Yanzhen Yang

This study proposed a new magnetic abrasive finishing (MAF) method, in which a 6-axis robot with a magnetic machining tool was used to polish the inner surfaces of curved tubes. We have also developed a magnetic machining tool jig, which can be fixed at the front of the 6-axis robot, rotating freely and suitable for polishing the inner surfaces of curved tubes. In this study, we focused on investigating the machining parameters in the initial machining stage and precision finishing stage. Based on the characteristics of machining parameters, a multi-stage MAF process was conducted to obtain an inner surface with high quality and high efficiency. The experimental results showed that both the roughness Ra and Rz of inner surface in the initial machining stage significantly decreased with the increase in the mixed magnetic abrasives, to as low as less than 20 nm Ra in the precision finishing stage when the machining parameters were appropriately adjusted. In addition, the roughness Ra of inner surface could be further reduced to less than 10 nm Ra in the multi-stage MAF process. Finally, the magnetic flux density cloud map and the magnetic field line distribution map were analyzed in Ansys Maxwell.

A liquid mercury target, which is used to explore the neutrons produced by spallation reactions, has been installed at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). As the proton beams bombard the target, pressure waves are generated on the interface between liquid and solid metals due to thermal shock. The negative-pressure-induced cavitation causes severe pitting damage to the vessel surface of the mercury target. To reduce the surface damage of the mercury target and prolong its service life, we developed vibratory horn experiments in bubbly water. In this study, the effect of microbubbles on cavitation damage on the workpiece surface was investigated using ultrasonic erosion tests. Experimental results showed that surface damage was significantly reduced under the condition of injecting microbubbles. Additionally, we developed a simulation code to analyze the change in pressure waves in the water. The analysis results showed that the pressure amplitude of the pressure waves was significantly reduced under the condition of injecting microbubbles, and the fluctuation of the pressure waves became more regular when injecting microbubbles. We also found that the pressure amplitude of the pressure waves was decreased with a decrease in the diameter of the microbubbles.

This paper proposes a novel magnetic abrasive finishing (MAF) process that uses an auxiliary magnetic machining tool for the internal surface finishing of a thick-walled tube. The auxiliary magnetic machining tool and external poles form a closed magnetic field circuit. Thus, a stronger magnetic force can be generated during the process. In the current study, we focus on analyzing the distribution of the magnetic field and magnetic flux density and investigating the finishing characteristics of a mixed magnetic abrasive finishing process and speed of relative revolutions. Based on the finishing characteristics, we also conduct a stage-by-stage finishing process by changing the combinations of the mixed magnetic abrasive finishing process. The finishing quality of the internal surface was mainly evaluated by the measured roundness and surface roughness. The experimental results show that the roundness and surface roughness Ra are affected when the total amount of WA abrasive and iron powder is too much; a better surface roughness could be obtained when the difference in the speed of relative revolutions is considerable, but the roundness is the worst. Furthermore, the original roundness measurement of 270 µm can reach 10 µm, and the surface roughness Ra can increase from an original surface roughness of 4.1 µm to reach 10 nm after 105 min of the stage-by-stage finishing process.