The method of pressing offers a lot more design freedom, compared to bending. This allows for more complex shapes, such as free-formed surfaces and a series of different strengthening geometries. Being aware of the possibilities regarding pressing and what design features are preferred is beneficial.
The following notes are a small snapshot of what can be considered as part of component design. The applicability of each suggestion depends on the component, and in some cases, the desired solution is not possible and has to be solved in another way. The impact of not following a design guideline is different for each guideline. It will, however, result in a less cost-effective component as it compromises the simplicity of manufacturing the component.
Basic Tenets for Designing of Pressed Components
- Avoid having sharp three-edged corners by placing large radii in corners. The radius where the three corners meet is the most crucial and should increase with increased depth. Having a too small radius will risk tearing of the material.
- Drawn three-edged corners can be hard to predict. Avoid having tight tolerances on such corners.
- Holes need to be processed from above. Since pressing machines operate up and down, holes need to be punched from above as no force will come from the side. An alternative is to process holes after.
- The minimum diameter of punched holes should be equal to one material thickness. Having holes smaller than the material thickness will reduce the life of the punch and cause premature failure of tooling Higher punching force will be required and there will be excessive burring.
- The distance between two holes should be equal to at least two times the material thicknesses. Punching holes too close to each other could result in deformation of the material between the holes. Keeping a fair amount of distance between holes also acts to ensure the integrity of the finished product.
- The distance between a hole and an edge should be equal to at least one material thicknesses but preferably one and a half times the material thickness. Punching a hole too close to an edge could result in deformation of the edge. Having a hole too close to an edge also decreases the strength of the product.
- When pressing using sheet metal from a coil, components need to have tabs or material that keeps in the ‘skeleton’ of material. in order to allow the strip to feed through the tool. Components are separated from the coil in the last stage/s of the process.
Other Features to Consider
- Instead of having large radii in corners, consider using chamfers. Chamfers will help increase the stiffness of the corner as well as reduce the risk of tearing the material.
- Consider tool design in order to achieve efficient manufacturing cycle times.
- Pressing one or several ribs or gussets into the bend during the process reduces the spring back and stiffens the bend. The ribs should be equally distributed over the bend, as the bend would otherwise spring back unevenly.