Periodic Reporting for period 2 - CROSSONT (CROwned Spline Surface Optimization using New Treatments)
Período documentado: 2020-07-01 hasta 2022-08-31
Clean Sky 2 aims to reduce CO2, NOx and noise emissions in order to maintain the quality of life in Europe through environmental protection. At the same time, the competitiveness of the aviation industry must be strengthened in international competition in order to secure and create jobs. Therefore, the targets of ACARE 2020 will facilitate the first steps to the Flightpath 2050 targets that include 75% cut of CO2 and 90% of NOx emissions as well as 65% noise reduction.
The overall objective of the CROSSONT project was to find new surface treatments and coatings that allow spline joints to be more resource efficient, e.g. increasing their power density. This contributes to the overall goal of the Clean Sky 2 joint undertaking of reducing CO2 and noise emissions of aircrafts by enabling lightweight aerospace power train designs.
In order to fulfil this top-level objective, different sub-objectives have been addressed. As first sub-objective, robust surface treatments by means of combined laser/ PVD processes have been developed. As second sub-objective, a valid spline connection model has been developed and compared to small and full scale experiments. And as third sub-objective, full scale spline testing has been carried out to assess the concerning surface treatments and analyse the operational behaviour of surface optimized crowned spline joints under misaligned conditions. Finally, design recommendations have been deduced based on the test results.
The overall objective of the CROSSONT project was to find new surface treatments and coatings that allow spline joints to be more resource efficient, e.g. increasing their power density. This contributes to the overall goal of the Clean Sky 2 joint undertaking of reducing CO2 and noise emissions of aircrafts by enabling lightweight aerospace power train designs.
In order to fulfil this top-level objective, different sub-objectives have been addressed. As first sub-objective, robust surface treatments by means of combined laser/ PVD processes have been developed. As second sub-objective, a valid spline connection model has been developed and compared to small and full scale experiments. And as third sub-objective, full scale spline testing has been carried out to assess the concerning surface treatments and analyse the operational behaviour of surface optimized crowned spline joints under misaligned conditions. Finally, design recommendations have been deduced based on the test results.
The consortium has carried out a state of the art analysis in regards to surface and heat treatments, coatings and fatigue mechanisms in spline connections. In this analysis, existing literature has been searched, reviewed and evaluated. IWT focused on the topic PVD solid lubrication, BIAS focused on the topic of laser structuring with the scope on tribology and WZL focused on topics of spline joint fretting-wear and -fatigue. Furthermore, a model of the spline connection concerning clearances, displacements and misalignments, friction and resulting pressure distribution has been implemented by WZL.
The consortium took different combinations of laser structuring combined with physical-vapour-deposition (PVD) into account to create new, durable spline surfaces. Simple specimen have been produced, to assess these different surface treatments and coatings. IWT applied different surface coatings onto the specimen and BIAS applied the foreseen laser structuring. Additionally, some specimen have been coated a second time before all specimen have been characterised. IWT has performed Pin-on-Disk tests with the manufactured specimen, to gain knowledge about the wear behaviour of the surface treatments under contact load.
WZL designed a spline coupling, suitable for full scale spline investigations. Based on the implemented FE-model and analytical calculations, the macro- and micro geometry of the spline joint has been optimised in order to meet the required contact pressure and sliding velocities in the tests. In addition, the required shaft misalignment and rotational speed for the investigations have been determined. The full scale splines have been manufactured and the spline shafts have been optimized with surface treatments in terms of PVD-coating and laser structuring systems. Finally, the splines have been characterized to document their pre-testing conditions.
A test bench has been designed to perform conclusive testing of the full scale splines. The developed test bench design is based on an extension of a back-to-back test bench according to DIN ISO 14635. For the extension, the spline-joint has been integrated into the shaft system and the dedicated spline misalignment has been applied.
The manufactured full scale splines have been tested on the newly developed test bench. For the testing, the to be tested variants with the concerning surface treatments have been used. To investigate the wear and fatigue behaviour of the different test variants, the full scale spline-joints have been investigated under the same test conditions for each test in terms of torque, rotational speed and dedicated angular misalignment. To compare the test variants, pre- and post-testing topography measurements have been used to evaluate the changes on the tooth flanks. With this data, the test variants have been compared to each other according to their operational behaviour.
The consortium took different combinations of laser structuring combined with physical-vapour-deposition (PVD) into account to create new, durable spline surfaces. Simple specimen have been produced, to assess these different surface treatments and coatings. IWT applied different surface coatings onto the specimen and BIAS applied the foreseen laser structuring. Additionally, some specimen have been coated a second time before all specimen have been characterised. IWT has performed Pin-on-Disk tests with the manufactured specimen, to gain knowledge about the wear behaviour of the surface treatments under contact load.
WZL designed a spline coupling, suitable for full scale spline investigations. Based on the implemented FE-model and analytical calculations, the macro- and micro geometry of the spline joint has been optimised in order to meet the required contact pressure and sliding velocities in the tests. In addition, the required shaft misalignment and rotational speed for the investigations have been determined. The full scale splines have been manufactured and the spline shafts have been optimized with surface treatments in terms of PVD-coating and laser structuring systems. Finally, the splines have been characterized to document their pre-testing conditions.
A test bench has been designed to perform conclusive testing of the full scale splines. The developed test bench design is based on an extension of a back-to-back test bench according to DIN ISO 14635. For the extension, the spline-joint has been integrated into the shaft system and the dedicated spline misalignment has been applied.
The manufactured full scale splines have been tested on the newly developed test bench. For the testing, the to be tested variants with the concerning surface treatments have been used. To investigate the wear and fatigue behaviour of the different test variants, the full scale spline-joints have been investigated under the same test conditions for each test in terms of torque, rotational speed and dedicated angular misalignment. To compare the test variants, pre- and post-testing topography measurements have been used to evaluate the changes on the tooth flanks. With this data, the test variants have been compared to each other according to their operational behaviour.
In the Pin-on-Disc testing it was shown, that wear phenomena can be reduced in loaded contacts within hertzian pressure and sliding velocities, throughout using the right combination of surface coatings and a matching coverage of laser structuring. With these findings, it is possible to optimize different machine elements, which include a rolling and sliding regime under contact pressure, in terms of upcoming wear.
In the full scale spline tests it has been shown, that the surface coatings TiN+DLC+MoS2:Ti:C and TiN+MoS2:Ti can raise the scuffing load capacity of crowned spline joints under misaligned conditions and reduce adhesive wear. Furthermore, the TiN+MoS2:Ti variants show a wear volume that is comparable to the uncoated and unstructured reference variant. Therefore, TiN+MoS2:Ti coatings are recommended for spline joint applications under misaligned conditions, to raise their scuffing load capacity and reduce adhesive wear.
During the CROSSONT project, a test rig for crowned spline joints has been developed and was build up. This test rig enables testing procedures regarding load capacity testing and dynamic investigations. Besides tests regarding wear and fatigue effects –as carried out in the project- future investigations according to the stiffness and damping behaviour of spline-joints under determined misaligned conditions can be carried out. Throughout such tests, knowledge regarding the dynamic behaviour of spline joints can be gained or calculation methods and simulation tools describing the operational behaviour of spline joints can be validated. Throughout these impacts, it is likely to improve the operational behaviour of spline joints in terms of their load carrying capacity or dynamics and therefor improve the overall systems.
In the full scale spline tests it has been shown, that the surface coatings TiN+DLC+MoS2:Ti:C and TiN+MoS2:Ti can raise the scuffing load capacity of crowned spline joints under misaligned conditions and reduce adhesive wear. Furthermore, the TiN+MoS2:Ti variants show a wear volume that is comparable to the uncoated and unstructured reference variant. Therefore, TiN+MoS2:Ti coatings are recommended for spline joint applications under misaligned conditions, to raise their scuffing load capacity and reduce adhesive wear.
During the CROSSONT project, a test rig for crowned spline joints has been developed and was build up. This test rig enables testing procedures regarding load capacity testing and dynamic investigations. Besides tests regarding wear and fatigue effects –as carried out in the project- future investigations according to the stiffness and damping behaviour of spline-joints under determined misaligned conditions can be carried out. Throughout such tests, knowledge regarding the dynamic behaviour of spline joints can be gained or calculation methods and simulation tools describing the operational behaviour of spline joints can be validated. Throughout these impacts, it is likely to improve the operational behaviour of spline joints in terms of their load carrying capacity or dynamics and therefor improve the overall systems.