Simulation And Experimental Studies Of Precision Ground V-Shaped Micro-Structure On Superhard Materials

Up to date, as the application of micro-structured optical elements is expanding rapidly, the requirement for the corresponding surface quality is accordingly increasing. The most appropriate methodology to realize the mass production of micro-structured optical elements is the integration of ultra-precision machining and replication technology in terms injection molding and glass hot pressing. The molds for replication process are of usually fabricated by means of ultra-precision diamond turning and diamond grinding respectively. Therefore, the surface and subsurface quality of ultra-precision machined molds will determine the replicated optical element performance. With regard to the hard-to-machine super hard mold materials, the only feasible resolution is still ultra-precision diamond grinding. However, the generated complicated stress field and surface and subsurface damage during the ultra-precision grinding process will affect the fabricated surface integrity. Therefore, to carry on the study and investigation upon the mentioned two aspects is either necessary or meaningful.This thesis focuses on the investigation of diamond grinding V-shaped microstructures of three typical super hard materials deals including silicon carbide, silicon nitride and tungsten carbide. ABAQUS software was applied to simulate the ground mechanical residua stress of V-shaped microstructures. After the grinding experiments the MRF method was used to polish the ground V-shaped micro-structured surface in aiming to investigate the surface and subsurface damages.In summary, the following aspects were studied and investigated in terms of the modeling and simulation of diamond ground stress field of V-shaped microstructure, as well as the corresponded experimental trials.(1) By applying novel modeling method, i.e., through obtained fundamental properties including elastic, plastic and brittle with indentation tests, combined with load-depth curves, the dimensional analysis method was used to obtain the equations of strain-stress of three materials, accordingly, the corresponded constitutive models were created.(2) The grinding experimental trials of V-shaped microstructures were conducted on SiC, Si₃N₄ and WC. On the basis of comparing different modeling methods, the modeling method by integrating regression analysis with grinding force values and empirical formula was finally selected, then the grinding force model that near the real grinding condition of V-shaped microstructure was created.(3) Along with moving even distributed normal load on the surface, the elastic-plastic analyzing method was used to simulate the formation of mechanical stress during the grinding of V-shaped microstructure. The simulated results illustrated the distribution regulation of mechanical residual stress on the machined surface of three super hard materials, as well as the effect of grinding variables on the degree of mechanical stress.(4) The experiments of precision grinding of V-shaped microstructure were conducted on SiC, Si₃N₄, and upon the results the measured grinding forces was compared to the before created formulated grinding force in order to verify the validity of the grinding force model. The MRF method was adopted to non-destructively polish the precision ground V-shaped microstructure, then the machined surface, subsurface region with non-even removed depth by MRF around top closed angle, side surface and bottom closed angle were scanned by MRF. Thereafter, the morphology, distribution regulation and mechanisms of the surface and subsurface damages along normal orientation to the V-shaped microstructures was analyzed and summarized on SiC and Si₃N₄ respectively.