| There are some problems such as high cost, low efficiency and poor surface quality existing in the traditional machining technologies of engineering ceramics. Abrasive waterjet cutting, which offers the advantages such as high machining versatility, small machining force, negligible thermal effects and low machining cost as compared to many traditional and other non-traditional technologies, has increasingly achieved acceptance in various industries. Consequently, this study attempts to apply the abrasive watejet cutting technology to machine engineering ceramics. The material removal mechanisms of engineering ceramics turned by abrasive waterjet is studied and the process parameters in the abrasive waterjet turning of ceramic materials are optimized, which has established a base for the practical application of abrasive waterjet turning for engineering ceramics.The abrasive waterjet turning rotary table is developed, which consists of a three jaw chuck, a centre, an alternating-current motor, a main spindle box, a control panel and a foundation. The abrasive waterjet turning rotary table adopts the direct-drive structure and employs the variable-frequency speed control system. The motor model is Y90-4which is determined by calculating the rotational inertia, torque and power of the motor. The bearing assembly, the structure of spindle and the assembling of the spindle parts are determined by analyzing the power and torque of the spindle in the course of abrasive waterjet turning. The maximum revolution speed generated by the abrasive waterjet turning rotary table is3000rpm and the clamping diameter is110mm.The influence of process parameters on material removal rate when turning96%alumina ceramic and95%zirconia is investigated using orthogonal experiment and single factor experiment. The results show that the influence on the material removal rate for96%alumina ceramic decreased in the order of the abrasive mass flow rate>the feed speed>the water pressure>the nozzle tilted angle>the surface speed. While for95%zirconia ceramic, the influence on the material removal rate decreased in the order of the water pressure>the abrasive mass flow rate>the nozzle tilted angle>the surface speed>the feed speed. The material removed through brittle facture mode has a lager removal rate than that removed though ductile mode. The properties of target of material have no effect on the dependence of material removal rate on water pressure and abrasive mass flow rate.The interaction effect of machining parameters on material removal rate is analyzed based on the response surface methodology when turning96%alumina ceramic. It is noted that the material removal rate is influenced firstly by the interaction effect between water pressure and abrasive mass flow rate (P×ma), secondly by the interaction effect between water pressure and nozzle tilted angle (β×P), and finally by the interaction effect between abrasive mass flow rate and surface speed (ma×Vs).The response surface models of turning depth, material removal rate and surface roughness are established when turning96%Al2O3by abrasive waterjet. The sequential approximation optimization (SAO) method is used to find optimum values of process parameters in order to obtain higher material removal rate at given tuning depth and surface roughness of96%Al2O3ceramic. In this study, the optimum machining parameters obtained by SAO method are u:0.06mm/s, P:310MPa, ma:11.5g/s, Vs:6.8m/s and β:105°at the conditions of the turning depth ranging from490μm to510μm and the surface roughness ranging from3μm to5μm. Thus, the material removal rate that can be gotten is6616.95μm3/μs while the surface roughness and the turning depth are4.18μm and509.6μm respectively.Based on quasi static indentation fracture mechanics, an analysis on erosion process with single abrasive particle is conducted. The critical conditions of ceramic materials for radial/median and lateral cracks in erosion process are obtained. The effect of nozzle tilted angle on the material removal rate of96%Al2O3and95%ZrO2has been studied. It is shown that the material removal rate increases with an increase in the nozzle tilted angle and gets the maximum at approximately90°for96%A12O3. While for95%ZrO2the material removal rate decreases with an increase in the nozzle tilted angle. Microscopic analysis of the eroded surface after turning reveals that the material removal mechanism of96%Al2O3mainly involves brittle facture damages featured by intergranular cracks and fragmentation, while for95%ZrO2the erosive process is primary plastic deformation accompanied with lots of pits.The relationship between the impact energy of abrasive particles and the volume of material removal under a certain time interval has been investigated when turning96%A12O3and95%ZrO2at90°nozzle tilted angle. The results indicate that there exists a strong linear relationship between the impact energy of abrasive particles and the volume of material removal under a certain time interval. It is noted that the energy needed to remove per unit volume of96%Al2O3ceramic through brittle fracture mode or to remove per unit volume of95%ZrO2ceramic through plastic deformation is changeless. The models of turning depth generated by a radial-mode abrasive waterjet turning process on96%Al2O3and95%ZrO2ceramic are established respectively. The experimental results indicate that the prediction values of the models are in good agreement with the experimental data. |
PDF Full Text Request