EXPERIMENTAL INVESTIGATIONS INTO PULSED MAGNETORHEOLOGICAL FINISHING OF HARD METAL

Abstract

Ball end magnetorheological finishing (BEMRF) is a high level nanofinishing process used to finish different kinds of surfaces include flat, two dimensional and three dimensional and curved surfaces. The preliminary experiments have been conducted on EN-31 flat work-piece surface using DC power supply with and without pulse at magnetizing current (MC) 2.5 A, feed rate 50 mm/min, working gap (WG) of 1.5 mm and rotational speed of the tool (RST) 500 rpm. The preliminary study has been carried out to analyze the effect of Duty cycle on the response percentage reduction in surface roughness (%∆Ra). It has been observed that an improved %∆Ra has been found with the use of pulsating DC power supply as compared to %∆Ra obtained with DC power supply without pulse at same process parameters. Taylor Hobson surface analyzer instrument was used with cut-off length 0.8 mm and data length of 4 mm to measure the surface roughness before and after pulsed ball end magnetorheological finishing (PBEMRF) process. The surface roughness has been measured initially after grinding of work-piece samples and then after finishing of work piece through BEMRF process. After conducting the preliminary experiments, the detailed experimental study has been conducted with PBEMRF at 0.16 duty cycle. The statistical analysis was done to analyze the effect of various process parameters on %∆Ra using response surface methodology (RSM). The maximum predicted %∆Ra has been found as 55.52% through actual regression equation at optimum process parameters 3.5A magnetizing current, 30 mm/min feed rate, 0.5mm working gap and 700 rpm rotational speed of finishing tool. The experiment was conducted on PBEMRF process at optimum process parameters. The value of %∆Ra obtained through experimentation was found to be 51.23% which is close to the predicted value of %∆Ra with error of 4.29%. xviii The residual stress plays an important role on finished components. The performance of the machine component can be improved with reduction of residual stress. The residual stress and surface finish play an important role in overall efficiency and durability of the components. The present work is aimed to relieve the residual stress of work-piece surface with the improvement in surface finish using pulse DC power supply in BEMRF process. The preliminary experiments have been conducted at magnetizing current (MC) of 2.5A, Feed rate (F) 50 mm/min, tool rotational speed (RST) 500 rpm, and working gap (WG) 1.5 mm on flat EN-31 steel in finishing time 30 minutes with and without pulse DC power supply. The residual stress of grinded EN-31 surface before experimentation and of finished surface after experimentation on BEMRF process has been measured with X-ray residual stress analyzer using Cosα method. It has been observed that the residual stress was found reduced from 122 to 78 MPa after finishing with BEMRF process using DC power supply without pulse while residual stress was reduced from 102 to 55 MPa after finishing with BEMRF process using pulse DC power supply at 0.16 duty cycle. After preliminary experimentation, the statistical analysis with design of experiment has been conducted with pulse DC power supply using 0.16 duty cycle to visualize the effect of various process parameters on residual stress. The maximum predicted %∆RS of 70.35% was found at optimum process parameters 3.5A current, 30 mm/min feed rate, 700 rpm tool rotational speed and 0.5 mm working gap while maximum experimental %∆RS was found as 64.70% which is very close to predicted %∆Ra with error of 5.65%. The residual stress was found reduced from 119 to 42 MPa after finishing with BEMRF process at optimum process parameters using pulse DC power supply