Gear materials – What else is there to research?

(28.06.2019)
For every gear that is made and used, a suitable material and heat treatment must be chosen. Hence, a lot of effort was invested to improve and further develop gear material properties in the past. Therefore, questions arise: Why is there still gear material related research necessary? What more is needed to be explored about gear materials? What else is there to research?

The brief answer is: YES, gear material related research is still necessary! But why?

Today, downsizing and cost reduction are important goals for every company worldwide to compete in a globalized world. Therefore, materials are still a main topic when developing new gearing systems. Materials have to meet new or higher requirements nowadays, for example due to the electrification of drive trains: The higher the speed of an electric engine of a final drive, the smaller the electric engine can be built. Therefore, gear materials with improved characteristics such as higher strength and increased reliability are needed. This can be achieved by new manufacturing routes (i.e. shot peening), new production routes (i.e. higher degree of cleanliness) and/or new chemical compositions or alloying components.

While some knowledge has been obtained already, these new requirements can only be met by gaining a deeper understanding of the altered material characteristics. A higher power density is often achieved by application of a shot peening process. Shot peened gears are characterised by increased compressive residual stresses near the surface and a significantly increased fatigue strength. However: cracks can now initiate below the surface at non-metallic inclusions. Current standards, like the ISO 6336, do not yet directly consider the influence of these residual stresses or the degree of cleanliness respectively non-metallic inclusions. In addition, alternative heat treatment processes, like carbonitriding and induction hardening, are getting more and more important, due to cost reduction requirements. Also, materials with modified or new chemical compositions are being developed with lower rates of alloying components or different alloying components.

At the gear research centre (FZG), several research projects are undertaken to face these new material requirements. Both comprehensive experimental research as well as detailed theoretical studies are done as a basis for future industrial application. Selected gear material related research results from FZG will be presented at the 2019 International Conference on Gears. Find out more about the investigations on non-metallic inclusion crack area characteristics, the flank load capacity of hard-soft gear pairings or the pitting load capacity of internal spur and helical gears. We are looking forward to sharing our experience with you during the conference.


Authors

Fuchs, D.; König, J.; Tobie, T.; Stahl, K.
Institute of Machine Elements - Gear Research Centre (FZG)
Technical University of Munich