IN-PROCESS CONTROL OF BLANK HOLDER FORCE IN AXISYMMETRICAL DEEP-DRAWING WITH DEGRESSIVE GAS SPRINGS

A new blank-holder system with degressive gas springs has been develop ed and evaluated for axi-symmetric deep drawing. In contrast to most p ublished works in this field, in which hydraulic systems are utilized, the new system is integrated with the tool body instead of with the p ress, the advantage with this approach being that the system is indepe ndent of press facilities. The new system consists of inter-connected active and passive gas springs, moving parallel during forming. With t he new system, degressive, constant and progressive blank-holder force (BHF) trajectories can be obtained. The BHF-trajectories were pre-det ermined with a specially developed software. Two materials, an ordinar y deep drawing steel and a high-strength rephosphorized steel, have be en analysed. The thickness was 0.7 mm and a water emulsion was used as lubricant. The blank holder force, punch force, total force and the s eparation of the blank holder (wrinkle detection) were recorded contin uously during the pressing operation. With a degressive BHF-trajectory the process window between fracture and wrinkling in axi-symmetric de ep drawing is larger compared to those obtained with constant and prog ressive trajectories, and also, the LDR is higher. (C) 1998 Elsevier S cience S.A.