An improved model for predicting limiting drawing ratio

During the material selection and the tool design stage for a new component the knowledge of formability of the material under consideration is required. Limiting drawing ratio is one such measure. In the present work the model of Liu [D.K. Liu, The limiting drawing ratio for plastic instability of the cup-drawing process, J. Mater. Process. Technol. 86 (1999) 168–176] in which LDR is a function of material properties, coefficient of friction (taken into account in an approximate manner) and the die arc radius, is improved. The present model considers the bending and the unbending around the die arc radius. The friction effect is considered more realistically by taking into account the blank holding force (BHF). Since in the drawing operation the BHF should be just enough to prevent wrinkling, this is calculated using the expression of Siebel and Beisswanger [K. Lange, Handbook of Metal Forming, McGraw-Hill, 1985, p. 20.10]. The prediction from the present model is in good agreement with the experimental results and is an improvement over that predicted from the existing model of Liu [D.K. Liu, The limiting drawing ratio for plastic instability of the cup-drawing process, J. Mater. Process. Technol. 86 (1999) 168–176]. The effect of various material properties, blank holding force, friction coefficient and the die arc radius have been predicted in the comprehensive parametric studies.