Development of efficient and precious finishing method of ceramic balls with magnetic fluids

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Advanced ceramic balls are expected as ball element for high speed bearing or ultra precision bearing used in jet turbine engine or ultra precision grinding machine. However, the applications of ceramic bearings are limited because of their high prices. One of main causes of high price is high manufacturing cost since ceramic balls take significant grinding and finishing time even by using expensive diamond abrasives in order to avoid introducing surface defects as cracks. In these ceramic balls, mirror-surface are required for low rolling friction and small noise in operating.To overcome these problems, new polishing method with magnetic fluids was proposed, and a special element named 'float' was introduced by investigators to increase the grinding force and improve the shape accuracy. As a result, the combination of magnetic fluid, a float, abrasive grains, and magnetic field showed to form a new practical grinding method named "Magnetic Fluid Grinding."In the present research project, more high efficient and precious finishing methods for ceramic balls with magnetic fluids were tried to proposed.For those purposes, investigator Umehara visited at the laboratory of Prof. Komanduri who is an expert in the field of manufacturing of brittle materials in US and discuss about how to improve this method with magnetic fluid in the first year. On the basis of the discussion, polishing test of Si3N4 balls were done and showed design concept for optimum abrasives for this method. In the second year, single crystal silicon balls were tried to polished with this method. As a result, it was shown that magnetic fluid polishing is adequate for the polishing of single crystal Silicon balls because of thin damage layer of Silicon balls during polishing.