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Effect of the Process Parameters on the Surface Roughness during Magnetic Abrasive Finishing Process on Ferromagnetic Stainless Steel work-pieces

ABSTRACTStudy of new and cost effective finishing processes has always been an area of keen interest to overcome the difficulties of existing finishing process. Magnetic Abrasive Finishing (MAF) is a process in which a mixture of non-ferromagnetic abrasives and ferromagnetic iron particles is used to do finishing operation with the aid of magnetic force. The iron particles in the mixture are magnetically energized using a magnetic field. The iron particles form a lightly rigid matrix in which the abrasives are trapped. This is called Flexible Magnetic Abrasive Brush (FMAB), which when given relative motion against a metal surface, polishes that surface.The major studies concerning MAF have been done regarding the behaviors of the process under the effect of various parameters like working gap, mesh number of abrasive, speed of relative motion on cylindrical and flat work-pieces taking one type of material, non-ferromagnetic or ferromagnetic only. But limited comparative study by taking stainless steel with ferromagnetic behavior has been done to analyze the surface roughness that is generated during the process.

This paper has aim of development of Magnetic Abrasive Finishing Process & studying the effect of the process parameters (percent composition of iron powder, mesh number of abrasive and current) on the surface roughness during MAF of ferromagnetic S.S. work-piece material for flat work-pieces. The results of the experiments are statistically analyzed using design expert v.7 software for the responses generated during the process.In case of ferromagnetic work-piece, percent composition of iron powder has more effect than the other parameters. With increase in mesh size of abrasive, percent improvement in surface roughness increases. With increase in current the percent improvement in surface roughness value increases much more than the other parameters, therefore effect of applied current is seen to the most significant amongst all the parameters.

A. Working PrincipleThe working gap between the work piece and the magnet is filled with magnetic Abrasive particles (MAP), composed of ferromagnetic particles and abrasive powder. MAP is prepared by sintering of ferromagnetic particles and abrasive particles.The magnetic abrasive particles join each other along the lines of magnetic force and form a flexible magnetic abrasive brush (FMAB) between the work piece and the magnetic pole .This brush behaves like a multi-point cutting tool for finishing operation. When the magnetic N-pole is rotating, the Magnetic Abrasive Finishing Brush (MAFB) also rotates like a flexible grinding wheel and finishing is done according to the forces acting on the abrasive particles. .In external finishing of cylindrical surface, the cylindrical work piece rotates between the magnetic poles, with the MAP filled in both the gaps on either side (Fig 1). Whereas in internal finishing of cylindrical surface, the work piece rotates between the magnetic poles and the MAP .as shown in Figure 2. The magnetic field generator can be either electromagnetic coils or permanent magnets. The relative motion between the induced abrasive particles of the FMAB and work piece generates the necessary shearing action at the abrasivework-piece interface to remove material from the work-piece in the form of miniature chips.

II. LITERATURE REVIEWChange in the strength of magnetic field in the direction of the line of magnetic force near the work-piece surface will actuate the magnetic abrasive particle. The effective way of changing the force/finishing pressure and rigidity of MAFB is through the change in diameter D of magnetic abrasive particle. Hence, ferromagnetic particles of several times the diameter of diamond abrasive d are mixed to form the magnetic abrasive brush. MAF is affected by the material, shape and size of the work-piece, and shape and size of the magnetic pole. Pressure increases with increase in flux density and decreases as the clearance gap between tool & work-piece increases. Larger the particle size, poorer the finishing (except for 50m particles) but higher is the stock removal which increases linearly with finishing time [1].The surface roughness is predicted as a function of finishing time by a model that has been derived from the removed volume of material. Thus, it is possible, from the surface-roughness model, to predict the time when existing scratches are completely removed [2]. The magnetic force acting on the magnetic abrasive, controlled by the field at the finishing area, is considered the primary influence on the abrasive behavior against the inner surface of the work-piece. [3].