Research On Surface Quality Of Abrasive Waterjet Milling Bioceramics

Bioceramic materials have good physicochemical stability and affinity with biological tissues,but they also have characteristics such as high hardness,high brittleness,and low toughness,which will cause many problems using traditional machining methods to manufacture the complicated parts such as profiled surfaces.These feature lead to poor machining ability,high cost,low efficiency,and high chance to produce small cracks and stress concentration.Lately,it will reduce the fatigue strength,affecting the overall performance and lifetime of the workpiece.Abrasive waterjet milling is a new type of special cold machining method.It has unique advantages such as high flexibility,wide processing range,and no heat deformation zone.Therefore,based on the theory of abrasive water jet machining,this paper focus on surface quality of abrasive water jet milling bioceramics from the following aspects.They are the abrasive water jet erosion performance,influence of the process parameters on milling surface topography,mathematical model of milling depth and surface roughness.The main research contents are as follows:1.Study on abrasive waterjet working principle and bio-ceramic machining mechanism.Based on the analysis of the principle and the structure of the abrasive water jet,the main jet parameters are introduced and discussed.The impact force model of the waterjet is established based on the fluid flow of the short pipe,and the comparation with the impact of the abrasive waterjet on the workpiece material is made.Abrasive water jet erosion experiment was conducted to investigate the interaction between the abrasive water jet and the workpiece material and its crushing mechanism.2.Study on abrasive water jet erosion performance.The inner outer flow field of the nozzle system was numerically simulated by Fluent.The flow characteristics of inner flow field in the nozzle were analyzed,as well as the jet structure,the velocity distribution of water and abrasive at outer flow field.Through the numerical simulation of the erosion process of outer flow field,the pressure and velocity distributions and attenuation rules of the jet and its centerline are analysied during the erosion process.Then the mathematical model of the velocity distribution of the water in the jet and the distribution of the abrasive particles is created.Then we conclude the mathematical model of the energy distribution of the abrasive flow field.Based on the experiment of erosion of bio-ceramic materials by abrasive waterjet,the effects of different parameters of pressure and nozzle distance on the erosion hole diameter were analyzed,and the erosion performance of abrasive water jet was analyzed comprehensively with the simulation results.The results also the compared with the erosion performance by pure waterjet.3.Research on the influence of abrasive water jet milling process parameters on surface morphology.The influence of process parameters such as pressure,target distance,traverse speed,and feed rate on the single and multi-pass milling profiles were investigated.Then we can get the maximum width,maximum depth,and half-depth width variation rule.The influence of process parameters on the surface integrity of milling different planar shape is discussed.These help futher understand the influence of the process parameters on the surfaceroughing at the direction of the traverse speed and feeding.4.Mathematical models construction of milling depth and surface roughness for bioceramic materials.Based on the material removal models of abrasive waterjet machining on brittle materials,combined with the experimental results,the surface forming process of abrasive waterjet milling on bioceramic materials was discussed.According to the effect of process parameters on the width of single-pass milling bioceramics,the model of maximum single-pass milling width was corrected,and then the mathematical model of maximum singlepass milling depth was build.After comparing with the experimental results,we find the maximum error is-4.98%.Using the response surface method to optimize the process parameters,the surface roughness mathematical model at the x direction of the traverse speed was obtained through the regression analysis.The model predicted value Ra is 3.14037?m by optimizing the surface roughness mathematical model,the experimental value is Ra3.22?m with the error 2.47%.