PROCESS MODELING OF ECH WITH FEM

Abstract

This thesis reports the process modelling of Electrochemical honing with FEM. Gears which run at high speed and transmit large forces may be subjected to additional dynamic forces due to errors in tooth profile. Therefore, the gear teeth must be smooth and error free. These errors may be reduced significantly by finishing the tooth profiles. Several types of conventional gear finishing processes are available to improve the quality of gears. But the finishing that can be obtained and productivity of these conventional processes is low which led to the evolution of advanced finishing process of gears like electrochemical honing (ECH). ECH is a hybrid electrolytic micro finishing technology characterized by a distinct coupling of electrochemical machining (ECM) and conventional honing processes to provide controlled functional surface generation capability of honing and fast material removal capability of ECM in a single operation. It can produce surface roughness as low as 0.05 gm while material removal rate is 2-8 times higher than conventional processes. I In the present work, a new setup for ECH of spur gears has been developed by designing and fabricating a tooling system and its various components. The experimental investigations involved studying the effects of three key input parameters namely finishing time, current and rotating speed on the measure of ECH process performances namely percentage improvement in average surface roughness (PIRa) , percentage improvement in maximum surface roughness (PIR) and amount of material removed (MR). The Experimentation, consists of three-phases: pilot experimentation, main experimentation, and confirmation experimentation. Pilot experiments were conducted to study the time dependent behaviour of ECH to fix the finishing time and to fix the composition of electrolyte for main experiments. Based upon the pilot experiment results, range of 2-6 minute for finishing time and 75%NaCI + 25 % NaNO3 as electrolyte composition was fixed for the main experimentation. Main experimentation was designed using Box-Behnken approach of Response Surface Methodology (RSM) in which finishing time, current, and rotating speed of the workpiece were varied in the ranges of 2-6 min, 10-30 A and 50 — 80 rpm respectively. Development of regression models and their statistical analysis including ANOVA, for the responses have been done with the help of Design-Expert 6.0.8. software to study the main and interaction effects of the process parameters on measures of process performances. Optimum combination of the process parameters has been found using the desirability analysis. Confirmation experiments have been conducted to validate the regression models. Micrographs are taken using Wyko NT 1100 interfaced with Vision®32 software to study the surface roughness values before and after the process. Results of confirmation experiments shows that at the optimum setting of input process parameters, the process can provide 77.6% PIRa, 83.86% PIR,,n and material removal upto 1024.62 mg. SEM n photographs were taken before and after the experiments to identify the improvement of work surface after ECH process. SEM images have revealed that ECH produces a surface having uniform structure and free of scratches and micro-cracks. The modelling and simulation of the material removal due to honing is performed by finite element approach. A Comparison of actual and modelled MR shows that the developed finite element model can be used to predict the values of material removed by honing in ECH. iv