The studies on surface deflections in forming of autobody outer panels

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The studies on surface deflections in forming of autobody outer panels

Hayashi, Y. / Takagi, M.

By using an experimental die for fender panel, the investigation is carried out on what properties have the large infuence on surface deflections such as an undesired localized bend of sheet in the cavity after blank-holding and wrinkles caused by non uniform stretching. The localized bend at the instant of its occurrence is more marked in materials with low yield strength. This deflect, however, disappears soon when the punch for fender panel begins to form the sheet. The relation between the tendency of the loaclized bend and material properties is also examined by a simplified simulation test including theoretical analysis. The results of the examination confirm the tendency observed informing of fender panel described above. The wrinkling which is caused by non uniform stretching grows in an early stage of forming, in particular, largely in the case of materials with hgih yield strength. This wrinkle, then, reduces with the increase of punch travel. It is observed that the major principal stress along the longitudinal direction of the wrinkle produces the shrinking in its transverse direction and that this shrinking absorbs the wrinkle. Therefore, the high r value is considered to be favourable for diminishing the wrinkle effectively.