On my list of pet peeves are die shops and stampers that use only draw pad pressure-also known as blank holder pressure-to control metal flow. If the part wrinkles, they increase the draw pad pressure; if the part splits, they reduce the draw pad pressure. They find themselves changing the pressure from shift to shift and day to day While this method can offer limited success, problems with inconsistent parts may result. The key to any successful metal drawing or stretching operation is the ability to control metal flow consistently. Numerous factors determine how much stretch and flow take place during a metal forming process; the mechanical properties of the metal being formed, the geometry of the part being produced, and friction are just a few. However, in this article I will focus on controlling metal flow through the use of the forming die's draw pad.
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