Qingzhi Zhou’s research while affiliated with Donghua University and other places

High-speed grinding technology is being applied to the precision machining of 20CrMnTi steel gears, shafts and bearings suffering from fatigue damage. The response surface methodology (RSM) was used as an optimization method of high-speed grinding parameters to reach a higher anti-fatigue performance of 20CrMnTi steel workpieces. The mathematical formulas were established to clarify the effect of grinding parameters on surface integrity indexes including surface roughness, hardness and residual stress. The distribution of residual stress and the thickness of thermal influenced layer on the subsurface were measured, and the thermal field was analyzed by finite element simulation of grinding process. Results show that an appropriate increase in workpiece speed and a decrease in wheel speed and depth of cut can result in lower surface roughness and higher residual compressive stress to promote anti-fatigue performance. The thickness of the heat affected layer and grinding temperature is extremely sensitive to the depth of cut, which should be controlled below 15 μm to avoid embrittlement induced by re-quenching and subsurface heat damage. To improve anti-fatigue performance, the grinding parameters with wheel speed, workpiece speed and depth of cut of 90 m/s, 0.836 m/s and 12 μm with desirability function 0.931 are the ideal solution under the processing conditions in this study.

Subsurface residual stress and damaged layer play a vital role in determining the accuracy maintenance and fatigue performance of parts. Due to the advantages of machining quality and efficiency, high-speed grinding technology is being applied to the machining of precision parts. At present, the influence of high-speed grinding on the damaged layers generation and residual stress distribution has not been completely recognized, and there has been little quantitative research on the mechanism of thermo-mechanical coupling influence on the distribution of residual stress generated in the high-speed grinding process. In this study, a finite-element model comprehensively considering grinding force and thermal field was proposed to investigate the subsurface residual stress and heat influenced layer of AISI 52,100 bearing steel. The subsurface damaged layer and residual stress fields were measured to validate the analytical results. Mathematical models were proposed to quantitatively analyze the thermo-mechanical coupling influence on the distribution characteristics of subsurface residual stress. The theoretical and experimental results demonstrate that when the grinding speed surpasses the critical value of 45 m/s, the depth of residual stress and damaged layer decrease simultaneously with the increase of grinding speed. Higher grinding speeds exceeding 60 m/s are supposed to restrain the maximum value of both the tensile and compressive residual stress, which helps to enhance the precision retention and fatigue performance of components. Base on this study, the performance of the subsurface can be controlled by selecting the proper grinding speed in the high-speed range.

Rolling contact fatigue (RCF) is the critical damage from rolling bearings constraining the service, performance, and reliability, which is directly caused by fatigue crack propagation. The crack paths on both the contact surface and subsurface were observed after the bearing fatigue test. The three-dimensional geometry of the RCF crack was characterized and reconstructed based on experimental statistics. Finite element analysis was performed to obtain the mixed mode stress intensity factors (SIFs) along the crack fronts, and the crack propagation behavior was numerically studied. Results indicated that the propagation of cracks on the contact surface and subsurface causes the gradual formation of micropits and the sudden spalling of material respectively. Initial micro-cracks with an inclination angle of 15–30° have the highest growth rate, which should be prevented during the bearing raceway manufacturing process. The propagation paths of the RCF cracks can be more accurately predicted by considering the superposition of fracture mode I + II + III in three-dimensional, and mechanisms of crack propagation on contact surface and subsurface were revealed respectively.

Subsurface residual stress and damaged layer play a vital role in determining the accuracy maintenance and fatigue performance of parts. Due to the advantages of machining quality and efficiency, high-speed grinding technology is being applied to the machining of precision parts. At present, the influence of high-speed grinding on the damaged layers generation and residual stress distribution has not been completely recognized, and there has been little quantitative research on the mechanism of thermo-mechanical coupling influence on the distribution of residual stress generated in the high-speed grinding process. In this study, a finite-element model comprehensively considering grinding force and thermal field was proposed to investigate the subsurface residual stress and heat influenced layer of AISI 52100 bearing steel. The subsurface damaged layer and residual stress fields were measured to validate the analytical results. Mathematical models were proposed to quantitatively analyze the thermo-mechanical coupling influence on the distribution characteristics of subsurface residual stress. The theoretical and experimental results demonstrate that when the grinding speed surpasses the critical value of 45 m/s, the depth of residual stress and damaged layer decrease simultaneously with the increase of grinding speed. Higher grinding speeds exceeding 60 m/s are supposed to restrain the maximum value of both the tensile and compressive residual stress, which helps to enhance the precision retention and fatigue performance of components. Base on this study, the performance of the subsurface can be controlled by selecting the proper grinding speed in the high-speed range.