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Deep drawing

German standard DIN 8584 defines deep drawing as a tensile/compressive forming process used to create hollow parts from sheet metal, or as narrowing down a hollow part from a larger circumference hollow part without any deliberate change in wall thickness.

The tool used for deep drawing is a press, or punch. The cut-to-size sheet metal, known as a blank, is placed in the workpiece mount. A blankholder pushes the blank onto the draw die to prevent the material from wrinkling. Now the punch moves downward pulling the blank into the die to give the workpiece its desired shape. Where larger length-to-diameter ratios are to be achieved, several re-draws may be required to create the basic shape of the part.

Deep drawing is one of the most important sheet metal forming processes. It is used for both mass production and small lot sizes, e.g. in the automotive and aircraft industries. The hydromechanical drawing process has a number of benefits which reduce the cost of production and enhance manufacturing quality. Some of the key benefits are:

  • Low production cost by eliminating the need for a tool die
  • Lower number of drawing steps
  • Superior part surface quality
  • Significant improvement in formability when using high-strength steels, aluminium alloys, copper and stainless steels

Hydromechanical deep drawing is a variation of the traditional drawing process. In this method the rigid draw die is replaced by a pressure-regulated, liquid-filled cushion. In its downward motion the punch pushes the blank against the cushion membrane and pulls it along while plunging into the cushion, giving the part its exact geometry.

The active medium distributes the pressing forces exerted on the blank by the ram. This ensures the critical draw area is moved away from the base of the workpiece towards the drawing radius. This method can produce a higher length-to-diameter ratio than traditional drawing processes while the relatively small footprint of the device serves to cut production costs. The achievable pressing force, however, is lower than in traditional processes, thus limiting the spectrum of producible sheet metal parts.

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