The Process Robust Research Of Ultra-high Speed Centrifugal Grinding

As the key fitting of advanced manufacturing equipment, thin-walled bearing has some features, such as high rotary precision and positioning precision, good reliability, great resistance to impact and bad environment, etc. Nowadays, the finished surface residual stress control of thin-walled bearing is an important research direction in the field of bearing manufacturing. And ultra-high speed centrifugal grinding is a new method applied to the processing of thin-walled bearing ring. The essential of this technology is that, centrifugal effect and circumferential prestress caused by high workpiece speed can lead to greater residual compressive stress of workpiece obtained after grinding. In the grinding process, it is difficult to develop the surface residual compressive stress just by improving workpiece speed at random.Moreover, the influence on processing quality is unsatisfactory.In this study, something had been done to solve the problems of residual stress and temperature control during ultra-high speed centrifugal grinding. On one hand, a3 D mathematical model for ring in the action of inertia force and magnetic attraction force is derived by space stress solution based on the review of relevant literature,especially on ultra-high speed grinding. And the relationship between prestress,residual stress and rotating speed of ring is revealed. On the other hand, GCr15 bearing steel is used to make clip-on thermocouple temperature sensor. A grinding temperature experiment is performed on MKL7132X8/17 ultra-high speed CNC machine. Through the experiment, not only the mechanism of temperature is analyzed,but also the variation of surface roughness at different workpiece speeds. Besides, the phenomenon about Salomon curve's peak moves at different workpiece speeds is explained according to the theories of ultra-high speed grinding and adiabatic cutting.The main conclusions are as following.Firstly, according to the prestress formula, radial prestress, circumferential prestress and axial prestress are proportional to the square of palstance if two independent variables r, z and magnetic attraction force are given relatively. And the circumferential prestress of workpiece surface, contrary to axial prestress, is tensilestress, which at least 20 times as much as the axial. Moreover, because the proportional coefficient K of prestress and residual stress is 1 to 0.9-1.1, so residual stress is proportional to the square of palstance as well.Secondly, with the increase of wheel speed, grinding temperature increases then decreases. This variation tendency is consistent with Salomon curve. In addition, the curve peak gradually moves to lower right with the increase of workpiece speed.Thirdly, with the increase of workpiece speed, the surface residual compressive stress, dynamic stiffness and gyroscopic couple, specific material removal rate and specific grinding energy are developed in the process of grinding. Furthermore,grinding temperature might finally converge to a certain value, along with the increase of surface roughness.Based on the analysis of residual stress, the maximum rotate speed, 30000 rpm,of ultra-high speed centrifugal grinder is given. The grinding mode is up-grinding while the eccentricity of electromagnetic coreless fixture is located in the second quadrant. Moreover, the power of workpiece motorized spindle is calculated. The clamping mechanism, connecting rod, support, base and box of grinder fixture are designed according to motorized spindle's geometry and installation requirements.