CONSIDERATION OF THE REDRAWING OF SHEET METALS BASED ON FINITE-ELEMENT SIMULATION

The effects of the work-hardening characteristics of blank material, the first-stage drawing ratio, the tool shape and interstage annealing on the limiting re-drawing ratio have been considered, based on the results of the rigid-plastic finite-element simulation of the direct and reverse re-drawing processes. In an attempt to increase the drawing limit, re-drawing experiments have also been carried out using a partially thickened blank, the thickness of which is somewhat greater at the punch-head portion than at the flange portion. The simulation results show that the success or failure of the re-drawing process depends not only on the re-drawing ratio but also on the material and process parameters described above. It is predicted also that the difference in the limiting re-drawing ratio achieved by the direct and reverse re-drawing processes results from the severity of bending and unbending at the profile radius portions of the die and the cup holder. The use of a partially-thickened blank contributes appreciably to an increase in the drawing limit. For steel sheet, for instance, the total drawing ratio achieved by the first and second drawing processes can be increased from 2.94 for a normal blank with uniform thickness to 3.45 for a partially-thickened blank.