Effects of Ultrasonic Assisted Magnetic Abrasive Finishing on Surface Integrity of Titanium Alloy

To study the effect of ultrasonic assisted magnetic abrasive finishing (UAMAF) on the surface integrity of titanium alloy, a method of combining comparative experiment with theoretical analysis by the established cutting force and material removal model was employed. The surface topography, roughness, micro-hardness, residual stress and subsurface structure of the titanium alloy after UAMAF were analyzed, and the mechanism of ultrasonic in machining was discussed. Results show that the surface roughness (Ra) can be decreased to 0.075 mu m after 40 min of machining, under the conditions of ultrasonic frequency of 21.91 kHz, amplitude of 10 mu m, spindle speed of 1000 r/min, machining gap of 1.5 mm and magnetic abrasive particle size of 300 mu m. The surface roughness can be reduced by nearly 60%, compared with magnetic abrasive finishing (MAF). The additional ultrasonic increases the cutting force and material removal rate, therefore the surface roughness of UAMAF is reduced rapidly due to the vertex effect in the machining. Meanwhile, due to the impact of ultrasonic vibration, the surface is more uniform and smooth after UAMAF. A grain refined layer of nearly 20 mu m is formed in the sub-surface and the surface micro-hardness can reach up to 450.6 HV0.2, which is about 15% higher than that of MAF. The surface residual stress of titanium alloy changed from the tensile stress of +68 MPa after MAF to the compressive stress of -34.1 MPa after UAMAF. The surface integrity and comprehensive performance of workpiece are effectively improved by UAMAF.