ON THE DEVELOPMENT OF NEW CHARACTERISTIC VALUES FOR THE EVALUATION OFSHEET-METAL FORMABILITY

Until now the r- and n-value have been used for the characterisation o f the deep-drawing and stretch-forming ability of sheet metals. In thi s context high r- and n-values indicated good deformation characterist ics. New developments within the steel industry lead to new isotropic steel qualities with increased strength and very good deformation abil ity. Here, the r-value approximately is about or equal to one, which, with regard to a good deep-drawability, contradicts the assessment mad e up to now. The parameters already known for the description of the m aterial behaviour don't consider the states of stress leading to failu re? or they can only be applied to a spectrum of parts which has a geo metry similar to that of the samples used in the test. This paper pres ents new ways of developing more precise characteristic values for the evaluation of deep-drawing and stretch-forming abilities of sheet met als, especially for the new isotropic steel qualities. For this, new t esting methods considering the states of stress occurring in the indiv idual zones of the drawing part were developed at the Institute for Me tal Forming and Metal Forming Machine Tools (IFUM). These new testing methods are the cross tensile test used for the simulation of the 'pla in-strain' state of deformation as well as the flange insertion test u sed for the combined tensile and compressive stale of stress. (C) 1997 Elsevier Science S.A.