Polymer gear surface thermal wear and its performance prediction

This paper will concentrate on acetal gear wear behaviour and its performance prediction based on the extensive investigations on the gear thermal mechanical contact both experimentally and numerically. It has been found from the tests that acetal gear wear rate will be increased dramatically when the load reaches a critical value for a specific geometry and running speed. The gear surface will wear slowly with a low specific wear rate if the gear is loaded below the critical one. The possible reason of the sudden increase in wear rate is due to the gear operating temperature reaching the material melting point under the critical load condition. Gear surface temperature has been then investigated in details through three components: ambient, bulk and flash temperatures. Through extensive experimental investigations and modelling on gear surface temperature variations, a general relation has been built up between gear surface temperature and gear load capacity. An approach for acetal gear transition torque prediction has been proposed and this method is based on the link between polymer gear wear rate and its surface temperature. The method has been related to test results under different operating speeds and gear geometries. Good agreements have been achieved between the proposed method predictions and experimental test results.     

Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear

Gear wear is one of the most common gear failures, which changes the mesh relationship of normal gear. A new mesh relationship caused by gear wear affects meshing excitations, such as mesh stiffness and transmission error, and further increases vibration and noise level. This paper aims to establish the model of mesh relationship and reveal the vibration characteristics of external spur gears with gear wear. A geometric model for a new mesh relationship with gear wear is proposed, which is utilized to evaluate the influence of gear wear on mesh stiffness and unloaded static transmission error (USTE). Based on the mesh stiffness and USTE considering gear wear, a gear dynamic model is established, and the vibration characteristics of gear wear are numerically studied. Comparison with the experimental results verifies the proposed dynamic model based on the new mesh relationship. The numerical and experimental results indicate that gear wear does not change the structure of the spectrum, but it alters the amplitude of the meshing frequencies and their sidebands. Several condition indicators, such as root-mean-square, kurtosis, and first-order meshing frequency amplitude, can be regarded as important bases for judging gear wear state.     

齿轮传动中磨损问题的研究及修复方法综述

齿轮传动是机器传递运动和动力的一种主要形式。如何减少齿轮工作中的磨损、延长其使用寿命是工业生产中至关重要的问题.总结了齿轮磨损问题的基本类型、研究历程、研究方法以及失效齿轮的常用修复方法等.     

An analysis of the wear features of worm gear tooth flanks

Worm reducers with a double enveloping toroidal surface are a new type of reducer with higher wear resistance and longer service life. A series of contact fatigue tests of worm pairs has been carried out on a microcomputer-controlled test stand of closed power flow type, using an incremental method of increasing the load. During the test, the worm tooth flank completed 2.2 × 10⁷ cycles, and the worm gear tooth flank 1.1 × 10⁶ cycles. Meanwhile, the state of the flank was duplicated by means of a chemical film. This paper discusses the whole process of the occurrence and development of surface cracks as well as the formation of fatigue peeling. It should provide a reliable basis for definition of the law of fatigue damage of the worm gear tooth flank.     

基于逆向工程的齿轮磨损件无损检测技术

齿轮减速器零件由于长期处于高速的工况下而磨损剧烈,其磨损位置、磨损量具有不确定性及复杂性等特点.对磨损部位进行快速、定量、精确无损检测是对其进行绿色再制造的前提和关键.采用基于逆向工程的原理,对齿轮磨损件进行表面信息获取、磨损实体模型重构,并与标准件进行对比分析,得到了磨损部位定量、精确的待修复信息,为磨损件的绿色再制造提供数字化依据.     

Effect of varying load on wear resistance of carbon steel under unlubricated conditions

Pin-on-disk type wear tests of mild steel in contact with itself were conducted under unlubricated conditions in moist air to investigate the effect of changes in load on the transition behavior between severe and mild wear. Machines in operation are usually subjected to varying loads. In this study, two contact load levels were used as a simple varying load condition. The load was changed in a step-wise manner between the low and high levels either once or twice during certain tests.Severe wear appears at the high load levels and mild wear at the low load levels in wear tests under constant loading. After oxidized, work-hardened wear surfaces have been formed under mild wear at the low load during the first stage, the wear mode changes to “quasi-mild wear” having a low rate at the high load in the final stage. The load range, where the low wear rate can be maintained under quasi-mild wear, extends to the higher load level after the change(s) in load. Once the quasi-mild wear surface has been generated, the wear mode can be maintained even at the high load for a very long sliding distance.     

Organophosphorus chemistry structure and performance relationships in FZG gear tests

A model investigation was conducted involving several different molecular weight phosphorus compounds prepared in base stocks of various polarities. The study involves two different parts. In one part, the same phosphorus compound was blended into several base stocks of differing polarities and was observed to give differing FZG gear test results. In part two, several different phosphorus compounds of various molecular weights were blended into the same base fluid and were observed to give differing FZG gear test results. Solution properties were studied by dielectric thermal analysis and afforded data as to mobility and surface reactivity. X-ray photoelectron spectroscopy was performed on sectioned gear teeth and provided elemental composition as well as thickness of the reacted surface layer. This data was correlated with the recorded FZG gear test results. A surface interaction mechanism is proposed that accounts for the relative phosphorus content and thickness of the wear protection films. The mechanism is based on correlating the additive molecular weight and base stock polarity as it relates to the FZG gear stage test pass result.     

The wear behaviour of polymer composite gears

In order to examine the wear of polymer composite gears, a test facility has been developed which has enabled the wear of gear trains to be measured continuously during gear operation. Brief details of the method are given. The purpose of this paper is to report some of the results obtained from this facility and, in particular, to discuss the effect of temperature on the wear of acetal gears.     

Dynamic interaction between contact loads and tooth wear of engaged plastic gear pairs

This study investigates the interaction between the dynamic contact load and the tooth profile wear of POM and Nylon 66 plastic gear pairs. A dynamic model of a plastic gear pair is presented. This model incorporates the effects of position-varying tooth mesh stiffness, damping ratio, load sharing, tooth profile wear and temperature on the dynamic contact load. The tooth wear equation developed by Flodin and Andersson [Simulation of mild wear in spur gears. Wear 1997;207:16–23] is utilized to simulate tooth wear and tooth profile variation. The variation of the contact load generated by the cumulative tooth profile wear is simulated and examined. A computational algorithm is developed to simulate the interaction between a dynamic contact load and tooth profile wear. Numerical results demonstrate that the dynamic load histogram of an engaged plastic gear pair can change markedly due to tooth wear.     

考虑磨损与变形的谐波齿轮精度可靠性分析与优化设计

针对谐波齿轮减速器中存在的磨损和变形因素导致减速器传动精度低、可靠性差等问题,建立考虑磨损与变形的谐波齿轮减速器传动误差模型,并进行精度可靠性分析与优化设计。通过分析传动误差的影响因素建立了传动误差模型;基于磨损经验模型和试验数据,应用贝叶斯修正方法建立动态磨损模型,同时根据试验数据和高斯过程回归建立柔轮变形模型;综合获得的传动误差模型、磨损模型和柔轮变形模型建立谐波齿轮精度可靠性模型,并应用基于拉丁超立方抽样的Kriging代理模型和蒙特卡洛法求解某谐波齿轮减速器传动精度可靠度。最后采用序列二次规划法对谐波齿轮减速器进行优化设计。优化结果表明,在工况参数(输出端负载17.5 N·m,输入端转速100 r/min)下,优化后的谐波齿轮减速器在工作时间3 000 h处的可靠度达到99.02%,相比未优化前提升7.85%,而成本却只增加1.70%。     

The energy pulse: A new wear criterion and its relevance to wear in gear teeth and automotive engine valve trains

The paper follows an earlier study in which the various standard test procedures for assessing the extreme pressure and anti-wear properties of lubricants were classified and evaluated in terms of a number of parameters. The significance of the frictional heating energy was apparent and a new parameter, the energy pulse, was proposed. This concept has been further developed in the present paper and applied to an analysis of contact conditions and patterns of wear in gears and valve trains.     

Effect of hob wear on the sounds emitted in the gear hobbing process

Increasing demand for precision and economy in gear manufacture necessitates control of the essential parameters in the hobbing process. Recognizing this necessity, research was undertaken to develop a hob wear detector. Using an empirical procedure, the acoustic signal emitted in hobbing was assessed with respect to its capacity to provide information about the extent of hobbing cutter wear. It was shown that signals from measurement of acoustic pressure in full bandwidths are unsuitable for the purpose. Frequency analysis of the acoustic signal enabled a third-octave frequency range with a centre frequency of 160 Hz to be singled out, wherein the acoustic signal level showed a close correlation with hob wear. The suitability of the signal is independent of most of the basic machine and process parameters and, for the purposes of hob wear detection, is reduced with higher values of module pitch of the hobbed gear     

Tool wear rate prediction in ultrasonic vibration-assisted milling

Abstract

In the current study, a predictive model on tool flank wear rate during ultrasonic vibration-assisted milling is proposed. One benefit of ultrasonic vibration is the frequent separation between tool and workpiece as the cutting time is reduced. In order to account for this effect, three types of tool–workpiece separation criteria are checked based on the tool center instantaneous position and velocity. Type I criterion examines the instantaneous velocity of tool center under feed movement and vibration. If the tool is moving away from workpiece, there is no contact. Type II criterion examines the position of tool center. If the tool center is far from the uncut workpiece surface, there is no contact even though the tool is getting closer. Type III criterion describes the smaller chip size due to the overlaps between current and previous tool paths as a result of vibration. If any criterion is satisfied, the tool flank wear rate is zero. Otherwise, the flank wear rate is predicted considering abrasion, adhesion and diffusion. The proposed predictive tool flank wear rate model is validated through comparison to experimental measurements on SKD 61 steel with uncoated carbide tool. The proposed predictive model is able to match the measured tool flank wear rate with high accuracy of 10.9% average percentage error. In addition, based on the sensitivity analysis, smaller axial depth of milling, larger feed per tooth or higher cutting speed will result in higher flank wear rate. And the effect of vibration parameters is less significant.     

弧齿线圆柱齿轮齿面形成原理

弧齿线圆柱齿轮是一种新型齿轮,它具有齿面弯曲强度高、低噪声、更好的润滑性能、对轴线平行度误差适应性强、无轴向力等一系列优点。但由于该齿轮发展历史不长,在理论上还缺乏系统性的研究,这就给该齿轮的设计应用带来了困难。着重从弧齿线圆柱齿轮齿面的齿面形成原理及啮合特性方面对该齿轮进行了分析和研究,推导出被加工齿轮齿面方程,目的在于为该齿轮的设计提供必要的理论依据。     

Effect of temperature fields on wear of nonmetallic materials at abrasive machining

Wear characteristics of silicate glass and sapphire at abrasive machining have been studied. The data obtained and the analysis of images of worn surfaces have allowed the authors to conclude that two modes of material damage run simultaneously; these are the local melting of the glass followed by its squeezing towards the contact exit and periodical fatigue fracture (growth of microcracks). Under a short-term effect of high thermal stresses the glass was found to undergo thermal cracking even outside the contact site. The crystalline material (sapphire) demonstrated anisotropy of fatigue strength under abrasive wear, when its wear rate in two perpendicular directions differed almost by an order of magnitude. The possibility of sapphire damage outside the contact site is explained by the position of the maximal surface temperature region being some distance ahead of the zone of the abrasive tool-blank contact.     

Tool wear estimation in machining based on the flank wear inclination angle changes using the FE method

Abstract

In this study, a FEM-based tool wear approach with a focus on the geometry of the worn tool, especially the changes of flank wear land inclination angle, was developed. The relationship between the variables of the wear rate equation and the average nodal temperature on the flank wear land through integrating FE-simulations of the cutting process and Response Surface Methodology (RSM) was determined in order to define the temperature as a function of wear rate model parameters. Then, that data was used to calibrate the wear rate equation which was obtained by establishing the relationship between the Usui wear rate equation and the geometry of the worn tool, using a MATLAB program. This approach was validated by comparing the predicted flank wear rates and experimental measurements. The estimated flank wear shows some improvement compare to the model with a constant inclination angle.     

The repeatability of friction and wear results obtained from unlubricated reciprocating sliding tests

Laboratory tests can help in the analysis of tribological failures of elements, and improve tribo‐systems by choosing appropriate materials. In order to characterise the friction and wear behaviour of candidate materials, various different test methods have been developed in the past and are still in use. One such method is the reciprocating sliding of a ball against a disc. In the work reported here, the repeatability of friction and wear results was evaluated with ten tests under identical conditions with a steel (100Cr6) or alumina (Al₂O₃) ball against a steel (100Cr6) disc under unlubricated conditions at room temperature. The influence of ambient humidity on friction and wear behaviour was determined in three additional tests in dry and in moist air, respectively. The repeatability of friction coefficient in normal air was better than 5% for alumina/100Cr6 and 12% for 100Cr6/100Cr6, while the repeatability of volumetric wear was slightly better than 10% for alumina/steel, and slightly worse than 10% for steel/steel. For both couples the coefficient of friction is lowest in moist air and about 50% higher in dry air. The coefficient of wear is also least in moist air and higher by a factor of 3(5) in dry air for tests with a 100Cr6 (alumina) ball.     

基于人工神经网络预测磨合磨损的最佳分形维数

基于BP人工神经网络的L-M算法,建立了磨合磨损的分形参数预测模型。将该模型用于销一盘磨合磨损试验。对最佳分形维数进行了准确预测。该模型收敛速度快、误差小,输出结果与实验结果有极好的吻合性。     

Evaluation of surface fatigue performance of gear oils

The effect of additive chemistry on the surface fatigue of gears was investigated using an FZG gear tester and fluids based on an API GL-5 grade gear oil. Surface fatigue lives were determined as a function of load and additive chemistry. At 1.52 GPa, the removal of the primary extreme pressure (EP) additive from the fully formulated gear oil decreased the fatigue life of gears slightly (4%). However, the removal of the primary antiwear (AW) additive decreased the fatigue life of gears significantly (83%). At 1.86 GPa, the removal of the EP additive from the fully formulated gear oil decreased the gear fatigue life by 27%. However, the removal of the primary AW additive decreased the fatigue life of gears significantly (75%). Micro-pitting was the dominant surface morphology in the dedendum of the gears tested with two oils at load stage eleven: one using the complete additive package, and a second where the EP additive had been removed. However, spalling was the primary failure mode of gears tested without an AW additive, independent of whether an EP agent was present. Surface analysis of the pinion gears showed the formation of a mixed phosphate/phosphite—oxide layer on the surface of gears tested with fluids containing an AW additive. Formation of this layer seems to be the key to a long fatigue life.     

Friction and wear properties of Kevlar pulp reinforced epoxy composites under dry sliding condition

In this work, the friction and wear properties of Kevlar pulp reinforced epoxy composites against GCr15 steel under dry sliding condition were evaluated on a reciprocating ball-on-block UMT-2MT tribometer. The effects of Kevlar pulp content on tribological properties of the composites were investigated. The worn surface morphologies of neat epoxy and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms discussed. The results show that the incorporation of Kevlar pulp into epoxy contributed to improve the friction and wear behavior considerably. The maximum wear reduction was obtained when the content of Kevlar pulp is 40 vol%. The friction coefficient of epoxy and its composites increased with load while increase in the sliding frequency induced a reverse effect. Fatigue wear and scuffing were notable for the neat epoxy. The fatigue cracks were greatly abated when the filler content was 40 vol%. The wear grooves appeared on the worn surface at higher filler content.