Chemical assisted ball end magnetorheological finishing of aluminium 7075 alloy

Abstract

Areas like aerospace, solar, medical, electronics, optics widely use nano-finished or high precision aluminium alloys. These nano-finished aluminium alloys are being used as metal mirrors, micro-electronics devices, diaphragm in optical sensors etc. In general, aluminium alloys are finished by conventional processes such as grinding, lapping. However, to achieve nano-level finish on soft material like aluminium alloys which possess high malleability and ductility is difficult for traditional processes without producing high residual stresses, subsurface damage etc. In this work, the surface finish of aluminium 7075 alloy workpiece was improved using a novel finishing technique viz. chemical assisted ball end magnetorheological finishing (CA-BEMRF). To validate the results a comparison of % decrease in surface roughness obtained after ball end magnetorheological finishing (BEMRF) as well as achieved after CA-BEMRF process is carried out. Results showed a 1.84 % improvement in % decrease in surface roughness after CA-BEMRF process as compared to BEMRF without chemical assistance. The statistical and graphical effects of various changing process parameters on % decrease in surface roughness are addressed. Using analysis of variance (ANOVA) and the F-test, significant process factors impacting surface roughness during workpiece finishing are identified. Optimum value of % decrease in surface roughness has been found as 55.316 at magnetizing current 3.43amp, tool rotational speed 326.97 rpm and working gap of 0.74 mm. Confirmatory experimental tests have been conducted and results obtained were found very close to the predicted outcome. Scanning electron microscopy (SEM) of the workpiece finished using BEMRF process and CA-BEMRF technique are compared to assess the effects of magnetizing current, tool rotation and working gap on surface topography of machined surface.