Gear Rolling Research Articles

Micromechanical analysis of gear fatigue-ratcheting damage considering the phase state and inclusion

Abstract Despite the fact that high-quality steels are manufactured in recent years, non-metallic inclusions such as Al2O3 are still inevitable during steel manufacturing process. Early failures of bearings and gears are widely associated with the non-metallic inclusions, especially in some heavy duty machines such as wind turbines, ships and high-speed rails. Inclusions commonly act as a stress raiser, forming the micro-crack at the matrix material, which severely limits the service performance of heavy-duty components. Besides, the phase component of such steels represents a typical multiphase state, which makes the inclusion-induced failure mechanism still remain unclear. In this study, the gear rolling contact fatigue (RCF) performance is evaluated on the micro level by considering the effect of the inclusion and different phase states. The crystal plasticity framework is implemented to model different phase states, describing the stress-strain response on slip systems. Fatigue damage and ratcheting damage are both considered in a local area surrounding the subsurface inclusion. The influence of different phases, including martensite and austenite, around the inclusion on the damage accumulation are also investigated. The simulation results reveal that the fatigue damage and the ratcheting damage surrounding the inclusion occur at different areas. The inclusion induces the ratcheting damage at the neighboring matrix within a highly localized area. The higher ratcheting damage is mainly found following the direction of approximately 45° with respect to the rolling direction. Besides, the different contributions of subsurface inclusions and grain boundaries on the ratcheting damage are found.

Ratchetting–multiaxial fatigue damage analysis in gear rolling contact considering tooth surface roughness

Under the combined effect of the tooth surface roughness and heavy load condition, gear materials might experience both the fatigue damage and the ratchetting damage. An elastic-plastic finite element contact fatigue model is proposed considering the optically measured tooth surface roughness and the gear contact geometry. The kinematic hardening constitutive equation and the Jiang and Sehitoglu ratchetting-multiaxial fatigue model are applied, and the contribution of the ratchetting-fatigue damage in the mechanism of gear contact fatigue problems is discussed. Results reveal that the surface roughness can promote the emergence of ratchetting behavior within a very shallow area near surface. Furthermore, the effect of the normal load condition on the ratchetting-fatigue damage is also discussed.

Investigation on gear rolling process using conical gear rollers and design method of the conical gear roller

A type of gear rolling process using conical gear rollers was firstly proposed in this study. Different with the cylindrical gear rollers used in the traditional gear rolling process, the roller which looks like a conical gear with different tooth profile along the axial direction was adopted in the rolling process. Besides, the radial feed applied on the roller in traditional rolling process was replaced by the axial feed applied on the blank. The proposed rolling process was divided into three stages, viz., tooth graduation, tooth forming and tooth finishing. According to the function of the roller in each stage, the structure of the conical gear roller was designed. Importantly, the detailed formulas to calculate the essential parameters of the gear roller’s tooth in tooth forming stage were established, such as the diameter of addendum circle, the radius of addendum tip, the pressure angle, and the cone angle. Through the numerical simulation, the variation and forming mechanism of the tooth profile at different stages were analyzed. The results revealed that the proposed process achieves better uniform tooth graduation and refining of the tooth profile, which increase the forming accuracy of the tooth to some extent in rolling process. Moreover, the experimental device was developed and the feasibility of the conical gear rolling process was verified.

Effects of the material and its temperature state on the tooth morphology in gear rolling

The “rabbit ear” defect in gear rolling is closely related with the flow state of the metal in local area. The material of the blank and its temperature state affect the flow state of the metal directly, thus affecting the tooth morphology. In this paper, the quantitative evaluation index of the tooth morphology in gear rolling is established. Through the numerical simulation, the change law of the tooth morphology with different materials such as carbon steel, pure aluminum, and wrought aluminum and that with different forming temperatures are acquired and the reasons are analyzed. Using self-developed gear rolling experiment device, the experiment study of gear rolling is done while pure aluminum, Al_2017, and lead are selected as the material of the blank; the simulation results are verified experimentally. The results provide a scientific basis for the choice of the blank’s material and the forming temperature, controlling the rabbit ear defect and improving the forming quality of gear rolling.

The Effects of Blank Geometry on Gear Rolling for Large Gear Modules: Experiments and Finite Element Simulations

Gear rolling is a forming process to produce gear wheels by plastic deformation. The advantage of the process is to eliminate the chip formation during production and also to improve the product properties since the non-metallic inclusions will be oriented along the cog surface and not perpendicular to it. The method has been developed in the past years for gear production for automobile application with modules up to 3 mm. The successful application of gear rolling in those cases raises the question regarding the feasibility of using cold rolling to manufacture gears with larger modules which can be used for heavy vehicles. In this paper, a gear wheel with normal module of 4 mm has been studied in order to investigate if such large modules can be manufactured by gear rolling. One of the issues in rolling of gears is the design of the blank geometry in order to obtain the right gear geometry after the rolling process. Blank shape modifications are necessary to control and to reduce the undesired shape deviations caused by the large plastic deformations in rolling. The blank modifications also help the process designer to control the forming force and torque. In this paper, the process has been modeled by finite element simulation and the influence of different blanks has been simulated. The validity of the FE model has been checked through several experiments. Both the numerical and experimental results revealed favorable blank modifications to apply for further developments of the gear rolling process.

Effect of process factors on the rabbit ear based on numerical simulation and experimental study in gear rolling

The “rabbit ear” defect, which is the protrusion on the tooth top of the blank, is a typical deformation characteristic in gear rolling and severely influences the forming quality of the formed gear. The main factors affecting the rabbit ear formation, including rolling feed of the gear roller, friction condition, and number of teeth on the gear roller, are demonstrated through analyzing the gear rolling process condition. In order to quantitatively describe the rabbit ear volume, a quantitative evaluation index of the rabbit ear volume was given. The effects of rolling feed of the gear roller, friction condition, and number of teeth on the gear roller on the rabbit ear volume were numerically simulated by Deform software. The effect of different rolling feeds of the gear roller on the rabbit ear volume was studied experimentally, which verified the reliability of the finite element simulation. The results can provide scientific evidences for establishing reasonable process parameters, and improving the forming quality in gear rolling.

A Study on 5-Axis Machining of Roller Gear Cam for Rotary Table

A Study on 5-Axis Machining of Roller Gear Cam for Rotary Table

Damage on Roller Bearing Races and Gear Teeth – Classification and Methods of Analysis

Damage on Roller Bearing Races and Gear Teeth – Classification and Methods of Analysis

Numerical-experimental investigation on the rabbit ear formation mechanism in gear rolling

The formation of rabbit ears during the gear rolling process, caused by the generating motion between the gear roller and the blank, is a common and undesirable phenomenon encountered in gear rolling. It generally leads to fold defects, waste of material, and decline in mechanical properties after removal, seriously affecting the quality of the gear to be formed. In this paper, a finite element model of gear rolling is first established, the gear rolling process are simulated, and the rabbit ear formation mechanism and its morphology change are studied. The phenomenon and the morphology of the rabbit ear are then verified experimentally. The formation mechanism of the rabbit ear was analyzed by means of the stress state, the deformation distribution, and the material flow. The results show the following: (1) the continuous localized contact between the gear roller and the blank induces the material on the surface area of the tooth sequential plastic deformation, while at the same time, the material is squeezed by the tooth flank of the gear roller and flows towards the direction of the smaller resistance, that is, the flank of the tooth. The difference in the material flow velocity between the flank of the tooth and the center of the tooth leads to the formation of the rabbit ear; (2) the asymmetric shape of the ears appears to be related to the different direction of friction exerted on two sides of the tooth depending on the rotational direction of the gear roller. These findings provide a scientific basis to further explore measures to control the rabbit ear defect and improve the forming quality in gear rolling.

Compound faults detection in gearbox via meshing resonance and spectral kurtosis methods

Kurtosis-based impulsive component identification is one of the most effective algorithms in detecting localized faults in both gearboxes and rolling bearings. However, if localized faults exist in both gear tooth and rolling bearing simultaneously it is difficult to tell the differences between the two types of defects. As such, this study proposes a new method to solve the problem by using the meshing resonance and spectral kurtosis (SK) algorithms together. In specific, the raw signal is first decomposed into different frequency bands and levels, and then the corresponding Kurtogram and MRgram are calculated via the fault SK analysis and the meshing index. Furthermore, the resonance frequency bands induced by localized faults of the gear tooth and rolling bearing are separately identified by comparing the Kurtogram and the MRgram. Finally, the compound faults are respectively detected using envelope analysis. The effectiveness of the proposed method has been validated via both simulated and experimental gearboxes vibration signals with compound faults.

Numerical simulation and experimental investigation on the gear rolling process

Abstract Besides having advantages including high utilization rate, high productivity and superior mechanical properties, gear rolling also overcomes many problems of closed die forging such as bad mold working conditions and difficult ejecting from the die due to heavy loads. In gear rolling process, the main problems to solve are tooth graduation non-uniformity in the initial forming phase and formation of rabbit ears in later forming stage. In this paper, according to the requirements of tooth graduation correctness and uniformity, several methods to determine the initial blank diameter were proposed and compared to each other. The main factors affecting the slippage is obtained through the applied forces on the blank, the tooth graduation process is simulated, and the influence laws of the main factors on the slippage are acquired in the initial forming phase of gear rolling. The forming stage of gear rolling process was simulated, the forming mechanism of rabbit ears was analyzed based on deformation distribution, material flow and friction force state during tooth forming. The slippage phenomenon and morphology of rabbit ears in the tooth forming stage were experimentally studied respectively with a set of cylindrical gear rolling device. The experimental results accorded with that of simulations well.

A new calibration guideline for worm and worm-gear rolling testers

The evaluation and calibration of gear testers are considered as a key point to ensure the obtained results in gear metrology. Although ISO TC 60 working group has developed standards in this regard, the fact is that for the time being, there are not specific international standards for gear rolling tests. In this work, a periodical calibration guideline for gear rolling testers, particularly for worm gear transmission, is proposed, allowing the reduction of possible error sources in the measurement process. A series of tasks distributed over time are suggested in this work to maintain the accuracy of the gear rolling test machines.

Hot forming of large spur gears

Forming processes are generally characterized by a high degree of material utilization as well as short process times and, consequently, a decent economic efficiency. Considering their application in the manufacturing of large spur gears, forming processes offer a significantly attractive characteristic for the production of essential gearing components commonly used in wind turbines or marine engines. Furthermore, the hot forming process can be defined as an incremental forming process which enables the use of relatively low forming forces and results in a more compact design of the used machines. These conveniences are utilized in terms of roll forming with round tools to form gears and threads in a competitive way. Based on experiences gained over many years of researching rolling technologies, a cross-rolling process characterized by round tools with outer gearings was elaborated to realize a hot forming process for gear rolling of large spur gears at the Fraunhofer IWU Chemnitz. Based on the already researched forming of smaller dimensioned gears, rolling trials utilizing a new hot-forming machinery - including defined inductive heating process before rolling - to realize large gears with outer diameters of up to 1000 millimeters were conducted. In terms of realizing this ambition, the derivation of the designated machine parameters for rolling large gears in real-life dimensions can be defined as a crucial factor. Consequently, the experimental research was followed by a mathematical analyzation of the forming forces, momenta as well as the necessary steps to determine the best possible scaling factors for the work pieces.

STRESS ANALYSIS IN DURABILITY TESTS OF SINTERED STEEL GEARS WITH DIFFERENT DENSITIES USING FEM MODEL CONSIDERING VOIDS

Gear-running tests were first carried out using casecarburized Ni-Mo pre-alloy sintered steal gears with different densities of 7.30 g/cm3, 7.40 g/cm3 and 7.54 g/cm3. The load bearing capacity of P/M gears was increased by 5-15% by gear surface rolling, whose effect was most remarkable for P/M gears with a middle density. The surface fatigue strength after 1.0×107 cycles of surface rolled P/M gears with a density more than 7.40 g/cm3 were higher than that of case-carburized Cr-Mo wrought steel gear. These experimental results were then analytically investigated by examining the contact stress distributions around the operating pitch point of P/M pinion using an original two-dimensional finite element model considering voids. The peak of the maximum shear stress τmax decreased as the amount of fully surface-densified depth δ increased, and there was only a slight difference in the τmax distribution for every P/M pinion when δ reached 0.3mm. These simulation results appear to explain the durability test results well and reveal the appropriate δ level.

Enhanced Orthogonal Matching Pursuit Algorithm and Its Application in Mechanical Equipment Fault Diagnosis

The vibration signal measured from the mechanical equipment is associated with the operation of key structure, such as the rolling bearing and gear. The effective signal processing method for early weak fault has attracted much attention and it is of vital importance in mechanical fault monitoring and diagnosis. The recently proposed atomic sparse decomposition algorithm is performed around overcomplete dictionary instead of the traditional signal analysis method using orthogonal basis operator. This algorithm has been proved to be effective in extracting useful components from complex signal by reducing influence of background noises. In this paper, an improved linear frequency-modulated (Ilfm) function as an atom is employed in the proposed enhanced orthogonal matching pursuit (EOMP) algorithm. Then, quantum genetic algorithm (QGA) with the OMP algorithm is integrated since the QGA can quickly obtain the global optimal solution of multiple parameters for rapidly and accurately extracting fault characteristic information from the vibration signal. The proposed method in this paper is superior to the traditional OMP algorithm in terms of accuracy and reducing the computation time through analyzing the simulation data and real world data. The experimental results based on the application of gear and bearing fault diagnosis indicate that it is more effective than traditional method in extracting fault characteristic information.

Study on induction heating of workpiece before gear rolling process with different coil structures

The temperature distribution of heated workpiece has a great impact on the subsequent gear rolling process. To get a satisfied temperature distribution, longitudinal magnetic flux (LMF) coil and transverse magnetic flux (TMF) coil were designed. The influences of current density and current frequency on the heating efficiency and the temperature distribution of the workpiece corresponding to two coil structures were investigated by establishing an induction heating model combing the coupling of electromagnetic and thermal fields and the rotary motion of the workpiece. In addition, an induction heating experiment was conducted to verify the model. From the numerical results, a conclusion can be made that compared with TMF coil, the LMF coil can reduce the inner hole temperature and improve the heating efficiency. With proper current density and current frequency, the workpiece heated by LMF coil can obtain a better temperature distribution than that heated by TMF coil.

Numerical and experimental investigations on large-diameter gear rolling with local induction heating process

Gear rolling with local induction heating process is a novel method to produce large-diameter gears with great advantages. To investigate the gear forming process, a simplified finite element (FE) model coupling electromagnetic-thermal and deformation fields is developed in the DEFORM-3D software and is validated by corresponding experiments. According to the numerical and experimental results, producing large-diameter gears using gear rolling process with local induction heating is feasible. Moreover, the blank heated by local induction heating has a temperature gradient distribution in the radial direction, which results in the defect reduction of inner hole enlarging. Thanks to the heat compensation function of induction heater, the defect of metal folding in the tooth top of the blank is reduced. In addition, the formability is improved by using local induction heating and the rolling force drops drastically compared with cold rolling process.

Modelling the Meshing of Cycloidal Gears

Abstract Cycloidal drives belong to the group of planetary gear drives. The article presents the process of modelling a cycloidal gear. The full profile of the planetary gear is determined from the following parameters: ratio of the drive, eccentricity value, the equidistant (ring gear roller radius), epicycloid reduction ratio, roller placement diameter in the ring gear. Joong-Ho Shin’s and Soon-Man Kwon’s article (Shin and Know, 2006) was used to determine the profile outline of the cycloidal planetary gear lobes. The result was a scatter chart with smooth lines and markers, presenting the full outline of the cycloidal gear.

Numerical simulation and experimental study of slippage in gear rolling

Gear rolling has the advantage of efficient material application, contour-related fiber orientation, and can overcome forming difficulties of gear forging. In the initial stage of gear rolling, often the slipping phenomenon occurs. Slippage and the degree of slippage significantly affect the forming quality of the tooth shape. In this paper, the applied forces on a blank in the initial forming phase of the gear rolling were analyzed, and the main factors affecting slippage were determined. Then, the quantitative evaluation index of the slippage was established. The effect of initial bite depth, friction condition, and number of teeth on the gear roller on slippage was obtained using finite element analysis. The effect of different initial bite depths and number of teeth on the gear roller on the slippage was studied experimentally. Moreover, the reliability of the finite element simulation results of gear rolling was verified. The results can provide a scientific basis for establishing reasonable process parameters, control of slippage, and improving the forming quality in gear rolling.

An Approach for the Gear Rolling Contact Fatigue Acceleration

This study proposes an approach for the acceleration of the experimental gear rolling contact fatigue (RCF) crack formation. By increasing the rotational velocity of a gear pair, the RCF experimental time period is reduced. However, the film thickness is increased to improve the fatigue performance, to counteract which it is proposed to raise the lubricant temperature to reduce the film thickness. A physics-based gear contact fatigue model is used to quantify and offset the effects of the rotational velocity and the lubricant temperature on the crack nucleation.