THEORETICAL ANALYSIS OF PUNCH SPEED AND BLANK HOLDER FORCE CONTROL IN DEEP DRAWING PROCESS OF STRAIN-RATE-SENSITIVE MATERIALS

Various factors affecting the variable blank holder force (BHF) and punch speed in the circular cup deep-drawing process with formingspeed-dependent characteristics were analyzed in order to determine the optimal control conditions of the process and the effects on the permissible range of forming conditions. The isotropic blank material was assumed to exhibit strain hardening and strain-rate-sensitive characteristics given by a=Kp e”. Effects of material properties and process variables on the fracture and wrinkle limit BHF curves were simulated using an elementary analytical method. The simulated results show that the acceptable drawing range of highly strain-rate-sensitive materials strongly depends on the punch speed. It is confirmed theoretically that there is an optimal process control path in the acceptable range of the punch speed-BHF-drawing progress space even beyond the critical constant punch speed. Based on these results a new concept of optimal process control with variable punch speed and BHF control is proposed in order to reduce the forming time, improve the quality of the products and reduce the number of defective parts produced.