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航空工业焊接的新趋势麻省理工学院 帕特里西奥楼门德斯 摘要:焊接在航空业正经历着令人振奋的发展。广泛应用计算机和改善设备和设计新材料塑造的方式焊接，是实施过程和产品正在设计的主要要方法。有一种普遍的趋势，减少铆钉在在飞机结构组件的使用有一种普遍的趋势. 扩散焊和激光，电子束焊接是在加入材料情况下使用的。军用飞机的电子束焊接在加入钛合金下使用，并且有扩大趋势.大型商业飞机的激光束焊接，慢慢取代铆钉在大部份机身上使用, 航天工业也显示:航空业界承诺一些新的进程的发展.其中包括：搅拌摩擦焊接和变极性等离子弧焊，这已经被应用火箭的关键部件上, 目前, 铸件在飞机有日益增加的趋势,这样开辟了新的机遇和挑战. 而一些进程，包括扩散焊接铝合金和线性摩擦加入叶片盘。似乎并没有得到广泛应用. 本文侧重于焊接的基础，就其影响的焊接航空组件，以及对趋势的行业的预计，因此是一项基本的水平。维修焊接，无损检测，钎焊是本文章讨论的范围。导言: 焊接的过程，就是人类一个古老的处理金属的过程.其在历史上的大多数的时间,它一直被视为一个粗浅的艺术或施工技术. 19世纪推动现代焊接新的发展而且发展趋势比以往任何时候都要快. 不同的焊接工艺可以由不同强度的热源融合.也揭示了许多重要的趋势当中, 渗透率衡量的比例，深度,宽度（四/瓦特）焊缝截面的急剧增加与热源强度有关。这允许较高的焊接速度,使得焊接过程更有效率. 一个更有效率的过程中在焊接过程中需要较少的热输入，从而形成一个强大的焊缝 . 较小的热源,移动速度更快,也意味着停留时间在任何特定的点的时间大大减少. 如果停留时间太短，在过程中，无法手动控制，必须加以自动化, 最低的时间，仍然是可以手动控制的对应的电弧焊接（约0.3秒）. 因此，他们只能用自动控制热源更激烈的的焊接. 焊接工艺在更加集中热源的地方创建一个较小的热影响区（ HAZ组织）和形成较低后焊缝扭曲力. 它可以推断：所带来的好处是: 更加集中热源, 资本设备的费用大约与强度热源成正比的.航空业的特点是：低单位生产，单位成本较高，在营运条件极其严重情况下,焊接就十分重要了, 这些特征对较昂贵的和更集中热源如等离子弧，激光束和电子束焊接作为焊接进程的选择,是焊接的关键部件的重要选择焊接过程在航空业中的使用.摩擦焊接）在这个过程中，通过机械变形加入金属。既然没有熔化,就不存在基础的材料熔化-凝固现象的相关缺陷. 这个过程中可以加入铝起落架组件,组成了一个比较简单的横截面. 性摩擦（微动）焊接被认为是由通用电气公司和普惠公司发明的一种替代，为制造和修理高温合金盘为喷气发动机. 虽然没有透露这些进程，他们也会演变成商业应用.搅拌摩擦（搅拌摩擦焊）契维语在1991年发明了这一焊接方法, 这是一个坚实的焊接进程，通过机械变形加入金属, 在这个过程中,圆柱等工具与异型探头旋转，慢慢地陷入了联合线之间的两块资产负债表或板材，这样就对接在一起，这个过程可以焊接以前报告铝合金飞机结构在使用. 实力焊缝与弧相比是弧30 或50 . 在一些小热影响区的地方，残余应力，微观结构也得到了改变. 波音公司出了1500万美元的投资在使用搅拌摩擦焊焊接助推器为三角洲的范围的国家运载火箭，这是美国的第一生产搅拌摩擦焊的地方. 1998年8月, 在德尔塔II,首次发射一个使用搅拌摩火箭. 这一进程目前正在考虑加入铝berilium合金，如2005年，为中央智囊团的航天飞机，就得到了应用。钛合金也有其他航空用途. 作为搅拌摩擦焊的一种,为了更好地使用，它可以取代等离子弧焊（足）和电子束焊接（电子束焊接）,在一些具体的应用中用铝和用钛是有分别。 闪光焊为是一种在熔化过程中, 应用一对焊接接头焊接在短期的内弧和压力而作用的。这是能够产生强大的焊缝的基础材料. 这个过程可以焊接铝和表面耐高温合金使用没有特别准备或屏蔽气体。它可以焊接各种复杂的截面, 这是用在航空业加入环喷气发动机,主要是出于耐高温合金和挤压铝构件的作用而考虑的。 气体金属弧焊这个过程中，其中一个是世界上进心最热门的焊接工艺，因为它的灵活性和低成本是呆以广泛使用在航空业. 缺点是大尺寸的热源(处理流程，与如电子束焊接，运作）的焊缝有着不太好的力学性能. 这个过程是在主要的焊接工艺用于建造该燃料和氧化剂坦克火箭（ 2219为第一阶段）, 目前应用在自动焊接的叶片爱国者导弹上. 这些叶片由一个框架17-4 pH值超级不锈钢组成，其中金属薄板的相同的组成是welded8, 此应用程序的好处，从成本降低，而可靠性增强。钨极氩弧焊（氩弧焊）氩弧焊可以使用比的GMAW更激烈的热源. 因此，它可以产生较小的焊缝，从而降低的成本。对于大多数结构,在应用这一过程中，不能与其他焊接方法如电子束焊接，激光焊接或等离子弧相焊接相单混用。氩弧焊是一起使用的GMAW与焊接在2014年和2219的铝合金在燃料和氧化剂坦克在土星v rocket7使用. 梅塞施米特blkow blohm在德国目前使用的GMAW为喷嘴延长镍，阿丽亚娜发射vehicles9上也使用过这种焊接. 大部分的焊接主要表现在商用飞机及对管道及油管使用焊接. 这个过程也可以用在换热器的核心上，喷气发动机百叶窗和排气外壳上，不锈钢和inconel1无论是在商业和军事都得到了使用. 不锈钢叶片在多伦多也用在堵塞焊缝在爱国者导弹也得到了使用. 允许应用到航空焊接结构的组成部分包括弧长控制和救济的应力用散热器在焊接上, 这项技术，是由洛克希德马丁公司在土卫六四运载火箭上使用的. 它是一种通过测量电弧电压来测量所期望的渗透率.这种技术在中国 北京航空制造技术研究所也得到了应用. 它已用于喷气发动机案件中的耐热合金和火箭燃料箱的铝合金。在这方面的技术，散热器步道背后的焊接电弧就是这样一种方式，他们的热领域的互动，大大降低了氩弧焊的过程产生的残余应力和扭曲力. 企图以取代铆由多伦多的焊接迈出皮肤板尚未成力，但由于严重歪曲了一些问题.等离子弧焊使用constricted弧之间的nonconsumable电极和熔池（转移弧）或之间的电极和制约喷嘴（ nontransferred弧）, 如果热强度不够高，这个过程是不可以运作，类似一个小孔模式，有人认为，激光或电子束焊接，虽然与规模较小但渗透率最高. 这个过程是用于焊接的先进的固体火箭发动机,使用材料是惠普- 9 - 4 - 30钢. 其中一个最新的变化，就是霍巴特兄弟将这个过程如变极性等离子弧焊焊接（ vppa ）商品化. 这种变化在航空航天工业焊接较厚路段铝合金，特别是为外部燃料箱的航天飞机得到了使用.这个过程中熔化的是在小孔模式中进行的.不好的一部分，是循环提供了一个阴极清洗铝工件，而好的部分，提供了理想的渗透和熔融金属流. 测试结果表明，最佳占空比为这个过程中涉及的负序电流15-20 MS和一个积极的2-5的电流中，一个积极作用是:当前的30-80 1高于负序电流. 集中供热原因是为了明显减少角扭曲力.激光焊接这个过程, 优势是电子束焊接技术可以提供最集中的热源焊接, 更高的精度,焊缝质量和规模较小的扭曲. 这个过程是用于焊接喷气发动机部件,其由耐热合金制成，如hastelloy，激光加工燃烧在普惠公司喷气发动机jt9d ， pw4000 ， pw2037和F - 100 - 22019得到了运用.激光焊接将很快取代铆在空中客车318飞机中使用. 显着的优点是可以预期并取得的取代铆接接头的不足. 铆，估计消费占制造业的40 左右 .电子束焊接如上所述，高强度的电子束产生焊缝与热影响区小，这个过程中的优势，电子束对熔融金属的对接已没有问题. 不过，它需要在真空中运作. 这一特点在使用这一进程中，特别适合焊接钛合金而不能焊接在一个开放的气体中的部件. 钛合金被广泛用于军用飞机，因为它重量轻，强度高，性能在高温下也较好. 应用电子束焊接，以焊接钛部件的军用飞机一直在不断扩大. 塔员额和机翼部件在Ti 6Al - 4V和f15战斗机也得到了广泛的应用. 机翼盒举行可变几何的翅膀，在旋风式战斗机，如f14 “雄猫”得到了使用. 在控制系统中,以及在以及在实施电脑自动化中有着显着的差异. 这项新技术，使连续一通焊缝超过曲线和曲面，并通过不同厚度来进行. 波音公司的F - 22的关键结构部件现在用钛电子束焊接这种方式来焊接的. F - 22是第一次飞机在60年的特点焊接机进行的. 前的前身用了铆接铝.将他们焊接在一起. 最近的应用的钛铸件在F - 22战斗机的焊接出现了问题，因此延迟开始生产时间至少五个月. 俄罗斯能源火箭应用电子束焊接建造该氧气和油缸. 由于庞大真空，是造成当地密封与铁电产生影响.扩散焊这是一个固态焊接,在焊接过程中在焊缝所在处产生应用的压力，在高温下，该件没有宏观变形或相对变化. 航空业是主要用户是dfw, 这个过程已证明,超塑成形（ SPF ）则钛合金特别有用相结合. 在这种情况下，复杂的几何形状可以得到在短短得到应用. 在某些情况下替代铆接铝构件,从而使成本降价. 传统的制作由500紧固件构成的16个部分,并一起进行. 有人建议，以取代设计，整体加筋所产生的SPF / dfw会得到很好的作用. 应用的SPF / dfw可以减少了原来的铆接的铝材构件，来自76个详细的零件和1000紧固件，以钛金属版只有14个细节和90紧固件与总成本可节省30 左右. 成功的SPF / dfw钛刺激了大量的研究与目标，完成了类似的过程与铝焊接过程. dfw钛和铝钛根本区别是钛可以解散其氧化物而铝不可以，因此, 剩余氧化氮在界面形成铝联合,极大地降低了力量的焊接在焊接中的扩散. 这个问题已妨碍了SPF级/ dfw铝的普遍采用.结论驱动的成本和重量的积累，技术进步使得更换铆钉和紧固件与焊缝得到紧密的结合. 在商用飞机中,一些铆接铝构件由SPF级/ dfw钛的替代品（ SPF级/ dfw铝仍处于试验阶段）形成了一种趋势. 在不久的将来，空中客车飞机（ a318和a3xx ）功能将机身出现激光焊接，以在飞机上的形成. 展望进一步,迈向未来, 这是有可能将搅拌摩擦焊用于对飞机结构组件的焊接, 它可以可靠地加入合金系列等材料.变极性等离子弧焊焊接（ vppa ） ，原本是设计为空间应用可能深入飞机工业入中的厚度较厚的铝。实施计算机控制使用电子束焊接钛合金的应用程序在过去是不可行的，制造业等焊接第一次为喷气式战斗机机身中使用，电子束焊接钛在未来的军用飞机的运用将增加，这种预期是合理的，在飞机使用铸件正在增加，这必将带来新的挑战。 Proceedings of the conference “New Trends for the Manufacturing in the AeronauticIndustry”, Hegan/Inasmet, San Sebastin, Spain, May 24-25, 2000, pp. 21-38.NEW TRENDS IN WELDING IN THE AERONAUTIC INDUSTRY Patricio F. Mendez Massachusetts Institute of Technology 9Cambridge, MA 02139, USA Abstract Welding in the aeronautic industry is experiencing exciting developments. The widespread application of computers and the improved knowledge and design of new materials are shaping the way welding is implemented and process and product are being designed. There is a general trend to reduce the use of rivets in structural components in airplanes. Diffusion welding and laser, and electron beam welding are used to join the materials in these cases. In military airplanes electron beam welding is continually gaining ground in the joining of titanium alloys. In large commercial planes laser beam welds are posed to replace rivets in large parts of the fuselage. Some new processes developed for the space industry also show promise for the aeronautic industry, among them: friction stir welding and variable polarity plasma arc welding, which are already being used for critical applications in rockets. A current trend of increasing the use of castings in newer airplanes opens up new opportunities and challenges. Some processes that do not seem to have gained widespread application include the diffusion welding of aluminum alloys and the linear friction joining of blades for blisks. This paper focuses on the welding fundamentals, on its implications for welding of aeronautical components, and on the trends in the industry that can be expected from progress at a fundamental level. Repairs by welding, NDT, and brazing are left outside the scope of this paper. Introduction Welding is a process almost as old as the processing of metals by humans. For most of its history it has been regarded as an obscure art or a crude construction technique. New discoveries and the availability of electric energy in the nineteenth century pushed the development of modern welding with an ever-accelerating rate (Figure 1). The different welding processes can be ordered by the intensity of the heat source used for fusion (Figure 2). This ordering reveals many important trends among them. The penetration measured as the ratio of depth to width (d/w) of the weld cross section increases dramatically with the intensity of the heat source. This makes the welding process more efficient and allows for higher welding speeds. A more efficient process requires less heat input for the same joint, resulting in a stronger weld, as indicated in Figure 3. A smaller heat source moving at a faster speed also implies a much reduced dwell time at any particular point. If the dwell time is too short, the process cannot be manually controlled and must be automated, as shown in Figure 4. The minimum dwell time that can still be controlled manually corresponds to arc welding (approximately 0.3 seconds). Heat sources more intense than arcs have shorter dwell times; therefore, they can only be used automatically. Welding processes with a more concentrated heat source create a smaller heat affected zone (HAZ) and lower post-weld distortions, as indicated in Figure 5 to Figure 7. The benefits brought by a more concentrated heat source come at a price: the capital cost of the equipment is roughly proportional to the intensity of the heat source as it can be deduced from Figure 8. The nature of welding in the aeronautical industry is characterized by low unit production, high unit cost, extreme reliability, and severe operating conditions1. These characteristics point towards the more expensive and more concentrated heat sources such as plasma arc, laser beam and electron beam welding as the processes of choice for welding of critical components. Welding Processes used in the Aeronautic Industry Friction Welding (FRW) In this process, the joining of the metals is achieved through mechanical deformation. Since there is no melting, defects associated with melting-solidification phenomena are not present and unions as strong as the base material can be made. This process can join components with a relatively simple cross section. It is used for the joining of aluminum landing gear components. Linear friction (fretting) welding was considered by General Electric and Pratt & Whitney as an alternative for the manufacture and repair of high temperature alloy blisks for jet engines2. Although little was disclosed about these processes, they do not seem to have evolved into commercial applications. Friction Stir (FSW) TWI invented this process in 1991. It is a solid-state process that joins metals through mechanical deformation. In this process a cylindrical, shouldered tool with a profiled probe is rotated and slowly plunged into the joint line between two pieces of sheet or plate material, which are butted together, as shown in Figure 9. This process can weld previously reported unweldable aluminum alloys such as the 2xxx and 7xxx series used in aircraft structures. The strength of the weld is 30%50% than with arc welding3. The fatigue life is comparable to that of riveted panels. The improvement derived from the absence of holes is compensated by the presence of a small HAZ, residual stresses, and microstructural modifications in the welding zone4. Boeing made a $15 million investment in the use of FSW to weld the booster core tanks for the Delta range of space launch vehicles, which was the first production FSW in the USA5. The first launch of a FSW tank in Delta II rocket happened in August 19993. This process is currently being considered for the joining of aluminumberilium alloys such as 2195 for the central tank of the Space shuttle, and also titanium alloys for other aeronautical uses. As FSW becomes better established, it can replace plasma arc welding (PAW) and electron beam welding (EBW) in some specific applications in aluminum and titanium respectively. Flash Welding (FW) FW is a melting and joining process in which a butt joint is welded by the flashing action of a short arc and by the application of pressure. It is capable of producing welds as strong as the base material. This process can weld aluminum and temperature resistant alloys without especial surface preparation or shielding gas. It can join sections with complicated cross sections, and it is used in the aeronautical industry to join rings for jet engines made out of temperature resistant alloys and extruded aluminum components for the landing gear6. Gas Metal Arc Welding (GMAW) This process, one of the most popular welding processes in the world because its flexibility and low cost is not used extensively in the aeronautic industry. The drawback for its is that the large size of the heat source (compared with processes such as EBW, LW, PAW) causes the welds to have poor mechanical properties. This process was the main welding process used for the construction of the fuel and oxidizer tanks for the Saturn V rocket (2219 aluminum alloy for the first stage)7. One of the current applications of GMAW is in the automatic welding of the vanes of the Patriot missile. These vanes consists of an investment cast frame of 17-4 PH stainless steel over which sheet metal of the same composition is welded8. This application benefits from the low cost of GMAW, while extreme reliability is not as important as in manned airplanes. Gas Tungsten Arc Welding (GTAW) GTAW can use a more intense heat source than GMAW, therefore it can produce welds with less distortion at a similar cost. For most structural critical applications this process cannot compete with other welding methods such as electron beam welding, laser beam welding or plasma arc welding. GTAW was used together with GMAW to weld the 2014 and 2219 aluminum alloy in the fuel and oxidizer tanks in the Saturn V rocket7. Messerschmitt Blkow Blohm in Germany currently uses GMAW for the nozzle extensions of Inconel 600 in the Ariane launch vehicles9. Most of the welds performed on commercial aircraft are done on ducting and tubing using GTAW10. This process is also used in heat exchanger cores, louvers and exhaust housings for jet engines, both commercial and military in stainless steel and Inconel11. GTA plug welds are also used in the stainless steel vanes of the Patriot missile8. Creative innovations that permit the application of welding to aeronautical structural components include arc-length control (ALC)12 and relief of stress by using a heat sink during welding (LSND)13. This technology, shown schematically in Figure 10, was developed by Lockheed Martin for the Titan IV launch vehicle. It permits one to detect the desired penetration by measuring the arc voltage, as shown in Figure 11. The Low Stress No-Distortion (LSND) technique has been developed at the Beijing Aeronautical Manufacturing Technology Research Institute in China. It has been applied to jet engine cases of heat resistant alloys and rocket fuel tanks of aluminum alloys. In this technique, a heat sink trails behind the welding arc in such a way that their thermal fields interact, significantly reducing the residual stresses and distortions created by the GTAW process. Attempts to replace riveting by GTA welding of stringers to the skin plate have not been sucessful yet due to serious distortion problems14. Plasma Arc Welding (PAW) PAW uses a constricted arc between a nonconsumable electrode and the weld pool (transferred arc) or between the electrode and the constricting nozzle (nontransferred arc). If the heat intensity of the plasma is high enough, this process can operate in a keyhole mode, similar to that of laser or electron beam welding, although with smaller maximum penetration. A schematic of PAW is shown in Figure 12. This process is used for the welding of the Advanced Solid Rocket Motor (ASRM) for the Space Shuttle15. The ASRM is made of HP-9-4-30 steel by Lockheed. One of the latest variations of this process is variable-polarity plasma arc welding (VPPA) commercialized by Hobart Brothers. This variation was developed by the aerospace industry for welding thicker sections of alloy aluminum, specifically for the external fuel tank of the space shuttle16. In this process the melting is in the keyhole mode. The negative part of the cycle provides a cathodic cleaning of the aluminum workpiece, while the positive portion provides the desired penetration and molten metal flow. Tests showed that the best duty cycle for this process involves a negative current of 15-20 ms and a positive one of 2-5 ms, with a positive current 30-80 A higher than the negative current17, 18. The concentrated heat of VPPA causes significantly less angular distortions than GTAW, as shown in Figure 13. Laser Beam Welding (LBW) This process, together with electron beam welding can deliver the most concentrated heat sources for welding, with the advantages of higher accuracy and weld quality and smaller distortions. This process is used for welding and drilling of jet engine components made of heat resistant alloys such as Hastelloy X. Laser-processed combustors are used in the Pratt & Whitney jet engines JT9D, PW4000, PW2037 and F-100-PW-22019 Laser beam welding will soon replace riveting in the joining of stringers to the skin plate in the Airbus 318 and 3XX aircraft20. A schematic comparing a riveted and a welded stringer is shown in Figure 14. Significant savings are expected to be made by replacing riveted joints by LBW. Riveting is estimated to consume 40% of the total manufacturing man-hours of the aircraft structure4. Electron Beam Welding (EBW) As mentioned above, the high intensity of the electron beam generates welds with small HAZ and little distortion as shown in Figure 5 and Figure 6. This process presents the advantage over LBW that it has no problems with beam reflection on the molten metal; however, it needs to operate in a vacuum. This characteristic makes this process especially suitable for the welding of titanium alloys that cannot be welded in an open atmosphere. Titanium alloys are widely used in military aircraft because of its light weight, high strength, and performance at elevated temperatures. The application of EBW to the welding of titanium components for military aircraft has been expanding constantly. Pylon posts and wing components in Ti 6Al-4V for the F15 fighter have been EB welded by McDonnell Douglas since the mid 70s21. The wing boxes that hold the variable geometry wings in the fighters Tornado, and F14 “Tomcat”, are also Ti 6Al-4V EB welded (Figure 15 and Figure 16). Progress in control systems and in the implementation of computers for automation made a significant difference in the EBW of titanium alloys for military aircraft. This new technology enables continuous one-pass welds over curved lines and surfaces, and through varying thicknesses. Critical titanium structural components are being EB welded this way for the Eurofighter (attachment of the wings and fin to the fuselage22) and Boeings F-22 (aft fuselage10). The F-22 is the first airplane in 60 years to feature a welded fuselage. Prior fuselages were made of riveted aluminum. The recent application of titanium castings in the F-22 presented welding problems that delayed the start of production by at least five months23. A remarkable application of EBW is in the construction of the oxygen and fuel tanks of the Russian Energia rocket (Figure 17). Due to the large size of the tanks, the vacuum is created locally, and sealed with ferroelectric liquids24. Diffusion Welding (DFW) It is a solid-state welding process that produces a weld by the application of pressure at elevated temperature with no macroscopic deformation or relative motion of the pieces. The aeronautic industry is the major user of DFW25. This process has proven particularly useful when combined with the superplastic forming (SPF) of titanium alloys. In this case, complicated geometries can be obtained in just one manufacturing step as shown in Figure 18. The quality and low cost of the joint enables in some cases the substitution of riveted aluminum components with SPF/DFW titanium replacements. Figure 19 shows a possible improvement for the door panel of an aircraft fuselage. The conventional fabrication consisted of 16 parts held together by 500 fasteners. It was proposed to replace that design by a 2-sheet assembly, integrally stiffened produced by SPF/DFW. Figure 20 shows an exit hatch for the British Aerospace Bae 125/800. The application of SPF/DFW reduces the original riveted aluminum design from 76 detail parts and 1000 fasteners to a titanium version with only 14 details and 90 fasteners with a total cost savings of 30%. Figure 21 shows a wing access panel for the Airbus A310 and A320 in which switching from riveted aluminum to SPF/DFW titanium achieved a weight saving in excess of 40%. The success of SPF/DFW with titanium stimulated much research with the goal of accomplishing a similar process with aluminum. The fundamental difference between DFW of titanium and aluminum is that titanium can dissolve its oxides, and aluminum cannot. Therefore, the residual oxide at the interface of an aluminum joint dramatically reduces the strength of the diffusion weld. This problem has prevented the SPF/DFW of aluminum from being generally adopted. Conclusions Driven by cost and weight savings, technological progress is moving in the direction of replacing rivets and fasteners with welds. In commercial aircraft this trend is already in motion with the replacement of some riveted aluminum components by SPF/DFW titanium substitutes (SPF/DFW of aluminum is still at an experimental stage). In the near future, Airbus planes (A318 and A3XX) will feature fuselage stringers laser welded
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