Research On Micro-damage Mechanism In Grinding Of Silicon Carbide And Its High Performance Grinding Technology

High speed grinding an advanced machining technology started from European countries and USA since 1970s.It is altered by different materials and featured by a higher materials removal rate,better machining economy within required machining quality.High speed grinding(HSG)has been widely used in applications of machining difficult-to-machine materials.However,the huge impact to materials may be produced in high speed grinding process because of the extremely high wheel speed,which will definitely make the study of grinding mechanism difficult.As the typical brittle and hard materials,the engineering ceramics has shown its universal applications in different engineering industries for the excellent wear resistence,erosion prevention,heat resistence and so on.However,it is inevitably to cause microcracks and thus deteriorate the surface and subsurface quality in HSG processes.Therefore,in order to promote further application of engineering ceramics,the control of microcracks and understanding of this damage mechanism under different process parameters should be lifted to a higher level.This paper is trying to put some basic understanding of the dynamic features of ceramics in HSG process.The grinding mechanism,damage mechanism and its control and predictions will be detailedly analyzed.The main aim is to lower the grinding damage and promote the surface and subsurface quality under a higher grinding efficiency.The main research results and innovations can be concluded as follows:(1)Based on the analysis of strain rate sensitive dynamic fracture toughness of hard brittle materials,a new critical chip thickness model,considering the material mechanical properties and process parameters,was established.This critical model is different from the traditional understanding of ductile grinding under a certain value,which does not change with the process parameters and just relates to the mehcanical properties.The model was validated and verified under a series of experiments of surface and subsurface damages.It has been found that the elevation of grinding wheel speed or decrease of the chip thickness can significantly improve the ceramic material of critical depth and lead to a ductile grinding.When the wheel speed is140m/s,the critical chip thickness for ductile grinding of SiC is 0.32?m,which is much more higher than the traditional model of 0.06?m.Therefore,the improvement of grinding wheel speed or a chip thickness reduction helps ductility domain grinding into critical thickness increases,and help to realize ductility domain grinding.Moreover,the experiemental results show that the increase of wheel or decrease of chip thickness will help to achieve a better surface finish and more ductile surface can be expected.(2)Based on the indentation fracture mechanics and grinding damage theory model,a grinding damage characterization model was built to incorporate the effects of grinding speed,chip thickness,processing load and material mechanics performance on grinding damages.Compared with the traditional indentation-based damage model,this model help to cut the predicted error of original 20%to 6%,which shows a much better prediction accuracy.Furthermore,the experiemnts was conducted to validate and correct this model to explain the grinding wheel speed and chip thichness effect on grinding damage.The increase of the grinding wheel speed was put forward to inhabit the surface and subsurface damage.The increase of grinding wheel speed helps to improve the surface plastic scratches and its proportion and thus significantly lowers brittle fracture in both surface and subsurface.Moreover,with the increase of chip thickness,the surface and subsurface cracks increased and brittle removal mode dominates.Therefore,in order to obtain better grinding quality,reduce the damage degree of surface and subsurface,it is suggested to a combination of decrease fo the chip thickness and increase of the grinding wheel speed.(3)The coexistence of brittle and ductile removal model was proposed to model the ground surface roughness,which comprehensively considers the effect of grinding damage,ductile grinding proportion and the process parameters on the surface roughness.Furthermore,the quality-oriented process design was given to provide more application cases in high performance grinding of Silicon Carbide.The grinding experiemntal results show that brittle removal dominates and the surface roughness fluctuates when the ductility domain grinding ratio is less than 50%;while when ductile removal is more than 50%and increases gradually,the brittleness removal of roughness are stably dropping down and the ductile griding dominates,the surface roughness value decreases with the increase of ductile grinding ratio;when the ductile grinding ratio is above 90%,ductility is the main meterial removal mode and the brittle surface roughness fell sharply to a relatively low surface roughness value.In high performance grinding of Silicon Carbide,the elevation of grinding wheel speed or reduction of chip thickness is helpful to increase the material removal rate and keep the grinding damage low.In order to abtain a surface roughness of below 0.2?m and removal rate of 1.1mm~3/mms,the grinding wheel speed and chip thickness was suggested to higher than 137 m/s and lower than 0.55?m.For a ductillty-dominant removal(above 50%ductility),a wheel speed of above 53 m/s and chip thicknes below 0.8?m is recommended to abtain a material removal rate up to1.7mm~3/mms.