eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing

125
2022
Linus Everlid
Martin Bengtsson
Morteza Najjari
Florian Reinle
Andreas Storz
Boris Zhmud
ict2310299
23rd International Colloquium Tribology - January 2022 299 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Linus Everlid Applied Nano Surfaces Sweden AB, Uppsala, Sweden Martin Bengtsson Applied Nano Surfaces Sweden AB, Uppsala, Sweden Morteza Najjari Xtrapid Innovations, Toronto, Canada Florian Reinle OTEC Präzisionsfinish GmbH, Straubenhardt-Conweiler, Germany Andreas Storz Applied Nano Surfaces Sweden AB, Uppsala, Sweden Boris Zhmud Applied Nano Surfaces Sweden AB, Uppsala, Sweden Corresponding author: boris.zhmud@appliednanosurfaces.com 1. Introduction Powertrain electrification has been a growing trend in the automotive industry. While having multiple advantages over traditional powertrains, the drivetrains of hybrid (HEV) and full electric vehicles (EV) also bring up some new challenges, such as increased requirements for NVH performance in high speed e-drives, the need to deal with higher torques and loads while keeping an eye on the vehicle weight, and compatibility issues with some common lubricant additives. One challenging requirement is the increased sensitivity related to the NVH behaviour. Surface specifications and tooth geometry have a big impact on the noise originating from the gear mesh excitation. Improving energy efficiency is another important topic: while in ICE powered vehicles, friction power losses run in of kilowatts, for BEVs, each watt makes a difference. The mechanochemical surface finishing technology pioneered and developed by Applied Nano Surfaces in Sweden opens up new possibilities for gear tribology optimization. The technology combines elements of mechanical burnishing with a tribochemical deposition of a solid lubricant tribofilm. Despite significant differences in the process flow and hardware, the treatment results in the development of a progressively plateaued roughness profile with reduced gradient roughness and increasingly negative skewness, incorporating doping elements from the process fluid. Mechanochemically finished gears are expected to reveal improved scuffing resistance, reduced friction and wear, and less noise. In this study, some early experimental findings and simulation data are presented. 2. Experimental 2.1 Sample preparation Ground steel pins and standard FZG gear sets have been finished using the ANS Triboconditioning ® CG finishing method implemented on two different machining platforms: centrifugal finishing and stream finishing. Fig. 1: Centrifugal barrel finishing process (Courtesy Tipton Corp, Japan) 300 23rd International Colloquium Tribology - January 2022 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Fig. 2: Stream finishing process (after V. Schulze et al., CIRP Annal, 66 (2017) 523) A wet finishing process was used with water-based and neat-oil-type process fluids. Several different media types were compared: cemented tungsten carbide beads, sintered silicon nitride beads, and traditional bauxite media. 2.2 GD&T controls and tribological studies Changes in the surface roughness profile and form of the test pieces were evaluated under different process conditions using Zygo NewView 5032 and Alicona G5+ optical instruments. Gradient surface roughness was characterized using angle-resolved light scattering (OptoSurf). Elemental surface analysis was carried our using X-ray fluorescence (Niton XL3t Goldd+, ThermoFisher Scientific). Besides that, FZG scuffing and efficiency tests have also been carried out, comparing mechanochemically finished gears with standard ones. 3. Results and Discussion 3.1 Surface characteristics The Triboconditioning ® treatment brings about a triad of effects: (i) a modified surface roughness profile with increasingly negative skewness and reduced gradient roughness, (ii) compressive residual stress build-up; and (iii) tribofilm formation. Fig. 3: Surface finishes produced by conventional grinding (left) and mechanochemical finishing (right) 23rd International Colloquium Tribology - January 2022 301 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Fig. 4: Compressive residual stress profiles produced by shot peening and mechanochemical finishing using two different mass-finishing platforms. Fig. 5: Tungsten carbide particles embedded into the surface after barrel finishing with WC beads. Gear tribology simulations comparing conventional ground and mechanochemically finished gears were carried out using the thermal EHD model [2]. The simulations predict reduced friction shear and higher lubricant film strength for mechanochemically finished gears. Fig. 6: Gear tribology simulations References [1] B. Zhmud, Mechanochemical surface finishing and the Triboconditioning ® process, MPR034: Manufacturing Processes, Chalmers, October 1, 2021. [2] M. Najjari, R. Guilbault, Edge contact effect on thermal elastohydrodynamic lubrication of finite contact lines. Tribology International 71 (2013) 50.