Research On Sheet Metal Deep Drawing Using Servo Press

Clutch housing is an important plate part in automotive transmission system. Its accuracy and strength have direct influence on clutch performance and life. Typical features of this part include circumferential teeth, local wall thickness change, complex appearance and mostly cup-shaped. In addition to spinning process, cup drawing combined with bulge forming or compound drawing technology can be applied to realize forming of this part. In compound drawing process based on conventional mechanical press, material thickness near punch corner area went through serious reduction, which caused fracture during the subsequent sizing process. Aimed at solving the problem, this thesis took sheet metal deep drawing using servo press as the research point, influences of slide motions on forming quality and forming limit were studied. On this basis, servo technology was further applied in compound forming of clutch housing, thus servo press in complex sheet metal forming was researched. The main achievements obtained are as follows:1) The effect of speed variations on sheet tensile property was studied. The Material testing machine was set "position control", on basis of which different dwell time, dwell positions and dwell steps were analyzed during tensile test. Results showed that "step motion" loading in dwell period led to "stress relaxation" phenomenon. Stress releases most in the initial dwell stage and then tends to be stable. For tensile test with one temporary pause after yielding, stress relaxation extent has nothing to do with dwell position. For tensile process with multiple pauses, stress relaxation slightly increases with the increase of loading speed and successively decreases with the increase of pause steps. During the same dwell step, stress relaxation amount is unrelated with overall steps and its dwell position. In addition, different dwell positions lead to "necking lag" effect, namely, dwell steps set in earlier period can effectively improve uniformity of material deformation, which delays the formation of necking.2) Sheet metal drawing performance under three typical servo controlled slide motions: speed motion, oscillation motion and step motion was investigated. Influences of various motions on sheet metal forming were summarized. For speed motion, slower speed improves the sheet metal forming limit and reduces maximum forming load. For oscillation motion, oscillations set during earlier period of deformation is better for improving uniformity of the subsequent deformation, so as to improve the forming limit. For step motion, appropriate extension of dwell time and steps is beneficial to material plastic deformation. Besides, dwell position has the most impact on forming. Compared with two other motions, step motion has the best performance in sheet metal drawing improvement.3) In order to accurately obtain material flow rule during compound drawing process of an internal geared cup and find key areas and key period of wall thickness reduction, numerical analysis based on FEA software MSC.Marc was carried out. According to comprehensive results of simulation and experiment, the whole deformation process of internal geared cup can be divided into three stages: pure drawing, drawing-extrusion compound forming and pure extrusion. Through the investigation of wall thickness reduction at bottom corner, it was found that thickness reduction occurs mainly in the first and second stages. On this basis and combining with previous achievements, targeted oscillations or dwell steps were set during key stages of forming in order to carry out optimizations of servo controlled slide motions for compound processing of the part. Results showed that slide motion optimization set during earlier stage of tooth forming is more conducive to improving part drawing performance. Compared with other motions, step motion processed part not only gets good surface quality with no "oscillation trail", but also eases the thickness reduction.In conclusion, the researches presented in this thesis can provide some theoretical and experimental basis for precision forming of clutch housing parts using servo press, which is also meaningful for compound forming production of such parts.