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With the modified die design, the actual stamping die for production was manufactured and the production part was found to be free from wrinkles, as shown in Fig. 14. The part shape also agreed well with that obtained from the finite- element simulation. In order to further validate the finite-element simulation results, the thickness distribution along the cross-section G–H obtained from the simulation result as indicated in Fig. 14, was compared with those measured from the production part. The comparison is shown in Fig. 15. It can be seen in Fig. 15 that the predicted thickness distribution by finite-element simulation agrees well with that measured directly in the production part. This agreement confirms the effectiveness of the finite-element analysis. 5. Summary and Concluding Remarks Two types of wrinkling occurring in stamping processes were investigated using finite-element analysis, and the causes for wrinkling were examined and the methods to eliminate such wrinkles were developed. The first type of wrinkling appears at the draw wall in the stamping of a tapered square cup. The occurrence of wrinkling is attributed to the large die gap, which is the difference between the side length of the die cavity opening and the side length of the punch head. The large die gap results in a large unsupported area of sheet metal when the metal is drawn into the die cavity and an unfavourable stretch between the punch head and die cavity shoulder. The large unsupported area of sheet metal is therefore prone to wrinkling. The finite-element simulations show that this type of wrinkling cannot be sup- pressed by increasing the blank-holder force. Another type of wrinkling investigated occurs in an actual stamping part that has a stepped rectangular geometry. It is found that wrinkling occurs at the draw wall above the step even though the die gap is not sufficiently large. The wrinkling is due to the uneven stretch between the punch head and the step edge, according to the finite-element analysis. Several attempts were made in the die design to eliminate the wrinkling, using finite-element simulations, and an optimum design in which the step was cut off is finally established. The modified die design for eliminating wrinkles was validated by the pro- duction of a defect-free production part. The good agreement between the simulation results and those observed in the drawn production part demonstrates the accuracy of the finite-element analysis, and the effectiveness of using finite-element simula- tions as a substitute for the expensive method of actual die try-outs is thereby confirmed. Acknowledgements The authors wish to thank the National Science Council of the Republic of China for the grant NSC-86–2212-E002–028 that made this project possible. They also wish to thank KYM for providing the production part. References 1. K. Yoshida, H. Hayashi, K. Miyauchi, Y. Yamato, K. Abe, M. Usuda, R. Ishida and Y. Oike, “The effects of mechanical proper- ties of sheet metals on the growth and removing of buckles due to non-uniform stretching”, Scientific Papers, Institute of Physics and Chemistry Research, 68, pp. 85–93, 1974. 2. T. X. Yu, W. Johnson and W. J. Stronge, “Stamping and spring- back of circular plates deformed in hemispherical dies”, Inter- national Journal of Mechanical Sciences, 26, pp. 131–148, 1984. 3. W. J. Stronge, M. P. F. Sutcliffe and T. X. Yu, “Wrinkling of elasto-plastic circular plates during stamping”, Experimental Mechanics, pp. 345–353, 1986. 4. R. Narayanasamy and R. Sowerby, “Wrinkling of sheet metals when drawing through a conical die”, Journal of Material Pro- cessing Technology, 41, pp. 275–290, 1994. 5. W. F. Hosford and R. M. Caddell, Metal Forming: Mechanics and Metallurgy, 2nd edn, 1993.
冲压模具设计中的拉深起皱分析 在锥形方杯和阶梯形的矩形杯的冲压中发生起皱。这2种起皱的共同特征是：在拉伸壁上发现的皱纹是相对不受支持的。在一个锥形方杯的冲压中，工艺参数的影响，如模间隙和压边力，对起皱的发生是利用有限元模拟。仿真结果表明，模具间隙越大，越严重的起皱，和这样的起皱不能被抑制通过增加的压边力。在一个阶梯形的矩形杯的冲压成形过程中，在分析起皱时，检查了一个具有类似几何形状的实际生产零件。在画壁上发现的皱纹是由于在冲压头和台阶边缘之间的金属片的不平衡拉伸。利用有限元分析方法确定了消除皱纹的最佳模设计。模拟结果和无皱生产部分中所观察到的良好的协议验证的有限元分析的准确性，并演示了使用有限元分析的优点，冲压模具设计。论文网 1. 介绍