In this paper, ultrasonic fatigue testing results for “core hardened” AMS 6308 gear steel are presented. AMS 6308 is a gear and bearing steel with high tempering resistance and high hot hardness case targeted to high temperature applications
This paper is divided into two parts. The first part is a general digression on the pressure angle on cylindrical gears. The pressure angle is a variable that plays an important role in defining the geometry of gears and hobs, yet it is not widely discussed. This introduction serves as a prerequisite for the second part of the paper. The second part will show an application case of hoosing
the most suitable hob to cut a given gear. In this selection process, particular attention will be paid to the pressure angle of the hob for cutting with modified rolling, i.e., with a reduced pressure angle compared to that of the gear.
This study aims to investigate the effect of this identified type of shot peening on the micropitting resistance of the gear tooth flanks and the macropitting resistance and to compare the experimental results with the calculation results based on standard methods.
The following study presents an experimental methodology, employed to characterize the NVH behavior of plastic gears NVH in application-like operating conditions, presenting guidelines for material selection in terms of optimal gear NVH.
The approach developed in this research aims to aid a further understanding of the correlations between the energy generated during material removal and the power signals from the machine control during generating gear grinding.
If you are a true gear geek, you are probably aware of AGMA’s Fall Technical Meeting (FTM). However, we have true gear geeks attending the FTM for the first time each year, and we are thrilled to see that!
Overall developments and widespread public awareness of man-made climate change are transforming the way people think. The awareness has inspired a shift towards a more ecologically sustainable way of life. Driven by policymaking and technological innovation, ambitious efforts are underway to reduce greenhouse gas emissions to curb the rise in average temperatures. A key focus of these efforts is the mobility sector.
For cylindrical gears, speed-increasing transmission stages are well known, and regarding profile shift, preferred pressure angles, and helix angles a set of rules applies, which is not much different from the rules for speed reducers. It is important to acknowledge that basically, a speed increaser has to be designed just like a speed reducer, but then the gear with the lower number of teeth is the output. Of course, the torque and the speed of the gear with the lower number of teeth (output) and the gear with the higher number of teeth (input) must be the same as if this transmission was used as a speed reducer. In the case of straight bevel gears, spiral bevel gears, and hypoid gears the same rules apply with some additions. Spiral bevel gears have many applications as speed increasers.
This report uses an application case to demonstrate the optimization potential of gear skiving in the production of internal splines on a universal machining center. The process established in the example is then analyzed using the software tool OpenSkiving developed by the wbk Institute of Production Science of the Karlsruhe Institute of Technology (KIT) and the results are discussed. Finally, the most important findings are summarized.
This paper presents a comparison of the linear and nonlinear approaches for damage accumulation of tooth root breakage damage of gears. In the beginning, the theoretical fundamentals of damage accumulation are presented compactly. To compare the suitability of the methods an extensive set of experimental data is presented at first. The data is evaluated with both the linear and the nonlinear approach and the results are compared. For the linear approach, the method according to Miner and Palmgren is applied. For the nonlinear approach, the method developed by Subramanyan is used. The objective of this evaluation is to assess if the more complex method yields a potential benefit for a more accurate service life prediction of gears.
For wind turbine main gearboxes (MGBs) with about 1 MW or higher power, gearbox designs with multiple power paths are used. They handle several mega-Newton-meter of torque economically. Earlier wind turbines with lower power ratings used parallel shaft gearboxes with only one power path but soon they were superseded by planetary gearboxes having typically three to five planets per stage. This paper describes experiences using planetary gears where “Flexpins” are used to improve the load sharing between the individual planets—representing the multitude of power paths—and along the planet’s face width.
An extremely wide selection of different plastic materials is currently available on the market. A major limitation, however, is a huge gap in gear-specific material data on these materials, which is a problem that has been persisting for decades now. Providing a step towards a solution is the German guideline VDI 2736, which proposes design rating methods (Ref. 2) along with testing procedures (Ref. 3) to be followed to generate reliable data required in the gear rating process. This paper delves into the current state of the art in plastic gear testing, providing a comprehensive overview of employed testing methods, supplemented with case studies.
This paper shows a methodology to extensively evaluate different designs of epicyclic gear systems. As outlined, no choice is required on the part of the designer who is free to probe all design variables.
This paper recommends a 2-speed-automatic transmission for passenger cars with power <100 kW and for all trucks.
This paper presented some steps to get more insight into the effect of meshing damping on the dynamic response and noise emission of a two-stage gearbox transmission system. For this purpose, two variants of the model with different gear materials, one with plastic gears and one with steel gears, were considered. Both variants were designed for the same number of cycles of operation with similar root and flank safeties. The forced response analysis of the models was carried out and the exciting reaction bearing forces were calculated to evaluate which model can achieve better NVH characteristics results with lower noise emission from the housing.
This report investigates the wear morphology on the large end of tapered rollers and the inner ring's large end rib on a planet carrier TRB from a multi-megawatt wind turbine gearbox. The literature on abrasive wear has many classifications, including 2-body abrasion, 3-body abrasion, scratches, grooving abrasion, rolling abrasion, cutting abrasion, and plowing abrasion. For this analysis, we have selected grooving abrasion, a common problem in wind turbine gearboxes and a prominent failure mode on many bearings, particularly planetary carrier bearings and planet bearings. Grooving abrasion is frequently observed on cylindrical roller bearings (CRB) and tapered roller bearings (TRB). Fitzsimmons and Clevenger conducted tests on roller end/rib wear for TRBs with contaminated gear oil, and they provided an excellent explanation of the mechanism.
Gear Technology sat down with David Goetz, Corporate Applications Engineer at Norton | Saint-Gobain Abrasives to learn the latest about abrasives for gear manufacturing. The interview took place during Motion+Power Technology Expo 2023 in Detroit.
Gear skiving is used for both soft and hard finishing. As a quality critical final step in hard finishing, the process can be used to create modifications to the tooth flank. At present there is no knowledge of the extent to which topological modifications can be applied by gear skiving. In this report, the feasibility of manufacturing topological modifications on an external gear through adapted kinematics for gear skiving has been investigated.
Tactile or contact probes are the most common metrology technique in the coordinate measurement world, including the more specialized gear measurement community. Tactile probes can be active or passive, scanning or touch only, and may vary in cost and performance depending on the system itself. They are offered by multiple industrial companies as standalone OEM products (e.g., Renishaw) or only included in their coordinate measuring machines (e.g., Zeiss, Klingelnberg, and Hexagon). Their overall performance, especially their robustness and flexibility, have led to a gold standard for most metrology tasks.
The main objective of this study is to perform an experimental evaluation of the structural model of a five-planet first planetary stage from a modern 6MW wind turbine gearbox.
As the challenges in bevel and hypoid gear manufacturing need to be addressed, the objective of this paper is to show the tool and process design can be optimized based on the results of the manufacturing simulation BevelCut.
This report discusses grain size and its influence on metallurgical properties including its effect on yield strength, ultimate strength, fatigue strength, and fracture toughness. Also discussed are manufacturing issues such as heat treatment, hardenability, and machinability.
This paper deals with the residual stress depth profiles in case-carburized gears, their effects on the fatigue behavior as well as the enhancement of ISO/TS 6336-4 to include the consideration of tensile residual stresses in the tooth core area. For this purpose, an equation is also presented with which these tensile residual stresses can be estimated so that they can be used in the enhanced evaluation of TFF risk.
The objective of this report is to determine the origin of the phrase “profile shift.” Several technical books, technical papers, and industrial standards were reviewed for nomenclature associated with profile shift. The phrase “profile shift” translates directly to the German term “Profilverschiebung,” which originated in the last quarter of the 19th century. At first, profile shift was used to avoid undercutting pinions with small numbers of teeth. Later, it was recognized that profile shift improved the load capacity of the gear mesh and extended the service life of manufacturing tools.
Bevel gears are widely used in various industrial applications, such as automotive, aerospace, and marine industries, due to their ability to transfer power between non-parallel shafts. The conventional manufacturing of bevel gears involves several time-consuming and costly processes, including gear blank preparation, gear cutting, and gear finishing. The increasing demands on gear components regarding increasing power density, reducing installation space, reducing weight, and increasing efficiency are also reflected in the design of gear components. The reduction of installation space and weight as well as the increase in power density often leads to an optimized wheel body design that interacts with the gearing in terms of load capacity and stiffness. This leads to an increase in the required geometric degrees of freedom (DOFs). Due to the resulting complex wheel body shapes and different production-related effects, production-related geometry adjustments may also be necessary. Tools for evaluating the gearing in combination with the wheel body shape and its influences nowadays form the basis for unlocking the holistic optimization potential of transmission components.
This investigation reviews calculations using ISO/TS 6336-22 Method A and Method B, comparing the calculations against field results. Extensive reviews were made of geometry, surface roughness, load conditions, and lubricant conditions to best understand the influences of micropitting on each example and the applicability of the calculations to the results.
The toothed belt and pulley system known by the designation T, which has been selected as an example within this paper, was developed in the 1950s and standardized first in DIN 7721 (1977) and then in ISO 17396:2014. In this case study, the authors check if a single hob can properly cut T5 profile pulleys with 25 and 30 teeth—and if
so, define the range of the number of teeth covered by this hob.
In the present paper, a spline-joint design and the extension of a back-to-back test rig were presented, which enable the testing of crowned spline-joints under high rotational speed, medium torque, high test temperature, and angular misalignments.
For the research developed in this work, an existing simulation model of the generating gear grinding process based on a penetration calculation approach is used. Further, an extension of the model considering a realistic modeling of the grinding worm topography and the macro movements of the grinding worm during the process is presented. The result of the simulation is the microinteraction characteristics throughout
the grinding of the gear flank. In the end, the information about microinteraction characteristics obtained will be used for the calculation of force and energy in generating gear grinding.
The conjugacy of meshing gears is one of the most important attributes of gears because it ensures a constant velocity ratio that gives smooth, uniform transmission of motion and torque. Some of the world’s greatest gear theoreticians like Earle Buckingham, Wells Coleman, and John Colbourne laid the foundation for understanding conjugacy. Their teachings and interpretations of the law of gearing have been used by generations of gear engineers to design and manufacture gear transmissions for almost everything that is mechanically actuated.
The closed-loop concept has become widespread in recent years, especially in relation to the Industry 4.0 concept. The term “closed loop” will be used herein to refer to the pairing of specifications and checking (Figure 1) which all ISO standards, starting with ISO 1, the “mother” of all standards, use in relation to GPS (Geometrical Product Specifications).
Mechanical power loss in gears is generated through sliding and rolling of the contact resulting in frictional work and elastic hysteresis generation of heat. This action is both a parasitic loss of energy from the drivetrain and a source of engineering costs to control system temperature to avoid heat-related failures of the gearbox components. Therefore, from both a cost and durability standpoint it is of great interest to minimize the frictional losses at the gear tooth contact interface.
In modern automotive vehicles, gear noise becomes more and more of an issue. The main reason is the reduced masking noise of the engine, which vanishes completely in the case of an electric driveline. Improved gear quality unfortunately does not correlate with a better noise performance in any case. High gear quality makes sure that the gear flanks are inside tight tolerances and that all teeth are nearly identical. Even if the running behavior of such gear sets shows a very low sound pressure level, the noise perception for human ears may be annoying.
Variable loads resulting from a working process, starting process, or operation near a critical speed will cause varying stresses at the gear teeth of a drive system. The magnitude and frequency of these loads depend upon the driven machine, the motor, the dynamic mass elastic properties of the system, and other effects.
Due to near-net shape production, additive-manufactured (AM) gears have a high potential to decrease costs and increase resource efficiency. The decreasing product life cycles as well as the increasing individualization of components demand high flexibility in manufacturing processes
A brief history of AGMA's Fall Technical Meeting, along with a discussion of why this year's meeting (Oct 17-19 in Chicago) is as relevant as ever.
Gear skiving offers great opportunities for production with step-changing productivity, particularly for internal gears, whilst offering high-quality finishing capabilities and being applicable on a 5-axis machine tool with its inherent flexibility and multifunctionality.
To increase cost efficiency in wind turbines, the wind industry has seen a significant rise in power density and an increase in the overall size of geared components. Current designs for multimegawatt turbines demand levelized cost of energy (LCOE) reduction, and the gearbox is a key part of this process. Since fatigue failures nearly always occur at or near the surface, where the stresses are greatest, the surface condition strongly affects the gear life. Consequently, an improved surface condition effectively avoids major redesign or increased material cost due to an increase in part size. Additional finishing methods such as shot peening (SP) and superfinishing (SF) significantly increase the gear load capacity, but these effects have not yet been adequately considered in the current ISO 6336 standard or in any other gear standards. The combination of SP followed by SF will be described here as an “improved gear surface” (IGS).
The research presented in this paper extends the work done on CAD-based simulation approaches with an investigation of the surface topography of gears produced through gear skiving and the investigation of the cutting tool characteristics on the geometry of the produced gear. The study is complemented with the investigation of the cutting forces required in the machining process.
The fascination of the automotive differential has led to the idea to build a second differential unit around a first center unit. Both units have the same axes around which they rotate with different speeds. The potential of double differentials as ultrahigh reduction speed reducers is significant. Only the tooth-count of the gears in the outer differential unit must be changed in order to achieve ratios between 5 and 80 without a noticeable change of the transmission size.
Aircraft engines can be made more efficient by integrating planetary gears. In such an application, the planetary gears experience very high load cycles under fully reversed bending loads. Pulsator test rigs, which nowadays offer the possibility to perform UHCF investigations, can only be used for purely pulsating loading of gears. Therefore, for the investigation of the UHCF tooth root load carrying capacity under fully reversed bending load, a back-to-back test rig is required. Back-to-back test rigs usually have speeds of n = 3,000 rpm, which makes investigations in the UHCF range take a very long time. Therefore, a high-speed back-to-back test rig was developed.
The objective of this paper is to improve the methodology for determining the tooth flank temperature. Two methods are proposed for assessing scuffing risk when applying AGMA 925 for high-speed gears. Both methods provide similar results.
The objective of this paper is to develop a method for the algorithm-based design and optimization of the macrogeometry of stepped planetary gear stages.
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