| High-precision balls are the key components in high performance bearing and high precision ball screw,their accuracy and quality have a great impact on the products’ accuracy and even the accuracy of machining equipment.The existing methods and equipment for high precision balls generally have a series of problems such as low machining accuracy and poor consistency.As a new method for precision balls,the variable-radius groove method automatically changes the rotation angle of the ball during the lapping process,realizing the high efficiency and high consistency processing of precision balls.Based on the sphere-shaping mechanism,ball’s kinematics,balling process,material removal are studied in this paper under the processing method of the single turntable with variable-radius groove.The main work of this paper includes the following aspects:(1)Aiming at the problem of the consistency of the processing trajectory on the spherical surface,the kinematics model of a single ball under the method of variable-radius groove is established based on the sliding and geometric kinematics theories.Spherical trajectory simulation model is established based on Matlab.The simulation results indicate that the trajectory formed by each contact point can uniformly envelop the entire spherical surface after a single processing cycle,which is good for precision machining of high-precision balls.(2)Aiming at the difficulty of accurate and quantitative evaluation of processing trajectory,a quantitative evaluation system of trajectory is established by optimizing the trajectory model sampling method and analyzing the density of trajectory points(SD)in each grid.The lower the standard deviation of SD is,the more uniform the trajectory is.The influence of geometric parameters on the standard deviation SD is analyzed by univariate simulation The results indicate that the SD value is minimum when the eccentricity is 4 times as large as the ball radius and the groove half angle is 45°.The results of Analysis of Variance(ANOVA)and Student-Newman-Keuls(S-N-K)posttest show that the eccentricity is significant at the level of α=0.01,and the half-angle of groove is significant at the level of α=0.05.(3)Aiming at the problem that the no uniformity of the diameter of the ball in the multi-sphere system which affects the material removal rate,the ball sphere-shaping mechanism and the influence of loading system are analyzed based on the mechanism of single-ball fluid loading system is conducive to increasing the amplification coefficient to increasing the ball processing efficiency.The finite element software is used to simulate the force condition of the multi-sphere system to optimize the material removal model.And the change curve of the ball material removal rate in a single processing cycle is drawn in this paper.The results show that the material removal rate of the ball during single-cycle machining has no significant change,which is conducive to the consistency of high-precision ball processing.(4)A horizontal single-disc eccentric experimental platform is set up.The processing parameters of the ball during fine finishing are optimized by taking the bearing steel ball as the research object.The results show that the optimum processing parameters are: 2 N/ball load,20%wt slurry concentration,20 rpm rotation speed of lapping pad.Taking zirconia ceramic balls as the research object,the parameters needed for semi-finishing,finishing and ultra-finishing were analyzed to improve the fine finishing efficiency.The highest lapping efficiency can be reached when the sphericity reach 0.7μm after semi-finishing,and 0.3μm for finishing,and it increased by 14.7%.the ball surface roughness and sphericity are 14 nm and 0.13μm respectively after polishing,and it reached the G5 grade of national standards. |
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