Study On Response To High Velocity Impact Of Particle On Ceramics And Processing Parameter Optimization Of Abrasive Waterjet Turning

Aimed at the problems in study on abrasive waterjet turning, which are the lack of study on turning performance and machining mechanism of hard and brittle materials, the lack of widespread generality about predicted models on turning process, and the lack of multiple response optimization of turning process parameters, the dissertation focused on study on the response to high velocity impact of particle on ceramics and processing parameters optimization of abrasive waterjet turning. Through the experimental study on performance of abrasive waterjet turning, the influence trend of processing parameters on the turning performance is revealed. Through the study on material response to high velocity impact on alumina ceramics by abrasive particles, the micro removal mechanism was acquired during impact process. The predicted model on performance of abrasive waterjet turning was developed based on finite element method. By deep understanding of the complex relationship between turning process and turning performance, the problem of controling the depth of penetration (DOP) was solved during radial mode abrasive waterjet turning. The processing optimization model was developed during abrasive waterjet turning of ceramics. These research achievements will provide theoretical basis and technical support for the promotion and application of radial mode abrasive waterjet turning of hard and brittle materials.The effect of main processing parameters on depth of penetration and the material removal volume was analyzed by experimental study. The traverse speed and waterjet pressure have the most significant effect on depth of penetration and the material removal volume. However, the standoff distance and surface linear speed of workpiece have a little effect on depth of penetration and the material removal volume. The material removal mechanism was analyzed during abrasive waterjet turning of alumina ceramics. The ceramic materials were mainly removed by plastic shear mode during abrasive waterjet turning with a smaller nozzle tilt angle. However, the ceramic materials were mainly removed by brittle fracture mode during abrasive waterjet turning with a larger nozzle tilt angle.The response of high velocity impact on alumina ceramics by abrasive particles was investigated. The impact kinetic energy efficiency was obtained by finite element model at different impact velocity, impact angle and abrasive size. Higher impact kinetic energy efficiency can be acquired at a higher impact velocity, larger impact angle and larger abrasive size. Higher impact kinetic energy efficiency implied that the abrasive particles had more powerful impact abilities. Meanwhile, the impact kinetic energy efficiency is increased with an increase in the abrasive size. Through the finite element model, the x-stress under the condition with various impact velocity and impact angle was compared at different time. The x-stress of the elements near the impact contact zone was analyzed at various abrasive sizes. The elements at the contact surface after impact were under compressive stress. Meanwhile, the elements at the non-contact surface after impact were under tensile stress. The response to high velocity impact on alumina ceramics by abrasive particles with various shapes was also studied. The spherical and cone abrasive paricles obtained higher impact kinetic energy efficiency, and also acquired larger crater depth and volumes. However, the cube and cylinder abrasive particles obtained lower impact kinetic energy efficiency, and also acquired smaller crater depth and volumes. The effects of abrasive shapes on impact kinetic energy efficiency, crater volumes and depths have the same varied trend. The crater volumes and depth of alumina ceramics impacted by abrasive waterjet with a high velocity can be effectively predicted by the developed 3D finite element model. The experimental results of crater volumes and depth at different impact velocity, impact angle and abrasive size were in accordance with the predicted results by finite element model.The material removal mechanism of ceramics impacted by single particle with a high velocity was investigated. The main material removal mechanisms of ceramics are the crack branching and coalescence as well as micro holes. The response to high velocity impact by four abrasive particles arranged in different patterns was investigated. When the alumina was impacted by four particles with a high velocity, the main material removal mechanism of cermacis was that the large-scale ceramic materials stemmed from the superposition and coupling effect of stress wave caused by the abrasive particles. The general model of depth of penetration of alumina ceramics turned by abrasive waterjet was developed by finite element method. The predicted results are in accordance with the experimental results. The average relative error between the predicted and the experimental valus was below 15%.Modeling and optimization of processing parameters for abrasive waterjet turning alumina ceramics were investigated by response surface methodology. The effect of the interactive effect among the processing parameters of abrasive waterjet on depth of penetration and surface roughness (Ra) was studied. The maximum depth of penetration was acquired under these conditions which are lower traverse speed in combination with higher waterjet pressure, lower traverse speed in combination with higher abrasive flow rate, or larger standoff distance in combination with lower traverse speed. The minimum surface roughness was obtained at a middle of their (the pressure and abrasive flow rate) experimental range due to their significant quadratic effect. The interactive effect between the traverse speed and the abrasive flow rate has a significant influence on both depth of penetration and surface roughness. The processing parameters were simultaneously optimized using desirability function for the desired DOP and surface roughness. According to the first criterion, the optimal process conditions would lead to the maximum depth of penetration (480μm) and simultaneously acquire relative little surface roughness (Ra 10.3μm). Meanwhile, according to the second criterion, the optimal process conditions would lead to the maximum depth of penetration (390μm) and minimum surface roughness (Ra 5.3μ2m) at the same time. Therefore, the results of processing parameters optimization were validated by experiments.