Parametric Analysis of Permanent Mould Material EN31 Steel using Ball End Solid Rotating Core Magnetorheological Finishing Process

Abstract

Most plastic products are produced by the process of permanent mould casting as it is the most efficient and economical process. In some plastic product applications, aesthetics and surface topography play a vital role and in such cases the surface roughness of the permanent mould directly affects the final product. For such plastic products, those are to be produced by the process of permanent mould casting, the permanent mould being used, should have its surface roughness value as low as possible. EN31 is one of the most widely used materials for permanent mould manufacturing. Being hard, the mould manufactured using EN31 material is very tough to finish. The existing traditional process for finishing the moulds using die grinders make the process of finishing a very tedious task. Recently developed ball end magnetorheological finishing process has demonstrated its feasibility in finishing of flat as well as 3D surfaces of various materials. In the present work, its potential advantages have been used to finish hardened EN31 steel. The response surface method has been used to obtain the optimized parameters that can be used for finishing of hardened EN31 material. For the experimentation, the ball end solid rotating core magnetorheological finishing process has been used. The effects of five different variable parameters, that are, current, tool rotation, feed, abrasive concentration and carbonyl iron particles concentration on the percentage change in roughness value have been examined. Each variable parameter has 5 levels and these levels were decided on the basis of previous literature and preliminary experimentation conducted. Current was varied from 1 A to 5 A, tool rotation from 700 rpm to 2300 rpm, feed from 10 mm/min to 50 mm/min, abrasive concentration from 10 % to 30 % and CIP concentration from 10% to 30%. It was observed that maximum contribution was given by CIPs followed by tool rotation, abrasive concentration, current and feed. The minimum average roughness value obtained was 30 nm at 2A current, 1900 rpm tool rotation speed, 40 mm/min feed rate, 25 vol. % abrasive concentration and 25 vol. % CIP concentration in a given time of 60 minutes. After parametric optimization, the average surface roughness obtained was 24 nm at 2A current, 2300 rpm tool rotation, 50 mm/min feed, 15 vol. % abrasive concentration and 30 vol. % CIP concentration in just 40 minutes. Scanning electron microscope was also used for studying the surface morphology.