2025 Fall Technical Meeting

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10:00am – 1:00pm
Session 1: Design and Rating
Room 410A
Our kickoff session is planned to be a great one! We have new technology for bevel gear manufacturing relating to profile shift as well as a deep dive into sub-case fatigue fracture for automotive straight tooth bevel gears. Crown gears will be examined for their load capacity compared to bevel gearing. Not all of this session is on bevel gearing though! We will hear about planetary gear micro-geometry design factoring in carrier deformation and a unique gear repair using additive manufacturing methods. The session will wrap up with a special presentation by the convenor of ISO Technical Committee 60, working group 6, which is responsible for all ISO gear rating standards, on the scope and current work being performed by that international group of experts.

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Independent Pinion and Gear Profile Shift for Bevel Gears
Hermann Stadtfeld, Gleason Corporation

In bevel and hypoid gears, as well as straight bevel gears, the pinion profile shift coefficient X1 and the gear profile shift coefficient X2 have the same absolute amount but opposite signs. In bevel gears, this prevents a shaft angle change. This means that a positive profile shift in both members of a bevel gearset would change the shaft angle by (X1 + X2) * mn / Mean Cone Distance. The new developed independent profile shift allows a positive profile shift in pinion and gear without a change of the shaft angle, yet having all the advantages like elimination of undercut, increased contact ratio, and improved NVH as well as stronger tooth profiles, especially in case near miter ratios with a low number of teeth.

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Repair and Fabrication of Gears Using Laser Directed Energy Deposition
Diego Montoya, Ikergune, INZU Group

Additive manufacturing has been positioned in the manufacturing industry due to its capabilities to fabricate complex parts. The use of Laser Directed Energy Deposition (LDED) in repairs reduces considerably the lead times, and the gear industry could benefit from this advantage. However, there is a lack of research and data on the performance of gears repaired by LDED. In this work, we chose the martensitic tool steel Dievar to repair the teeth of a gear, damaged during the assembly process of a machine for aluminum parts production. We also investigate the bending fatigue response, and the corresponding S-N curve of gear teeth manufactured with Dievar. The results of the experiments demonstrate that LDED has large potential for being widely adopted in gear repair applications.

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Gear Scuffing Analysis Comparison Study
Zhiyuan Yu, Drive System Design

This research focuses on addressing gear scuffing in electric vehicle (EV) transmission systems. Gear scuffing, caused by metal-to-metal contact under high load and speed, poses a significant challenge to EV gearbox durability. To tackle this, the study utilizes advanced software tools: Masta and Windows LDP. Masta uses ISO 6336 and empirical correlations, while Windows LDP employs an elastohydrodynamic lubrication (EHL) model for a physics-based approach. Despite improvements in scuffing temperature predictions, discrepancies exist between the tools due to variations in surface roughness, torque load, speed, and lubrication. The research proposes a dual approach, combining both tools and correlating results with physical testing on custom-designed rigs, enhancing EV transmission reliability and accelerating gearbox development.

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Design and Load Capacity of Crown Gears in Comparison to Bevel Gears
Joachim Thomas, ZG Hypoid GmbH

The demand for more efficient gearboxes makes new types of gear sets increasingly interesting in order to realize such transmissions. The crown gear (also known as face gear) is not actually a new type of gear, but it has led a rather niche existence in the past. New manufacturing methods and new design and calculation options are bringing the crown gear back into focus. Today, crown gears are designed with the help of modern flank generators. With the help of the tooth model complex tooth contact analysis under load (LTCA) now can be carried out in the same way as for bevel gears. Two examples are used to show possible applications of crown gears in comparison with similar bevel gears.

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TIFF Identification and Resolution of Automotive Straight-Toothed Bevel Gears
Caleb Gurd, Eaton Corporation

This paper introduces a practical framework for identifying and mitigating Tooth Interior Fatigue Fracture (TIFF) in straight-toothed, net-forged bevel gears used in automotive differentials. As drivetrain systems evolve to deliver higher torque in compact designs, subsurface failures like TIFF pose increasing challenges. Unlike well-understood surface failures, TIFF demands deeper insight into material behavior and internal stress. Drawing from real-world case studies, industry practices, and academic research, the paper evaluates diagnostic and preventative methods including visual inspection, MPI, SEM, microgeometry optimization, and heat treatment. It offers actionable strategies for both newcomers and seasoned engineers, aiming to enhance drivetrain reliability and gear performance. This work supports the ongoing advancement of high-performance gear systems by addressing complex, often-overlooked failure modes.

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Local Damage Based Micro Geometry Design Method for Planetary Gears Considering Axis Misalignments and Load Deformations
Simon Nohl, Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University

CAE-based micro geometry design of cylindrical gears enables to optimize the operational behavior of gearboxes and enhances the lifetime due to the reduction of root stress and flank pressure.In this paper, a tooth contact analysis software for planetary gears with a numerical contact algorithm is extended to calculate the damage accumulation both concerning pitting durability and tooth root bending fatigue strength. This approach is further used to design the micro geometry in lead direction based on the safety factors on flank and root as a design target for a load collective of a wind turbine gear stage. The method is then compared to a particle swarm optimization approach with higher calculation time yet being able to optimize the static transmission error additionally.

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Special Presentation: Activities and Responsibilities of ISO/TC 60/SC 2/WG 6
Karsten Stahl, Gear Research Center (FZG), Technical University of Munich (TUM)
International standards are essential for ensuring consistent, reliable, and high-quality engineering practices worldwide—and they serve as a common technical language. For cylindrical steel gears, typical damage modes and their corresponding safety factors are addressed in the ISO 6336 series. This series is developed and maintained by ISO/TC 60/SC 2/WG 6 “Gear Calculations,” active since 1994 with the goal of making state-of-the-art calculation methods widely accessible. Currently, the group is working on upgrading several key Technical Specifications to full International Standards, including ISO/TS 6336-4 (tooth flank fracture), ISO/TS 6336-20 and -21 (scuffing), and ISO/TS 6336-22 (micropitting). This presentation will provide an update on the standardization process and highlight recent technical developments of particular relevance to gear researchers, developers, and practitioners worldwide.

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1:00pm – 2:15pm
Awards Luncheon
Room 410B

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2:30pm – 5:30pm
Session 2: Electric Vehicles and Emerging Technology
Room 410A
A new session for this year! As the session title indicates, the papers presented here will cover a lot of emerging topics such as plastic gear performance, plastic gear coatings and their performance, and additive manufacturing gear designs for NVH characteristics. We will also hear about optimization techniques and performance goals for EV drivetrain design. Normally incorporated by a factor in gear rating formulas, impact loading in automotive applications will be discussed in depth. Quite a way to round out our first day.

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Nanocomposite Coatings for Thermoplastic Gears
Peter Schmidt, United Protective Technologies, LLC, UNCC PORTAL
Borut Černe, RD Motion, d.o.o.

Gears formed with thermoplastic materials have made significant strides in strength over the last decade. With the goal of reducing wear and potentially improving fatigue durability, gears manufactured from reinforced Polyetheretherketone (PEEK) were examined, analyzed, and coated using Plasma Enhanced Chemical Vapor Deposition (PECVD). A thin film coating system was applied after surface finish improvement to the gears under evaluation. Results of standard tribological testing (ASTM G99) and standard thin film coating testing (ISO 26423, ISO 20502, VDI 3198), documenting performance on the PEEK substrate are reported. Coated gears were then tested in accordance with VDI 2736 in oil lubricated conditions for comparison with previously obtained results from tests on the same material in uncoated conditions.

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Performance-Driven Design of Multi-Stage Gear Transmissions for E-Drive Systems
Claudio Autore, Ferrari S.p.A.

This work presents a multi-objective optimization method for multistage spur gear transmission design in e-drive systems, focusing on compactness, efficiency, and weight. The approach incorporates manufacturing and geometric constraints into the optimization process, ensuring designs are aligned with production requirements. The framework supports both simple and compound gear trains, enabling exploration of an extensive design space characterized by macro-geometry and tooth profile variables. Optimization is executed using a genetic algorithm, complemented by KISSsoft and established load-independent models that estimate power losses under ISO safety criteria. When applied to a two-stage gearbox, the results indicate that the compound configuration offers enhanced design flexibility and produces a denser Pareto front. This method provides a systematic alternative to trial-and-error approaches, aligning mathematical optimization with industry best practices.

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Investigations on the Wear Behavior of Plastic Crossed Helical Gears
Martin Weber, Gear Research Center (FZG), Technical University of Munich (TUM)

Compact electric drives are increasingly in demand. Crossed helical gears are well-suited due to their high transmission ratio and freely selectable axis crossing angle. Using plastic materials improves NVH performance, efficiency, emergency running capabilities, and enables cost-effective, compact drives. Research on plastic crossed helical gears is limited; existing wear calculation and testing methods are mainly type-specific and based on steel/plastic pairings, thus only partially applicable. Methods for metal gears neglect plastics’ complex, temperature-sensitive properties. Weight-based wear measurements are unsuitable due to material-lubricant-air interactions. This paper presents a novel in-situ method for evaluating wear in plastic crossed helical gears using angular difference measurements. Its applicability is demonstrated through experiments on a PEEK/PEEK pairing. Results show strong correlation with common techniques while significantly reducing measurement effort.

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Impact Load Considerations in Automotive Gear Design
Hareesh Kurup, Eaton India Innovation Center

Uneven gear shifting, particularly with manual clutches, is a significant source of transient loading in automotive drivetrains. If not accounted for during gear design, transient loads may influence transmission performance under certain operating conditions. Gear rating standards, recommend accounting for all potential torsional vibrations and impact loads in the calculations. An overload or application factor is used to account for all the loads exceeding the nominal load on the gear. These standards allow gear engineers to define the overload factor based on their experience, acknowledging the wide and complex nature of load variations. This paper presents an approach to incorporating the effect of drivetrain shocks in transmission gear rating and includes a case study identifying impact loads from gear shifting events as a significant factor.

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High-Damping Lightweight Design for Laser Powder Bed Fusion 20MnCr5 Gears
Bruno Henrique Lima, Aeronautics Institute of Technology
Main Author: Matheus Fernandes Vieira, Aeronautics Institute of Technology

The growth of the electric vehicle market is reshaping the gear industry, demanding improved Noise, Vibration, and Harshness (NVH) performance. Laser Powder Bed Fusion (L-PBF) enables complex geometries with suitable mechanical properties for gears. This study presents a method to explore the L-PBF’s design freedom and topology optimization to reduce pinion gear mass and enhance damping behavior through polymer infiltration. The approach calibrates stiffness changes to improve NVH while incorporating transmission error simulations to avoid resonance. Results show a 22% weight reduction and significantly improved damping. The adjusted stiffness also modified the transmission error pattern, avoiding critical frequencies. This method supports the development of advanced, lightweight, and sustainable gear systems aligned with electromobility demands.

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Interaction of Gear and Bearing Simulation for Planetary Gear Stage Optimization
Michael Otto, Gear Research Center (FZG), Technical University of Munich (TUM)

Achieving compact gearbox design requires high-end simulation by local tooth contact analysis. Recent developments show a trend towards more complex planetary gear designs to further increase power density. This can be observed in the field of e-mobility or e-micromobility. For high ratio and small housing dimensions not only classical minus planetary gear stages are designed but also designs with stepped planets are discussed. In this paper, the authors present a simulation approach for such designs based on the algorithms implemented in the software package RIKOR. The influence of the level of detail in the simulation of gear mesh on the bearing contact conditions and vice versa is documented in theory and by an example gearbox design.

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6:00pm – 9:00pm
Wednesday Social Networking Event – The Materials Fusion Experience
Additional Ticket Required

Join us for The Materials Fusion Experience, an exclusive social networking event, offering a dynamic and immersive environment for professionals to connect, collaborate, and explore the city’s vibrant history and industry. This event seamlessly blends the city’s cultural roots with modern innovation, creating a multifaceted experience designed to inspire, engage, and foster meaningful connections.

Don’t miss this opportunity to engage with thought leaders, expand your professional network, and immerse yourself in Detroit’s unique blend of history, culture, and industry. Whether you’re looking to collaborate, discover new ideas, or simply enjoy. The event will take place at Waterview Loft.

Who Should Attend – All those attending or exhibiting at Motion + Power Technology Expo, the Heat Treat Conference & Exposition, or IMAT events.

8:00am – 10:00am
What’s Brewing in Aerospace and Defense: Breakfast and Panel
Room 410B
Additional Ticket Required

Join us for a series of short presentations from a panel of experts as they explore the latest innovations in aerospace. This session will focus on emerging topics, including new plane designs, advancements in eVTOLs (electric vertical take-off and landing), and the future of air mobility. Gain insights into how these innovations are shaping the aerospace and defense industries, from cutting-edge technologies to economic implications, and the impacts to the power transmission industry.

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10:00am – 1:00pm
Session 3: Manufacturing and Inspection
Room 410A
Where the part goes from concept to reality, Manufacturing and Inspection is always a topic with continuous innovation. We will hear about optical inspection techniques, using acceleration data to monitor tool wear, and new developments in hard gear skiving. Microstructure impacts on residual stress relaxation will be investigated in one of the papers in this session. In another, surface geometry characterization will help evaluate contact fatigue damage potential.

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Areal Surface Characterization of Involute Gears With Microgeometry Corrections and Contact Fatigue Damage for Tooth Contact Analysis
Tom Reavie, Newcastle University

Characterizing the surface geometry of involute gears is crucial for many high-performance applications. Traditional measurements are well-defined by international standards however guidelines for flank surface measurement are not available. The UK’s National Gear Metrology Laboratory, have recently developed a method which evaluates surface parameters, including corrections such as tip, root, and end relief, and calculates measurement uncertainty. To demonstrate the method, gears were contact fatigue tested and measured using a Klingenberg P65 gear measurement machine. Contact stress and transmission error were simulated in a tooth contact analysis model. Various surface conditions: no modifications, nominal modifications, as-manufactured surfaces, and subsequently damaged surfaces were analyzed and are discussed. Future work includes quantifying surface run-in effects, coatings, micropitting progression, and other gear performance standards and model validation.

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Acceleration Data-Based Analysis of Tool Wear in Gear Hobbing
Steffen Hendricks, Manufacturing Technology Institute (MTI) of RWTH Aachen University

Gear hobbing is a commonly used soft machining process in gear production due to its high productivity. Monitoring tool wear and workpiece quality is essential for cost-effective manufacturing. Tool Condition Monitoring (TCM) offers a structured approach for detecting critical tool wear. This report introduces a TCM method that analyzes individual generating positions during hobbing, using a fly-cutting trial as an analogy trial. This analysis provides deeper process insights and enables wear monitoring of each area of the cutting edge. In generating positions with multiple tool engagements, higher-order characteristic values proved effective for wear detection, while lower-order values were better suited for single engagements. This knowledge allows for improved monitoring and optimization of the hobbing process.

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Extraction of Imaged Tooth Contact Patterns by Iterative Least Squares Approach
Tom Abraham, Rochester Institute of Technology

Crowned gears exhibit localized contact forming an area on the tooth surface known as the tooth contact pattern that is indicative of misalignment insensitivity and excited noise, making it a critical design factor for many types of gears. As it is in consideration while designing gear geometry, it is often inspected. In this work, a method of extracting tooth contact patterns is established using only the virtual model of the gear tooth, an image of the gear, and a known calibration fiducial. A reproducible mathematical approach is presented and utilized to identify contact patterns and extract them back to the 3D model. Once there, it can be mapped into the commonly known radial projection and used for manufacturing and assembly corrections.

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Residual Stress Evolution and Stability: Assessing Heterogeneity and Relaxation in Gear Operation
Bruno Henrique Lima, Aeronautics Institute of Technology

This study addresses the sensitive aspects of the residual stress heterogeneity and its impact on the relaxation phenomena during the gear’s initial operation. Fatigue tests were performed in which the samples were evaluated with different conditions of number of cycles to observe the residual stress relaxation. This approach enabled the evaluation of the residual stress stability of the samples based on their initial residual stress intensity and heterogeneity. Preliminary results of the surface residual stress relaxation have already provided relevant information. A heightened tendency for relaxation during gear operation due to a higher heterogeneity level was observed. The comprehensive analysis of the residual stress state highlights the potential to optimize the gear manufacturing chain.

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Vibration Analysis for Fault Diagnosis of Cycloidal Gearbox Using Wavelet Transform
Sandeep Thube, Sumitomo Drive Technologies

Vibration analysis has been increasing playing an important role in analyzing the behavior of rotary machineries. Traditional digital methods- time and frequency (Fast Fourier Transform) spectrum analysis – are useful to analyze ‘stationary signal’ generating rotary components such as bearings and involute gears. These methods, however, fall short to deduce firm results when it comes to the cycloidal gearing, which is used in a variety of applications in recent days. The frequency spectrum may not be able to clearly distinguish a faulty cycloidal gearbox from a normally operating one. The paper discusses Wavelet transform method to process non-stationary vibration signal to diagnose the health of the cycloidal gearbox component, viz. Cycloidal disc, using multifractal spectrum.

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Hard Gear Skiving With High-Performance Tools – An Innovative Technology for Future Drivetrains
Andreas Hilligardt, Reishauer AG

Internal gears with high load capacity and geometric accuracy in a thin-walled design are required for drivetrains with higher power densities, high efficiency and low noise emissions. These requirements can be met by hard fine machined, case-hardened gears. The high hardening distortions of thin-walled components create major challenges for hard fine machining. Reishauer has developed a completely new tool system with a special high-performance cutting material to make the hard finishing of internal gears to high quality economical. The tool system is complemented by the new, highly specialized Reishauer RS 300 machine. This work presents application examples and shows how this innovative technology can be used to machine internal gears in qualities of ISO class 5 and better with tool lives of over 2000 workpieces.

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1:00pm – 2:15pm
Lunch on the Show Floor

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2:30pm – 5:30pm
Session 4: Efficiency and NVH
Room 410A
Wrap up our second day with some in-depth topics on transmission error, plastic gear NVH considering wear, lubrication, and materials, and powder metal gearing optimization to reduce NVH. Also, presenters will discuss bevel and hypoid gear efficiency and statistical analysis of manufacturing deviations and component damping effects on NVH.

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A Novel Prediction of the Transmission Accuracy by Means of the Integrated Position Error Phenomenon for a Gear Pair
Bahadir Karba, Bursa Uludağ University

The foundational studies for this body of work were conducted by Michalec, who identified positional deviation as a composite result of gear inaccuracies. The present study proposes a novel framework for understanding and quantifying the transmission accuracy of gear systems. The development of this framework entailed an integrated evaluation of integrated backlash and integrated transmission error. Conventional methods rely exclusively on empirical approximations or isolated tolerance values. Conversely, the proposed approach introduces the concept of Integrated Position Error as a composite performance indicator derived from the summation of gear and pinion mesh errors. This exhaustive investigation and proposed roadmap, which aims to bridge the gap between geometric tolerances and dynamic performance prediction, resulted in the proposal of a classification metric: the Integrated Transmission Accuracy Number.

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Investigating the Effects of Wear, Lubrication and Material Pairing on the NVH Performance of Plastic Gears
Damijan Zorko, RD Motion, d.o.o.

Growing demands for improved user experience necessitate minimizing noise, vibration, and harshness (NVH) in gearbox systems. Polymer gears offer a promising solution, with steel–polymer or polymer–polymer pairings enabling substantial NVH reductions compared to steel gear pairs. However, key factors influencing polymer gear NVH—such as material pairing, wear, and lubrication—remain underexplored. This study systematically investigates six gear material combinations, including a steel–steel reference, to evaluate NVH performance under consistent conditions. Additionally, it examines the effects of progressive wear and grease lubrication. While the benefits of grease and the impact of wear on NVH are generally acknowledged, they have not been rigorously quantified. The results provide new insights to inform material selection and design strategies for NVH-optimized polymer gears.

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Application of PM Solutions for Optimization of Transmission Gear Noise in Battery Electric Vehicles
Philipp Kauffmann, Johnson Electric Aachen

The shift to BEVs amplifies transmission gear noise due to high-frequency electric motor vibrations. Powder metallurgy (PM) gears offer unique NVH optimization opportunities through material properties and design flexibility. Johnson Electric proposes an innovative solution using PM materials for noise damping, adjusting gear body designs to disrupt resonance frequencies and reduce noise perception. Case studies demonstrate significant noise reduction. The solution employs AI-driven design optimization, accelerating development and meeting market demands for quieter BEV transmissions.

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Efficiency of Bevel and Hypoid Gears – Calculation Approach and Comparison with Experimental Test Results
Lorenz Constien, Gear Research Center (FZG), Technical University of Munich (TUM)

Due to the increasing challenges of climate change and its consequences at the present time, gear engineers are encouraged to design sustainable gears that are both efficient and have a high load-carrying capacity. Currently, for bevel and hypoid gears, only basic calculation methods are available, given in ISO/TS 10300-20:2021 and ISO/TR 14179-1:2001, for load-depending calculating the gear power loss P_VZP. This paper presents a newly developed method based on the standard calculation approach of the virtual cylindrical gear given in method B1 of ISO 10300‑1:2023 for calculating the gear power loss P_VZP. The calculation method is validated by experimentally determined gear power losses for bevel and hypoid gears using the FZG bevel gear efficiency test rig.

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Holistic and Statistical Approach to the Impact of Manufacturing Deviations on the Transmission Error, Structural Vibrations and the Acoustic Behavior of Gearboxes
Dennis Tazir, FVA GmbH

In electric-drive systems, NVH (Noise, Vibration, and Harshness) optimization is crucial due to the absence of masking noise from combustion engines. A key factor is transmission error (TE), significantly influenced by gear manufacturing deviations. Early identification is vital, especially with shorter development cycles. Relying solely on limit values can lead to excessive tolerances and costs. A statistically balanced approach enables efficient development. This paper presents a workflow to assess TE, structural vibration, and acoustics. A gear design tool models tolerances as normal distributions, focusing on the first gear stage. Multibody dynamics simulations evaluate structural responses at critical speeds, while acoustic simulations analyze noise impact. The approach emphasizes optimizing manufacturing tolerances to enhance NVH performance effectively.

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A Comparative Study of the Effect of Damping in the Dynamic Analysis of Drivetrains for NVH Performance Evaluation
Saeed Ebrahimi, KISSsoft AG.

This study compares effect of internal damping of the elements of a drivetrain under various loading conditions and evaluates the damping effect on the NVH characteristics. The forced response analysis is carried out in KISSsoft to calculate the dynamic behavior subjected to dynamic loads from different excitation sources. The investigation is carried out for a wide range of running speeds, input torques, and damping values. For intuitive characterization of the emitted noise of the gearbox model, the exciting bearing reaction forces of the forced response are then imported to RecurDyn and applied to the housing. This can be particularly useful for designers and engineers to observe how different sources of damping can result in the improvement of the NVH characteristics of a drivetrain.

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6:30pm – 8:30pm
Corktown Taphouse Reception – FTM Networking Reception
Additional Ticket Required | Included with FTM Full Pass Registration

Join us for an evening of networking, entertainment, and connection at Corktown Taphouse. This high-energy reception brings together professionals from across the gear industry in a relaxed setting, offering a chance to meet new attendees, reconnect with colleagues, and set the stage for a week of innovation and collaboration. Enjoy interactive games like augmented reality darts and duckpin bowling, designed to spark conversation and fun. With over 70 self-pour beverage options, including craft beers, ciders, wines, and non-alcoholic choices, there’s something for everyone. Whether you’re looking to grow your network or simply enjoy a lively evening with colleagues, this event is the perfect way to start the 2025 Fall Technical Meeting.

7:30am – 9:00am
Registration Open
Lindbergh Foyer

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9:00am – 12:00 pm
Session 5: Materials and Performance
Room 410A
Our last session focuses on the major elements of a geared system: the building block of material and the end goal of performance. Methods to evaluate the performance of tooth roots under various conditions such as shot peening and superfinishing will be presented, as well as a review of the state of the art in surface hardening techniques. We will be treated to a summary of testing specific to helicopter transmissions covering 20 years of test information and hear about a unique combination of vacuum heat treatment and spray quenching to achieve high cooling rates. These in-depth papers will make sure to finish up the FTM with our trademark quality and new topic presentations.

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Strategy for Accounting Residual Stresses Heterogeneity on the Stress Modelling Oriented to Tooth Root Bending Fatigue
Caio Felipe Siqueira Gomes, Aeronautics Institute of Technology

The residual stress is a key factor for achieving higher power densities, due to its fatigue resistance influence. Due to its complexities, such as heterogeneity along the component surface, this knowledge is not properly incorporated into gear standards, hindering it to be widely accepted as a design tool. The study objective is the development of a strategy to account for the residual stress heterogeneity influence on the fatigue life estimation in gear’s tooth root. The Finite Element Method was used to simulate the shot peening process at the tooth root, allowing the quantification of residual stress heterogeneity. By coupling the residual and actuating stresses using Dang Van and Fatemi-Socie models, the residual stress heterogeneity was verified to induce distinct failure tendencies along the tooth.

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Optimizing the Surface Integrity of Gears: Combined Effects of Peening and Superfinishing Processes
Gilberto Martins, Aeronautics Institute of Technology

This study investigates the optimization of agricultural gear flanks to enhance load capacity by improving fatigue resistance without increasing component size. Case hardened gears underwent shot peening (SP) to induce compressive residual stresses, followed by isotropic superfinishing (IS) to homogenize surface topography. The effects of SP, IS, and combined SP+IS treatments on surface integrity were evaluated through roughness, profile deviation, and residual stress. Results show that the combined SP+IS treatment improved compressive residual stresses, reduced surface roughness, and decreased intergranular oxidation. The manufacturing quality improved from DIN class 7–8 to 8–9. The IS process preserved residual stress heterogeneity introduced by SP, demonstrating a clear link between surface roughness and residual stresses on gear teeth.

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Twenty years of pulsator tests on Helicopter Gears
Luca Bonaiti, Politecnico di Milano
Sergio Sartori, Leonardo Helicopters

The gears of Main Gearboxes of Helicopters must be designed on the basis of validated methodologies and of reliable data: bending fatigue is not the most limiting failure mode, but the exact knowledge of the safety margins is fundamental due to the catastrophic consequences of its occurrence. The fatigue strength data of the material must be fully representative of the specific experience and practices of the manufacturer, and must include the effects of several parameters related to geometry, manufacturing, heat and mechanical treatments, and finishing processes. A systematic campaign of tests on bending fatigue strength of gears for almost twenty years has been performed, with the Single Tooth Bending Fatigue (STBF) approach, on several variants of case hardened gears, nitriding and precipitation hardening materials.

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Surface Hardening of Gears: Current State of the Art and Prospects
Noah Kantor, Worcester Polytechnic Institute

This paper provides an overview of key surface hardening techniques for gears. It first explains conventional thermochemical methods, including gas- and vacuum carburizing, carbonitriding, and ferritic nitriding. Additionally, high-temperature solution nitriding is highlighted as a promising approach for hardening martensitic and ferritic stainless steels while maintaining corrosion resistance. The second part explores fast quenching as an alternative to traditional hardening processes. Fast quenching enhances surface hardness, likely due to changes in martensite formation mechanisms, and induces high compressive surface stresses, improving fatigue performance. Rather than covering all surface hardening methods in depth, this paper reflects ongoing research and development efforts at the Center for Heat Treating Excellence.

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Water Spray Quenching – A New Intensive Quenching Process for Case Hardening of Gears
Volker Heuer, ALD Vacuum Technologies GmbH

Water Spray Quenching (WSpQ) has been established in industry for many years, e.g. in steel production. WSpQ provides very high cooling rates that are much higher than quenching in liquid medium (e.g. with oil or with polymers). However, for the heat treatment of complex shaped serial parts, such as gear-wheels, this process could yet not be applied successfully. So far this was not possible, since the water spray could not reach into the center of the heat treat loads consisting of multiple layers where the outer parts of the load shield the inner parts. With a new combination of vacuum heat treatment in single layers with subsequent WSpQ, this intensive quenching process can now be applied on serial parts.

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