The polishing process of advanced ceramic balls using a novel eccentric lapping machine
Abstract The finishing process of advanced ceramic balls can be divided into two steps. The first step is lapping in which most of the stock from the ball is removed at a higher material removal rate. The second step is polishing in which the required ball surface roughness, roundness, and dimensional and geometric accuracy are achieved. In polishing, the abrasive particle size is 1 μm, and the load and speed are lower than lapping. A novel eccentric lapping machine is used for polishing hot isostatically pressed (HIPed) silicon nitride balls. In the initial polishing stage, the polishing load is demonstrated as being most influential in the reduction of surface roughness value Ra. However, in the later polishing stages, the erosive process played a major role in the further reduction of Ra, although the high roughness peaks cannot be removed by erosive process alone. Experimental results also show that, in order to achieve desired surface roughness value, the initial surface quality of the upper plate should be reasonably high, and deep scratches on the ball surface from previous lapping processes should be avoided. The best polishing results achieved were surface roughness values of Ra of 0.003 μm and r.m.s. (Rq) of 0.004 μm, ball roundness of 0.08–0.09 μm. This proves that the novel eccentric lapping machine is also suitable for polishing advanced ceramic balls.
Effect of Various Parameters on Material Removal Rate in Flashing Operation of Precision Steel Ball Manufacturing Process
Precision balls are used in critical aeronautical bearings, guidance system balls for space and military applications, precision valves, automotive bearings and other applications where higher precision is necessary. However, since the surface finishing process necessary for the balls to achieve the required surface quality and geometric accuracy is time consuming and expensive, it increases the manufacturing cost significantly and therefore confines their widespread application. Hence, the development of a more economical finishing method becomes a critical problem in the application of advanced Steel ball manufacturing. The major concern of the current study is to investigate the performance of the Flashing machine in the initial stage. In flashing of steel balls, the influence of the groove depth of plates on the Material Removal rate of balls is analyzed experimentally. Five flashing plates with different groove depth are used. A shallow round groove is equivalent to a V groove with a large angle. A deep round groove corresponds to a V groove with a small angle. From the experimental readings, regardless of the groove depth of the Gap plate, the one where the groove of the rotary plate is deep it is found that MRR is large. Best MRR is found at the combination of 0.1 D ‐ 0.3 D. The experiment for Flashing was designed using a full factorial design with two levels for each input variable (2 k factorial design). Since there are three factors, each at two levels, the design is 2 3 factorial design which requires 8 runs to complete all the possible combinations. Factors taken for the experiments are Pressure between two plates, No. of Grooves in plates & RPM of Ring Plate. From the main effect plots, to achieve higher Material removal rate pressure should be at its higher level, RPM should be also at higher level, No. of grooves should be at its lower level. Also from the experiments the percentage contribution of various parameters on Material removal rate are Pressure having 58.16% , RPM having 16.86%, No. Of grooves having 23.90%. Analyzing the various process parameters, their influence in the operation & experiments are conducted at NHB Bearings Company.
Refinement of crystal structure parameters using convergent‐beam electron diffraction: the low‐temperature phase of SrTiO3
The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.