超声辅助磁性磨料光整加工工艺对钛合金表面完整性的影响

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

为了研究超声辅助磁性磨料光整加工工艺对钛合金表面完整性的影响,采用对比试验和建立切削力和材料去除模型理论分析相结合的方法,分析加工后的表面形貌、粗糙度、显微硬度、残余应力和亚表面组织,并讨论了加工中超声的作用机理。结果表明:在超声频率为21.91 kHz、振幅10μm,主轴转速1000 r/min,加工间隙1.5 mm,磁性磨料粒径300μm条件下,经过40 min加工后,表面粗糙度Ra降低到0.075μm,与普通磁性磨料光整加工相比降低近60%。超声的引入,增大了切削力和材料去除率,由于加工的尖点效应,使超声辅助磁性磨料光整加工的表面粗糙度快速降低;同时超声振动的碰撞作用使加工后的表面更加均匀光滑,在亚表面可形成一层近20μm的组织细化层,表面显微硬度可达到450.6 HV0.2,与普通磁性磨料光整加工相比提高了15%,表面残余应力由普通磁性磨料光整加工的+68 MPa的拉应力变为–34.1 MPa的压应力,可有效改善工件表面完整性,提高加工表面的综合性能。

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 μm after 40 min of machining, under the conditions of ultrasonic frequency of 21.91 kHz, amplitude of 10 μm, spindle speed of 1000 r/min, machining gap of 1.5 mm and magnetic abrasive particle size of 300 μm. 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 μm 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.