汽車設計師和制造商的首要目標是找到提升燃油經(jīng)濟性的方法，這個任務如今變得越來越復雜。美國法規(guī)要求，所有汽車制造商都要在2025年前達到54.5 mpg的CAFE（公司平均燃料經(jīng)濟性）標準。這一標準要求的巨大提升，在以前看來是不切實際，也不可能實現(xiàn)的，但現(xiàn)在卻是汽車制造商必須達成的目標。
為了應對排放法規(guī)的要求并迎合消費者偏好，汽車制造商們開展了一個“技術海嘯”（Technical Tsunami）運動——變革的大潮催生了許多新技術和新材料的應用，如金屬鋁、金屬鎂、碳纖維、先進高強度鋼，以及先進的車輛電子裝置的廣泛采用。許多新材料和新技在汽車中的應用，都需要進行專門的維修培訓與之配合。僅在2015年，汽車制造商就推出了142款新車型，其中包括全新設計的，也包括現(xiàn)有車型的升級改造版。
與以往的車型相比， 2015款福特F-150車型大量使用了鋁材料，實現(xiàn)減重318 kg（700 lb）。福特的F-150是享譽全美的暢銷車型之一，其使用材料的重大調整引起了汽車行業(yè)的廣泛重視。
鋁制車輛的維修安全性標準
汽車架構中采用的鋁制材料越來越多，領先的汽車廠商也認識到，為了保證汽車在使用大量鋁材料后的安全性，除了制造工藝外，還必須審慎考慮汽車維修維護方面的問題。技術人員必須明確了解如何使用碰撞修護設備，以便充分、安全、高質量地完成鋁架構的維修維護。
在整個汽車行業(yè)內，技術人員正在學習必要的鋁制車身維修新技術，這也是I-CAR焊接培訓與認證（I-CAR Welding Training & Certification）課程的內容之一。
在F-150車型上市之前，I-CAR就與福特汽車合作，為碰撞維修技術人員開設了I-CAR培訓課程。而在此之前，業(yè)內的常規(guī)做法都是先發(fā)布新車，再進行相關維修培訓。F-150的車輛架構維修培訓課程FOR06已成為I-CAR歷史上最受歡迎的課程之一。該課程的特色是重點培訓適用于鋁制車身的焊接、鉚接，以及沖鉚-粘接技術。
鋁焊接——難度不大，但工藝不同
鋁焊接本身并不比鋼焊接難多少，但需要在許多方面采取不同的做法。
建立操作區(qū)——汽車制造商建議的最佳做法之一是，將鋁制車輛維修區(qū)與鋼材料焊接區(qū)分開。原因是空氣中的鋼材料微粒會污染鋁材料，如果長時間接觸水，也可能會導致腐蝕。
設備——技術人員普遍采用MAG（金屬活性氣體）焊接法對鋼制車身進行維修，這需要使用一種由75%的氬氣和25%的二氧化碳混合而成的保護氣體，即“C-25”混合氣體。與此不同的是，鋁材料需要使用MIG（金屬惰性氣體）焊接法，保護氣體100%為氬氣。
使用氬氣是因為這種氣體有助于焊接金屬表面的凈化。當焊接表面接觸到空氣時，鋁材料會立刻形成一層較薄的氧化鋁。氧化鋁的熔點是2050°C（3725°F），遠高于金屬鋁熔點650°C（1200°F），因此必須將氧化鋁清理干凈，否則焊接就只能透過氧化鋁涂層進行，這會使得焊接效果大打折扣。
技術人員應使用鋁材料專用的焊接導電嘴，中間的焊絲通道也應更大。專用焊槍上應刻有“A”或“AL”的字樣。此外，鋁焊接所使用的保護氣體噴孔也必須大于鋼焊接，以便供應更大的保護氣流。
為了避免鋼材料顆粒污染金屬鋁表面，鋁和鋼材料加工也會使用不同的手動工具。鋁材料應配有專門的切割工具和研磨工具，以避免與鋼材料發(fā)生交叉污染。
準備工作——在開始焊接鋁之前，技術人員需要清除所有的表面涂層，之后再用特殊溶劑擦拭干凈，目的是清除所有的表面污染物。技術人員需要用砂紙或不銹鋼刷子清除焊接區(qū)域的氧化鋁，在即將開始焊接操作前還需再次進行清理。
焊接技巧——鋁焊接的技巧與鋼焊接不同，技術人員應該用“推”的方式進行鋁焊接，而不是“拉”的方式。這種方法可以增強保護氣體的應用效果，有助于更好地將氧化鋁清除干凈。
此外，在鋁焊接中，焊絲需要與焊炬保持較遠距離，而焊炬需要離焊接表面更遠。須注意的是，技術人員應使用汽車廠商推薦的焊絲。
鋁焊接通常比鋼焊接需要更大的電流，并且焊接中的金屬過渡形式也有所不同。鋼焊接通常使用短路過渡法，當焊絲接觸到鋼時，會發(fā)生短路和爆斷。而在鋁焊接中，最好的方法是脈沖噴射過渡，在焊珠噴進熔池之前就會爆斷。
鋼焊接時，焊炬的熱量通常會集中在一個區(qū)域，而鋁材料會將熱量傳遞到整個部件。因為鋁的熱傳遞效率更高且熔點更低，因此焊接動作應該先慢后快，而焊炬在部件上移動時，速度應該更快。
為了避免鋁焊接開始時溫度過低，技術人員需要使用引弧板（run-on tab），或具有預熱功能的設備。在焊接收尾時，在金屬鋁表面往往會形成弧坑，因此技術人員需要在收弧時通過額外動作將弧坑引至焊件外，或者使用引弧板將其引出。
技術新前沿：下一步會是什么？
為了應對未來的諸多挑戰(zhàn)，我們需要合適的設備和充分的培訓，以及勤奮好學、技術過硬的維修人員。汽車行業(yè)正在發(fā)生巨大改變，因此碰撞維修行業(yè)必須培養(yǎng)腳踏實地、樂于學習的文化，將技能學習和知識掌握視為戰(zhàn)略性資產(chǎn)的積累，對其進行妥善的管理、促進和保持。
明確了未來發(fā)展的核心要務，我們也就準備好了采用鋁焊接的新技術，并建立起更加卓越的方法架構，將來無論出現(xiàn)怎樣顛覆性的材料應用或創(chuàng)新技術，我們都可以有辦法應對。
文章來源：《汽車工程雜志》。本文作者是I-CAR的產(chǎn)業(yè)技術關系總監(jiān)Jason Bartanen。I-CAR是一個非盈利性機構，主要進行教育培訓、知識積累與解決方案開發(fā)，旨在滿足碰撞維修產(chǎn)業(yè)不斷變化的需求。
作者：Jason Bartanen
來源：SAE《汽車工程雜志》
翻譯：SAE上海辦公室
Aluminum welding: The next frontier for technicians
For automotive designers and manufacturers, finding ways to increase fuel economy has become a primary—and increasingly complicated—goal. In the U.S., regulations now focus on a requirement that every automaker achieve a corporate average fuel economy (CAFE) of 54.5 mpg by 2025. Such dramatic improvements once seemed impractical or impossible, but today they are the new reality for automakers.
In response to these emissions regulations and to the evolving preferences of consumers, automakers have generated a “Technical Tsunami”—the waves of change resulting in new technologies and new materials like aluminum, magnesium, carbon fiber, advanced high-strength steels, and vehicle-wide proliferation of advanced electronics. Many of these require specialized training to repair. In 2015 alone, automakers introduced 142 new or redesigned vehicle models.
The aluminum-intensive 2015 Ford F-150 shed 700 lb (318 kg) compared with previous models. The drastic material change to the F-150, with its longstanding reputation as one of America’s best-selling vehicles, caused the industry to stand up and take notice.
Maintaining a standard of vehicle repair safety with aluminum
As progress has been made toward adopting aluminum for automotive structures, industry leaders have realized that, to keep aluminum vehicles safe, they must consider not just their manufacturing process but also their repair. Collision repair facilities needed to be confident that their technicians knew how to properly achieve complete, safe, and quality repairs on aluminum structures.
Technicians across the industry are learning the necessary new methods for working with aluminum as part of the I-CAR Welding Training & Certification program.
Prior to the launch of the F-150, I-CAR and Ford Motor Co. worked together to create and make an I-CAR training curriculum for collision repair technicians. Historically, vehicles debut before the training begins. The F-150 structural repair training course FOR06 has become one of the most popular courses in I-CAR’s history. In particular, the program emphasizes processes for welding, riveting, and rivet bonding aluminum vehicles.
Welding aluminum—not difficult, just different
Welding aluminum is not more difficult than welding steel, but it requires a different mindset in a number of areas.
Setup space—One best practice that is often recommended by vehicle makers when repairing aluminum vehicles is to set up an environment separate from the steel welding area. The concern is that steel particles in the air could contaminate aluminum and possibly cause corrosion if exposed to water over time.
Equipment—When repairing steel bodies, technicians commonly employ MAG (metal active gas) welding, using a shielding gas that is 75% argon and 25% carbon dioxide—a mixture known as C-25. Aluminum, however, requires the use of MIG (metal inert gas) welding with a shielding gas composed of 100% argon.
Argon is specified because it offers good cleaning action on the metal being welded. Aluminum materials immediately form a thin coat of aluminum oxide on their surfaces when exposed to air. Moreover, aluminum oxide melts at 3725°F (2050°C), while aluminum itself melts at 1200°F (650°C), so the aluminum would melt before its oxide covering does. The aluminum oxide must be removed, or the technician will be trying to weld through it, which is certain to produce a less-than-desirable weld.
Technicians should use contact tips specifically designed for aluminum, with an oversized hole for the electrode wire. These tips are stamped with an “A” or “AL.” Similarly, shielding gas nozzles must be larger than those used with steel to accommodate the increased gas flow.
Further, to avoid contaminating aluminum surfaces with steel particles, separate hand tools are often used. Cutting tools and abrasives should be dedicated specifically to aluminum as well to avoid cross-contamination.
Preparation—Before starting to weld aluminum, technicians need to remove any coatings from the surface and then wipe it clean with a solvent to eliminate any surface contamination. They should use sandpaper or a stainless steel brush to remove the aluminum oxide from the weld zone and clean the area again immediately before the welding operation begins.
Technique—Creating welds with aluminum differs from working with steel. Technicians should use the push technique, rather than the pull technique. This method enhances the ability of the shielding gas to clear aluminum oxide from the aluminum.
Also, the electrode wire should stick out farther from the welding torch, and the torch should be held farther back from the welding surface. Note that the technician should always use the electrode wire recommended by the vehicle maker.
Typically, more amperage is required for welding aluminum than for steel, and the welding transfer method is different. When working with steel, generally the short-circuit method is employed so that, when the electrode hits the steel, it short circuits and breaks off. For aluminum, however, the preferred transfer technique is a pulsed spray in which the weld bead breaks off before it is sprayed into the molten puddle.
Whereas steel holds heat from the welding torch in one area, aluminum transfers the heat throughout the part. Because of this greater heat transfer efficiency and aluminum’s low melting point, the welding speed should start slowly but then increase as the welding torch moves across the panel.
To avoid cold starts with aluminum, the technician should create a run-on tab or use a machine with a pre-heating feature. At the end of the weld, craters tend to form in aluminum, so the tech should activate an extra trigger pull when completing the weld, or make a run-off tab.
The new frontier: What’s next?
To master the curves in the road ahead, we need the right equipment, training, and qualified technicians—along with an appetite for learning. Given the dramatic changes in vehicles, it is imperative that the collision repair industry support a robust and earnest “Learning Culture,” building businesses that treat learning and knowledge as strategic assets that need to be managed, developed, and maintained.
Once we understand the nature of this new road, we’ll be prepared to enter the new frontier of aluminum welding, building an even better framework for approaching whatever game-changing material or innovation is sure to be down the road.
Jason Bartanen, Director of Industry Technical Relations for I-CAR, wrote this article for Automotive Engineering. I-CAR is a not-for-profit education, knowledge, and solutions organization designed to support the evolving needs of the Collision Repair Inter-Industry.
Author: Jason Bartanen
Source: SAE Automotive Engineering Magazine
鋼焊接采用MAG保護氣體，而鋁焊接采用的是MIG氣體，這要求技術人員掌握一些新技術。
I-CAR的產(chǎn)業(yè)技術關系總監(jiān)Jason Bartanen
采用MIG氣體進行鋁焊接，比如搭接焊中的這個填角焊縫，應始終在與車身焊接之前進行外觀查驗和破壞性檢查。
通常建議使用MIG脈沖噴射過渡焊接設備進行鋁焊接操作。
I-CAR鋁焊接培訓與認證項目采用現(xiàn)場講解方式，由I-CAR的鋁焊接專家進行指導授課。