Study on the friction model in stamping forming of carbide-free bainitic steel sheets

Abstract

With the increasing demand for automotive lightweight leading to greater use of high-strength steel materials, the friction behavior between the sheet and the tool during the forming process has become more complex, significantly affecting the surface quality of stamped parts and tools, the amount of springback, and the uniformity of plastic deformation. To accurately predict the complex friction behavior during the stamping process and effectively evaluate the forming quality and springback precision, this study developed a friction model based on physical friction principles, incorporating key influencing factors such as contact pressure, temperature, and sliding speed. The model utilized laser confocal microscopy measurement and analysis techniques to statistically characterize the height distribution of the contact regions between carbide-free bainitic steel sheets and SKD11 tool surfaces. By combining image processing methods, the indentation depth of tool surface asperities was calculated, and the evolution of microscopic material surface morphology under loading, sliding and bulk strain conditions was investigated to analyze its impact on the friction coefficient. Comparative analysis between experimentally measured friction coefficients and model predictions validated the accuracy and effectiveness of the proposed friction model. Finally, the model was applied in finite element simulation to simulate the U-shaped stretch-bending process under different blank holder forces and sliding speeds. The results demonstrated that, compared to the traditional Coulomb friction model, the proposed model exhibited better agreement with experimental data, providing more accurate predictions of friction behavior during the stamping process.