Press forming is an operation where a blank is pressed between a set of shaped dies to produce a finished or semi-finished part. Presses can be set to produce a single part from a single set of dies in one operation, or a complex part produced in a series of operations in a progression tool. Due to the capital costs of the equipment and tooling, presses are usually employed for mass production. Again, as in most other forming processes, the inherent high strength of stainless steel increases the power requirements - up to 60% more force may re required than for carbon steel.
Due to the above, the tooling used in press forming stainless steel wear out faster and are more susceptible to fracture as a result of long runs at high loads. High strength tool steel such as D2 are used as they offer good resistance to shock and wear. However, in cases where galling and pressure welding is prevalent aluminium bronzes are used, and in cases where high wear is present, carbide is used. In practice, it is quite common for a tool to be subjected to the above factors. In such cases compound tools are made in tool steel with carbide and/or aluminium bronze inserts in critical areas.
Care must be taken to allow for factors such as "springback" in design of tools. Also due to their ductility, stainless steel (particularly the austenitic stainless steel grades) tend to be susceptible to wrinkling when subjected to compressive force. If a particular type of pressing is susceptible to this phenomenon, then a blank holder or pressure pad may be incorporated into the tooling. Figure 6 illustrates the above. With regard to lubrication, chlorinated or sulphurised oils, pigmented pastes, waxes and soaps are used. In high speed operations, heavy duty emulsions are used due to their superior coolant effect. In some cases PVC and PE coatings are used, not only as lubrication, but also to protect the surface finish. All the Columbus Stainless steel supplied in the annealed condition can be press formed, although the performance of the ferritic grades can be enhanced by PVC or PE coating.
Cold Forming - Blanking and Piercing | Press Breaking and Roll Forming | Spinning and Flow Forming | Coining and Embossing | Press Forming | Deep Drawing
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