Study Of Material Remove Mechanism Considering Lattice Effect During Micro Grinding Of Single Crystal Sapphire

In daily life and industrial application field,the demands of high quality,high accuracy micro parts that made of hard and brittle materials are raising.However,its hard to obtain a high quality and high accuracy brittle material micro parts by using the general machinging methods,such as turing and milling,because of itselfs material characteristics.The main problem happened in machining of brittle material is the brittle fracture appeared in the machined surface,and the machined quality could be affected by many factors,such as feeding velocity,cutting depth,rotation speed,chatter and tool deflection et al.Micro grinding is an important processing method for micro-machining of hard brittle crystalline materials.Modeling of material removal mechanism of MSG of crystal material is necessary to obtain a better understanding of precision micro-machining.In this paper,a predictive model of grinding force in MSG of three different orientations of single crystal sapphire:C-plane {0001｝,A-plane {1120} and R-plane {1102} are established,the crystalline effects such as density of A13+,DAl3+,and the density of O2hollows Do2-,the number of crystal layers ζ,the weak shape of different orientations are incorporated.Three group experiments(144 paths)are carried out and the differences of grinding forces from three orientations:｛0001},{1120} and {1102} are discussed.The grinding forces of A-plane {1120} are higher than the other two orientations {0001} and{1102},the crystal layers amount ζis proved to play a vital role in grinding force of MSG of sapphire.The force ratio rF(Fx/Fy)is between 0.5 to 1.0 and the rF of {1102} is more stable than {1120} and {0001}.From the comparison with exists model predicting results and experimental data,the model of this study shows a better fitting result especially at the lower feeding range.Except for the force model built during the machining process,based on the law of energy conservation,a surface fracture prediction model is established in this paper,surface fracture size and topography are measured and observed after above mentioned experiment.Basing on the observation of experimental results,it is found that the fracture size is increasing with the ascending of feeding rate speed and cutting depth.Furthermore,(1120)orientation owns the biggest fracture size,fracture on(0001)orientation is smaller than(1120)orientation,but all these two orientations have a much bigger fracture size than(1102)orientation,which makes(1102)the easiest machining orientation.Different fracture behaviors and cracks’ dimensions are also observed and measured.The fracture on(1120)orientation is concessive wavy structure,on(0001)orientation is lamellar tearing structure,on(1102)orientation is continuous small single fracture.In order to measure and observe the subsurface crack,a high temperature corrosion experiment is designed and conducted,the size relationship between subsurface crack and machining parameter is revealed,different internal topographies of subsurface crack are observed:on(1120)orientation is rectangle,on(0001)and(1102)orientations are triangle and rhombus respectively.Micro-structure and phase structure of subsurface of(1120)and(1102)orientations are revealed by scanning electron microscope(SEM)and energy dispersive spectrometry(EDS).Model verification work also has been done,and the comparison results indicate that the experimental results fit well with the model predicting outcomes.The knowledge this study presents is significant to the precision micro-grinding of sapphire.