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Technical University of Munich

Investigation of the Distortion Behavior of Nitrided Wheels of Bevel and Hypoid Gears

Research Topic

Short TitleNitrided Bevel Gears
Start of ProjectQ1/2025
FundingFVA-Nr. 513/VII
Research Association for Drive Technology e.V., FVA
Project PartnerLeibniz-Institut für Werkstofforientierte Technologien, IWT
KontactM. Geitner, M.Sc.

Project Description

Bevel and hypoid gears inherently exhibit relatively large profile and width crowning of the tooth flanks, known as microgeometry. In current production, the microgeometry of these gears is finalized through hard finishing processes, such as grinding or lapping, following case hardening. Hard finishing is essential to correct any distortions introduced during heat treatment. Compared to case hardening, nitriding has the advantage of lower dimensional and shape changes due to the lower treatment temperatures and lack of phase transformations. Eliminating hard finishing due to the reduced distortions achieved with nitriding, while maintaining sufficient microgeometry quality, would reduce both the cost and time associated with manufacturing bevel and hypoid gears.

In previous projects (FVA 615 I–III and FVA 386 III), nitrided spur gears were experimentally shown to exhibit higher tooth root and pitting load capacity in comparison to ISO 6336-5:2016 standards. However, the transferability of nitriding to bevel and hypoid gears, with respect to distortion behavior and load capacity, has not yet been investigated.

In a feasibility study, the distortion behavior of nitrided bevel gears will therefore be compared to that of case-hardened bevel gears of identical geometry from the series production process. Bevel gears are selected for this study, as their ring-shaped and asymmetric geometry is considered critical in terms of distortion behavior. Dimensional and shape changes resulting from the heat treatment will be assessed through comprehensive measurements of the bevel gears before and after heat treatment using a 3D coordinate measuring machine. The selection of gas nitriding parameters is based on the recommendations from FVA 386 III. Successful heat treatment will be verified through extensive microstructural characterization.

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