Finite element analysis of damage in hot forging of bearing rings

Hot forging process plays a key role in the manufacturing of aerospace bearings. As the materials used in bearing production typically undergo substantial deformation during hot forging, this leads to the evolution of damage. For this reason, the evolution of damage can influence both the material and the process and, consequently, the properties of the end product. This study aims to explore the evolution of damage during multi-stage hot forging of M50 steel bearing rings. The exceptional properties of M50, an aerospace bearing steel, originate from its alloying elements and carbides; however, this composition imposes limits on the hot forging processes, allowing forging within a specific range only. Therefore, to design and implement the process, an accurate representation and incorporation of damage in finite element simulations is essential. To ensure precise representation and incorporation of damage in finite element simulations, capturing accurate M50 material behaviour becomes a critical prerequisite. In this study, Gleeble 3800 hot compression tests were performed to explore the material behaviour of M50 steel at four temperatures (1000 degrees C, 1050 degrees C, 1100 degrees C, and 1150 degrees C) and three strain rates (0.1 s-1, 1 s-1, 10 s-1). Afterwards, hot tensile tests were conducted through experiments and simulations using Forge NxT 3.2 (R) software, to determine the triggering value for the Latham-Cockroft normalized (LCn) damage criterion. By calculating the set value for the LCn damage criterion, a simulation of the multi-stage hot forging process for M50 steel was performed using Forge NxT 3.2 (R). Forging process consists of four stages: upsetting, closed-die forging, and two stages of shearing to separate the rings and remove the scrap in the inner ring. This study focused on the third, shearing stage where an accurate smooth cut surface is required. Experiments were conducted with different die clearances at different temperatures and various tool speeds. To explore the effect of die geometry on shearing, radii and conical shapes at various angles were added to the tool edges that come into contact with the die's corners to achieve a smoother cut surface during shearing.