Sphericity Of Balls Research Articles

Influence of Supporting Characteristics on Sphericity of Ceramic Balls in Rotated Dual-Plates Lapping Process

Ceramic balls have become an important component in advanced bearings, and the sphericity of balls is a key qualification focused in lapping process. An investigation on the effect of dynamic behavior of ball support system on the performance of ball lapping in rotated dual-plates lapping method is carried out. Sinusoidal waveform in terms of Fourier analysis is employed to express the shape error of the ball surface, and a dynamic model for support is setup. It is found with numerical calculation that the variation of lapping load lags behind the variation of the shape error for the damping of support. A lower natural frequency of the support system, higher spin speed of balls and a larger value of spin angle in RDP lapping are better to rectify the shape error of balls and reduce the lagged effect. It is concluded that dynamics of lapping system must be taken into consideration in order to understand comprehensively the spherical surface generation mechanism.

Design and Error Analysis of Multiball Artifact Composed of Simple Features to Evaluate Pitch Measurement Accuracy

The strength and vibration/noise of gears are influenced by the pitch deviation of micrometer order and therefore, advanced quality control is needed in gear manufacturing processes using measuring instruments. The accuracy of the pitch measuring instrument is verified using a master gear or artifact, but their accuracy is not sufficiently high. An artifact with higher accuracy for the evaluation and calibration of the pitch measurement is necessary in order to respond to the requirement of gear accuracy. In this research, the multiball artifact, a novel high-precision pitch artifact, is proposed for use in the evaluation of pitch measuring instruments. The multiball artifact is composed of balls, a cylinder, and a plane, where the center cylinder or center ball is surrounded by the balls on the plane. The positions of those elements are decided automatically by the contact among those elements. Balls, cylinders, and planes can be manufactured with accuracy on the order of several tens of nanometers. Therefore, this artifact can realize high accuracy. In addition, this artifact does not need advanced techniques in manufacturing and assembly. This leads to the reduction in manufacturing cost. In this report, the concept and structure of the multiball artifact are proposed, and theoretical analysis on the measurement of the artifact is carried out. Feasible angular pitch is analyzed theoretically. For a cylinder-centered artifact, it is easy to realize the target angular pitch by adjusting the cylinder diameter. Ball-centered types suffer from the limitation of the variation in ball diameter if standard balls are used, but an angular pitch close to the target pitch is possible through the selection of an appropriate combination of balls. The effects of the dimensional deviation of the diameter of the center cylinder, the inclination of the center cylinder, the dimensional deviation of the surrounding ball diameters, the sphericity of balls, and the flatness of the base plane are analyzed. Deviations in the cylinder have a comparatively large effect on angular pitch. On the other hand, the effect of the deviation of the ball or base plane is smaller. The feasible angular pitch is clarified, and it is verified that the concept and structure of the multiball artifact are effective. The effects of deviations in the form and dimension of the composing elements are analyzed, and it is clarified that the accuracy of the cylinder is important.

Magnetic fluid grinding of advanced ceramic balls

A new method of finishing advanced ceramics, namely, magnetic fluid grinding with a float, has been developed especially for Si 3N 4 balls. The removal mechanism in this process and the optimum grinding conditions have been studied in the last seven years. In this paper, the results from the published papers are surveyed and summarized from the viewpoints of removal rate, surface roughness and sphericity of balls. From this review, it was found that magnetic fluid grinding can be applied to the rough finishing process at high speed. However, if a sphericity smaller than 0.1 μm is required, some new ideas are necessary.

セラミックスボールの新しいラッピング方法の提案

This paper treats the relation among lapping pressure, wear-distance-ratio, mesh number of abrasive sheet and sphericity of balls in the lapping circumstances of ceramic balls, and the new lapping method for ceramic balls are presented. Obtained results are as follows : 1) For green balls formed by CIP the optimum lapping conditions such as lapping pressure, the mesh number of abrasive sheet and others are found. 2) New lapping method for sintered balls using combined lapping tools is proposed, and the sphericity of balls can be considerably improved by this method. 3) The optimum share ratio of normal loads in combined tools is found for the rapid improvement of the sphericity of balls.