EXPERIMENTAL INVESTIGATIONS ON MAGNETIC ABRASIVE FINISHING PROCESS

Abstract

Magnetic abrasive finishing is a prevalent advanced method which by applying gentle forces using flexible magnetic abrasives for removing surface irregularities, provides a micro/nano range of defect-free surface finish. During magnetic abrasive finishing, magnetic forces allow the flexible magnetic abrasive particles to shear off the material from the surface in the form of microchips. In industries, MAF is highly recommended where zero or negligible post-process surface defects are an obligatory requirement. During the finishing of a material having high hardness value such as titanium alloy, nimonic alloy, and ceramics, etc., it is necessary to choose a proper magnetic abrasive considering the rate of improvement required in the surface finishing. Owing to the exceptional mechanical properties of Ti-6Al-4V, it is widely utilized in numerous critical mechanical parts for the uncompromised factor of safety. However, performing machining operations on this alloy in close tolerance is a challenging task. Moreover, establishing a process for its efficient finishing has become the interest of researchers. In the same context, process optimisation is essential for making it commercially viable. This research work mainly presents three phases of study considering the gaps found from the extensive literature survey. In the first phase a new magnetic abrasive has been developed, which is suitable for finishing of Ti-6Al-4 V. The sintering method was used to develop the magnetic abrasive, and hence the developed magnetic abrasive has been named as sintered magnetic abrasive (SMA). A mixture of abrasive powder of aluminium oxide and silicon oxide (Al2O3-SiO2) with carbonyl iron particles (ferromagnetic material) has been taken as components of sintered magnetic abrasive. The authors have studied the morphology of the sintered magnetic abrasive by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction technique. The findings reveal that the abrasives were uniformly and tightly rooted in the carbonyl iron particles. Also, magnetic abrasive finishing roughness studies on the Ti-6Al-4 V workpiece were carried to evaluate the performance of SMA. Change in the surface roughness from Ra = 1.14 μm to Ra = 0.85 μm were observed and atomic force microscopy (AFM) of the finished surface confirms an excellent finishing effect by the developed sintered magnetic abrasive on Ti-6Al-4 V during magnetic abrasive finishing. The second phase of study comprises a novel a robust modelling and optimisation tool i.e., artificial neural network and genetic algorithm (ANN-GA) that is applied to scrutinise and improve the performance of the magnetic abrasive finishing of stainless steel SS302 which focuses to find

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its applicability on MAF process. In addition, the results from ANN-GA modelling and

optimisation have been compared with conclusions drawn from conventionally used Taguchi- ANOVA analysis. An L27 non-orthogonal array design has been opted for as per machining set- up restriction. Abrasive size, voltage, machining gap, and rotational speed were the design

variables considered in the present research work. It was found that the parametric design used in this study provides a straightforward, methodical, and proficient method of modelling and optimisation of change of surface roughness or finishing behaviour during theme process. Modelling and optimisation done with ANN-GA show a maximum value of change of surface roughness equal to 0.256 μm, which is 7% better than the result obtained from Taguchi-ANOVA analysis. In the third phase of this research study, the magnetic abrasive finishing process (MAF) has been studied using the ANN-GA approach, where ANN has been used for modelling of input– output relations, and GA has been used to optimize the MAF process. The experiments were conducted on a pulsating DC sourced MAF set-up, and SiC-based loosely bonded magnetic abrasive media was used for material removal. During experimentation, the current, machining gap, speed of rotation, abrasive composition, and finishing time were taken as input parameters being arranged in an array of L16orthogonal. In contrast, output parameters were changed in surface roughness, change in the microhardness, and change in the modulus of elastic indentation. ANN-GA approach provides a set of optimal solutions for obtaining suitable output values. Furthermore, loosely bound SiC-based magnetic abrasive media and its composition is found to be a very critical factor for the performance of the finishing quality on Ti-6Al-4V.