Abstract
Cold helical rolling (CHR) is one of the most effective ways to produce small-diameter steel balls. In this study, one kind of work hardening model was established and implemented into Simufact 15.0 to investigate the work hardening phenomenon in the cold forming process. Firstly, based on the helical rolling theory, a set of finite element (FE) simulations was developed. The influence of CHR parameters, including the starting height of convex rib, forming area length, and rolling inclination angle, on the forming process was studied via simulation. Furtherly, the CHR process experiment and FE simulation were carried out; the results showed that the FE simulation was in good agreement with the experimental results and consistent with the predicted value of the theoretical calculation. Finally, the evolution of effective strain, effective stress, rolling force, work hardening, and microstructure during the cold helical rolling of Φ 5.2-mm steel balls was investigated via FE. As a result, the evolution trend of hardness was consistent with that of dislocation density, indicating that the model is credible. Besides, the microstructure of the steel ball at different positions further verified this point.
Highlights
Bearings are widely used in various fields of modern industrial technology and are a kind of key basic parts of the assembly manufacturing industry
The results showed that surface work hardening can improve the wear resistance of steel, but the increasing work hardening rate cannot promote the improvement of wear resistance
Cold helical rolling (CHR) rollers and guide plates are set as rigid bodies due to their low elastic and plastic deformation compared with the workpiece
Summary
Bearings are widely used in various fields of modern industrial technology and are a kind of key basic parts of the assembly manufacturing industry. Huo et al.[8] studied the forming process of bearing steel balls with a diameter of 30mm during warm skew rolling They developed a multiaxial constitutive model to predict the microstructure evolution, and experimental and simulation results verified the availability of constitutive model. With the help of FEM, a large number of scholars have carried out in-depth and meaningful work on roller design[12] and HR process optimization [13, 14], which has effectively improved the quality of rolled products. In the cold forming of steel balls, work hardening is an important parameter that reflects the quality of parts. Combined with the FE model and experiments, the forming mechanism and evolution of effective stress, strain and dislocation density were explored in the process of CHR
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