A Study Of The Erosion Mechanism And Processing Technology For Ultrasonic Vibration Assisted Abrasive Waterjet Polishing

In the present study, the abrasive waterjet (AWJ) with the aid of ultrasonic vibration was used to improve the processing efficiency of hard and brittle materials while guaranteeing the surface quality. The ultrasonic vibration can improve the ductile erosion ability, reduce the surface roughness and avoid the surface texture caused by the particle erosion. The ultrasonic vibration table and the ultrasonic vibration assisted fluidizing abrasive feed device were developed. The fluid field of the impinging jet on the workpiece surface in ultrasonic vibration assisted abrasive waterjet polishing (UVA-AWJP) was simulated. Through studying the kinematics of the ultrasonic assisted abrasive particle erosion, the mechanism of the material removal was analyzed and the material removal volume was modeled. As the same time, an explicit dynamic FEM analysis was conducted to investigate the erosion process in UVA-AWJP. The surface roughness of the polished surface was modeled and the model was verified by experiments. Meanwhile, the influences of the workpiece ultrasonic vibration on the polishing efficiency and surface roughness were investigated by experiments.The ultrasonic vibration table and the ultrasonic vibration assisted fluidizing abrasive feed device were developed. On the basis of analyzing the mode and harmonic response of the ultrasonic vibration table, the results showed that the table can meet the requirements of the research. The abrasive with the mesh number ranging from 400# to 2500# can be stabilized at a flow rate of 200 mg/s by using the ultrasonic vibration assisted fluidizing abrasive feed device.The fluid field of the impinging jet on the workpiece surface in UVA-AWJP was simulated. Moreover, the influences of the workpiece vibration on the pressure and velocity field of the impinging jet fluid field at the stagnation zone and the side flow zone were investigated. The impinging force on the vibration workpiece surface was experimentally measured. Furthermore, the fluid-solid coupling effect during the impingement of the jet on the vibration workpiece surface was analyzed. The results illustrated that in the case of workpiece vibration, the stagnation is weakened due to the shearing action at the boundary layer and the impinging velocity is lower. Meanwhile, the velocity magnitude with asymmetric distribution is higher. The force fluctuation in the case of workpiece vibration is obviously stronger, while the mean value of the force is lower than that of the non-vibration condition. The measured data was in reasonable agreement with the simulation results. The calculation results of the fluid-solid coupling analysis indicated that the coupled vibration of the amplifier appears due to the impinging jet. Compared to the simulation results of the vibrating boundary fluid field, the pressure at the impinging zone is lower. At the same time, the velocity value is higher and its distribution is more irregular.The material removal mechanism of the ultrasonic vibration assisted abrasive particle erosion was analyzed and the volume of material removal was modeled. An explicit dynamic FEM analysis was conducted to investigate the contact behavior of the erosion process in the ultrasonic assisted AWJ machining, the influences of the ultrasonic vibration on the contact status, the erosion rate and the stress field in the workpiece material. Under the vibration conditions, the results showed that the erosion rates are always higher than those under the non-vibration conditions. Moreover, the contact force magnitudes are higher and the duration time of the contact is remarkably increased, while the velocity of the particle during erosion process is reduced considerably. The influences of the vibration on the erosion rates of multiple particles under partially overlapping and fully overlapping conditions were also investigated respectively. The results indicated that the erosion rates under vibration conditions are higher. The compressive residual stress is generated after the erosion under partially overlapping condition. Smoothed particle hydrodynamics (SPH) is used to simulate the erosion process. The results suggested that the application of ultrasonic vibration can effectively improve the erosion rate due to the dynamics variation of the erosion process. The experiment of the ultrasonic assisted erosion by single abrasive particle was conducted. In the same impact angle, the results showed that the depth of the scratch under the vibration condition is larger.The analytical model of the polished surface roughness in UVA-AWJP was established. The optimization model of the processing parameters in UVA-AWJP was built by using the quadratic response surface methodology. The results showed that the analytical model can predict the polished surface roughness well. The polished surface is generated by erosion scratches of a large amount of abrasive particles, thus the material is removed in ductile mode and the inherent surface topography characteristics such as micro flaws and peaks are completely removed. The application of the ultrasonic vibration can improve the material removal rate and the processing efficiency. The Ra value of the surface polished by UVA-AWJP is generally a little higher than that of AWJP, which can be attributed to the larger erosion depths of the particles. Due to the relative motion of the impact particles against the vibrating workpiece, the scratching arrays are not so uniformly as those of AWJP and interact with each other on the surface polished by using UVA-AWJP; according to the response surface, the impact angle, the abrasive particle diameter, the water pressure, the interactive effect between the pressure and the impact angle, the particle diameter and the ultrasonic power, the impact angle and the ultrasonic power have great influences on the surface roughness.