Study on Friction Behavior of Ultra-High Strength Steel CP780 in Cold Stamping and Forming

To address the low accuracy of numerical simulation in traditional friction models during the prediction of the forming process of ultra-high strength steel, the influence of sliding speed and normal load on the friction behavior of ultra-high strength steel CP780 was investigated using a stamping friction testing machine of self-developed ultra-high strength steel. A dynamic friction coefficient model related to sliding speed and normal load for ultra-high strength steel stamping and forming was established, and the proposed model was verified by integrating U-bending experiments with numerical simulations. Research findings indicate that the friction coefficient of CP780 sheet materials increases with increasing sliding speed and decreases with increasing load. Under conditions of low load and low speed, the wear mechanism of CP780 sheet materials is primarily dominated by ploughing effects; under conditions of high speed and high load, the wear mechanism involves both ploughing effects and partial adhesive effects. A comparison of rebound test values from U-bending experiments with numerical simulation results reveals that the error in the rebound angle α predicted by the dynamic friction model is 1.509%, and the error in the predicted rebound angle β is 0.348%. In contrast, the error in the rebound angle α predicted by the traditional constant friction coefficient model is as high as 12.483%, and the error in the predicted rebound angle β is as high as 4.994%. The dynamic friction model developed in this study demonstrates greater precision in predicting rebound angles and significantly enhances the accuracy of numerical simulations for formed parts.