Deep Drawability of Polymer and Composite Sheets using a Flexible Punches with Hydraulic Counter Pressure

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Influence of hydrauric pressure on the cylindrical cup drawability of polypropylene (PP) and glass fiber reinforced polypropylene (GFPP) sheets is investigated using a flexible punch. Experimentally measured punch forces, the thickness of side wall and the height in the drawn caps are presented and compared with conventional drawing using a stiff punch. Using a flexible punch, the force needed to drawn a cup found to be lower than that needed when drawing with the stiff punch. Though it was seen to advantage, in this conventional drawing process with a die and a punch for the polymer and the composite sheets, an enlargement in thinning of the cup wall occurred. This phenomenon in thinning of the wall produces an outflow of liquid from the flange which causes the counter pressure to leak.Consequently free forming of a sheet polymer using a die ring and a urethane pad, and drawing deep cups with Maslennikov's technique using a thin urethane ring and a metal punch were carried out for polypropylene sheet. Drawing method of this technique can perfom the good function of the reduction in thinning of the cup wall for the deep drawing processing of polymers. There are several advantages to be gained with the use of flexible tools over the use of conventional tools for polymer forming.