Gear Surface Research Articles

Effect of Al Element on Retained Austenite, Residual Compressive Stress, and Contact Fatigue Life of Carburized and Quenched 20MnCr5 Steel Gear

To improve the contact fatigue life of gears, we studied the effect of adding a certain proportion of the Al element to a 20MnCr5 steel FZG spur gear under different heat treatment processes, characterizing the retained austenite and residual compressive stress on the tooth surface. The stability of the microstructure grain size on the gear surface under different heat treatment processes was studied, and the surface microstructure, phase structure, and composition of the gear were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The changes in the retained austenite content and grain size on the gear surface at a microscale of 2–100 μm were investigated. In addition, this study revealed the effect of adding the Al element and the optimization of the carburizing and quenching process on the residual compressive stress on the gear surface at a depth range of 200–280 μm. The effect of higher residual compressive stress and fewer non-metallic inclusions on the gear surface on the stress intensity factor of fatigue crack propagation was considered, along with the effect of deeper hardened layers on the improvement in wear resistance. The experiments in this study significantly improved the contact fatigue life of 20MnCr5 steel gears.

Computational model for fractal dimension of anisotropic gear surfaces based on improved structure function method

Computational model for fractal dimension of anisotropic gear surfaces based on improved structure function method

Study on oil film spreading characteristics on the jet lubricating tooth surface of aviation herringbone gear

Purpose During the oil lubrication process of aviation herringbone gears, lubricating oil is injected into and spreads around the tooth surface. Its spreading characteristics directly affect the lubrication state and transmission efficiency of gears. This study aims to investigate the effect of changing the injection parameters and gear operating conditions on the oil film deposition during injection lubrication. Design/methodology/approach The computational fluid dynamics method was used to establish the computational domain for the simulation and optimization using an orthogonal test. The oil film spreading and thickness of the tooth surface were calculated with the change in gear speed, fuel injection distance and fuel injection speed. Optimized oil injection lubrication parameters were obtained, and design ideas were provided for the oil injection lubrication analysis of aviation herringbone gears. Findings Under different operating conditions, such as varying the injection speed, gear rotational speed and injection distance, there were differences in the distribution of the lubricating oil film formed on the tooth surface. The thickness of the oil film decreases as the distance from the injection port increases. The thickness of the oil film deposition can be increased by increasing the injection velocity and reducing the gear rotation speed. The injection distance had a relatively small effect on the spreading thickness of the deposited oil film, affecting only the dynamic spreading process of oil film deposition. Furthermore, the simulation results are compared with the analytical calculation results, and finally the experimental verification is carried out. Originality/value Oil spray lubrication characteristics are important for achieving precise gear lubrication designs in the aerospace field. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2023-0250/

A fundamental analytical model for micro topography of skived gear surface

Surface topography is important for gear components, as it exerts influence on noise, wear, lubrication, and life expectancy. Different gear finishing processes result in varying micro tooth topographies, which lead to different driving and lubricating performances. The advanced technology of gear skiving, a recent industry application known for its high efficiency and flexibility in both roughing and finishing of cylindrical gears, has become the focus of extensive research. However, investigations into the micro topography of skived tooth flanks have been limited, primarily due to the absence of a highly efficient algorithm, which hinders the prediction and optimization of driving performance. By demonstrating that the skived surface can be obtained through the collection of micro-sections of the cutter trace in a specific order, this paper proposes a comprehensive analytical model for the micro topography of the skived surface. Both numerical and experimental studies reveal the topology texture, surface roughness, and the effects of the cutter and cutting settings. Results indicate that a higher installation angle, feed rate, and cutter tooth number are more effective in reducing roughness.

An Advanced DEM-FEM Method for Herringbone Gear in Shot Peening

Introduction: The complex geometry of herringbone gear can lead to uneven surface strengthening, which affects the overall effect of treatment. Methods: A discrete element model (DEM) of shot peening for herringbone gears was developed, incorporating accurate gear surface parameters to study impact characteristics along the tooth profile. A finite element model (FEM) was created for small local units of the gear surface to calculate the residual stress and roughness. Results: There are a large number of low-velocity shots at the root of the gear, and the closer to the top of the gear, the higher the impact velocity of the shots, but the number of impacts also decreases. The surface roughness Sa near the root of the tooth is the smallest, the Sa at the pitch circle is the largest, and the Sa at the top of the tooth is intermediate. However, the residual stress levels at different positions of the tooth surface are not significantly different. Conclusion: The difference in tooth surface roughness of herringbone gear is the synergistic effect of shot impact velocity and shot frequency, but this synergistic effect has no significant effect on the stress after shot peening.

Fatigue reliability analysis methodology based on fatigue life and failure mechanism for carburized gear

Gears are one of the important components in mechanical products, and their fatigue reliability determines the safety performance of mechanical products. In this paper, the fatigue characteristics of carburized gears under different torque and constant rotational speed conditions are investigated by using a gear contact fatigue testing machine, and combined with the dynamic maximum contact stress distribution on the subsurface of the meshing gears, the very-high cycle fatigue P-S-N curves of carburized gears under a stress ratio of −1 is established. Local stress concentration in the surface or subsurface of carburized gears causes grain dislocation movement under the combined influence of maximum contact and residual stresses, and then causes dislocation pileup and transcrystalline rupture after being hindered by grain boundaries, ultimately leading to pitting and fatigue failure of gears. Based on the dislocation energy method and combined with the fatigue failure mechanism of gears, a life prediction model of gears with good prediction results is established by considering the interaction of factors such as dynamic load, grain size, initial crack length, residual stress, slip band length and width. A fatigue reliability analysis method of gears is established based on the life state equation of gears considering the life prediction model. Further analyses of the influence of rotational speed, grain size, residual stress, slip band width, slip band length and initial crack size on the fatigue life reliability index of the gears resulted in the conclusion that the fatigue reliability of the gears not only decreases with the increase of the above-mentioned parameters, but also shows decreasing trend with the increase of time. This is of significance for evaluating the fatigue reliability of gears under very-high cycle fatigue conditions.

The Concept of Technological Support of Operational Properties Based on Stabilization of Mechanical Properties of Gear Materials in a Gas Turbine Engine Drive System

Modern production of gears for gas turbine engines for aviation, marine and land use is inherently related to the calculation of the stress state of the working surfaces of the mating teeth. To create conditions for the operability of the gear train and the drive system as a whole, an engineering analysis of the contact endurance of the mating surfaces is a necessary criterion. The contact strength determines the life of the gear mechanism. The value of the contact strength, taking into account its distribution in the contact zone of the working mating surfaces of the gears, is determined by the processing technology and operation, but the mechanical properties and texture of the material have the greatest influence. This determines the requirements for the stability of the mechanical properties of the materials used for the manufacture of gears, making a topical question on their study. The technology of manufacturing the gears in the gas turbine engine drives forms the layer structure of the toothed crown because of the use of chemical-thermal treatment. The surface hardened layer of the gear tooth after chemical-thermal treatment is saturated with carbon and nitrogen, and as a result of thermal action acquires mechanical properties and structure different from the material in the supply. The paper presents the results of practical research of evolution of mechanical properties of structural steels 20H3MVF-Sh, 18H2N4MA, 16H3NVFM-Sh and 12H2N4A-Sh based on various types of chemical-thermal treatment, as well as microstructure of toughened layer and core of the part. The steel mechanical properties stabilization evaluation in the process of gear technology was performed. The presented results of experimental studies of mechanical properties of the material prove stabilization of mechanical and structural indicators, which are responsible for the contact strength of the mating surfaces of toothed gears.

Improving the surface durability of wind gears via shot peening and superfinishing

Gearbox power density plays a key role in wind energy competitiveness. As wind turbines have become increasingly larger, gear surface durability and flank fracture load carrying capacity have become key elements in gearbox sizing. While shot peening and superfinishing have been studied independently as potential techniques to improve surface durability, few reported studies have combined both of these processes to increase the gear flank load-carrying capacity. In this work, spot pitting tests were carried out to evaluate the expected load-carrying capacity increase for wind gears through this combination of finishing processes. The results are consistent with previous research's conclusions and highlight the need for further investigations to evaluate potential increased flank fracture risk related to the near-surface residual stress distribution.

Mathematical model and generation analysis for crossed helical gear system

Purpose Crossed helical gears have point contact and their surfaces are subject to high surface stress. Contact stress and root tooth stress are the most common sources of failure in crossed helical gear. This paper aims to study the load-carrying capacity and performance of crossed helical gear teeth with different gear tooth profiles. To overcome defects and reduce the sensitivity to small shaft angle changes. The combined tooth profile is designed to reduce the bending stresses, contact stresses and tooth deflection, and prevent pinion failure in the gearbox. Design/methodology/approach The principle of the method is a line contact is introduced instead of a point contact between two teeth in mesh with each other. The tooth surface of the helical gear is designed and cut by a modified tool. Higher normal pressure angles like 25° and 35° are used. The modified involute is accomplished to eliminate interference between the teeth. Engineering software packages have been applied to generate all crossed helical gears gear profiles. The modification is compounding curves consisting of an epicycloid-involute-hypocycloid gear teeth profile generated by the cutter modified. Findings The stresses in the crossed helical gear teeth profile were reduced by increasing the normal pressure angle values. Using a 35° pressure angle the enhancement percentage in contact stress and teeth fillet region will be about 29.345% and 15.421%, respectively. The best enhancement in a gear’s resistance is the epicycloid-involute-hypocycloid gear teeth profile. The enhancement was 32.610% and 18.588%. The skew in line of action in skewed helical gear will be sensitive when the crossing angles are small. Their teeth surface tends to be easily worn out; however, the wearing process will be reduced by using a proposed gear teeth profile. Practical implications The gear teeth to be modified are cut by a shaper process. The modifying rack cutter of this study can be used as a reference for creating a different helical gears sample. The helical teeth surface is modified to become an envelope of the other. This makes an original point contact change into a line contact. The epicycloid-involute-hypocycloid gear teeth profile is preferred for a higher contact ratio and a large load capacity. This work explicitly introduces a new method of kinematic consideration to improve the load capacity of crossed helical gear. Originality/value This paper showed some novel results by the unique shape of the rack-cutter designed to generate different helical angles and different gear positions. In the future, it will make valuable contributions to the further development of the dynamic performance of a crossed helical gear system through the study in the field of using asymmetric teeth profiles of helical gears with tip relief as the manner to enhance the crossed helical gear performance. Investigation of crossed helical gear by applying a predesigned parabolic function of transmission error enables the absorption of linear discontinuous functions caused by misalignment.

A novel time-varying mesh stiffness model for orthogonal face gear drives considering EHL

PurposeThis study aims to research the time-varying mesh stiffness (TVMS) model for orthogonal face gear drives considering elastohydrodynamic lubrication (EHL) and provide a theoretical basis for understanding the dynamic characteristics of face gear drives.Design/methodology/approachConsidering EHL, a novel model is proposed to calculate the TVMS of orthogonal face gears using the deformation compatibility condition. First, the tooth surface equations of orthogonal face gears are derived according to the tooth surface generation principle. Then, the oil film thickness on the tooth surface of face gears is obtained by solving the governing equations of EHL. Furthermore, the proposed model is used to calculate the TVMS of face gears along the mesh cycle and is verified. Finally, the effects of module, tooth number of shaper cutter and pressure angle on mesh stiffness are analyzed.FindingsThe results indicate that when the contact ratio is greater than 1 and less than or equal to 2, the TVMS of face gears exhibits a phenomenon of double-single tooth alternating meshing where sudden changes occur. As the module increases, the overall mesh stiffness of face gears increases, and the magnitude of the sudden change at the moment of single-double tooth alternating meshing gradually increases. As the tooth number of shaper cutter and pressure angle increase, so does the TVMS of face gears. When the effect of oil film is considered, the calculated TVMS of face gears slightly increases overall and the increase in average oil film thickness leads to a rise in the TVMS. This study provides a theoretical basis for understanding the dynamic characteristics of face gear drives.Originality/valueThis study’s originality and value lie in its comprehensive approach, which includes conducting analysis based on loaded tooth contact, considering the influence of elastohydrodynamic lubrication, proposing a novel analytical–finite–element model, calculating TVMS of face gears, verifying the proposed model and analyzing the effects of typical structural parameters and oil film thickness.

Study of the microhardness ensuring the contact endurance of structural materials

The strength of the working surfaces of gears depends on the mechanical properties of the material and the quality of parts. We present the results of studying the strength of materials and working surfaces of a gear mechanism due to structural changes attributed to chemical and thermal treatment. The surface strength of the gears of gas turbine engines was studied. Nitrocementation and ion nitriding were used for chemical and thermal treatment of the contacting surfaces of steel samples under study (20Kh3MVF-Sh, 16Kh3NVFMB-Sh, 18Kh2H4MA, and 12Kh2H4A). Changes in the microhardness of the component layers (diffusion, transition and basic) of the toothed crown were analyzed. Metallographic analysis of the structure of materials was carried out to describe the factors determining the surface strength of working surfaces. Systematized data on the change in the microhardness of materials obtained experimentally in conditions of mass production are presented. Presented experimental results on changes in the mechanical properties of materials are based on data on the microhardness and structural state of the surface layers of the working profiles of gears. A comparative assessment of the surface strength of the studied samples during contact interaction was performed. The dependence of the surface strength on the multifactorial volumetric structure and structure formation of the material in the process of operation is determined. It is shown that the method of surface saturation forms the structure of a material with different mechanical properties accompanied with the formation of a transition zone having characteristic distinctive values of the hardness. The results obtained can be used in the design of gears, taking into account changes in the mechanical properties and structure of materials to ensure the necessary operational requirements.

Fault Intelligent Diagnosis for Distribution Box in Hot Rolling Based on Depthwise Separable Convolution and Bi-LSTM

The finishing mill is a critical link in the hot rolling process, influencing the final product’s quality, and even economic efficiency. The distribution box of the finishing mill plays a vital role in power transmission and distribution. However, harsh operating conditions can frequently lead to distribution box damage and even failure. To diagnose faults in the distribution box promptly, a fault diagnosis network model is constructed in this paper. This model combines depthwise separable convolution and Bi-LSTM. Depthwise separable convolution and Bi-LSTM can extract both spatial and temporal features from signals. This structure enables comprehensive feature extraction and fully utilizes signal information. To verify the diagnostic capability of the model, five types of data are collected and used: the pitting of tooth flank, flat-headed sleeve tooth crack, gear surface crack, gear tooth surface spalling, and normal conditions. The model achieves an accuracy of 97.46% and incorporates a lightweight design, which enhances computational efficiency. Furthermore, the model maintains approximately 90% accuracy under three noise conditions. Based on these results, the proposed model can effectively diagnose faults in the distribution box, and reduce downtime in engineering.

Laser Cladding Path Planning for Curved Metal Parts

In depositing multiple layers on the surface of failed metal parts, the overlap rate is a critical factor in determining the surface smoothness and uniformity of the coating thickness. Therefore, special attention must be given to the spacing between adjacent melt tracks when planning laser paths on complex metal parts. A strategy for selecting the overlap rate for multi-track cladding is proposed, based on the key parameters of surface curvature, mass conservation, and the profile of single-track coatings. A multi-track overlap model is developed, expressing the relationship between coating morphology and the overlap rate. The optimal spacing value is determined to achieve the goal of high-quality coating remanufacturing. To verify the effectiveness of this method, nickel-based powder was used for laser forming on the surface of metal gears. The results showed that the surface of the cladding layer was smooth and flat, further demonstrating that this model helps improve the repair quality and overall performance of curved metal parts. Thus, it provides valuable guidance for the remanufacturing of failed metal parts.

Study on Temperature Field Distribution of a High-Speed Double-Helical Gear Pair with Oil Injection Lubrication

The temperature field distribution of high-speed double-helical gears under oil injection lubrication is investigated by obtaining heat flux density and convective heat transfer coefficients through theoretical calculations and CFD (computational fluid dynamics) simulations. Based on the CFD method, fluid simulations are performed to obtain the distribution of lubricating oil on the surface of the double-helical gears, the velocity streamline diagram of the lubricating oil, and the convective heat transfer coefficients of different surfaces of the gears. The friction heat flux density is calculated using Hertzian contact theory and theoretical formula of heat generation. The double-helical gears’ steady-state temperature field simulation uses this heat flux density as a boundary condition. The correctness of the calculation method is verified through experiments. The study shows that increasing the jet velocity allows the jet to reach the tooth surface more effectively, improving the cooling effect and reducing the maximum gear temperature. However, the relationship between the jet velocity and the minimum gear temperature is non-linear. Within a certain range, increasing the jet diameter makes the jet wider, and the area covered by the lubricating oil becomes larger as the jet spreads around the gear teeth, enhancing the cooling effect. An increase in gear speed leads to an increase in frictional heat flux density; moreover, the high-velocity airflow generated by the increased speed reduces the amount of lubricant entering the mesh zone, which in turn causes the maximum temperature of the gears to continue to rise.

A novel forward performance-driven design method for gear parameters

Gear is one of the most crucial components of the transmission system, and the performance of gear directly affects the efficiency and reliability of the transmission system. Conventional methods for designing gear parameters involve several time-consuming and complex steps, which may not guarantee optimal performance. Therefore, we propose a new method for designing gear parameters that aims to improve efficiency and accuracy. First, the tooth surface equations of spur and helical involute gears suitable for symmetric and asymmetric teeth are deduced based on the gear-forming machining principle. Second, the performance evaluation models for load capacity, dynamic performance, efficiency, and power density of the gears are established based on the precise gear surface. The design objectives are standardized and evaluated comprehensively using a linear weighting method. Finally, a forward performance-driven design method of gear parameters is established. The proposed method is applied to a helical gear pair design case, and the results show that 90.7% of the individuals in the Pareto optimal front are asymmetric gears, with 9.3% being symmetric gears. This suggests that asymmetric gears have more opportunities to be optimal than symmetric gears. The highest-ranked gear designed using the proposed method is superior to the gear designed using conventional methods.

Evolution of tooth surface morphology and tribological properties of helical gears during mixed lubrication sliding wear

In mixed lubrication, the interplay of lubricant flows, solid asperity contact, and material wear between tooth surfaces creates complex and unpredictable contact states on tooth surface. To comprehensively understand the interaction between the lubrication and wear characteristics of the rough tooth surfaces of helical gears, this study established a mixed lubrication sliding wear calculation model for helical gears based on the mixed elastohydrodynamic lubrication model and Archard’s model. Specifically, the study aimed to examine the effects of surface topography features on average film thickness, contact area ratio, and accumulated wear at the meshing point. The findings demonstrated that the texture and power spectral density distributions of a non-Gaussian reconstructed surface closely resembled those of the actual ground surface. Furthermore, for non-Gaussian rough surfaces, a larger wavelength ratio enhanced microwedge motion, which increased film thickness and reduced wear. Additionally, a negatively skewed surface demonstrated better lubrication performance compared to both positively skewed and Gaussian surfaces. This improved performance is evident in the smaller contact area ratio and lower accumulated wear value of the negatively skewed surface.

Mechanical and metallurgical characterization of contact fatigue mechanisms in ADI spur gears

Surface pitting of gear teeth flanks is one of the most common causes of gear failure. The increase of the contact fatigue strength of gears is usually achieved through the development of new combinations of materials and heat-treatment processes. Austempered Ductile Iron (ADI) is one of the results of this research field that leaded to a material which is replacing conventional steel in many mechanical applications. This paper shows the experimental results obtained from tests performed on ADI spur gears in order to characterize the contact fatigue crack nucleation and growth and understand the possible interaction with the graphite spheroids and casting defects. Using a four-square test rig, it was carried out a systematic monitoring of the evolution of the damage, collecting several images concerning crack development at gear surfaces. At the end of the tests several metallurgical analyses of surface and sub-surface areas were performed to understand the fracture mechanism at the base of the pitting failure in ADI. All experimental analyses were complemented by theoretical calculations, useful for a better understanding of the phenomenon.

Multi-physics field coupling interface lubrication contact analysis for gear transmission under various finishing processes

Surface integrity is crucial for the load-bearing capacity, transmission performance, and service life of gears. Finishing processes can effectively improve surface quality and are widely used in gear manufacturing processes to enhance surface integrity and improve the service performance of gears. Five precision machining tests of form grinding, vibratory finishing, barrel finishing, honing, and abrasive flow machining were conducted on spur gears. High-precision surface integrity characterization methods were used to analyze the surface integrity parameters of the finished gear surfaces, including surface roughness, surface microtopography, residual stress, texture aspect ratio, roughness peak curvature radius. The finishing processes uniformity and effectiveness of the tooth profile surface were also evaluated. By using the finished rough surfaces as inputs and considering the impact of thermal elasto hydrodynamic lubrication on the gear surface, a multi-field coupling contact analysis model encompassing solid, liquid, and thermal fields at the gear meshing interface was established. Lubrication performance parameters such as oil film pressure, oil film thickness, oil film temperature rise, and friction coefficient under various finishing surfaces were compared and analyzed. Experimental results indicate that barrel finishing can simultaneously improve various parameters, such as surface roughness, texture aspect ratio, and compressive residual stress. Finishing processes can effectively reduce surface roughness, improve lubrication performance and reduce the risk of scuffing failure. This approach provided an effective method for the comprehensive evaluation of the effects of various finishing processes. The developed program offers theoretical guidance and data support for the selection and optimization design of gear surface finishing processes.

Automation of control of geometrical characteristics of worm and bevel gears by means of coordinate measuring

The article contains the results of research on the automation of control of the geometric characteristics of gears. The use of coordinate measuring machines can significantly improve the productivity and accuracy of measurements. However, their use for testing gears requires the use of special programs for carrying out and processing the results of measurements of products with complex surface shapes. The use of software for metrological control of the geometric characteristics of worm and bevel gears makes it possible to achieve high accuracy of control and measurement work. To automate the control of geometric characteristics of worm and bevel gears, an additional module has been created for the standard program. With its help, all points of the measured curved surface of gears, obtained by contact method according to a standard measurement program, are structured into a single data array with a measurement protocol. Based on these data, the module generates a profile of the measured surface of a wheel tooth and builds a geometric contour of the profile of the measured tooth. The result of the module's operation is the formation of a general profile of the entire gear and its comparison with the original (theoretical) profile of the gear as a whole. The control process itself is carried out in a short time interval, which makes it possible to use the proposed approach to automating the control of gear profiles in small-scale production.

Wear Mechanisms of the Working Surface of Gears after Scuffing Tests.

Identification of changes occurring on the working surface of lubricated gears using analytical equipment, e.g., an FE-SEM scanning electron microscope with an EDS microanalyzer, a WLI interferometric microscope, or a GDEOS optical discharge spectrometer, enables the characterisation of wear mechanisms of this surface. Definition of the phenomena occurring on the surface of tribo-couples after scuffing tests enables a comparative analysis of scuffing resistance and surface properties of the micro- and nanostructure, and elemental composition of the tested gears. Recognition and analysis of the wear mechanisms occurring on the working surface of gears will reduce the risk of damage and losses resulting from the need for maintenance and repair. The study concerned the working surfaces of gears made of 17HNM and 35HGSA steels on which a W-DLC/CrN coating was deposited. Shell Omala S4 GX 320 commercial industrial oil with a synthetic PAO (polyalphaolefin) base was selected for the lubrication of the gears. Tribological tests employed an FZG gear scuffing under severe conditions test method and they were carried out on a T-12U test rig for cylindrical gear analysis.