A mathematical model of rough surface contact characterization in spot welding

Based on the elastic-plastic mechanics and the contact mechanics, an asperity contact model for the resistance spot welding of the rough surface is presented. The numerical results indicate that the real contact area is only a small section of the nominal contact area. The value of the real contact area is randomly fluctuating within 20%. The real contact area’s distribution and each point’s deformation can also be obtained from this model, which is primary in the calculation of the contact resistance and the temperature field of the spot welding.

Investigation of cathode spot characteristics in vacuum under transverse magnetic field (TMF) contacts

With the continuous improvement of current levels in power systems, the demands on the breaking capacity requirements of vacuum circuit breakers are getting higher and higher. The breaking capacity of vacuum breakers is determined by cathode spots, which provide electrons and metal vapor to maintain the arc. In this paper, experiments were carried out on two kinds of transverse magnetic field（TMF） contacts in a demountable vacuum chamber, the behavior of the cathode spots was recorded by a high-speed charge-coupled device（CCD） video camera, and the characteristics of the cathode spots were analyzed through the image processing method. The phenomenon of cathode spot groups and the star-shaped pattern of the spots were both discovered in the experiment. The experimental results show that with the condition of TMF contacts the initial expansion speed of cathode spots is influenced by some parameters, such as the tested current, contact gap, the structure of the contact, the contact diameter, the number of slots, etc. In addition, the influence of the magnetic field on the formation of the cathode spot groups, the distribution, and the dynamic characteristics of the cathode spots were analyzed. It is concluded that the characteristics of the cathode spots are due to the effect of the magnetic field on the near-cathode plasma. The study of the characteristics of cathode spots in this paper would be helpful in the exploration of the physical process of vacuum arcs, and would be of guiding significance in optimizing the design of vacuum circuit breakers.

Influence of Surface Condition on Expulsion in Spot Welding AZ31B Magnesium Alloy

Experiments were carried out to study the influence of surface condition on expulsion during the spot welding of AZ31B Mg alloy. A general electrical contact resistance theory for conductive rough surfaces and the relation between maximum temperature Tm in the contact and voltage-drop V across interface of two surfaces were employed to understand the reason of expulsion in Mg alloy spot welding. The main reason of expulsion is that the high electrical contact resistance induced by large roughness of the surface and oxide film covered on the surface leads to local melting of metal in the interface of two surfaces, and liquid metal of the local area ejected from the specimen under electrode force forms expulsion.

Formation of a 40 A DC Current Arc During the Opening of Silver Contacts

The erosion of silver contacts due to break arcs with length proportional to time and of variable duration has been measured by weighing the contacts following 5000 openings at a constant current equal to 40 A.The experimental results show that,for arc durations shorter than 60 μs,the transfer of metal from the anode to the cathode occurs,but after passing this stage,when the two electrodes are separated by greater distances,each will display erosion.This is the result of the diffusion of material outside the space between the two electrodes.In order to interpret these results,we have applied a classical model of the physical phenomena occurring at the root of the arc.Analysis of the experimental results shows that for an arc duration of less than15 μs,no distinct cathode root is seen to exist,but beyond this,several spots appear gradually on the cathode for arc duration up to 50 μs,after which they merge into a single spot.The comparison between experiment results and theoretical interpretation is reasonable up to 60 μs.

Formation Process of Intermittent Molten Bridge Between Au-Plated Contacts at Super Low Breaking Velocity

This paper presents the molten bridge behaviors of Au-plated material at super low breaking velocity conditions by introducing our new designed test rig. The typical waveforms of the contact voltage and contact force during breaking are investigated under the load of 5- 25 V/0.2-1 A and velocity of 25-150 nm/s. It is shown that the intermittent molten bridge is formed from the competition of multitude contact a-spots for current distribution and the solid- liquid mixing characteristics of a molten bridge. Also, it is proved that the bridge is not composed by the completed melted metal by using FEM thermal simulation and the voltage-temperature relation. The observed surface morphology reveals that the scattered and stacked melted regions are attributed to the intermittent bridge. Finally, the effects of breaking velocity and electrical load on bridge length and duration are also analyzed.

Measurement of dynamic resistance in resistance spot welding

The conventional methods of determining the dynamic resistance were mostly done by measuring the voltage and current at secondary side of transformer in resistance welding machines, in which the measuring set-up normally interferes with the movement of electrode, and the measuring precision is influenced by inductive noise caused by the high welding current. In this study, the dynamic resistance is determined by measuring the voltage at primary side and current at secondary side. This increases the accuracy of measurement because of higher signal-noise ratio, and allows to apply to in-process system without any wires connected to electrodes.

汽车变速器齿轮修形对齿轮疲劳寿命的影响研究

新能源卡车变速器齿轮受壳体变形影响易出现疲劳点蚀失效。针对壳体变形问题引入齿轮螺旋线补偿修形,利用Romax Designer对齿轮进行修形优化,改善齿轮的接触斑点,降低齿轮的最大接触应力。修形优化后的齿轮通过变速器疲劳耐久试验,对齿轮寿命提升约一倍。

重卡变速器齿轮螺旋角修形设计与试验

针对重卡变速器齿轮接触普遍出现的偏载现象,文章提出了一种变速箱齿轮螺旋角修形方法,通过调整齿轮螺旋角修形斜度以及改变螺旋角大小,改善齿轮接触偏载现象。以重卡12挡变速箱为研究对象,利用有限元仿真对齿轮副进行了数值模拟,并开展了接触斑试验、噪声试验和疲劳试验。结果表明,改进后的齿面接触应力分布均匀,接触斑居中,噪声无明显变化且仍满足疲劳试验要求,说明变速箱齿轮副的接触状况得到有效改善,验证了所提修形方法的可行性。该研究为重卡变速器偏载齿轮修正提供了理论依据与试验参考。

基于MASTA的大速比减速器齿轮综合修形优化设计

为了优化某大速比减速器斜齿圆柱齿轮传动系统的振动噪声水平,通过MASTA对其一、二级齿轮传动进行啮合及振动噪声仿真分析,发现存在偏载、应力集中、振动噪声较大等问题,存在较大的传递误差。以减小传递误差与齿面接触应力为目标,进行齿面修形优化设计,建立齿面修形优化模型并求解,采用MASTA对修形后模型进行分析,并对其样机进行噪声试验,验证齿面修形的有效性。结果显示:MASTA分析结果符合理论分析,仿真方法准确,修形后齿轮的接触应力和传递误差均明显减小,接触斑点分布均匀,振动噪声明显降低,且一级齿轮传动比二级齿轮传动效果更明显。可见此优化设计方案对减速器减振降噪具有较好的效果,为此类减速器齿轮设计提供理论参考。

弓网接触状态光纤传感监测技术研究

在弓网检测的应用场景中,传统的测力传感器和加速度传感器依赖电源供电,且必须安装在高电压的受电弓上,从而增加额外的设备和复杂性。文章研究采用无源光纤布拉格光栅(FBG)光传感器,这种传感器无需额外安装供电电源和充电控制系统等设备。通过介绍光纤传感器的基本原理,并分析其应用场景,提出在弓网状态监测的高电压环境中,光纤传感器具有独特优势:不仅无需供电,减少额外设备,还能实现信号传输的高低压隔离,有效抵抗电磁干扰。针对受电弓检测的特殊需求,开发基于光纤传感技术的接触力和加速度传感器,其便于在受电弓上安装且对受电弓结构无影响。在列车受电弓上的实际安装测试中,成功实现对弓网接触力、硬点等参数的高精度检测。该弓网状态监测系统能够适用于专用检测车和运营动车组,大幅扩展弓网监测的应用范围。

电极形态对铝合金电阻焊接头的影响

使用不同直径的球面和平面电极进行铝合金试板的电阻点焊,对焊点进行外观检查、剥离试验、宏观金相等试验,研究电极端面形状、直径大小、表面状态对铝合金电阻点焊接头的影响。研究表明:电极的端面形态通过影响电极和母材的受力、电极-母材接触电阻、电流受流情况,从而影响电流热效应产生的热量,最终影响点焊接头质量。球面电极由于其球面特征,受力和受流情况优于平面电极,抗变形能力强,可连续点焊160点以上。电极直径影响电流受流情况和受力,较小的直径导致热量和受力集中,形成板间喷溅和熔核孔洞缺陷;较大的直径导致电流密度和压强小,无法形成熔核。粗糙表面增大了电极-母材接触电阻,产生热量过大,使母材表面过度烧损,形成缺陷。

国产轿车变速器啸叫噪声源的识别与控制

对一款国产轿车变速器存在的啸叫问题进行了研究。首先进行了车内噪声实验和NVH半消声室台架实验,利用阶次分析找到了主要的阶次,然后利用声贡献量分析最终确定了啸叫特征阶次。计算发现该问题较为特殊,由于设计不当出现了不同传动部件阶次一致的情况。针对阶次一致的传动部件,通过接触斑点分析,最终确定了啸叫的噪声源。最后以实际接触斑点的位置和形状为依据,对齿轮进行了齿向修形设计,啸叫声降低约5dB(A)。

考虑接触电阻下的电缆接头热点温度

电缆接头内部热点温升是电力电缆的重要问题,有必要研究接触电阻对热点温度的影响。首先,建立了电缆接头及电缆本体的2维轴对称模型。通过不同接触电阻等效模型下的温度场仿真对比,其热点温度相对误差不超过1%,从而确定了接触电阻的等效模型。然后,分别对有无接触电阻的模型进行温度场仿真分析,其热点温度相对误差达10.2%,确定了考虑接触电阻的必要性。最后,在电缆接头温升试验平台进行了试验,比较了测量数据与有限元仿真数据,其热点温度相对误差不超过7%,可以满足工程应用的需要。

40Cr钢齿轮齿面点状剥落失效分析

通过化学成分分析、硬度检测、宏观以及微观分析等方法,对40Cr钢齿轮齿面发生点状剥落的原因进行了分析。结果表明,由于齿轮在渗氮处理前期,炉内发生了严重的短时超温,使经过调质处理的齿轮在渗氮前又发生了先期退火,造成基体组织强度和硬度过低,在强大接触负荷作用下,齿面发生了接触疲劳而造成点状剥落。

变速箱齿轮接触斑点试验台的研究与设计

为了检查变速箱加载变形后齿轮啮合情况,需要对齿轮进行接触斑点检测。根据对变速器结构及其工作过程的研究,提出一种变速箱齿轮接触斑点试验台的设计方案,驱动和加载分别采用直流电机和气动制动器,使该试验台具有稳定加载和低速稳定运行的优点。介绍了该试验系统的工作原理,重点描述接触斑点试验台的机械结构设计以及电控系统和软件设计,并利用该试验台对变速器齿轮进行了接触斑点检测,表明该试验台检测的接触斑点接近实际情况,再通过软件模拟进行齿轮修形设计,完全满足工程试验需求。

结合面静摩擦因数分形模型的建立与仿真

提出一个确定分形维数和分形粗糙度参数G*的分形函数,并用分形函数逼近结合面的表面粗糙度。根据分形理论和改进后的尺寸分布,推导了静摩擦因数f的解析解。数字仿真结果表明,f随量纲为一的总法向载荷P*增加而增加。当D较小或较大时,f与P*之间存在不同的微凸和微凹弧非线性关系,D=1.2时f与P*的关系基本上是线性的;当D较小时,f随D增加而增加;当D较大时,f随D增加而减小;f随分形粗糙度参数G*增加而减小,随相关系数K增加而增加,随材料特性φ增加而增加。

CuCr触头材料小电流下阴极斑点与截流值研究

研究了在峰值电流分别为10A和80A的小击穿电流下,CuCr25与CuCr50合金阴极斑点蚀坑形貌的差异。通过比较阴极斑点蚀坑的大小和分布,分析了CuCr触头材料显微组织中Cr相尺寸的大小对阴极斑点运动和蚀坑形貌的影响。采用示波器直接测量出截流值和电弧寿命,结合CuCr合金阴极斑点蚀坑形貌的分布,从现象和机理上解释了CuCr25合金截流值低于CuCr50合金的原因。这些结果对通过优化CuCr合金的显微组织以降低触头材料的截流值提供了有力的依据。

CuCr25纳米晶化对真空电弧阴极斑点扩散的影响

采用氩气保护气氛高能球磨和真空热压技术制备了致密度大于98%的纳米晶CuCr25合金,并在真空室内进行击穿试验。采用扫描电镜对纳米晶和粗晶CuCr25合金阴极斑点蚀坑形貌进行观察。结果表明:粗晶CuCr25合金真空电弧阴极斑点扩散表现为原地重复燃烧或整体的跳跃式移动,且有选择地分布在Cr相。而纳米晶CuCr25合金由于晶粒细化(<50nm),为电子发射提供了优越条件,阴极斑点的扩散表现为次级斑点的此起彼伏的准连续移动,击穿相均匀分布在整个阴极表面。

两弹性接触粗糙低速滑动表面温升的分形模型

采用球形微凸体的赫兹接触理论和MB模型,对微接触点的稳态温升、瞬态温升进行了分析,得到了低速滑动区域内的分形区域实际接触面积温升概率分布密度的封闭形式表达式.分析结果说明:摩擦副表面粗糙度、最大弹性微接触点的面积、域扩展系数均随分形维数增加而减小,域分开系数随分形维数增加而线性增加.最大温升随分形维数增加而减小,总体上随实际接触面积增加而线性增加,还随分形粗糙度参数增加而增加.当温升增加时,受给定温升的微接触点数减小会导致实际接触面积的温升概率分布密度下降.考虑了各接触微凸体之间相互作用的瞬态温升效应,但计算表明在低速滑动区域可以不考虑其影响.

不锈钢点接触结构的钎焊工艺

针对特殊要求的不锈钢0Cr18Ni9结构件,被连接件圆柱与圆盘的实际接触面积近似为1mm×1mm点接触,形位控制精度要求较高,同时要求连接边缘过渡圆滑,连接区域不应存在任何间隙和突起,表面要求较高。采用镍基钎料(7Cr/4.5Si/3.1B/3Fe/Ni),利用高温真空钎焊技术进行连接。圆柱与圆盘的钎焊接头界面发生反应,生成厚度均匀的扩散反应层,有效地保证了接头性能的可靠。采用同种材料的焊接工装以便更加有效地控制钎焊间隙,当钎焊间隙<0.05mm时,可以确保钎焊接头质量的可靠。同时利用阻流剂很好的解决了无效连接问题的产生,采用工装定位、整体加热、缓慢冷却等措施控制了焊接变形,确保构件的整体精度。