Experimental Study On Micro-grinding Surface Forming Process Of Hard And Brittle Crystal Materials

At present,high-precision micro-parts in the aerospace,medical,national defense and other fields have a great demand,so micro-grinding in the world engaged in manufacturing scholars in the cause of great attention.To achieve high-precision micro-components and micro-structural components of the efficient processing is very important to our country.Traditional processing methods have been unable to meet the needs of modern technology for precision parts,micro-grinding has a high potential in microstructure processing of hard and brittle materials,.First,the authors propose a new analytical roughness model that enables to predict the surface roughness of the generation of surface;the model is developed on the basis of the number of effective abrasives and the single abrasive depth of cutting into the workpiece.The authors now initiate an experimental investigation to establish the model.To reveal the mechanism of the formation of surface in hard and brittle materials and validate the accuracy and science of the proposed model,an orthogonal micro-grinding experiment on sapphire and silicon has been designed and conducted.With this new analytical roughness model,the roughness value of the micro-slot could be predicted.In this experiment,we use 200#tool to machine the micro-slot,so the surface quality is not good.A simple relationship between surface roughness and chip thickness was obtained,which was validated by the experimental results of silicon and sapphire micro-slot grinding.Measurements of process forces,surface quality,and accuracy were carried out,and the results are discussed.Second,the researches on "Ductile-brittle" transition in micro-grinding of brittle materials are important to the machining results,and this transition process could be affected by various factors,such as micro grit-material interaction,grinding force,material crystal structure and so on.In this study,a series of scratching tests are carried out by two different indenters to analyze the effect caused by grain shape and micro-interaction behavior between single grit and ground material on micro-grinding in micro perspective,two types of diamond indenters are employed to perform the scratching tests.The machined surfaces and forces are observed and measured.It can be found that there are slender and smooth fish bone shape on the scratched surface of obtuse indenter.The scratching results of acute indenter show a much smaller width than obtuse indenter and a fully cracked edge,and the scratching forces generated by these two indenters are significantly different.Consequently,a new predicting model of grinding force considering grain shape effect in micro-grinding of sapphire is built.Micro grinding experiments conducted by different micro grinding tools have been designed and carried out to verify the proposed grinding force model.Three machining modes are defined and there characteristics are observed.The rough critical values of undeformed chip thickness for micro-grinding of sapphire that under different machining modes are given.Based on the experimental results,it is found that big grain size grinding tool and low rotation speed is easier to generate a worse surface quality and a big crack size.Crack size is rising obviously with the increasing of feeding rate.The conclusions made in this study provide a theoretical reference and experimental basis for ductile zone micro-grinding of hard and brittle materials.