Effects of Different Hard Finishing Processes on Gear Excitation

Gearboxes are essential in mechanical drive trains for power transmission. A low noise emission and thus an optimized excitation behavior is a substantial design objective for many applications in terms of comfort and operational safety. There exist numerous processes for manufacturing gears, which all show different properties in relation to the process variables and, therefore, differences in the resulting accuracy and quality of the gear flank. In this paper, the influence of three different manufacturing processes for hard finishing—continuous generating grinding, polish grinding and gear skiving—on the surface structure of gear flanks and the excitation behavior is investigated experimentally and analyzed by the application force level. A tactile scanning of the gear flanks determines the flank surface structure and the deviations from the desired geometry. A torsional acceleration measurement during speed ramp-ups at different load levels is used to analyze the excitation of the gears. The results show only a minor influence of the surface structure on the application force level. The excitation behavior is dominated by the influence of the flank modification and its deviation from the design values.

Potentials of Vitrified and Elastic Bonded Fine Grinding Worms in Continuous Generating Gear Grinding

Continuous generating gear grinding with vitrified grinding worms is an established process for the hard finishing of gears for high-performance transmissions. Due to the increasing requirements for gears in terms of power density, the required surface roughness is continuously decreasing. In order to meet the required tooth flank roughness, common manufacturing processes are polish grinding with elastic bonded grinding tools and fine grinding with vitrified grinding tools. The process behavior and potential of the different bonds for producing super fine surfaces in generating gear grinding have not been sufficiently scientifically investigated yet. Therefore, the objective of this report is to evaluate these potentials. Part of the investigations are the generating gear grinding process with elastic bonded, as well as vitrified grinding worms with comparable grit sizes. The potential of the different tool specifications is empirically investigated independent of the grain size, focusing on the influence of the bond. One result of the investigations was that the tooth flank roughness could be reduced to nearly the same values with the polish and the fine grinding tool. Furthermore, a dependence of the roughness on the selected grinding parameters could not be determined. However, it was found out that the profile line after polish grinding is significantly dependent on the process strategy used.

Extended Calculation Model for Generating Gear Grinding Processes

Generally, hard finishing is the final step in manufacturing cylindrical gears. The most established processes for hard finishing are continuous generation grinding and discontinuous profile grinding [1]. Despite the wide industrial application of the continuous generation grinding process, only few scientific investigations exist. One possible reason for this are the complex contact conditions between tool and gear flank. Modelling the complex contact conditions between grinding worm and gear to calculate cutting forces, characteristic values as well as micro- and macroscopic gear geometry are the topics of this paper. The approaches are introduced and results for validation are presented and discussed.

Development of a Methodology for Analyzation of the Influence of Pitch Diameter Shift on the Generating Gear Grinding Process

In order to improve load carrying capacity and noise behaviour, case hardened gears are usually hard finished. One possible process for hard finishing of gears is generating gear grinding, which has replaced other grinding processes in batch production of small and middle sized gears due to high process efficiency. Especially generating gear grinding of large module gears with a module higher than mn > 8 mm can be challenging due to high process forces and the resulting excitation, which can influence gear quality negatively. TÜRICH suggested applying a pitch diameter shift during generating gear grinding to equal out the number of contact points between the left and right flanks of the gear with the grinding tool [1]. This qualitative approach is not sufficient to predict the process behaviour because it does not take the changing radii of the curvature of the involute into account and, therefore, the changing contact conditions along the gear profile. In this paper a methodology to quantify the influence of pitch diameter shift on the generating gear grinding process using a manufacturing simulation is introduced. Additionally this methodology is validated for one manufacturing test case.

A Methodology for Longitudinal Tooth Flank Crowning of the Helical Gear on a CNC Honing Machine

The gear honing is the most economical way for hard finishing an involute helical gear after hobbing and heat treatment or after shaving and heat treatment. The gear honing can also be applied to the modification of gear tooth surfaces to compensate for the distortions that occur during heat treatment process. Most published papers on the technology of gear honing describes on the principle of generated gear surface. However, the longitudinal tooth flank crowning of a helical gear with honing has not been investigated yet. Therefore, in this paper, we proposed a novel method for longitudinal tooth flank crowning of work gear surfaces by setting a crossed angle between the honing cutter and work gear axes as a linear function of honing cutter's traverse feed in the honing process. A mathematical model for the tooth profile of work gear honed by a standard honing cutter is also established. Three numeral examples are presented to illustrate and verify the merits of the proposed gear honing method in longitudinal crowning.

Coroning: High Performance Gear Honing Without Dressing

Gear honing with internally toothed tools was first used as a gear finishing process for improving unfavorable surface conditions of external cylindrical gears after grinding. Stock removal was minimal (less than 0.01 mm) and only dressable tools were used. From the beginning, the multi-directional surface structure created by gear honing was considered beneficial for gear noise performance. But limitations of the early machine and tool technology did not allow for more stock removal. For a long time gear honing represented an additional finishing process, performed after pre-finishing by shaving or grinding. In the early 1990’s, significant research and development efforts aimed at higher stock removal capacity as well as improved ability to eliminate pre-machining errors. The requirement of combining advantageous functional work piece characteristics after gear honing and the economic benefits of a single hard finishing process has led to the development of Coroning. Using similar process kinematics as in conventional gear honing, Coroning distinguishes itself by the application of highly aggressive electroplated diamond tools. Because of the increased stock removal capability of Coroning, it is a true single-finishing process for mass production. Coroning is applied after gear hobbing or shaping and heat treatment. It does not require prior shaving or grinding. This paper will explain the unique tool concept used for Coroning and discuss related process kinematics in comparison with conventional gear honing. Tool design aspects will be considered and suitable process strategies will also be presented. Application examples will be used to describe typical stock conditions, process parameters and the geometric quality that can be achieved with Coroning.