INVESTIGATION ON PRECISION FINISHING OF GEARS BY-ELECTROCHEMICAL HONING

Abstract

Machining processes produce finished products with a high degree of accuracy and surface quality. Conventional machining utilizes cutting tools that must be harder than the workpiece material. The use of difficult-to-cut materials encouraged efforts that led to the introduction of the nonconventional machining processes that are well-established in modern manufacturing industries. The need for higher machining productivity, product accuracy, and surface quality led to the combination of two or more machining actions to form a new hybrid machining process. The development of a hybrid machining process is mainly to make use of the combined advantages and to avoid or reduce some adverse effects the constituent processes produce when they are individually applied. Honing is described as a controlled, low velocity abrasive machining, which is applied primarily to generate the final functional characteristics, variety of geometries and surface character on load-bearing or sealing surfaces. Electrochemical honing (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 and fast material removal capabilities in a single operation. ECH can offer a unique range of benefits to the machined surface which cannot be obtained by either of the processes when applied independently. The ability of ECH to apply these benefits productively, has led to its widespread use in industries, especially in aerospace, automobiles, petrochemical reactor, roller and gear manufacturing industries. High quality gear finishing ensures smooth operation of gears in high speed transmission systems. As conventional methods used for gear finishing like gear grinding, gear honing and gear lapping are associated with low productivity and high costs, quest for more advanced methods is inevitable. ECH of gears because of its high productivity, accuracy and limited accumulative error is a good alternative to these conventional methods. Experimental setup for ECH of spur gears has been designed and fabricated. The design includes the tooling system and machining chamber, and redesign of many components of the system. An existing setup for ECH of internal cylinders has been modified to obtain the required design. The present experimental studies focus on the identification of process performance characteristics and key input parameters. Pilot experiments were conducted to determine the ranges and levels of parameters. Experimental investigations were planned according to Taguchi's experimental design technique. L9 orthogonal array was selected and the experiments were conducted in different phases. In order to observe the time dependent behavior of ECH different surface characteristics such as variation patterns of percent improvements in surface roughness values Ra, Rt and Rt,,,, were studied while changing the processing time (PT) with fully randomized one-factor at a time experimental design. The surface roughness values Were measured by using optical profilometer. After determining the process parameters levels from the pilot experiments, in the next phase, experiments were designed using Taguchi experimental design techniques to observe the effect of key process parameters on the performance characteristics of electrochemically honed gears. The results were analyzed using ANOVA (analysis of variance), F-ratio and Duncan's multiple range quadratic trends. The optimal results for different process performance characteristics are reported and confirmed through confirmation experiments. In the third phase effects of key process parameters, namely, current (I), electrolyte concentration (E), electrolyte composition (C) and finishing time (T) were investigated for work surface characteristics. The surface characteristics include the Percentage Improvement in surface roughness values of Ra, Rt,,,, Rt and microhardness. Results confirm the process feasibility and indicate that current (I), electrolyte concentration (E), electrolyte composition (C) and finishing time (T) are critical process parameters. ECH has promising capability for achieving nano — finished surfaces featured with high uniformity of