Bending fatigue strength of case-carburized helical gears with large helix angles up to 40 degrees

Case-carburizing of helical gears with large helix angles may form too large hardened layers near the tooth width end on the acute angle side (ACUTE-END), and adversely affect the bending fatigue strength. We investigated the bending fatigue strength of casecarburized helical gears with large helix angles up to approximately 40° through a bending fatigue test, hardness test, and residual stress measurement. We found that the case-carburizing formed large hardened layers near ACUTE-END, reduced the compressive residual stress near ACUTE-END, and restricted the improvement of the bending fatigue strength in a meshing state where tooth root stress became large near ACUTE-END. Based on the obtained bending fatigue limits, we revealed that ISO 6336-3:2006 overestimated the rate of increase of the permissible circumferential loads for helix angles exceeding approximately 30°, and ISO/DIS 6336-3:2018 underestimated this rate for helix angles near 30°.

     

Techniques for assessing the running temperature and fatigue strength of thermoplastic gears

Machines and techniques have been developed to study the running temperature and fatigue of lubricated thermoplastic gears. The results of preliminary tests on acetal and polycarbonate gears are presented and compared with other published data.     

Transient meshing performance of gears with different modification coefficients and helical angles using explicit dynamic FEA

The gearbox, as the main part of power transmission of many mechanical systems, plays a critical role for the performance of the system. The transient meshing performance of the gears is dependent on their structural parameters like modification coefficient and helical angle among others. In this paper, the effects of modification coefficients and helical angles on the transient meshing performance of the gears are investigated using the method of explicit dynamic finite element analysis (FEA) in an energy point of view. The relationships between the transient meshing performance and modification coefficient or helical angle of gears are obtained by explicit dynamic simulation. The simulation results demonstrate that explicit dynamic FEA can be used for choosing these structural parameters in the design and manufacture of gears to enhance their transient meshing performance.     

The forging of helical gears (II): comparisons of the forging processes

In this study, the forging processes of helical gears have been investigated wherein they have been classified into two types: the guiding type and the clamping types. These two types of forgings of helical gears have been analyzed by using the upper-bound method. New kinematically admissible velocity fields of the clamping-type forging of helical gears have been proposed, where an involute curve has been introduced to represent the tooth profile of the gear. The proposed velocity fields of the clamping-type forging of helical gears have been applied to the non-symmetric lateral extrusion forging and the result has been compared with the solution proposed by Plancak et al. [J. Mater. Process. Technol. 1992; 34:465–472]. Numerical calculations have been carried out to investigate the effects of various parameters, such as modules, number of teeth, helix angles and friction factors on the clamping-type forging of helical gears. For the forging of helical gears, the results of the upper-bound analysis of the clamping type have been compared with those of the guiding ones. Some experiments of the clamping-type forging were carried out with commercial aluminum alloy to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and the experimental forging load.     

The forging of helical gears (I): Experiments and upper-bound analysis

In this paper, the forging of helical gears has been investigated. A punch and a die are tooth-shaped for the guiding type forging of helical gears. The punch compresses a cylindrical billet placed in a die insert. As a consequence the material of a billet flows into the tooth region. The forging has been analysed by using the upper-bound method. Kinematically admissible velocity fields have been developed, where an involute curve has been introduced to represent tooth profile of the gear. Numerical calculations have been carried out to investigate the effects of various parameters, such as modules, numbers of teeth, helix angles and friction factors on the forging of helical gears. Some forging experiments were carried out with commercial aluminium alloy to show the validity of the analysis. Good agreements were found between the predicted values of the forging load and those obtained from the experimental results.     

圆柱螺旋弹簧疲劳强度的模糊概率设计

根据模糊概率设计理论,对圆柱螺旋弹簧的疲劳强度的模糊概率设计计算方法进行了初步的探讨,并给出了设计实例。     

减速齿轮传动中主动轮齿根弯曲疲劳的计算

传动齿轮强度理论认为,齿间滑动摩擦对齿轮齿根弯曲疲劳的影响可忽略不计。针对此说法,本文作者对带惰轮的起重减速齿轮传动中主动轮受国情况展开全面的分析研究,推导出包括齿间滑动摩擦力在内的,实际外载荷作用下的主动轮齿根弯曲疲劳应力计算公式。结果表明,齿间摩擦力对含惰轮的减速齿轮传动中主动轮齿根弯曲疲劳强度的影响不可忽视。     

表面镍磷、镍钴合金镀层提高铸铁齿轮接触疲劳强度研究

研究了HT200灰铸铁齿轮轮齿表面Ni～P和Ni—Co合金镀层的工作性能,采用电子显微镜、光学显微镜等对合金镀层进行了表面形貌、纵剖面界面组织、合金镀层成分,显微硬度等的分析,接触疲劳的试验结果表明能显著提高接触疲劳寿命。     

Influence of lubricants on the pitting fatigue of gears

Using the FZG gear tester with heat-treated and case-hardened gears the effect of lubricants and additives on the incidence of pitting fatigue was investigated. The influence of base oil type and additives requires further investigation before general conclusions can be derived. From the results now available extreme pressure additives which increase the scuffing load carrying capacity of case-hardened gears allow increased load testing without surface pitting failure. Additives have a direct beneficial influence on retarding the pitting of heat-treated gears. Of the additives tested, the most effective in reducing pitting fatigue failure was MoS₂, but with a high concentration of about 1.5%.     

渐开线圆柱齿轮螺旋线偏差的分析与检测

本文根据GB／T 10095．1-2001和GB／Z 18620．1-2002,简要分析介绍了渐开线圆柱齿轮螺旋线偏差的定义及其产生的原因和检测方法。     

二级斜齿圆柱齿轮减速器可靠性优化设计

在二级斜齿圆柱齿轮减速器的静态优化设计中引入齿轮强度可靠性约束条件,并运用相关数学理论和优化设计 方法建立了二级斜齿圆柱齿轮减速器可靠性优化设计数学模型,给出了设计实例。     

Development of a method to calculate the strength reliability of tooth gears based on the fatigue resistance when the teeth bend

A verified method is discussed regarding how to calculate the strength reliability of tooth gears when they bend and thus resist fatigue. It is based on the computer simulation of random values and the mathematical apparatus of nonparametric statistics. The effective and tolerable bending stresses are described with samples generated by nonparametric sensors. It allows for the correct assessment of the probability of the failure-free performance of tooth gears under any loading conditions.     

Effect of surface treatments on the strength of carburized gears

This paper deals with effects of surface treatment on the bending fatigue strength of SCM415 carburized spur gears. The test gears are treated by the combination of shot peening, chemical polishing and electropolishing after carburization. The fatigue tests demonstrate that the strength is sensitive to the surface condition of tooth fillet and the removal of the nonmartensitic layer caused by decarburization is considerably effective in enhancing the strength. In the first part of this paper, the influence of surface treatments such as shot peening, chemical polishing and electropolishing on the strength enbancement for carburized gears are summarized and discussed. In the second part, the crack lengths are calculated from the fatigue test results for the carburized and surface-treated gears, and the effect of surface treatments is discussed from the view point of fracture mechanics.     

CAD-based simulation of the hobbing process for the manufacturing of spur and helical gears

Targeting an accurate and realistic simulation of the gear hobbing process, we present an effective and factual approximation based on three-dimensional computer-aided design. Hobbing kinematics is directly applied in one gear gap. Each generating position formulates a spatial surface path which bounds its penetrating volume into the workpiece. The three-dimensional surface paths generated from the combination of the relative rotations and displacements of hob and work gear are used to split the subjected volume, creating concurrently the chip and the remaining work gear solid geometries. The developed software program HOB3D simulates accurately the manufacturing of spur and helical gears, exploiting the modeling and graphics capabilities of a commercial CAD software package. The resulting three-dimensional solid geometrical data, chips and gears provide the whole geometrical information needed for further research, such as prediction of the cutting forces, tool stresses and wear development as well as the optimization of the gear hobbing process.     

新型变螺旋角正弦斜齿轮的啮合特性分析

基于齿轮啮合原理、微分几何的理论,推导了变螺旋角正弦斜齿轮传动的啮合方程,应用MATLAB软件和对该啮合方程的分析仿真得到了该齿轮传动的啮合轨迹,通过对仿真图形的分析,得出了副值系数H和螺旋角对变螺旋角正弦直斜齿传动啮合轨迹的影响大小。     

Predicting the fatigue strength of structural elements

The development of models relating the fatigue strength of materials to their static strength and plasticity is considered. Statistical strength theories were developed to describe the results of fatigue tests and to predict the strength of machine components with variable loads. Experiments show that the strength of materials depends significantly on structural defects, and the limiting stress is a statistical quantity.     

20CrNi2MoA渗碳淬火齿轮齿根磨削对轮齿弯曲疲劳强度影响的试验研究

论述20CrNi2MoA渗碳淬火齿轮齿根磨削与否对轮齿弯曲疲劳强度影响的对比试验研究，并基于此项试验研究提出了具有应用价值的观点。试验研究结果表明，就20CrNi2MoA渗碳淬火齿轮而言，当齿根应力＞700MPa时，以磨削齿根为好；当齿根应力≤700MPa时，以不磨削齿根为好。齿根应力越低，不磨削齿根的优点越显著。     

基于Pro/E的渐开线斜齿轮参数化造型方法研究

渐开线斜齿轮是机械设备中常用的传动零件,其齿形复杂,传统的齿轮建模过程比较繁琐。介绍了在Pro/E环境下,运用三维参数化设计功能,实现标准渐开线斜齿轮的造型方法和步骤。该方法从原理出发,利用方程建立渐开线,保证齿轮齿形的准确性。通过修改相应的设计参数及关系式,能够实现不同模数、齿数齿轮的快速造型,提高设计效率。