Abstract:The thermal deep drawing process with vacuum environment was put forward to solve the problems in the forming of the high strength and difficult-to-deformation sheet metals such as difficult to form under normal temperature and easily to be oxidized at high temperatures. The vacuum hot drawing system was discussed and developed based on the integration of vacuum heating technology and variable blank holding force (BHF) system, which consisted of mainframe system, hydraulic system, vacuum system, heating system, water-cooling system, air-cooling system and computer control system, and the key parameters such as temperature, BHF and punch velocity were regulated in real time using PID closed-loop control technique. The deep drawing test of 2.0 mm-thick molybdenum sheets with temperature of 870 °C and vacuum degree of 10^-2 Pa was conducted on the system, and the molybdenum crucible with limiting drawing ratio of 1.94 was obtained, which indicated that the vacuum thermal drawing technology provided an effective solution for the formability improvement of difficult-to-deformation materials with strictly protecting against oxidation.

Key words: molybdenum sheet; thermal deep drawing; vacuum environment; variable blank holding force; system design; difficult-to-deformation materials; computer numerical control; drawing test