CROwned Spline Surface Optimization using New Treatments

The main goal of the project CROSSONT is to provide surface treatment methods for crowned splines which are able to fulfil the requirement of reducing the risk of wear and minimizing the friction in the spline connections between shaft and gear. It is the consortium's firm conviction that outstanding surface properties for crowned splines in UHBR applications can be generated with a combination of laser and physical-vapour-deposition (PVD) processes. Modelling of the crowned spline will be conducted to predict its behaviour. In combination with the coatings, laser local hardening is to be used, and, on the other hand, laser textured gear steel surfaces are to be considered. The latter are becoming more and more important due to their tribological properties. It is mandatory that the results of the project are low in maintenance, highly reliable and allow long life time.

The proposed laser-based surface treatments technologies are laser local hardening, laser micro structuring and laser nano structuring. Additionally, multi-layered coatings will be investigated in terms of PVD and in specific by reactive magnetron sputtering. These systems may be doped with silver in order to control heat balance or to introduce a wear indicator as a smart coating. The most effective methods will be identified by using a statistical test plan, which will also investigate the combination of such methods. While PVD is able to realise thin hard coatings to protect the surface from wear, the named laser processes can either reduce wear (e.g. laser hardening) and/or reduce the coefficient of friction (e.g. micro-/nanotextures). In general, laser local hardening can be considered as an almost established process, while laser texturing is still an innovative approach to further improve the surface properties of crowned splines. The most promising methods will be applied to full scale splines and evaluated in dynamic fatigue testing. The findings are summarised in a technical recommendation.