EXPERIMENTAL INVESTIGATIONS ON MAGNETIC ABRASIVE FINISHING OF SS 304L

Abstract

Magnetic Abrasive Finishing (MAF) is a super finishing technique, employs the magnetic force and magnetic abrasive for finishing variety of engineering materials. This paper presents the development of experimental setup to carryout MAF operations in a flat Stainless Steel grade 304L material. Experimentation was planned according to Taguchi’s L16 (42) design of experimentation technique. The different cutting conditions selected for the investigations are: voltage applied to electromagnet, machining gap, rotational speed of electromagnet and mixing ratio (Fe+; Al2O3). Surface finish and percentage improvement in surface finish (%Δ Ra) were estimated after each experiment. From the experimental results it was found that the average surface finish value has been achieved as low as 0.09 µm.

Introduction

Finishing operations in manufacturing of precise parts are always of concern owing to their most critical, labour intensive and least controllable nature. Traditional fine finishing of precision components is a challenging and time consuming operation in manufacturing. High precision finishing methods are of utmost importance and are the need of present manufacturing scenario. Conventionally, premachined surfaces are subjected to finishing operations like grinding, super finishing, lapping, honing, etc. If properly carried out, these abrasive machining processes can produce a surface of higher quality with a controlled surface roughness combined with a desirable residual stress distribution and freedom from surface and sub-surface damages . New advanced finishing processes were developed in last few decades to overcome limitations of traditional finishing processes in terms of higher tool hardness requirement and precise control of finishing forces during operation.

The application of magnetic field in the control of manufacturing processes in general and finishing in particular has become of interest. Magnetic abrasive finishing (MAF) is a technology in which a magnetic field forms a magnetic abrasive tool composed of abrasive particles and possessing ferromagnetic properties. Some obvious MAF advantages over existing methods of abrasive finishing include (a) preliminary performance tools (grinding wheels, abrasive sticks and bells, and so on) are not necessary; (b) abrasive tools can be quickly replaced; (c) an abrasive tool can be reshaped without bond destruction when finishing ferromagnetic parts of machines of complicated shapes; and (d) because of the distance of the magnetic field, it is possible in some cases to treat inaccessible surfaces, for example, the inner surface of tubes . The schematic representation of the plane MAF process is shown in Figure 1.

Figure 1. Plane Magnetic abrasive finishing

The basic principle of the MAF process was studied by Shinmura et al and it was reported that material removal and surface finish value (Ra) increase as the magnetic abrasive particle diameter increases. Jain et al studied MAF of non-magnetic stainless steel with the use of loosely bounded MAPs has been carried out. It was concluded that working gap and circumferential speed of workpiece are the parameters which significantly influence the material removal and surface finish. Shinmura et al found that magnetic flux density and working gap greatly affect the surface roughness and stock removal. Further they reported that an experimental study on plane workpieces using the MAF process. They observed that the surface roughness value decreases with increasing finishing time upto a certain limit of time beyond which no further improvement was noticed.

Ching et al studied the magnetic abrasive finishing process in free-form surface operations using the taguchi experimental design, considering the effect of magnetic field, spindle revolution, feed rate, working gap, abrasive, and lubricant. By this study they revealed that MAF provides a highly efficient way of obtaining surface finish.

This paper deals with the design and fabrication of MAF Setup for plane surfaces. Using this setup, experiments have been conducted to evaluate the MAF process performance. The main objective of the present investigation is to study the effect of voltage applied to electromagnet, machining gap, rotational speed of electromagnet and mixing ratio (Fe+; Al2O3) on change in surface finish and percent improvement in surface finish specifically when using loosely bounded MAPs.