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2 2024

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Numerical and experimental investigation of helical rolling process for producing steel balls with large diameter

Liu Wei, Wang Baoyu, Feng Pengni, Li Wei, Zhang Huibo, Zhou Jing

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 1

art. no. e5, 2024

Helical rolling (HR) with high temperature is an efficient forming process to produce bearing steel balls with diameter more than 25 mm. This article discusses the advantages and disadvantages of two HR roller designing methods: single side variable lead method and double side variable lead method. Finite element (FE) simulations of HR processes based on the two methods indicate that the double side variable lead method has higher forming accuracy and is more suitable for forming bearing steel balls. Experiments based on the double side variable lead method are carried out to verify the validity of FE model. The distributions of strain and stress, temperature evolution and rolling force parameters are analyzed based on the FE method. Axial motion analysis shows that the axial velocity of the rolled piece is closely related to axial push velocity of roller convex rib. Microstructure evolution indicates that grains near ball connector area and ball surface get refined due to drastic plastic deformation. The forming accuracy of HR process including radius deviations and ovalities of three cross sections are measured. The statistical results indicate that radius deviation of rolled balls can be controlled within 0.1 mm and ovality can be as small as within 1%. Effects of roller parameters on forming accuracy are analyzed including volume coefficient at groove closed position, forming zone length and starting height of convex rib. Forming accuracy gets better with the increase of volume coefficient, the increase of forming zone length, and the decrease of staring height of convex rib.

Influence of cryogenic-vibration compound field on the residual stress and forming accuracy during aluminum alloy forming

Li Cheng, Long Jinchuan, Wang Xinyun, Ning Bo, Li Desong, Feng Gang, Deng Lei, Tang Xuefeng

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 2

art. no. e136, 2024

Aluminum alloy parts are widely used in aerospace and other fields due to their light weight and good corrosion resistance. However, during the forming process, uneven deformation can lead to high residual stresses and low forming accuracy in the parts, ultimately seriously affecting the subsequent service performance. In this study, the influence of the cryogenic-vibration compound field on the residual stresses, microstructural evolution, and forming accuracy were investigated based on the deep drawing experiment of aluminum alloy cylindrical parts. The results indicate that when compared to the absence of cryogenic and vibration, the compound field can reduce residual stresses in the parts by 22%, which is attributed to lower dislocation density and more uniform distribution of low-angle grain boundaries. The cryogenic environment can weaken the degree of dislocation entanglement in low-angle grain boundaries, meanwhile, the dislocations are easily dissociated and released under the vibration. The maximum sidewall thickness difference, the sidewall height difference, and the surface roughness decrease by 68, 69, and 52%, respectively, which is due to the uniform distribution of microstructure and the reduction of frictional resistance caused by the boiling liquid nitrogen. This study provides a new method for the forming of high-quality aluminum alloy parts.