Fundamental Research On Ductile Regime Grinding Of Brittle Materials With Controllable Undeformed Chip Thickness Of Grains

The bottleneck of the further development of high efficiency precision grinding of brittle materialsis the difficulty of achieving the complete ductile machining of them, which will induce some surfaceand subsurface defects and influence the service performance and reliability of the brittle materialproducts. The traditional method to solve is to use superfine grinding wheel, or to introduce highspeed grinding. These methods are some kinds of solvent. But they can not solve the problem of notonly high efficiency but also ductile machining.The position of grains in the traditional grinding wheel surface is stochastic, which can not controlthe depth of cut of individual grain. Accordingly, many grains are in the mode of brittle machining,which can induce many defects in the surface and subsurface of the ground material.The dissertationconceives to use monolayer brazed diamond grinding wheel of large grit size, controlling theinter-grain space by means of orderly distributed grains, controlling the height uniformity of grains bymeans of precision dressing of the grains, and basically controlling the single grain cutting depth bymeans of regulating the process parameters, If single grain cutting depth is controlled under thecritical depth of cut which determines the transition from brittle mode to ductile mode for brittlematerial machining, then the ductile machining of brittle material is realized. The ductile machiningof brittle material with large removal rate can be achieved although traditional grinder and process areused. Consequently, the high efficiency precision process of brittle material is realized. For the sake ofthis, the paper has completed some following research work:(1)The experiment of ferrite material grinding with resin bonded diamond grinding wheel wascarried out. The surface roughness variation and the surface microscopic feature of ferrite withgrinding process parameter has been observed. The grinding wheel topography variation with wear isobserved. At last complicated shaped ferrite part has been manufactured. The grinding experimentproves that because of the random distribution of grains, lower grain retention, no grain heightuniformity and no grain micro-edges with respect to normal grinding wheel, the undeformed chipthickness and its uniformity can not be controlled accurately, which determines the ground surfacequality cannot be improved easily. Accordingly, it is speculated that grinding wheel with higer grainretention, orderly distributed grains, grain height uniformity and grain micro-edges will controlundeformed chip thickness accurately and realize ductile regime grinding.(2)The difficulty of ductile regime grinding with large grit size grinding wheel is analyzedtheoretically. The feature and statistical distribution of undeformed chip thickness are observed. Themethods of controlling undeformed chip thickness are proposed. At last the grinding wheel withorderly distributed grains has been developed, which address the problem of high temperaturedeformation of wheel matrix and controlling of undeformed chip thickness and its uniformity.(3)The dressing method of brazed diamond grinding wheel with cup shaped resin bonded grindingwheel is proposed. The experiment rig is equipped. The improved mild steel dressing method isproposed. The two dressing processes are studied. The grinding wheel topography and grain heightuniformity during dressing process are observed. After that various brittle material grinding process isstudied. The results show that the two dressing process improved the diamond grain height uniformity greatly and the ground surface quality of brittle materials has been increased greatly.(4)With the improved brazing process and the improved dressing process, the ductile regimegrinding is realized. The improved brazing process controls the overflow of brazing alloy fluid on alateral surface and the over-embedment of diamond grains, which makes grain height uniformity inthe direction of grinding wheel width more even and makes grain protrusion larger. With theimproved dressing process, the grinding wheel grains can achieve limited fracture, which not untilensure the grit height uniformity but also ensure the micro edges of grains. At last the ground surfaceroughness of zirconia achieves Ra0.1μm, of which the surface grinding texture is very consecutiveand dense, and the material removal is generally in the ductile regime.