STUDY ON ABRASIVE FLOW MACHINING OF CAST IRON

Abstract

In AFM process there is a mixture of abrasive particles and a polymer based carrier in a typical proportion which is extruded under pressure through or across the surface to be machined. The media acts as a flexible brush which is responsible for carrying out the cutting action. AFM is very effective for internal and complicated surfaces. A number of improved versions of AFM have been developed to enhance the material removal rate during machining, to machine the intricate shape and for faster reduction of surface roughness. In the present study, a drill bit assisted AFM process is used. In this process a stationary drill bit of a particular shape is held inside the work piece. Drill bit performs two functions; firstly it increases the pressure of media and secondly it provides a particular kind of flow. A particular kind of flow is the combination of three flows (straight reciprocating motion, flute flow along the profile of the drill bit and scooping flow), selfdeformability of the medium leading to intermixing of abrasives in the finishing region and the presence of an additional force on the abrasives that result in more material removal rate and high surface finish. In the present investigation, three profiles of drill bit - a spline, two-start and three- start helical profile have been used for experiments and to study the effect of these profiles on various response parameters such as reduction of surface roughness and material removal of workpiece (Cast Iron). L9 orthogonal array based on the Taguchi method has been used to study the effect of the drill bit and other main AFM process parameters. The main parameters are shape of the drill bit rod (H), number of cycles (n) and extrusion pressure (p) that have been selected at three levels considering no interaction among them. All the three process parameters have significant effect on the material removal rate and the result shows type of drill bit has maximum contribution. For reduction of surface roughness, the process parameters extrusion pressure and number of cycle are significant with the latter having maximum contribution whereas type of drill bit has been found to be insignificant. The experimental results show the maximum improvement in surface finish is 28.12% on the inner cylindrical surface of the cast iron work piece with the initial roughness 6.2 micron and the final value being 4.45 micron.