Optimization of process parameters affecting surface roughness in magnetic lapping with mixed-size abrasives

Abstract

The magnetic brush stiffness and density of magnetic lapping with single-size abrasives (SSA) is limited, thus a method of mixed-size abrasives magnetic lapping (MSA) of titanium alloy is proposed to improve the hardness and density of magnetic brushes. Mixing of large-sized magnetic abrasive (150 μm–250 μm) with other magnetic abrasive to form mixed magnetic abrasive, and the particle size ratio of small to large abrasives is denoted as a_psr. The optimal value of a_psr was obtained through one-factor comparative experiments of MSA, and the magnetic lapping mechanism of MSA was analyzed. The Taguchi experiment was used to explore the influence of each process parameter on the surface roughness of TC4 titanium alloy. Results show that: the surface texture of MSA treated titanium alloy is dense, and the scratches and pits on the initial surface of the workpiece were removed. However, there were still obvious new scratches when a_psr was relatively large (a_psr is 0.5), and the regular scratches on the surface were significantly reduced as the value of a_psr decreased. When a_psr is 0.25, the lapping performance of MSA is the best. At this time, there is no magnetic dipole force between the abrasive, which is conducive to the synergistic removal of large-sized and small-sized abrasives in MSA. That is, the material removal form in MSA is characterized as the synergistic effect of micro-cutting of large-sized abrasives and polishing of small-sized abrasives. The primary and secondary influence order of various factors on the surface roughness is: abrasive particle size, lapping gap, feed speed and rotational speed. Based on the optimized combination of process parameters (feed speed is 2 mm/min, rotational speed is 1000 rpm, lapping gap is 2 mm, and mixed particle size a_psr is 0.25, and the average surface roughness Ra dropped from 650 nm to 72 nm, which verified the feasibility of MSA process to realize the surface finishing processing of titanium alloy with high quality.