Effects of Helical Rod Profiles in Helical Abrasive Flow Machining (HLX-AFM) Process

Abstract

Abrasive flow machining (AFM) process is a fine finishing process employing abrasive laden self modulating putty for the finishing of mainly internal recesses. Though the AFM is suitable for the finishing of internal cavities, but the material removal is very low during this finishing process. Helical abrasive flow machining (HLX-AFM) has been recently developed to improve the machining efficiency of AFM process. This process employs a coaxially fixed helical twist drill-bit during the extrusion of the abrasive laden media through an internal cylindrical recess. The presence of a fixed drill-bit inside a cylindrical cavity of the work-piece results in considerable increase in material removal and improvement in surface finish. In the present investigation, the same HLX-AFM setup has been used and the effects of two more helical profile rods viz. a 3-start helical profile and a spline have been studied along with the helical twist drill-bit for improving the quality characteristics of material removal and percentage improvement in the surface roughness during the fine finishing of internal cylindrical surface of brass work-pieces. The experiments were planned according to L9 orthogonal array of Taguchi method and the optimal process parameters were selected. The employment of a rod with six splines and a 3-start helical profile results in improved finishing in comparison to the drill-bit profile, due to the presence of more number of flutes and grooves on the coaxially held stationary rods. The helical profile type has 3.75% contribution towards the percentage improvement in the surface roughness, but is not significant in affecting material removal. The presence of 3-start helical profile led to 61.40% improvement in surface roughness (from Ra - 1.3 μm to 0.5 μm) at optimal level with no effect on material removal, which means no extra machining is taking place. The parameter of abrasive-to-media concentration ratio (varying from 0.75 to 1.25) is the most contributing factor with 85.90% contribution toward suface finish improvement and 71.71% contribution towards material removal. The finishing performance of 3-start profile is 15% better than the standard helical drill-bit with no increase in the operating pressures. SEM micrographs corroborated the fact that 3-start profile led to more number of light abrasive cutting grooves and thus more surface finish. HLX-AFM with 3-start helical profile rods can be employed for the finishing, form corrections of internal cylindrical cavities of any size. Presence of the profile rod results in increase in the reduction ratio and thus more machining action. The developed process can also generate cross-hatch lay pattern on internal cylindrical surfaces.