Selection of parameters for μE-beam welding

Abstract

Electron beam welding is a well known process used where high precision, high reliability welds are needed, often in exotic materials. Recently, it has been proposed to apply the electron beam produced in a standard scanning electron microscope (SEM), with reversible modifications to increase beam current, for microscale welding. In addition to providing the clean environment associated with the column vacuum, the SEM in imaging mode provides exceptional capabilities in visualising extremely small parts. Furthermore, the standard stage and beam motion controls offer the possibility of flexible programming of beam path with relatively minor software additions. In order to better evaluate the requirements for and effects of μE-beam welding (μEBW) on typical microtechnologically important materials, a clear understanding of the characteristics of the SEM's beam and its interaction with possible target materials is needed. The penetration ability of electrons depends strongly upon their accelerating voltage and the target they are being directed at. Hence, in some circumstances the beam may interact as a surface heat source, while in others it may act as a volume heat source, with important consequences on weld schedule development for the parts and geometry being welded. In this work, the authors explore some of the factors involved and propose simple models for the electron beam heat source which depend on the parameters being used.     

先进材料与异种材料电子束焊接研究进展

电子束焊接是近年来飞速进步、蓬勃发展的一种先进连接技术，随着技术工艺的日益成熟，其在工业领域的竞争力也日渐增强，已为工业部门所广泛接受.文中综述了电子束焊接在高温钛合金、高温合金、难熔金属、金属间化合物等先进材料与各类互相固溶的、难以互溶的异种材料连接方面的研究现状，对国内外在焊接缺陷控制、焊接工艺优化、焊接机理研究等方面取得的典型研究成果进行了简要介绍，并从中概括总结了先进材料与异种材料电子束焊接的具体问题，归纳阐述了先进材料与异种材料电子束焊接中所采用的能量控制与冶金调控等特色技术方法.     

氦气保护超低真空电子束焊接束流散射及焊缝形貌分析

为了解决低真空和局部真空电子束焊接时,电子束严重散射而引起的熔深、熔宽降低和焊接过程不稳定的问题,文中研究了加速电压为100 kV,束流为60 mA,真空度在133.32 ~ 1 333.2 Pa变化时的电子束和焊缝形貌的变化规律,并提出了同轴氦气保护的焊接工艺方法. 结果表明,在进行低碳钢材料的焊接时,整个工艺过程稳定,得到了焊缝熔深为30 ~ 40 mm,大深宽比的电子束焊接接头.     

高温合金电子束焊接温度场数值模拟

根据熔池边界准则应用有限元方法对高温合金电子束焊接温度场进行了数值模拟.通过线性插值、等效代换等方式估计材料高温参数,模拟材料状态变化.针对电子束焊接特有的钉头状焊缝及其穿透深度大的特点,采用高斯面热源与柱体热源组成的组合热源模型,对焊接温度场进行分析,模拟结果与实际焊缝取得了良好的一致.获得了一定工艺条件下高温合金电子束焊接温度场的分布特征及焊接过程热循环曲线,为优化电子束焊接工艺和电子束焊接残余应力研究提供了参考.     

真空电子束焊接热源建模及功率密度分析

分析了真空电子束深熔焊接的热源作用形成钉状焊缝的特征,建立了峰值功率递增型旋转高斯体热源,即热源作用半径在深度方向呈高斯规律递减,热源功率密度在深度方向呈指数函数规律递增.利用该热源模型计算了聚焦状态和散焦状态下,真空电子束焊接特殊热效应的功率密度分布.结果表明,热源数学模型得到的功率密度分布规律符合理想状态下的电子束热源作用特征,可用于不同聚焦状态下的真空电子束焊接的热效应数值模拟研究.     

Part 2: Application of Kanaya–Okayama heat source in modelling micro electron beam welding

Abstract

A three-dimensional finite element model of micro electron beam welding is developed where the Kanaya–Okayama heat source formulated in Part I of this work is used to represent the electron beam. The large number of process variables is grouped into two non-dimensional parameters, namely, Peclet number and relative beam penetration, and their effect is analysed numerically to arrive at the optimum conditions of microwelding. Based on the minimum heat input of the process, the optimum Peclet number is found to be 100, and the beam penetration is twice that of the weld depth. The optimum parameters obtained using the Kanaya–Okayama heat source model are similar to the previous findings using the exponential decay heat source model; however, the predictions of the temperature field in the solid as a result of microwelding are relatively lower in case of the Kanaya–Okayama heat source model because of the differences in distribution of heat into the condensed matter. The lower weld surface temperatures in microwelding using the electron beam suggest significantly less ablation than in laser beams.     

Electron beam welding of SiCp/2024 and 2219 aluminum alloy

SiC_p/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding, respectively, and the microstructures and mechanical properties of these joints were investigated. The results revealed that SiC particle segregation was more likely during centered electron beam welding (than during deflection beam welding), and strong interface reactions led to the formation of many Al₄C₃ brittle intermetallic compounds. Moreover, the tensile strength of the joints was 104 MPa. The interface reaction was restrained via deflection electron beam welding, and only a few Al₄C₃ intermetallic compounds formed at the top of the joint and heat affected zone of SiC_p/Al. Quasi-cleavage fracture occurred at the interface reaction layer of the base metal. Both methods yielded a hardness transition zone near the SiC_p/2024 fusion zone,and the brittle intermetallic Al₄C₃compounds formed in this zone resulted in high hardness.     

航空发动机转子组件电子束焊变形预测

航空商用发动机组件尺寸精度要求较高,且组件焊接后盘心位置不能进行机械加工,因此采用数值模拟的方法对转子组件进行焊接变形预测. 试验将基于热弹塑性理论计算提取固有应变数值;通过理论计算得到GH4169合金电子束焊缝的固有应变值,分析焊接工艺参数对焊缝固有应变的影响规律;建立结构件模型,分析焊接工艺、焊接顺序及工装条件下组件焊接变形. 结果表明,相比于第一,第二和第三级盘,第四级盘心轴向变形最大,且通过增大扫描速度和改变约束方式的方法可以有效减小焊接变形,从而完成对转子组件焊接变形进行预测和控制.     

基于小孔形状的TCS不锈钢激光+GMAW-P复合焊热场模型

为合理描述激光能量在小孔内的分布特征,采用光线追踪法处理光线在小孔内的多次反射和孔壁的Fresnel吸收,对线热源小孔模型做出了改进.根据小孔形状尺寸的计算结果,确定激光焊体积热源的分布参数.将标定后的激光焊体积热源分布参数应用于激光+熔化极脉冲电弧(激光+GMAW-P)复合焊的组合式体积热源模型,对TCS不锈钢复合焊准稳态温度场进行了数值分析.开展了TCS不锈钢复合焊工艺实验,将复合焊焊缝形状尺寸的模拟结果与实测结果进行了对比,验证了所建立的复合焊热场模型.基于小孔形状的复合焊热场模型能较好地模拟TCS不锈钢复合焊温度分布与焊缝成形.利用该模型计算了不同工艺条件下TCS不锈钢焊接HAZ形状尺寸以及HAZ内不同位置处的热循环曲线,分析了TCS不锈钢复合焊的热循环特征,为接头组织与性能的预测分析奠定了基础.     

Thermal cycle and its influence on the microstructure of laser welded butt joint of 8 mm thick Ti-6Al-4V alloy

Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation. In the current study, the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm. A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process. The thermal cycle curves are produced on the strength of the simulation results. Meanwhile, the microstructure characteristics of the welded joint are investigated combined with simulation results. The results show that weld zone, heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure. Moreover, the simulation results are well matched with experiment results.     

镁合金真空电子束深熔焊接及焊缝成形数值模拟

对10mmAZ61镁合金板材进行了真空电子束深熔焊接数值模拟研究.考虑到焊接过程中高温金属蒸气等离子体的热效应及真空电子束焊接"匙孔"深熔热效应特征,建立了高斯面热源与双椭球体热源复合的移动热源模型,采用数值模拟的方法研究了镁合金真空电子束焊接温度循环特征及不同焊接工艺对焊缝成形的影响.结果表明,建立的复合热源模型能够获得电子束深熔焊接的效果,并可模拟不同焊接工艺下的温度场分布与电子束热源作用下的焊缝成形,这也证明了该模型在AZ61镁合金电子束平板焊接的热效应模拟中有较好的适用性.     

AZ61镁合金真空电子束焊接温度场数值模拟

对板厚10 mm AZ61镁合金板材进行了真空电子束焊接数值模拟研究.利用有限元模型以及三维移动双椭球热源模型,采用数值模拟的方法研究了电子束流与焊接过程温度场及焊缝熔深之间的关系.结果表明,建立的模型能够获得电子束深熔型焊接的效果,模拟焊缝成形及焊缝区、热影响区温度场分布与试验焊缝成形及实际电子束焊接特点较为一致,这也证明了该模型在AZ61镁合金电子束平板对焊有限元模拟中有较好的适用性.     

W6高速钢/16Mn钢电子束焊接接头组织及性能分析

高速钢作为一种高硬度、高耐磨性和高耐热性特殊工具钢,应用于刀具、模具及特殊结构件上时,往往需要结合异种钢使用. 但高速钢焊接工艺研究仍不成熟,焊接中产生的裂纹与碳化物缺陷是制约高速钢应用的主要因素. 文中通过对W6Mo5Cr4V2高速钢与16Mn钢预置镍填充层后进行电子束焊接. 结果表明,镍中间层的引入有效的抑制了高速钢侧热影响区的开裂,接头呈不对称“漏斗形”. 焊缝组织主要由镍基固溶体与少量M₂C碳化物构成,焊缝中无马氏体组织,其焊缝平均硬度为185 HV;接头抗拉强度达到378 MPa,为16Mn侧母材抗拉强度的75%. 拉伸断口断裂于距W6侧熔合线0.8 mm处的热影响区,为准解理断裂.     

钛合金电子束焊熔宽PID控制系统建模与仿真

由于焊接过程的复杂性,因此很难得到熔池动态过程的解析数学模型,使得焊接过程建模成为焊接过程控制的一大难题．为了建立电子束焊熔池动态过程模型,采用阶跃响应法确定出了钛合金电子束焊电子束流与熔宽的数学模型的类型和结构,计算出了该模型的参数,建立了电子束流与熔宽的传递函数模型．利用获得的电子束流与熔宽的数学模型,采用Z-N经验公式法确定出了PID控制器参数,在此基础上利用MATLAB／SIMULINK建模与仿真平台建立了钛合金电子束焊熔宽PID控制系统模型,并对该模型进行了仿真试验．结果表明,所设计的控制系统动态性能和稳态性能良好．     

真空电子束深熔透焊接原理浅析

分析了真空电子束深熔透焊接机理,在电子束焊接能量分配传热模型的基础上,阐明了深熔透焊接的熔池流动行为和熔质密度分布情况,为燃气轮机压气机静叶环真空电子束焊接试验和实际生产提供了强有力的理论依据。     

Electron beam welding of precipitation hardened CuCrZr alloy: Modeling and experimentation

In order to maintain the structural consistency during the welding of precipitation hardened copper− chromium−zirconium (PH-CuCrZr) alloy components, electron beam welding (EBW) process was employed. Experimental study and numerical modeling of EBW process during welding of PH-CuCrZr alloy components were carried out. A 3D finite element model was developed to predict the output responses (bead penetration and bead width) as a function of EBW input parameters (beam current, acceleration voltage and weld speed). A combined circular and conical source with Gaussian heat distribution was used to model the deep penetration characteristic of the EBW process. Numerical modeling was carried out by developing user defined function in Ansys software. Numerical predictions were compared with the experimental results which had a good agreement with each other. The developed model can be used for parametric study in wide range of problems involving complex geometries which are to be welded using EBW process. The present work illustrates that the input current with a contribution of 44.56% and 81.13% is the most significant input parameter for the bead penetration and bead width, respectively.     

焊接热输入对高速动车组转向架侧梁焊接变形的影响及优化

转向架构架是高速动车组(electric multiple units, EMU)的重要承载部件，其侧梁的焊接质量直接关系到列车运行的平顺性及安全性. 为了研究焊接热输入对转向架侧梁焊接变形的影响，在侧梁结构中提取了曲线T形接头模型，以熔化极气体保护电弧焊(gas metal arc welding, GMAW)的焊接速度、焊接电流和焊接电压为研究对象，基于热机耦合仿真分析方法和具有交互作用的正交试验设计(design of experimental, DOE)方法建立代理模型，采用粒子群优化算法(particle swarm optimization, PSO)获得了最优的焊接工艺参数组合. 在此基础上，基于极差分析和方差分析(analysis of variance, ANOVA)，进一步讨论了上述工艺参数对焊接热输入和焊接残余变形的影响. 结果表明，采用最优工艺参数的曲线T形接头模型焊接角变形比采用原生产工艺参数的结果降低了5.04%，采用最优工艺参数的侧梁模型可以保证上下盖板焊接残余变形满足平面度不大于1 mm的要求，无需焊后调平.     

Ti3Al金属间化合物电子束深熔焊接过程数值模拟

基于有限元法，采用改进的双椭球热源模型，对电子束深熔焊接Ti3Al过程进行了移动热源条件下准稳态三维温度场的数值模拟。该模型复合了熔深与电子束参数及材料性质的关系，考虑了对流和辐射散热、相变潜热、材料热物理性能参量随温度的变化以及液态金属的对流传热。通过比较熔深、熔宽的计算值和实际测量值，验证了该模型在电子束焊接温度场模拟中的适用性。     

A survey on future research about electron beam welding for aerospace applications

Electron beam welding plays an important role in the aerospace industry where components like sensors,gears,actuators and air frames used in aircraft and rocket engines were welded using this technique.Welding is normally performed in a vacuum to avoid the scatter of electron due to the presence of gas molecules in the atmosphere and hence electron beam welding process provides the greater results.But still joining of dissimilar metals is challenging.This paper represents review of process,generation and distribution of heat source various input parameters,materials,microstructure,mechanical strength and the possibilities of joining dissimilar metals using electron beam welding.     

7075铝合金电子束焊接温度场数值模拟

针对航空航天业中应用较广的7075铝合金,采用ANSYS有限元软件,按照划分单元、逐次计算并逼近真实值的近似计算方法,对该合金电子束焊接的热过程进行了计算机数值模拟的可行性研究.结果表明,7075铝合金电子束焊接过程中焊接热输入较大,焊缝较窄,熔深大.通过验证,用有限元数值模拟方法得到的焊接及热处理温度场分布规律与实测温度值基本一致.