INVESTIGATION INTO HYDROMECHANICAL REVERSE REDRAWING ASSISTED BY SEPARATE RADIAL PRESSURE - PROCESS-DEVELOPMENT AND THEORETICAL VERIFICATION

High-quality cups with a deep drawing ratio of more than four cannot b e simply drawn by conventional drawing and redrawing. A special techno logy is required to form cups of a high deep drawing ratio. In the pre sent study, after the conventional mechanical deep drawing process, su bsequent hydromechanical reverse redrawing with controlled radial pres sure has been developed. In order to increase the deep drawing ratio b y mon than four, the radial pressure is controlled independently of th e chamber pressure and thus an optimum forming condition can be determ ined by varying the radial pressure. The process has been verified by a rigid-plastic finite element (FE) analysis considering all the exter nal force boundary conditions induced by the hydrostatic pressure. The pressure distribution on the sheet is calculated numerically from the simplified Navier-Stokes equation. Through the experiment and the FE analysis, it has been shown that hydromechanical reverse redrawing ass isted by separate radial pressure, developed in the present study, hel ps to increase the drawability of cylindrical cups, and thus it is use ful when forming long cups.