Study On Grinding Thermal Characteristics And Surface Quality Of Silicon Nitride Ceramics

Engineering ceramics represented by silicon nitride ceramics are widely used in aerospace,precision machinery,electrical and electronic,military equipment because of their high strength,high hardness,high modulus of elasticity,low density,high temperature resistance and corrosion resistance.At present,the processing of engineering ceramic materials are mainly based on mechanical methods.And due to the hard and brittle properties of ceramics,grinding processing has become its main processing method.Grinding is different from other processing methods.The grinding power is large during the grinding process and most of them are converted by heat formation,which causes the temperature in the grinding zone to rise sharply.On the one hand,high surface temperature will have a great impact on ceramic surface quality,processing accuracy,processing efficiency,and grinding wheel performance.On the other hand,ceramic materials have low thermal conductivity and poor thermal shock resistance.In severe cases,burns and hot cracks are formed on the ground surface,which greatly affects the performance and life.In this thesis,hot isostatic pressing silicon nitride ceramics was taken as the research object.And the surface quality after grinding was taken as the starting point to study the effect of grinding thermal characteristics on surface quality.Firstly,the research status of grinding heat and surface quality were reviewed.Secondly,the removal mechanism and surface forming mechanism of ceramic materials were summarized.And the influence of removal mechanism on surface quality was analyzed.After that,the relationship between process parameters of grinding thermal characteristics and grinding parameters were obtained through the comparative analysis of finite element simulation and experiment.Finally,the effect of grinding thermal characteristics on surface quality was analyzed.The details are as follows:(1)The grinding heat distribution ratio model,the grinding heat source model,the grinding thermal characteristic simulation,the grinding thermal characteristic experiment,the grinding temperature measurement method and the influence of grinding heat on the surface quality of engineering ceramics were summarized and analyzed.On this basis,the shortcomings were found out and the research content of this thesis were formulated.(2)The removal mechanism and surface formation process of ceramic materials were summarized.The effects of longitudinal crack and transverse crack propagation on the material during the removal process and the effect of maximum undeformed chip thickness on removal method were mainly analyzed.And the surface fracture damage model was used to state the impact of the material properties,the grinding wheel properties and the grinding processes on surface fracture rate.Then the effects of material removal mechanism on surface morphology and surface roughness were discussed.And the relationship between surface roughness and surface removal was obtained.It provides the theoretical basis for studying the effect of grinding heat on surface quality.(3)The finite element simulation model of a single diamond abrasive grain grinding silicon nitride ceramic workpiece was established.The effects of grinding parameters on grinding force,grinding temperature and specific grinding energy were obtained through comparison analysis of experiments and simulations.Then the influence of grinding parameters on surface roughness and removal method were obtained through a large number of experiments.And the relationship between grinding force,specific grinding energy,surface roughness and removal method was obtained.(4)According to the theory of grinding chip forming and the theory of heat transfer,the heat distribution ratio model of the grinding zone was established by the inverse method.And the relationship between the grinding parameters and the heat distribution ratio of the incoming grinding wheel,the incoming workpiece and the incoming grinding chip was obtained by grinding experiments.Then the effects of grinding thermal characteristics on surface quality were studied.And the suitable grinding temperature range,the influence of grinding heat on crack propagation,the composition of the surface burn and the metamorphic layer were found out.Finally,the control measures of grinding heat were proposed.