Experimental Investigations into Improved Finishing of Punch and Mould Materials using Solid Rotating Core Magnetorheological Finishing Process

Abstract

The need of finishing has drastically increased in order to obtain products with high quality and productivity. Chrome steel finds its application in the field of punch and dies because of its hardness which varies upto 62 HRC. This makes it possible to use chrome steel as punch for making bolt head, while tungsten carbide is used as a material for manufacturing injection mould used for producing various optical components such as magnifying glasses, cameras, microscopes, telescopes etc. In punching operation, the punch undergoes adhesive wear which can be controlled, if the surface roughness of the punch is minimized. The surface roughness plays an important role in determining the quality of product manufactured. The traditional method used for finishing chrome steel punch involves diamond lapping while CNC ultra-precision grinding is preferred for tungsten carbide in which machining marks and surface micro crakes are mostly observed. Further improvement in surface finish is required in order to overcome these defects. There are continuous development in magnetic field assisted advanced finishing processes. The present work is focused on improving the surface finish and productivity of chrome steel punch using modified solid rotating core magnetorheological finishing process. The final surface roughness value of circular tapered punch has been obtained as 22 nm from 408 nm in 90 minutes of finishing. Also, the investigations are made in order to determine the effect of process parameters on finishing of tungsten carbide workpiece using solid rotating core magnetorheological finishing process. Response surface methodology is used to perform screening of experiments in order to identify the significant parameters affecting the surface roughness of tungsten carbide. The process parameters used in the present work are concentration of diamond abrasives, magnetizing current, gap maintained between the workpiece surface and solid rotating tool core tip surface, and rotational speed of tool core. The analysis of experiments shows the optimum process parameters which include 4.5% of diamond abrasives, current of 1A, gap of 0.6 mm gap and 700 rpm rotational speed of tool core. The minimum surface roughness value obtained for tungsten carbide workpiece is as low as 51 nm from the initial value of 248 nm in 45 minutes of finishing by solid rotating core magnetorheological finishing process.