Influence of process chain on fold formation during flange upsetting of tubular cold forged parts

摘要

The present paper analyses a multi-stage cold forging process focussing the final upsetting stage regarding to annular fold formation during upsetting. Recent numerical and experimental investigations showed that annular folding is not only affected by geometrical instability of tubular parts or buckling respectively but also by high local strain hardening effects interacting with forging temperature, specific material flow and surface quality of inner lateral surface of the tubular part. Depending on mentioned influencing factors three different mechanisms or kind of folds respectively have been determined and analyzed. It has been shown, that annular folding occurs at related free upsetting heights (h_s/?D_o) hitherto known as uncritical if strain hardening of semi-finished tubular part is considered. A newly developed semi-empirical fold criterion for prediction of fold of 2~(nd)-order has been implemented into commercial code DEFORM~(TM) and assessed using experimental data.