Gear Surface Research Articles

A time‐varying meshing stiffness model for gears with mixed elastohydrodynamic lubrication based on load‐sharing

AbstractIn mixed elastohydrodynamic lubrication (EHL), the load distribution between the gear meshing surfaces is shared by the oil film and the asperities of the gear's rough surface. Based on the load‐sharing concept, this paper proposes a time‐varying meshing stiffness (TVMS) model for gears with mixed EHL. The initial step involves the utilization of the Greenwood‐Williamson model to calculate the contact stiffness of surface asperities, while the lubricating film is assessed using a curve‐fitting formula to investigate the influence of gear surface morphology on TVMS. Subsequently, the incorporation of gear fillet foundation deformation and friction enables accurate TVMS determination. The proposed method is employed to examine the meshing stiffness of the gear pair under both dry lubrication and EHL conditions. Comparative analysis reveals favorable agreement between the proposed model and experimental results obtained under dry lubrication, thereby highlighting the superior performance of the proposed approach. Moreover, the time‐varying friction coefficient under EHL is computed, and the impacts of gear surface morphology parameters, temperature, speed, and load on lubrication conditions and TVMS are investigated. The findings presented in this paper contribute significantly to advancements in gear design and performance.

Evaluating the Influence of the Disc Tool Axis Position Errors on the Machined Helical Gear Surface

This work has presented advanced methods for determining disc tool profiles for machining helical gears and how to evaluate gear errors, as well as the influence of tool axis position errors on the machined gear surface by 3D comparing the tool surfaces corresponding to the tool axis positions. Experimental results for ISO standard helical gears confirm that the precision of the disc tool determined by the proposed method is very high (0.01 mm), with a helix angle greater than 20 degrees, undercutting is likely to occur, the influence of the angle between the tool axis and the machined gear axis on the gear surface deviation is on the order of 0.05 mm per 0.5 angular deviations.

Primena endoskopa kod ispitivanja motornih vozila

Industrial endoscopes are devices that are intended for visual inspection of inaccessible spaces without disassembling parts or any destructive method. Industrial endoscopes use their own light source, strong enough to illuminate inaccessible spaces where there is no natural or artificial light. Endoscopes are used to inspect pipelines in steam boilers, central openings of turbines, condition of internal parts of generators, surfaces of gears in transmissions, surfaces of cylinders and damage to valves of engines and reciprocating compressors, pressure vessels, position of core transformers, condition of axial compressors, jet engines. In the case of assemblies and parts of modern motor vehicles, where, due to their compact structure, it is not possible to perform inspection and control without complex and expensive disassembly, the application of the endoscope simplifies and significantly lowers the cost of the procedure. Industrial endoscopy began to be applied as a method of control and inspection, with a certain amount of subjectivism. The hardware, and especially the software used in today's endoscopes, has enabled industrial endoscopy to become an exact measurement method. This allows industrial endoscopy to be included in the equal methods of a laboratory accredited according to the SRPS ISO IEC 17025:2017 standard. as repeatability and reproducibility criteria given in the series of standards SRPS ISO 5725:2007. A brief critical review in the application of existing standards, is presented. In conclusion, recommendations related to risk management are given.

Mathematical modeling and simulation of generation milling process to manufacture complex face gear surface through multi-axis machine kinematics

Manufacturing of face gear is a complex process, due to its varying geometry, hence the application is not wide as conventional gear geometry. The developments in analytical tools and kinematics of the CNC machine tools motivate researchers to explore the manufacturing process and associated applications. This article presents an efficient method for the generation milling of spur face gear utilizing a nutating head multi-axis CNC machine tool where the tool swings about an arbitrary axis in an inclined plane. The mathematical model of the disk milling cutter and face gear geometry were derived from the shaper geometry by applying the theory of gearing, equation of meshing and coordinate transformation. The cutter location (CL) data was evaluated by aligning the tool orthogonal unit vector and the tooth surface normal vector at the contact point by calculating the appropriate transformation matrices. The evaluation of machine coordinates on a multi-axis CNC milling machine was analyzed with respect to the machine pivot point and the axes movement during generation milling for the face gear drive was studied on the nutating head machine. The NC data is derived from the CL data using the inverse kinematics and the machining simulation was carried out using suitable software. The tooth surface deviation of a maximum of 43.5 μm was observed between the simulated model and the theoretical model, which is well within the requirement of roughing. The generation milling process with the proposed machine configuration is concluded as a profound face gear manufacturing technique.

Fractographic research of destruction of 34CrNi1Mo steel gear shaft

Goal. The purpose of this research work is to establish the causes and mechanisms of destruction of gear shaft made of 34CrNi1Mo steel, to provide recommendations to prevent this type of product damage. Methodology. The gear shaft made of 34CrNi1Mo steel destroyed during operation was studied. The fracture surface of the investigated steel was studied by macroanalysis and scanning electron microscopy using a SEM-100У microscope at a magnification of 1500-10000 times. Microstructural analysis of 34CrNi1Mo steel was carried out on Neophot-21 optical microscope at x250, 300; 800 magnification. Microhardness was measured according to the standard method on a PMT-3M microhardness tester at a 50 g loading. Results. The causes and nature of the operational destruction of the gear shaft made of steel grade 34CrNi1Mo were analyzed. The fatigue nature of fracture was determined. The unsatisfactory quality of the surface of the experimental product was established: shells, pores, scratches, chips were found on the surface. The destruction began in the place of the geometric stress concentrator (surface defect – shell) due to metal chipping. Originality. The features of the destruction of the gear shaft were determined: at the break, there is a significant distance between the fatigue grooves, which indicates a high crack propagation rate, the fatigue grooves are weakly expressed, irregular, which indicates the limited possibilities of steel to plastic deformation. The fractographic surface of the fracture is shiny and consists of cleavage facets, covered with coarse scars, fan-shaped diverge from the focus, has a coarse-grained structure, typical for brittle fracture. The brittle nature of the fracture was confirmed by scanning electron microscopy. The surface microrelief contains cleavage facets, microcracks, and intergranular spall cells. Non-metallic inclusions of MnS, which are additional structural stress concentrators, have been revealed. Microcracks originate near non-metallic inclusions; at the boundaries of former austenite grains, especially at their triple junctions; at the interface between matrix and secondary phases. An increase in microhardness from 2500 to 4750HV after heating to 840–860°C with subsequent cooling in air was established, which can be explained with the probable hardening of the experimental steel, which, along with an increase in hardness, leads to a decrease in steel ductility. Practical value. It is recommended to use steel with a low sulfur content, additional gear shaft surface treatment to prevent the formation of stress concentrators in places of surface discontinuities; compliance with the nominal temperature regime also prevents spontaneous hardening of the product material.

Influence of idler misalignment fault on contact and dynamic characteristics of helical gear

Due to the advantages of stable helical gear transmission, it is widely used in industry, agriculture, and national defense. Shaft misalignment has a great influence on the vibration, bearing capacity, and life of gear transmission. Based on the idler wheel drive system as the research object, according to the principle of gear meshing, the helical gear time-varying contact wire length model was deduced. The dynamic model of the gear transmission system with faults is established considering the faults of the idler's center distance error and angle error, and the influence law of idler misalignment fault on the vibration of the idler transmission system is revealed. On this basis, the finite element model under angle error is established to analyze the contact stress of the tooth surface under different faults and reveal the contact stress distribution law of the tooth surface. The results show that the misalignment fault will change the length of the helical gear contact line. When the gear shaft misaligns, it will increase the axial force of the gear and increase the axial vibration of the gear. Moreover, the angle error will cause uneven load distribution on the tooth surface of the helical gear, which will reduce the contact area of the gear and increase the contact stress. The phenomenon of off-load of gear accelerates the wear of the gear tooth surface and shortens the life of the gear. The study of idler misalignment fault is of great significance for prolonging the life of gear and providing the basis for gear fault diagnosis.

Non-contact flank modifications of spur gears using cathodic gear tools and mechanisms: an experimental study

ABSTRACT This paper introduces cathodic gear tools designed for non-contact modification of spur gears through pulsed electrochemical flank modification. Operating with continuous rotary motion, these tools achieve profile crowning, lead crowning, tip relieving, root relieving, and end relieving. Anodic workpiece gears experience constant or variable reciprocating velocity based on the modification type. Experimental investigations confirm that the tools not only achieve the intended flank modification but also reduce flank surface roughness, eliminating hob cutter marks and cracks from the modified spur gear surfaces. The magnitude of intended modifications increases with higher voltage and longer modification duration. Notably, root relieving requires a longer duration (20 minutes) compared to other modifications (12 minutes). Details of variation in surface roughness and surface morphology using scanning electron microscopy are also presented to validate the developed mechanism.

A computationally robust solution to the contact problem of two rotating gear surfaces in space

A computationally robust solution to the contact problem of two rotating gear surfaces in space

Contact Analysis for Cycloid Pinwheel Mechanism by Isogeometric Finite Element

Cycloid drives are generally used in precision machinery requiring high-reduction ratios, such as robot joint (RV) reducers. The contact stress of cycloidal gears greatly affects lifetime and transmission performance. Traditional finite element method (FEM) has less computational efficiency for contact analysis of complex surface. Therefore, in this paper, isogeometric analysis (IGA) was employed to explore the multi-tooth contact problem of the cycloid pinwheel drive. Based on the nonuniform rational B spline (NURBS) curved surface generation method, the NURBS tooth profile of the cycloid gear was reconstructed. In addition, the NURBS surface of the cycloid gear–pin tooth–output pin was generated via the element splicing method. A geometrical analysis model of cycloid pinwheel drive was established to solve the contact force of the meshing pair under different input angles and compared with the finite element method in terms of convergence, resultant accuracy, and solving timeliness. The results show that isogeometric analysis has higher accuracy and efficiency than the finite element method in calculating the contact stress and contact force. The error of the IGA is only 8.8% for 10 × 10 elements in contact, while the error of the finite element method reaches about 40%. The method can improve the contact simulation accuracy of the cycloid drive and provides a reference for the design evaluation of RV reducer.

Thermoelastoplastic hydrodynamic lubrication contact analysis of three dimensional rough tooth surface considering micro-scale effect and thermal effect

The contact properties of gear rough surfaces during meshing are influenced by various factors. The analysis of rough surface thermoelastoplastic hydrodynamic lubrication (TPEHL) considering micro-scale effect and thermal effect has not been addressed in the literature. This study establishes a new TEPHL model with multi-factor coupling of thermal field, fluid lubrication, stress-strain, and geometric profile. Based on strain gradient theory (SG), a new thermoelastoplastic material constitutive considering micro-scale effect is developed. Subsequently, the three-dimensional rough surface TPEHL-SG analysis of gear is conducted. The paper investigates the impact of thermal and micro-scale effects on various parameters during the meshing of gear in the full oil film lubrication condition, including surface pressure, oil film thickness, surface temperature, surface deformation, and friction coefficient.

Effects of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gear

Bionics research has revealed the remarkable fatigue resistance exhibited by intertidal zone shellfish, attributed to their radial ribs and multi-layered microstructure. Leveraging the analogous stress and working conditions shared by shellfish and gears, we adopted the discrete laser surface melting (DLSM) technology to create discrete laser surface melted (DLSMed) units on gear tooth surfaces. This paper aimed to scrutinize the influence of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gears. In terms of laser selection, we opted for the Nd: YAG pulsed laser. Across various laser parameters, the proportion of DLSMed units on gear tooth surfaces varied. Scanning Electron Microscopy (SEM) facilitated the observation of microstructures and fatigue morphology of the DLSMed gear. X-ray Diffraction (XRD) measurements gauged residual stress along both the surface and cross section of the DLSMed unit, unveiling the residual stress distribution. Microhardness and surface roughness were assessed through a microhardness tester and a surface profilometer, respectively. Fatigue tests were conducted using both the Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine and a high-frequency fatigue testing machine. Experimental findings disclosed that the DLSMed unit comprised a melting zone and a heat-affected zone. The depth of the residual compressive stress layer increased alongside current intensity, albeit with the unexpected emergence of residual tensile stress. Enhanced current intensity corresponded to a noticeable elevation in the DLSMed gear's hardness value. Differing fatigue behaviors were evident between the as-received gear and the DLSMed gear. The DLSMed gear exhibited reduced fatigue damage compared to the as-received gear. The DLSMed units effectively curbed crack initiation and propagation, markedly enhancing gear fatigue performance. A direct relationship between the DLSMed unit's area proportion on the gear surface and gear fatigue strength was established. Finally, we delved into the anti-fatigue mechanism underlying the DLSMed gear's performance.

Theoretical modeling and transmission characteristics analysis of a novel double-roller hourglass worm drive based on enveloping principle

Traditional planar double-enveloping hourglass worm pairs have the characteristics such as the strong bearing capacity, high transmission efficiency and long life-span. However, the high relative sliding velocity and the serious agglutination or abrasion may also occur at the contact point on tooth surfaces. In this paper, a novel type of double-roller hourglass worm pair is proposed and analyzed, wherein, the worm part adopts from the planar double-enveloping worm pair, the corresponding meshing tooth surface of worm gear is replaced by two rows of cylinder rollers for reducing friction and enhancing meshing efficiency. That is, the original meshing tooth surfaces in worm gear are replaced by the common tangent plane of rollers to form a special type of meshing drive, the original line-contact form between tooth surfaces was changed to point-contact so that the sliding friction was transformed into rolling friction, and the meshing efficiency can be greatly improved. The theoretical model of double-roller hourglass worm pair was established based on spatial enveloping principle, the meshing equation and tooth surface equations were derived. The solid models of worm and gear were established and assembled. The parameters of enveloping surface angle, roller radius and friction coefficient, which affecting relative motion velocity at meshing contact point and efficiency during the whole transmission process was analyzed and discussed systematically. The results showed that comparing to the traditional worm pair, the roller’s rotation greatly reduced the relative sliding velocity and improved meshing efficiency at the contact point in this double-roller hourglass worm pair.

Switching backdrivability of a planetary gear by vibration: design parameter setting and excited force estimation

Switching backdrivability according to use status is important to attain energy-saving and compliance in co-worker robots. Authors have proposed switching backdrivability by exciting gear surface, eliminating the need for sensors while switching. We have confirmed that exciting 2K-H planetary gear can switch its backdrivability. To systematically design the switching backdrivable 2K-H planetary gear, this study reveals less back-drive condition and the required torque for a vibrator. In the less-backdrivable condition, the tooth number difference between the fixed and output gears is dominant. Furthermore, the required torque for the vibrator increases as the load of the output shaft and the vibration frequency increase. The experimental results of the less-backdrivable condition and the required torque for the vibrator are almost entirely consistent with simulation result of the mechanical model

Bidimensional local characteristic-scale decomposition and its application in gear surface defect detection

Visual image-based inspection methods can directly reflect the type of defects on the surface of gears. However, these methods have many problems: firstly, as a two-dimensional signal, the data volume of images is large and the processing is relatively time-consuming. Although some existing image signal processing methods (e.g. bidimensional empirical mode decomposition (BEMD)) have good decomposition results, their decomposition speed is slow. The bidimensional local characteristic-scale decomposition (BLCD) method is proposed in this paper, which adaptively decomposes an image from high to low frequencies into several bidimensional intrinsic scale components. It is demonstrated that the BLCD method maintains the advantages of the BEMD method in terms of good decomposition ability and adaptive capability while significantly reducing the processing time and improving the computational efficiency. Secondly, in the running state of the gears, the obtained images sometimes contain noise, which is not convenient for detecting surface defect types. A gear surface defect detection method based on BLCD image denoising is proposed in this paper. Firstly, it uses the BLCD denoising module for preprocessing to provide high signal-to-noise ratio images for the subsequent detection module, and then uses the detection module for defect identification and classification. Experiments prove that the BLCD denoising module has excellent performance and it is well coupled with the detection module, giving the whole method higher accuracy and stability than other classification methods.

Intelligent classification framework for gear surface damage and gear type using CNN transfer learning

In the mechanical transmission system gear has a very important role, and Gear surface damage is an important factor affecting gear transmission. Regular inspection of each gear and its surface damage is of great significance for ensuring the stable operation of a whole mechanical system. To improve the identification efficiency and accuracy for gears and their surface damage, In this paper, we propose a gear and its surface damage recognition method based on PyTorch deep learning library, expand the dataset using data augmentation and data extension techniques, compare the performance of gear and its surface damage recognition under three typical models, namely AlexNet, VGG16, and ResNet-101, and optimize each training model through migration learning and hyperparameter comparison. The results show that the speed and accuracy of model training can be improved by applying transfer learning. By extending the dataset using data augmentation techniques, the robustness of the network is improved considerably. When the batch size is 6 and the initial learning rate is set to 0.01, the model training effect is the best, and ResNet has higher recognition accuracy and stability than AlexNet and VGG16, which is more suitable for the classification of gears and their surface damage. In order to find the optimal ResNet model, four ResNet models with different number of layers, ResNet-34, ResNet-50, ResNet-101 and ResNet-152, were compared, among which the ResNet-101 model showed the optimal performance in gear surface damage recognition.

Scientific Basis for the Substantiation of Process Regulations for the Micro-Cutting of Hardened Gears

Abstract The paper considers scientific principles of technological procedure development for the selection and assignment of parameters of velocity machining by blade tool at gear milling with due regard to the required parameters of the gear surface layer. Optimum micro-cutting conditions are determined when full participation in stock removal of all mill teeth is provided. Technological regulation of selection and setting of machining parameters is spread for gear hobbing of the spur gear wheels with fine-modular and coarse-modular hardness (220...320 HV) and after heat treatment (HRC46...63). Correlation with essential parameters of the surface layer, cutting depth, feed, speed and radius of rounding of the cutting edge of milling cutters’ teeth is established. It is scientifically grounded, tested, and proved at what modes of cutting, the radius of rounding of cutting edge of the cutting tool is made metal removal at oncoming and passing high-speed micro milling. The process of determining of minimal sliding angle, or maximum value (without the use of coolant and with coolant), in which there is no micro-cutting process taking into account variation of variable parameters of cutting conditions and geometrical parameters of hobbing cutters is modelled. For the first time, we ascertained the relation between the sliding angle and the maximum contact angle of the mill tooth with the work surface, which allowed determine the efficiency of the shaping process through coefficient (without coolant and with coolant).

Investigation on wear behavior for SUS420 steel gear based on discrete laser surface melting

Gears are critical components that ensure the stable operation of a gearbox. In the era of mechanical equipment advancing towards higher speeds and heavier loads, more stringent requirements have been set for the wear performance of existing gears. Drawing inspiration from observations of natural organisms, particularly scallops, which have developed unique microstructure and excellent wear properties through long-term evolution, this paper focuses on the application of discrete laser surface melting (DLSM for short) technology to prepare units on the surface of SUS420 steel gears, simulating the radial rib structures found on scallop surfaces. The laser processing was carried out with varying defocusing amount and distribution types of discrete laser surface melted (DLSMed for short) units. The study encompassed microstructure observations, microhardness and residual stress testing, and bench wear experiments on DLSMed gears. The experimental findings reveal that a crack-free and porous-free hardened layer has formed on the tooth surface. The hardened layer consisted of the melting zone, heat-affected zone, and substrate, resulting in a surface structure characterized by alternating soft and hard phases. Comparing the wear behavior of as-received gear to DLSMed gears, it is evident that the wear damage on DLSMed gears is less pronounced. The DLSM treatment had altered the wear mechanism of the gears. During the wear test, the quantity of wear debris and iron (Fe) concentration in DLSMed gears consistently remained lower than that of as-received gears, indicating superior wear resistance in DLSMed gears. Furthermore, an increase in the defocus amount led to a deterioration in the wear performance of DLSMed gears. Notably, transverse units exhibited better efficacy in enhancing the wear resistance of gears compared to longitudinal units. There exists a positive correlation between the percentage of DLSMed unit area on the gear surface and the wear behavior of the gear.

Development of analytical models for tip, root, and end relieving of spur gears by pulsed electrochemical finishing process

This paper describes analytical modelling for the non-contact tip, root, and end relieving of spur gears and their associated volumetric material removal rate (MRR) by the pulsed electrochemical finishing (PECF) process. The models were developed using Faraday’s law of electrolysis and involute geometry of spur gears. The developed models are validated experimentally using the innovatively designed and developed cathode gears and experimental apparatus by varying voltage, pulse-on time, and pulse-off time at four levels each. It found that minimum prediction errors for the developed models for the amount of tip, root, and end relief are 0.8%, 0.3%, and 1.3%, respectively, and minimum prediction error for models of volumetric MRR of tip, root, and end relief are 6.9%, 0.6%, and 9.8% respectively. A study of microgeometry along the profile and lead direction of spur gear confirmed that the PECF process not only successfully imparted tip, root, and end relief but also reduced their arithmetical average roughness and maximum height by 61.1% and 62.5% for tip relief, 67.7% and 67.8% for root relief, and 63.8% and 66.6% for end relief respectively. It also removed hob cutter marks and cracks revealed from the comparison of surface morphology of spur gear flank surfaces before and after tip, root, and end relieving. Maximum values of % reductions in maximum height and arithmetical average roughness occurred for pulse-on and pulse-off times as 3 and 4 ms (i.e., 43% duty cycle). The developed models will be very useful in designing or predicting the amount of tip, root, and end relief that can be imparted for a given modification duration. Conversely, they can be used for parametric optimization of the PECF process and to compute the required duration for the PECF process to impart the desired amount of tip/root/end relief to spur gears.

Comparative tribological performance of a-C:H, ta-C and AlCrSiN coatings on 20CrMnTi gear steel under dry sliding condition

PurposeThis study aims to investigate the surface modification on 20CrMnTi gear steel individually treated by diamond-like carbon films and nitride coatings.Design/methodology/approachFor this purpose, the mechanical properties of a-C:H, ta-C and AlCrSiN coatings are characterized by nano-indentation and scratch tests. The friction and wear behaviors of these three coatings are evaluated by ball-on-disc tribological experiments under dry contact conditions.FindingsThe results show that the a-C:H coating has the highest coating-substrate adhesion strength (495 mN) and the smoothest surface (Ra is about 0.045 µm) compared with the other two coatings. The AlCrSiN coating shows the highest mean coefficient of friction (COF), whereas the ta-C coating exhibits the lowest one (steady at about 0.16). The carbon-based coatings possess excellent self-lubricating properties compared with nitride ceramic ones, which effectively reduce the COF by about 64%. The major failure mode of carbon-based coatings in dry contact is slight abrasive wear. The damage of AlCrSiN coating is mainly adhesive wear and abrasive wear.Originality/valueIt is suggested that the carbon-based film can effectively improve the friction-reducing and wear resistance performance of the gear steel surface, which has a promising application prospect in the mechanical transmission field.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0129/

Improvement of the wear resistance of 20CrMnTi steel gear by discrete laser surface melting

This paper studied the effect of discrete laser surface melting on the wear resistance of gears. The radial ribs on the surface of intertidal shellfish had the function of anti-abrasion. The discrete laser surface melted (DLSMed) units were processed on the gear surface, and they looked like radial ribs.The microstructure and wear morphology of the DLSMed unit were observed under a scanning electron microscope. The phase composition and residual stress of the DLSMed unit were analyzed through a X-ray diffractometer. The hardness of the DLSMed unit was measured with a microhardness tester. The roughness of the DLSMed unit was measured with a surface topography meter. The wear test of gear was carried out with a Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine. The lubricating oil analysis technology was used as the evaluation basis of gear wear performance. The experimental results showed that discrete laser surface melting could refine the grain on the gear surface, improve the hardness of the gear, and form residual compressive stress on the gear surface. The cross-sectional area of the DLSMed unit gradually decreased as the laser scanning speed increased. As the cross-sectional area of the DLSMed unit decreased, the wear resistance of the gear also deteriorated. Finally, the wear mechanism of the DLSMed gear was discussed from many aspects.