Predictive evaluation of draw-in, elongation and breakage during forming processes

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Predictive evaluation of draw-in, elongation and breakage during forming processes

Shiokawa, M. / Takizwawa, H. / Ujihara, S. / Usuda, M. / Ohwue, T.

Various aspects in the computer simulation of sheet metal forming in plane-strain deformation were investigated. It was shown that a value converting the material characteristics measured in the uniaxial tension test to that of plane-strain deformation should be used in the simulation. To obtain such values, the drawbead restraining force was computed to high accuracy by applying the coil friction formula. To predict the occurrence of fracture, three types of fracture are identified and the success or failure of forming is assessed for each type. These three types are stretch-bending fracture, fracture after passing the drawbead, and fracture of the wall due to lack of ductility. In particular, in strech-bending fracture, the tensile strength (TS)p in plane-strain deformation was found useful in clarifying the effect of the punch radius on the fracture stress. Forming simulations were performed for a model panel and a Rear Quarter panel. Although some improvements in the method are needed, results to date indicate that it is possible to estimate the amount of tension, elongation and movement of material in each part in the process of panel forming, and to predict the occurrence of fracture.