Investigations on surface quality, surface integrity and specific energy consumption in finishing of straight bevel gears by PECH process

Abstract

Applications of electrochemical finishing (ECF) and its hybridization with the other mechanical processes are attracting the interest for finishing various engineering components due to their flexible behavior. Pulse electrochemical honing (PECH) is a hybrid finishing process which provides benefits of pulsed ECF and mechanical honing processes simultaneously to improve the surface quality and surface integrity of the workpiece components. The present study is aimed at studying the effects of the three most important PECH parameters namely applied voltage, electrolyte composition, and electrolyte concentration on the aspects of surface quality (i.e., surface roughness, waviness, material ratio curve), of surface integrity (i.e., wear indicators, microhardness, microstructure, and residual stresses), and of finishing productivity (i.e., material removal rate) of the straight bevel gears made of alloy steel (20MnCr5) by the PECH process. An aqueous mixture of non-passivating electrolyte (i.e., NaCl) and passivating electrolyte NaNO₃ was used as electrolyte. The three input parameters were varied at three levels to identify their optimum combination using preidentified optimum values of other process parameters. The identified optimum values are 75 % NaCl + 25 % NaNO₃ as electrolyte composition, 7.5 % as electrolyte concentration, and 8 V as applied voltage while finishing the bevel gears for an optimum duration of 6 min. Results have shown significant improvement in surface roughness (i.e., the average surface roughness value reduced from 2.84 to 1.03 μm; the maximum surface roughness value decreased from 24.59 to 6.06 μm; depth of roughness reduced from 13.51 to 5.42 μm) and surface waviness (i.e., average waviness reduced from 5.04 to 1.58 μm; maximum waviness reduced from 30.17 to 5.52 μm). Analysis of microstructure, residual stresses, material ratio curve, wear indicators, and microhardness of the PECH-finished gears also showed significant improvement in them compared to an unfinished gear. Comparative analysis of energy consumption in PECH and ECH processes found that PECH consumes 25 % less energy than the ECH process does for achieving the same level of finishing. The present work proves that PECH is a superior, productive, and more energy-efficient process compared to the conventional gear finishing processes and ECH process.