Investigation On The Surface Integrity Evaluation Technology Of Engineering Ceramics For Rotary Ultrasonic Grinding Machining

Engineering ceramics have been widely applied to fields like aerospace,precision machinery,inertial guidance,nuclear equipment,for excellent physical and chemical properties.Index parameters and evaluation criteria of engineering ceramics for rotary ultrasonic grinding machining are those adopted surface integrity of the metal material,though the machining way is the development trend in the current field of precision manufacturing.The material properties and material removal mechanism of engineering ceramic are different from those of metal materials,so it is not accurate and comprehensive to evaluate the surface integrity characteristics of engineering ceramics with surface integrity evaluation parameters of metal materials processing.As the precondition of ceramic parts performance evaluation,it has important significance and practical value for engineering ceramic parts engineering applications to carry out the investigation on surface integrity evaluation technology of engineering ceramics for rotary ultrasonic grinding machining.In view of the fact that the studies on surface integrity evaluation of engineering ceramics are few,and the corresponding surface integrity assessment parameters are unreasonable or deficiency.The investigation on surface integrity evaluation technology was carried out in the paper for rotary ultrasonic grinding,taking Al2O3,ZrO2 reinforced Al2O3,self-reinforced Si3N4,nano-reinforced Si3N4 and other typical brittle homogeneous engineering ceramics as the representation.The characteristics evaluation parameters of three-dimensional surface roughness,micro-cracks and surface residual stress were proposed,based on machined surface morphology characteristics of engineering ceramics.And the surface integrity comprehensive evaluation of engineering ceramics was achieved initially.The machined surface morphology is one of the most important part of the geometric characteristics in surface integrity.The mechanism of engineering ceramic for rotary ultrasonic grinding machining is different from those of metal materials,and the investigation on surface morphology are not studied in literature.In order to evaluate surface integrity features and comprehensive evaluation,the surface topography features of engineering ceramics comprehensively for rotary ultrasonic grinding were analyzed.Surface morphology changes were investigated with the fractal dimension.The analysis done in this research includes the surface characteristics of amplitude distribution and power spectral density distribution,two-dimensional power spectrum and angular spectrum,with isotropic and homogeneous studies of surface carried out simultaneously.Due to the value is same for different surface when using current three-dimensional surface roughness parameters,and lacking of multi-scale features,the mathematical model of fractal-root-mean-square deviation was established with the Parseval equation of two-dimensional continuous signal,which is used to evaluate three-dimensional surface roughness.Meanwhile,its validity was tested.The measurement data which includes not only the surface roughness,but also surface waviness,machined surface shape error,etc..The s wavelet transform mathematical model of three-dimensional surface roughness of engineering ceramic for rotary ultrasonic grinding was established.Taking the reconstruct error and the energy distribution at different decomposition levels as the basis,the optimal wavelet basis and the optimal wavelet decomposition level were selected,decomposing surface roughness and the reference plane.Finally,the relationship between surface fractal dimension,root-mean-square deviation,the scale parameter of surface and fractal-root-mean-square deviation were investigated.A new assessment parameter was used for the three-dimensional surface roughness evaluation of engineering ceramics by the investigation,and it has the features of double absolute measurement and multi-scale.It provides the basis to establish the index layer for the surface integrity comprehensive evaluation.Traditional evaluation parameters for micro-cracks are relatively simple,not highly sensitive and can not reflect the complexity of the cracks,so the mechanism of micro-cracks generation was analyzed based on fracture mechanics in processing.Two-dimensional fractional Brownian random field model of machined surface grayscale image of engineering ceramics was established,and processing surface was divided into crack prone areas and non-prone areas with the Hurst exponent.Micro-cracks of machined surface were extracted through image processing.Information dimension calculation model of micro-cracks was established too.The parameter of fractal density was put forward and applied to evaluate micro-cracks features.Simultaneously,the validity of the evaluation parameter was tested,and the relationship between the cutting force,fracture toughness and fractal density of micro-cracks was investigated.The comprehensive evaluation index layer of surface integrity for engineering ceramics is improved,the investigation on surface micro-cracks of engineering ceramic for rotary ultrasonic grinding,and it provides the corresponding evaluation parameters.In the paper,the mechanism of residual stress was analyzed,and theoretical analysis of residual stress distribution for engineering ceramics in processing was carried out based on the elastic-plastic mechanics and dislocation pile-up density function model.Statistical analysis of residual stress distribution was realized through the test data for engineering ceramics surface.The result shows that surface residual stress field of engineering ceramics for rotary ultrasonic grinding is unstable,and it inevitably reduces the evaluation reliability by measuring the limited data points of residual stress on the surface.To solve this problem,the valuation parameters of surface residual stress-confidence stress tolerance and its mathematical model were proposed based on the above investigation.The evaluation precision was analyzed with the different number of sampling and sampling methods,and the impact of the material properties and cutting force on confidence tolerance values was put into effect.It further improves the surface integrity evaluation system of engineering ceramics,and provides more reasonable assessment parameters for the comprehensive evaluation.Based on the study of surface morphology,three-dimensional roughness evaluation,micro-cracks evaluation and surface residual stress evaluation,the mathematical model of the surface integrity comprehensive evaluation was established by using the analytic hierarchy process and gray correlation theory,taking rotor shaft part of ceramic for example.The correlation value was regarded as the comprehensive evaluation factor of surface integrity.The surface integrity comprehensive evaluation of engineering ceramics for rotary ultrasonic grinding was preliminarily realized.It provides support to realize engineering applications for engineering ceramics parts.