Experimental study on polishing of fluid magnetic abrasives for the wire electrical discharge grinding surface of micro-shafts

The recast layers, discharge craters and micro-cracks on the micro-shaft surface fabricated by wire electrical discharge grinding (WEDG) can negatively affect mechanical properties and fatigue life in particular as micro tools. An online polishing method using fluid magnetic abrasives (FMA) is proposed to improve the micro-shaft surface quality. A polishing device is designed that uses two permanent magnets to apply an external magnetic field and changes FMA container thickness to adjust magnetic field strength in the processing area. The FMA polishing device is integrated into a micro-EDM machine tool with a WEDG function, and the micro-shaft can be polished online by moving the set trajectory in the FMA. A single-factor experiment was employed on tungsten material micro-shafts fabricated by WEDG to explore the polishing ability. The effects of micro-shaft diameter, magnetic field strength, polishing time, spindle speed, abrasive particle size, and motion trajectory were analyzed. After FMA polishing, the surface roughness Ra could be reduced from 0.1 mu m to below 0.05 mu m generally, and the minimum could be reduced to 0.019 mu m. Results show that the surface material removal was uniform and obvious. The tungsten micro-shafts had almost no deformation compared to before polishing, while the brass micro-shafts deformated obviously. After FMA polishing, the recast layer was significantly removed and the micro-shaft surface quality was improved, which was discovered by observing the surface topography. It proves that the online polishing of micro-shafts by FMA is feasible and valuable.

Automated summary

This paper proposes an online polishing method using fluid magnetic abrasives to improve the micro-shaft surface quality. A polishing device is designed and integrated into a micro-EDM machine tool. Experimental results show that the proposed method can effectively improve the surface quality of micro-shafts and remove recast layers.