INVESTIGATION OF EJD PROCESS FOR DEEP MICROHOLE DRILLING

Abstract

This thesis reports about the experimental investigations on precision machining of nickel- chromium based alloy Incoloy 330 by electrolytic jet drilling process, one of the variant of electrochemical machining (ECM) process. In EJD, the acid electrolyte is passing under pressure through glass tube nozzle, coming jet acts as cathode and work piece as anode. Material removal takes place when stream of electrolyte strikes work piece causing removal of metal ions from work piece. In the present work the existing experimental setup for EJD has been modified to change feed rate with the help of gear reduction unit. The experimental investigations involved studying the effects of three key input parameters namely voltage, electrolyte concentration, and feed rate, on the measure of EJD productivity namely material removal rate (MRR) and the measures of hole quality characteristics radial overcut (ROC) and hole taper. Experimental plan involved two phase experiments: pilot and main experiments. Pilot experiments were conducted to study the effect of stand-off distance and electrolyte pressure on EJD process in order to fix their value by varying one parameter at a time. Based upon the pilot experiment results, 2.0 mm stand-off distance and 55 psi electrolyte pressure is fixed for the main experiments. Main experiments were designed using Box-Behnken approach of response surface methodology (RSM) in which applied voltage; feed rate and electrolyte concentration were varied in the ranges. Development of regression models and their statistical analysis including ANOVA, for the three responses namely MRR, ROC and hole taper was done with the help of design-expert 6.0.8 software. Study of the main effects and interaction effects of the variable process parameters on the responses has been done. Optimum combination of the process parameters has been found using the desirability analysis. Confirmation experiments have been conducted to validate the regression models and optimum values of the process parameters. It is observed that MRR increases with feed rate and electrolyte concentration. No significant interaction effects have been observed at the optimum setting of parameters. The present study shows an improvement of material removal rate obtained, with decreasing radial overcut