Study On Grinding Residual Stresses In Rolling Bearing Inner Ring Raceway

Rolling bearings are the key base parts and components, and widely used in equipment manufacturing industry. Rolling bearings will directly determine the performance and reliability of major equipment products. Compared with the developed countries, there still exists a wide gap in the field of high performance rolling bearing manufacturing. Short service life is one of the main problem of domestic machine tool spindle bearings. Fatigue failure of bearing raceway is one of the main failure modes of domestic machine tool spindle bearings. Residual stress distribution in the surface layer of bearing raceway will produce a great impact on bearing fatigue life. Grinding will influce the residual stress distribution in the surface layer of bearing raceway ditrectly, which is the key manufacturing process of bearing rings. There will produce force and heat in the grinding process of bearing raceway. The coupling of force and heat will determine the residual stress distribution in the surface layer of bearing raceway. B7008C bearing inner ring raceway grinding was taken as the research object in this paper. Based on the quantitative description of wheel surface, the generation mechanism of grinding force, generation and transfer mechanism of grinding heat, and generation mechanism of grinding residual stress in the surface layer of bearing raceway were deeply investigated. The main research works in this paper are summarized as follows.(1) Grain shape, grain dimension, grain protrusion height, and average number of grains per unit area were used to describe grinding wheel surface. The contact mechanism between a single grain and workpiece was investigated to obtain the determinant conditions of grain contact types. The contact types between a single grain and workpiece were analyzed and judged. The formulas of sliding grain number, plowing grain number, and cutting grain number were deducted using probability statistics method. The numbers of each type of contact grains were calculated. The influences of grinding parameters on the numbers of each type of contacting grains were investigated. The results showed that most contacting grains were plowing grains, then were cutting grains, and the least were sliding grains. The number and probability of each type of contacting grains will increase with decreasing wheel speed, increasing workpiece speed and grinding depth.(2) Grinding contact zone was divided into three areas, based on grain trajectory analysis. The grinding force model per grain was established based on grain contact analysis. A grinding force model was established based on the analyses of grain trajectory and grain workpiece contact. Nine sets of bearing inner ring raceway grinding experiment were pursued to validate the grinding force model. The results showed that the grinding force model can predict grinding force accurately. The maximum and minimum errors of grinding forces is 10.5% and 1.4%, respectively. The influences of grinding parameters on grinding forces were analyzed. The results showed that grinding forces and force components will increase with increasing workpiece speed and grinding depth, and will increase with decreasing wheel speed. The most contribution to grinding force among the force components is plowing force component, then is cutting force component, the least is sliding force component. The contributions of sliding and plowing decrease with increasing workpiece speed and grinding depth, and increase with increasing wheel speed. The contribution of cutting is reversed. Heat partition of an arbitrary point in grinding zone was analyzed. Without assuming the profile of total heat source and assuming uniform heat partition ratio in grinding zone, the heat source distribution model can obtain the heat source profile in grinding zone. And the quartic polynomial curve grinding heat source was obtained. B7008C bearing inner ring raceway grinding temperature field was simulated using finite element method. Experiments were pursued to validate the finite element model. The results showed that the finite element model can predict grinding temperature field accurately. The maximum and minimum errors of maximum grinding zone temperature rise are 14.8% and 3.5%, respectively.(3) The grinding residual stress field finite element model of bearing inner ring raceway was established. The generation mechanism of grinding residual stress in bearing inner ring raceway was investigated. The results showed that grinding force will induce compressive residual stresses in the surface layer of bearing inner ring raceway. The increases of contact stress and force ratio are in favor of the generation of compressive residual stresses. Grinding heat will induce tensile residual stresses in the surface layer of bearing inner ring raceway. Reduction of heat flux, increase of the velocity of heat source, increase of convection heat transfer coefficient, and reduction of the initial temperature of grinding fluid are beneficial to avoid tensile residual stresses. When grinding force plays the leading role, the coupling of grinding force and grinding heat will induce compressive residual stresses in the surface layer of bearing inner ring raceway. Compared with the compressive residual stress distribution induced by grinding force, the coupling of grinding force and grinding heat will induce less surface compressive residual stresses, less compressive residual stresses in the surface layer of bearing inner ring raceway, and less depth of the compressive residual stress distribution. When grinding heat plays the leading role, the coupling of grinding force and grinding heat will induce tensile residual stresses in the surface layer of bearing inner ring raceway. Compared with the tensile residual stress distribution induced by grinding heat, the coupling of grinding force and grinding heat will induced larger surface circumferential tensile residual stresses, larger circumferential tensile residual stresses in the surface layer of bearing inner ring raceway, larger depth of the circumferential tensile residual stress distribution, larger surface tangential tensile residual stresses, and larger tangential tensile residual stresses in the near surface layer of bearing inner ring raceway. The influences of grinding process parameters on the residual stress distribution in the surface layer of bearing inner ring raceway were investigated. The results showed that the increases of wheel speed and grinding depth are unfavorable for the generation of compressive residual stresses in the surface layer of bearing inner ring raceway. Workpiece rotational speed has less influence on the residual stress distribution compared with wheel speed and grinding depth. The influences of cooling and lubricating conditions on the residual stress distribution in the surface layer of bearing inner ring raceway were investigated. The results showed that the increase of convection heat transfer coefficient, and reduction of the initial temperature of grinding fluid are beneficial to the generation of compressive residual stresses in the surface layer of bearing inner ring raceway. The initial temperature of grinding fluid has less influence on the residual stress distribution compared with convection heat transfer coefficient. The reduction of force ratio will larger compressive residual stresses and larger depth of the compressive residual stress distribution in the surface layer of bearing inner ring raceway.(4) Experimental research on the influence of low temperature aerosol on the residual stress distribution in the surface layer of bearing inner ring raceway was conducted. A low-temperature-aerosol supply system was put up. The low temperature aerosol grinding experiment platform for bearing inner ring raceway was put up. A series of grinding experiment were carried out on the platform. Grinding force, grinding temperature and residual stress distribution in the surface layer of bearing inner ring raceway were measured. The results showed that there is a critical fluid flowrate, beyond which tangential grinding force will keep unchanged. Tangential grinding force will increase with decreasing flowrate of cold air. Compared with the grinding forces under flood grinding conditions, smaller grinding forces will be produced using the low temperature aerosol formed by Accu-lube LB-2000. The cooling performance and lubricating performance of low temperature aerosol were evaluated. The results showed that the low temperature aerosol formed by Accu-lube LB-2000 has better lubricating performance, compared with PC-621F water-soluble under flood grinding conditions. The influences of cooling and lubricating conditions on the residual stress distribution in the surface layer of bearing inner ring raceway were investigated experimentally. The results showed that low temperature aerosol can be beneficial to the generation of compressive residual stresses in the surface layer of bearing inner ring raceway.