Investigations on the performance characteristics of straight Bevel gears by Pulsed Electrochemical Honing (PECH) process

Abstract

Conical gears are used for transmitting power and/or motion between the intersecting shafts (i.e. straight and spiral bevel gears) or the non-parallel non-intersecting shafts (i.e. hypoid gears). Among these straight and spiral bevel gears are extensively used in the automobiles, aerospace, marine, machine tools, construction machinery, wind turbine, equipment used in the process, cement, steel, oil and gas industries, etc. Increasing demands of gears have motivated researcher to investigate and improve their performance characteristics using different conventional and advanced gear finishing processes. Performance characteristics of a gear include its load carrying capacity, service life, operating performance, surface characteristics, wear characteristics, transmission characteristics and noise generation characteristics. Most of the performance characteristics of gear namely service life, operating performance and characteristics related to wear, transmission and noise generation are significantly affected by surface characteristics of a gear. It has two major components namely (i) surface quality which includes surface finish, micro-geometry (i.e. form and location errors) and wear characteristics; and (ii) surface integrity that encompasses microstructure, micro-hardness and residual stresses.Improving surface characteristics of the bevel gears is very challenging and difficult due to complex geometry of their teeth. Gear grinding and lapping are the most commonly used conventional processes for finishing the bevel gears. But, these processes have some inherent limitations. Gear grinding is expensive in terms of initial investments and regular maintenance of the grinding wheels. It is laborious and highly skilled operator is required to perform the finishing operation. Also, form or generation grinding by a single formed wheel (or two single formed wheels) is time consuming. Moreover, Karpuschewski et al. (2008) highlight that it can also lead to undesirable effects such as (i) transverse grind lines on the finished surface which cause noise and vibration of the gears, (ii) grinding burns which damage the surface integrity of the ground gears and can sometime lead to even gear failure through tooth breakage. While, gear lapping is very slow finishing and used to finish a conjugate pair of gears. It can rectify only minute deviations from the desired gear tooth profile. Moreover, longer lapping cycle may affect the tooth flank profile and thus extensive care during the operation is required.It is evident that non-overlapping and limited capabilities and inherent limitations of the conventional processes of gear finishing do not allow a single process to simultaneously improve all the surface characteristics of any gear material and without inducing anyadverse effect. Most of the time, a combination of conventional finishing processes is required to achieve the required surface quality which become very time consuming and laborious and affects the requirement of high productivity. These limitations can be overcome by developing a non-contact, material hardness independent, more productive, more economical and a sustainable gear finishing process.