Abstract
Under a boundary lubrication regime, the effect of sliding velocity and normal loads on the friction coefficient in the sheet metal stamping process was investigated using a pin-on-disk sliding wear test. Software was used to analyze both the data generated and the friction coefficient; in addition, a variable friction model based on different velocities and normal loads was also initiated. Under different experimental conditions and numerous influences, both the analysis and microtopography examination of sheet metal helped to obtain the mechanism influence on the friction coefficient. Through further analysis of the microtopography of sheet metal, the law of the surface roughness of sheet metal after grinding with stamping die was established. The model was established to simulate the thickness distribution and spring-back of U-bend parts using ABAQUS software. The results show that the friction coefficient values between the sheet metal and the stamping die generally decrease with increasing sliding velocity and normal loads, and the decreasing tendency slows down under a higher sliding velocity and normal load. Furrow wear and abrasive wear are the main wear mechanisms, with slight sticking wear under the boundary lubrication; the surface roughness after grinding with stamping die generally increases with increasing normal loads and decreasing sliding velocity. The predicted results of thickness distribution with a constant friction coefficient of 0.1 and with the variable friction coefficient model are more consistent with the actual measured values, but the predicted accuracy of spring-back in the variable friction coefficient model is higher than that of the constant friction coefficient model.
Highlights
Sheet metals are widely applied in the automotive, ship-building and aerospace industries, and have high potential for energy conservation, emission reduction, and safety improvement, and comes with many new problems
According to the principle of tribology, under the boundary lubrication condition, the friction coefficient is mainly composed of fluid friction coefficient, fL, and solid friction coefficient, fS [13]
To test the effectiveness of the variable friction model, based on different normal loads and sliding speeds, in predicting the numerical simulation of sheet metal forming, the model established in this paper was used to simulate body
Summary
Sheet metals are widely applied in the automotive, ship-building and aerospace industries, and have high potential for energy conservation, emission reduction, and safety improvement, and comes with many new problems. Due to their poor plasticity at room temperature, defects are created in the forming process, such as wrinkling, cracking, poor forming accuracy, and spring-back [1]. At present, regarding the optimal way of forming steel plates to solve these problems, the optimization method for the forming process cannot be effective because of the different properties of the sheet metal, which lead to a longer life cycle and a higher product cost. Studies have shown that material properties, processing techniques, and friction are the main factors which affect the formability and the quality of the parts. The effect of the processing techniques on the formability of the sheet is achieved mainly through changing the friction between the sheet metal and the stamping die. Friction mainly affects the formability of the sheet by changing the stress distribution in the Metals 2019, 9, 853; doi:10.3390/met9080853 www.mdpi.com/journal/metals
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