Investigations on microgeometry of meso bevel and meso helical gears manufactured by WEDM process

Abstract

This article reports about investigations on microgeometry of meso bevel and meso helical gears manufactured by wire electro discharge machining (WEDM) process. Effects of eight WEDM parameters (namely, peak current, pulse-on time, pulse-off time, servo-gap voltage, wire feed rate, wire tension, dielectric pressure and percentage cutting speed) on single pitch error and total pitch error for meso bevel gear and total profile error and total pitch error for meso helical gear were studied. A total of 31 experiments for meso bevel gear and 31 experiments for meso helical gears were conducted using one-factor-at-time approach to identify optimum ranges/values of the eight WEDM parameters for further experiments. It revealed existence of optimum ranges of servo-gap voltage, pulse-on time, pulse-off time, and percentage of the cutting speed to minimize microgeometry errors in meso bevel and helical gears and that use of higher values of peak current, wire feed rate, wire tension, and dielectric pressure yields better quality of meso bevel and helical gears. The best quality meso helical gear has better quality (DIN 6, DIN 6, and DIN 8) than the best quality meso bevel gear (DIN 7, DIN 7, and DIN 10) for single pitch error, total pitch error, and radial runout; whereas for successive pitch error, reverse is true. Meso helical gear has better surface finish (Ra 1.1 μm and Rmax 7.3 μm) than meso bevel gear (Ra 1.3 μm and Rmax 8.0 μm). Examination of tooth profiles of the best quality meso gears by scanning electron microscopy revealed that they have uniform tooth profiles that are free from burrs, nicks, asperities, dimples, undercutting at the root, and sharp edges on both end faces of the gears. It also revealed that tooth flank surfaces are free from micro-cracks, pores, and globules. The present work proves that WEDM has potential to be a better alternative for manufacturing better quality net-shaped meso bevel and helical gears which will not require any further post-manufacturing processing. © 2017, Springer-Verlag London Ltd.