Study On Acoustic-Liquid Coupling Dynamics Characteristics Of Abrasive Waterjet And Its Processing Technology For Bioceramic

The micro abrasive waterjet machining technology has the advantages of small cutting force,no material selectivity and high processing flexibility.It has become an important method to machine effectively parts with high profile precision and high surface quality.However,during the traditional micro abrasive waterjet machining,the water cushion on the workpiece surface reduces the impact pressure of abrasive waterjet on the target material,which can reduce the machining efficiency of hard-brittle materials.With an aim to strengthen the machining ability of abrasive waterjet,the acoustic-liquid coupled micro abrasive waterjet processing technology is proposed in this paper.The acoustic energy and waterjet kinetic energy are fully coupled in the nozzle.Ultrasonic vibration is used to stimulate the abrasive waterjet and enhance the fluctuation intensity of waterjet beam,which can improve the erosion performance of micro abrasive waterjet.The main research contents include the following aspects: the acoustic-liquid coupled micro abrasive waterjet machining device was developed and the acoustic-liquid coupling dynamics characteristics were analyzed;the processing mechanism and the removal mechanism of hard-brittle bioceramic materials were investigated;the effects of various factors on bioceramic surface roughness and erosion depth were studied through relevant experiments,and the processing parameters were optimized.The detailed research contents are as follows:(1)The acoustic-liquid coupled micro abrasive waterjet machining device was developed.The pre-mixed device was used as the abrasive supply device.The ultrasonic nozzle device is the key of the system.The cylinder-cone-cylinder three-section composite horn was designed.The horn is installed inside the nozzle so that the end vibration directly affects the abrasive waterjet.And the modal analysis and harmonic response analysis were carried out through ANSYS software to confirm that the designed horn has appropriate size coefficient and working performance.(2)The acoustic-liquid coupling dynamics characteristics of micro abrasive waterjet were studied.COMSOL software was used to simulate the propagation rule of ultrasonic wave in the fluid,the acoustic pressure distribution of the flow field inside the nozzle was obtained.The influences of ultrasonic vibration on the velocity distribution of waterjet flow field and the movement track of micro abrasive particles were analyzed by FLUENT software.Relevant experiments were carried out to measure the actual impact force of acoustic-liquid coupled abrasive waterjet,and the simulation results were verified.The results indicated that the high-intensity periodic acoustic pressure exerted by ultrasonic vibration can enhance the pulsation behavior of waterjet.The low pulsating and continuous waterjet were modulated into high pulsating and unsteady waterjet,which can effectively improve the machining performance of micro abrasive waterjet.(3)The material removal mechanism of acoustic-liquid coupled micro abrasive waterjet machining bioceramic was investigated.Taking hydroxyapatite(HAP)bioceramic as the experimental object,the effects of system pressure,vibration amplitude and impact angle on the removal mechanism of bioceramic materials were analyzed.The results showed that when the vertical impact load of acoustic-liquid coupled abrasive waterjet is low,the shear wear removal is dominant,and there are a large number of shallow and narrow scratches on the machined surface.With the increase of vibration amplitude,the vertical impact load of abrasive particles increases,brittle fracture occurs on the material surface.(4)The optimization model of processing parameters in acoustic-liquid coupled micro abrasive waterjet machining bioceramic was established.The Box-Behnken Design method was used to design the experimental scheme with the system pressure,target distance and vibration amplitude as variables.The experiments of polishing and grooving were carried out on dense and porous HAP bioceramic materials,respectively.Based on the response surface method,the parameter optimization models of surface roughness and erosion depth were established.Aiming at the the best surface quality and maximum erosion depth,the optimum combinations of processing parameters were obtained.