.
Bending operations should be performed with awareness of the risk or distorting the material, as the material on the interior and exterior surfaces of the bend point are compressed and stretched respectively. The minimum bend radius should be approximately equal to the thickness of the workpiece, again to avoid stress concentration build up. Flange lengths should be more like three times the workpiece thickness as a good practice.