Elektronenstrahlschweißen an Atmosphäre – von der Entwicklung bis zum industriellen Einsatz

Non vacuum electron beam welding – from development to industrial application Attributable to the increasing degree of standardisation in many fields of industrial manufacturing, the saving of resources and thus the demand for light weight constructions and also the rapid development on the material sector have made joining tasks increasingly complex. This involves the joining method which must meet the metallurgical demands of the base materials to be welded and also the method’s profitability. In this connection, electron beam welding in atmosphere – NV‐EBW ‐ as a joining method is getting more and more important and is, from the side of the industry, becoming increasingly popular. NV‐EBW combines the many, well‐known advantages of electron beam welding in vacuum with the possibility to work under normal ambient pressure. With an equipment efficiency of more than 50 % and very high, achievable welding speeds of up to 60 m/min for aluminium materials, the electron beam in atmosphere is an efficient and profitable tool for welding. Under the direction of Professor U. Dilthey, the ISF has for many years and in close contact with industrial partners carried out research work in the field of the NV‐EBW technology. At that, elementary contribution to the development of rotationally‐symmetrical orifice assemblies and also to the testing and optimization of the method with regard to respective welding tasks has been carried out.     

Innovative Fügeverfahren zur Herstellung von Al‐Leichtbaustrukturen im Schienenfahrzeugbau

Innovative joining techniques for creating light‐weight aluminium structures in railway vehicle production Starting from the development in railway vehicle manufacture, the authors describe today's materials, types of construction, joining techniques, joint and weld types, filler materials and regulatory documents. In addition, they present new processing equipment and engineering principles. On the basis of these findings, they show the perspectives of new construction principles for light‐weight aluminium structures and identify the requirements, the new joining techniques have to meet. The innovative joining techniques, such as: • electron‐beam welding under atmosphere (NV‐EBW) • Friction Stir Welding (FSW) • Laser beam welding (LBW) • Laser beam/electric arc hybrid welding (LBW/LB) are studied with regard to their • properties and particularities • advantages and disadvantages • available equipment • possible applications for railway vehicle manufacture. In addition, costs are compared and an analysis of the benefit is made. Finally, the authors give an outlook on possible applications of the innovative procedures.     

新型高效真空电子束焊机

因真空电子束焊机具有焊接能量利用率高、焊接质量好等优点, 但目前真空电子束焊机存在辅助工作消耗时间长、消耗能源多的缺点, 直接影响着产品的成本和价格。本文针对一空心轴盘形齿轮的焊接, 通过对两个关键问题的解决, 提出了一种新型真空电子束焊机。首先, 实现了全时真空工作仓系统;然后, 实现了真空工作仓内的上、下料工作;最后, 通过实验, 对比了新型焊机和普通焊机的生产效率。实验结果表明, 该新型焊机应用于批量生产中, 优势明显。对真空电子束技术的发展提供了有价值的参考。     

Low Heat Welding of Titanium Materials with a Pulsed Nd:YAG Laser

Titanium materials exhibit a property profile that is just as versatile as that of steel materials. Titanium materials therefore have outstanding properties, such as excellent resistance to corrosion and high strength values at low densities, which makes them ideal for use in the chemical industry and as structural materials in lightweight construction. Due to the high affinity of titanium to atmospheric gases at increased temperatures above 500 °C, titanium components have to be welded in a sophisticated process under inert shielding gas by TIG welding or by an electron beam in a vacuum. A novel innovative laser beam welding process using a pulsed laser with free pulse shaping will be presented here with which oxidation‐free titanium weld seams with excellent mechanical and technological properties can be produced. For this low heat welding process, the otherwise commonly used inert gas covering can be substituted with a shielding gas nozzle. The process‐specific low heat input and the resulting low energy input per unit length both have a positive effect on the microstructure and thus on the mechanical properties. This welding process offers both technological and economical advantages over the processes used up until now, particularly for the machining of complex components and for series production.     

Soft vacuum processing of materials with electron beams

The use of soft vacuum (10^–3 to 1 Torr) rather than high vacuum (10^–5 to 10^–4 Torr) in connection with electron beam processing of materials is discussed. It is argued that practical, technical and economic advantages can be realized in a wide range of applications from heat-treatment, through welding and melting processes, to vapour deposition and gas processing. The new technology of glow discharge electron beam sources is especially suited to soft vacuum processes. While mainly developed so far for welding applications, it can be applied to this much wider field which presently employs thermionic guns working in high vacuum conditions.     

Verhalten geschweißter Magnesiumlegierungen unter mechanisch‐korrosiver Komplexbeanspruchung

Corrosion and corrosion fatigue of welded magnesium alloys In addition to the prevalent use of magnesium cast alloys a high potential for lightweight constructions is offered by magnesium‐wrought alloys, in particular in the automobile industry. The use of rolled and/or extruded magnesium alloys (profiles and sheet metals) requires suitable and economic join technologies like different welding procedures in order to join semi finished parts. Thus, the realization of lightweight constructions asks for high standards of materials‐ and joining‐technologies. In this context, the mechanical properties as well as the corrosion behaviour of the joints are of large interest. During welding of magnesium alloys, influences concerning the surface, the internal stresses and the microstructure occur. These influences particularly depend on the energy input and thus, on the welding procedure as well as the processing parameters, which all affect the corrosion behaviour of the joints. Sheets of magnesium alloys (AZ31, AZ61, AZ91) were joined with different welding procedures (plasma‐, laser beam‐ and electron‐beam welding in the vacuum and at atmosphere). The corrosion behaviour (with and without cyclic mechanical loading) of the welded joints was investigated by different methods such as corrosion tests, polarisation curves, scanning electron microscopy and metallography. Furthermore, substantial influencing variables on the corrosion behaviour of welded joints of magnesium alloys are pointed out and measures are presented, which contribute to the improvement of the corrosion behaviour.     

高能束焊接技术在舰船建造中的应用

高能束焊接技术具有集束、高功率密度、焊接精度高等优点,应用领域非常广泛,本文着重分析了电子束焊接和激光焊接技术在舰船建造方面的应用。     

真空激光焊接技术研究现状与展望

真空环境下激光焊接熔深得到显著提高,焊缝成形及气孔等缺陷得到极大改善,可以获得常规激光焊接方法难以获得的显著效果。近些年,有关真空激光焊接过程机理,低真空甚至局部负压环境激光焊接装置的研究日益完善,真空激光焊接技术在船舶、核电及压力容器等领域大厚板焊接中展现出良好的应用前景。本文首要概述环境压力变化对激光焊缝熔深,焊缝表面成形及气孔等缺陷的影响规律,从焊接过程等离子体羽辉及匙孔、熔池的动态行为特性方面总结国内外学者有关真空激光焊接机理的研究成果,并介绍了真空焊接技术在工业领域的应用情况,最后对目前已报道的研究中存在的问题进行分析并对真空焊接技术的发展前景进行展望。

     

Fügen von Magnesium und Magnesiumlegierungen

Welding of Magnesium and Magnesium alloys Magnesium is mainly connected by screws. In this paper the results of experiments with different welding processes will be presented. The following methods have been applied: TIG, MIG, Nd: YAG‐Laser and CO₂‐Laser welding, electron beam welding and High Power Diode Laser welding.     

TECHNOLOGICAL PROCEDURES OF ELECTRON BEAM WELDING AND REPAIR

The most developed fields of electron beam welding (EBW) industrial application in the world are aerospace industry, nuclear power engineering, turbine manufactures, instrumentation, automobile industry, manufacture of bimetal strip. The expansion of EBW application is associated with the manufacturing of thick-wall steel structures. A short review of EBW techniques is given. The expediency of applying the electron beam facing of edges before welding the relatively contaminated plate materials is explained. The procedure of welded joint repair is presented. The acceptability of rewelding the defective weld areas is shown for the case of high-strength steel.     

Influence of focusing thermal effect upon AZ91D magnesium alloy weld during vacuum electron beam welding

The influence of focusing thermal effect upon the weld shape, microstructure and alloying elements distribution in the welded joints during vacuum electron beam welding on AZ91D magnesium alloy was studied. The results show that the focus state affects the offset of DOF, and further significantly affects the actual welding heat input in the process of vacuum electron beam welding. The sharp focusing state is characterized with higher welding energy density, but the welding energy density of defocusing state is lower. Therefore, the welding process with sharp focusing state and smaller calculation welding heat input can obtain the same weld penetration as the welding process is the conditions of defocusing state and larger calculation welding heat input. And the welding process of sharp focusing state and smaller calculation welding heat input can induce more strongly burning loss of Mg element than the conditions of defocusing state and larger calculation welding heat input. Then, which will affect the distribution of alloy elements in weld seam.     

Influence of gravity state upon bubble flow in the deep penetration molten pool of vacuum electron beam welding

The governing equations of two-dimensional bubble flow model for gas–liquid two-phase system in deep penetration molten pool of vacuum electron beam welding were developed according to the laws of mass and momentum conservation. The separation models of gas and liquid convections in bubble flow were formed by regarding the gas phase in molten pool as a particle phase, and the vacuolar fraction, velocity slip, pressure gradient and other factors were introduced into the models. The influences of the gravity state upon the convection of bubble flow and the distribution of cavity-type defects in molten pool of AZ91D magnesium alloy were studied by the method of numerical simulation based on the mathematical models. The results showed that the gravity is an important factor to drive the convection of the bubble flow in the deep penetration molten pool during vacuum electron beam welding. The gravity has an impact on the gas distribution in molten pool, thus affects the distribution of cavity-type defects in weld. Because of the gravity contributing to driving the convection of bubble flow, it is conducive to the escape of gas phase in molten pool and reducing the air rate. A larger convection velocity of gas phase is helpful to the escape of gas phase, thus reduce the tendency of cavity-type defects.     

Formation and expansion of the plasma column under electron beam-metal interaction

The process of expansion of low-energy electrons and ions produced from electron beam evaporation of a metal target in the technological vacuum chamber of an electron beam welding machine is studied. Analyzing the spatial distribution of the particle density that is measured, the radial collisionless plasma motion from the beam region is shown to be prevailing. A model of the free plasma expansion out of the cylindrical source is developed. The relative distribution of the electron density and the electrostatic potential obtained are compared with the experimental results. The knowledge of the plasma parameter distributions in the technological vacuum chamber can be used for remote diagnostics and control of the technology process.     

等离子焊箱真空控制系统研制

在钛及钛合金熔炼生产中,真空等离子焊接是电极制备的重要工序,而真空等离子焊接的真空度对铸锭的质量影响很大。针对真空等离子焊箱真空控制系统的工艺和控制要求,研制基于工控机+PLC(S7-300)+INFICON PCG410-S真空计的集散控制系统,实现了对真空泵组、电磁阀、真空压力和枪抽空进行实时监测与控制优化。生产实际应用表明,该系统在提高抽真空效率,降低漏率,确保高质量钛及钛合金电极生产方面效果显著,具有一定的应用前景。     

Laser- und Elektronenstrahlschweißen von Magnesiumwerkstoffen

Laser- and Electron Beam Welding of Magnesium Alloys Designing and constructing complex structures using magnesium raises the necessity to solve joining problems. Laser beam welding and electron beam welding are two methods which are very fast and allow short clock cycles. Together with fast magnesium processing like die casting and extrusion pressing these welding methods help to increase productivity and reduce production costs. The experiments were carried out on two different electron-beam-welding-machines: while some of the experiments took place on a conventional high-vacuum electron-beam welding machine (EBW), a non-vacuum electron-beam welding machine (NVEBW) was used to weld under atmospheric pressure conditions. The laser beam welding experiments were carried out with CO₂- and Nd:YAG-Lasers. The investigations show that beam welding of magnesium-wrought and die-cast alloys is possible without crack formation. The mechanical properties of the welded wrought alloys were in the range of the base material. Only the fracture strain of the joints was reduced. When welding die-cast alloys, the formation and the properties of the welding joints were determined by the quality of the base material, such as pore content and contamination of the alloys. Thus, using vacuum die-cast alloys with high purity can reduce the porosity within the joining zone. By the use of wire filler material, the quality of the welding seam could be improved, because the porosity was reduced, and the vaporising material was compensated.     

铜与奥氏体不锈钢异种材料电子束焊接

目的研究不同参数下铜钢电子束异种焊接以获得符合要求的接头质量。方法以无氧高导热铜(OFHC)和奥氏体不锈钢(304)作为研究对象,控制扫描幅值、焊接速度等工艺参数,采用500 Hz真空电子束偏束"O"形扫描焊接的方式进行焊接。结果在电子束偏钢侧0.2 mm,电子束流为17 mA,聚焦电流为501 mA,焊接速度为600 mm/min的参数下,添加半径为1 mm,频率为500 Hz的圆形扫描波得到了抗拉性能为310.9MPa、硬度大于180 MPa的优质焊接接头。结论不同参数下的接头宏观均出现焊缝上表面下陷缺陷,接头铜侧热影响区存在大量颗粒状、块状、条状的铜钢固溶体析出相,接头钢侧热影响区存在宽度随扫描波幅值减小而减小的黑色过渡带。     

An analytical model and tomographic calculation of vacuum electron beam welding heat source

According to the analysis to the characteristics of welding heat source and thermal effect, a mathematic model of rotary Gaussian body heat source with incremental power-density-distribution was developed, which was in line with the characteristics of heat source during vacuum electron beam welding. The affecting radius of source model decreases progressively with the law of Gaussian function and the power density varies gradually with the law of exponential function in depth direction. The evaluation of peak-power-density coefficient β and the tomographic calculation of the source model in different focused conditions were discussed. The results showed that the focused conditions, which were the deviation of depth of field in electron beam, were dependent on the coefficient β in the source model. Simulation of thermal effect and the analysis of weld formation in vacuum electron beam welding validated the feasibility of the model.     

真空电子束焊接技术应用研究现状

简要概括了真空电子束焊接技术在不同材料连接方面的应用现状及研究发展动态,包括铝及其合金、钢铁材料、铜及铜合金、钛及钛合金、难熔金属钨/钽/铌/钼及其合金、金属间化合物及复合材料电子束焊接的发展现状。针对电子束焊接技术,简述了国内外学者已取得的部分研究成果,包括工艺试验、组织分析、数值模拟和力学性能等;分析了目前电子束焊接技术在材料连接方面还存在的问题,并展望了电子束焊接技术应向高温新型结构材料、异种材料、功能复合材料等方向发展,丰富了连接过程中的理论基础,揭示了工艺与组织及性能的对应关系,扩展了电子束焊接技术的应用领域。     

Model-based approach for quality improvement of electron beam welding applications in mass production

A model-based approach is presented to obtain a definite geometry of the seam as well as to find the regimes where the results will repeat with less deviation from the desired values in the electron beam welding. Using the response surface methodology, polynomial regression models for the behaviour of weld depth and the weld width are found. In order to improve the quality of the process in mass production, by a decrease of the deviation from a target value of the performance characteristic, parameters in two models describing the mean value and the variance for the weld depth and for the weld width in mass production are estimated. Using these models quality improvement, defined as an optimisation problem to produce reproducible welds while keeping the mean value of weld depth or/and width constant, is discussed. This approach is applied to the electron beam welding of stainless steel, for beam powers in the region of 4.2-4.8 kW and welding speeds of 3.333-13.333 mm/s.     

Joining of cemented carbides to steel by laser beam welding

Welding of dissimilar materials such as steel and cemented carbides (hardmetals, cermets) is particularly challenging e.g. because mismatches in their thermal expansion coefficients and thermal conductivities result in residual stress formation and because of the formation of brittle intermetallic phases. Laser beam welding of cemented carbides to steel appears as an attractive complementary technique to conventional brazing processes due to its high precision, high process speed, low heat input and the option of welding without filler. Here a laser welding process including pre‐heat treatment and post‐heat treatment was applied successfully to joining as‐sintered and nitrided hardmetals and cermets to low alloyed steel. The microstructure and mechanical properties of the welds are investigated by microscopy, X‐ray diffraction, microhardness measurements, and bending tests. The results reveal that the three‐step laser beam welding process produced crack‐free and non‐porous joints. Nitridation of the cemented carbides results in a significant reduction of the amount of brittle intermetallic phases. The mechanical properties of the joints are competitive to those of the conventional brazed steel‐cemented carbide joints.