Modeling and Experimental Investigations of Novel Magnetorheological Finishing Process for Blind Hole Surfaces

Abstract

In modern high performance machinery, parts which are highly finished and dimensionally accurate play a vital role. Surface finish enhances characteristics like wear, corrosion, pitting and oxidation resistance of the surfaces. A novel magnetorheological polishing process using permanent magnets is developed to finish the internal and bottom surfaces of blind hole cylindrical workpiece. The process is capable of finishing the internal cylindrical and flat bottom surfaces of tubular and non-tubular shaped blind hole workpiece. Finishing of blind hole surfaces find extensive application in dies and automotive components such as automobile actuators, cylinder body, valve seats etc. In this study two different tools for finishing the internal and flat bottom surfaces of blind hole cylindrical workpiece have been developed. The causal factor for material removal in the form of micro-chips is abrasive wear. The present study focuses on the calculation of forces acting on abrasive particles and mathematical modeling and simulation of surface roughness. The performance of both newly developed tools for finishing the cylindrical blind hole mild steel workpiece is evaluated. After 275 finishing cycles, the Ra values improved by 55.2% in internal cylindrical ferromagnetic workpiece and by 53.33% after 75000 cycles in flat surface of ferromagnetic blind hole workpiece. The theoretical and experimental values of surface roughness are found to be consistent. The experimental surface roughness values of blind hole internal cylindrical surfaces are within 6.26 % of theoretical values whereas in finishing blind hole bottom surface it is found within 7.9% of theoretical values. The factors influencing finishing performance of both tools is also investigated for finishing P20 tool steel having 41 Rockwell C scale hardness. Response surface methodology using central composite design has been utilized for design of experiments and regression analysis. The effect process parameters like rotational speed, reciprocation speed, abrasive volume percentage and abrasive mesh size on percentage change in surface roughness has been studied and optimized. Rotational speed has significant effect on percentage change followed by abrasive volume, reciprocation speed and abrasive mesh number in surface roughness during finishing of internal cylindrical blind hole workpiece. During the finishing of bottom flat surfaces of blind hole workpiece rotational speed is the most significant parameter followed by abrasive volume and abrasive mesh number. Experimentation at optimized parameters (RPM = 700, reciprocation speed = 35 cm/min, abrasive volume % = 30 and abrasive mesh number 1000) results in final surface finish of 83 nm on internal cylindrical surface whereas at optimized parameters (RPM = 600, abrasive volume % = 30 and abrasive mesh number 1000), 93 nm of surface finish is obtained on bottom flat surface of blind hole workpiece.