Theoretical and experimental recommendations for the elimination of grinding cracks during the processing of permanent magnets

Abstract

The manufacturing technology of permanent magnets has high precision characteristics and is based on extreme dependencies of physical and mechanical properties of magnets from the contents of the alloy, crystalline structure and temperature and force factors during their processing. Grinding of magnets in high-coercivity state relates to low productivity and relatively high flaw regarding cracks and scratches. Quality analysis of the preliminary and terminal size processing of permanent magnets shows that the main defects of the magnets are microcracks, surface cracks, chips. Their appearance during the grinding of the magnets is the consequence of relatively low mechanical characteristics of the alloys, wrong choice of characteristics of the grinding wheel, breaking proper grinding modes, presence of the defects that were formed during the previous technological stages of permanent magnets manufacturing. The objective of this research is the development of theoretical and experimental recommendations for eliminating grinding cracks during permanent magnets processing. The mechanism of grinding cracks appearance was considered regarding to the influence of geometry of structural components and their orientation related to the direction of grinding of the magnets in high-coercivity state. The problem of defining stress-strain state of the surface layer of the grinded magnets in high-coercivity state weakened by the system of foreign inclusions was solved. Analytical balance conditions of the structural defects of hard magnet alloys depending on the coefficient of crack resistance and the value of the contact temperature of grinding which is defined by the technological parameters were discovered. These technological parameters make possible the building of the algorithm for choosing technological parameters that provide the required quality of the processed surfaces. Technological backgrounds for controlling quality characteristics of the parts being grinded using the criteria of maximum allowable temperatures of grinding, heat flow, size of structural parameters, cutting forces, crack resistance coefficients were developed.