The welding of aluminum alloys is not as simple as it might seem, since the material itself has several characteristics that need to be considered and overcome. Aluminum and its alloys have become very popular during the 20th century in transport industry applications, due to their rather exceptional strength-to-weight ratios.
Aluminum is considered a soft metal. On the other hand, it is highly praised for its other properties, such as high thermal and electrical conductivity, nontoxicity, corrosion resistance, high reflectivity, and lightness. Although not very strong by itself, some of the more complex aluminum alloys have mechanical characteristics equivalent to steels. It is also one of the most malleable and ductile materials in the world. That is why aluminum and its alloys have earned a spot among the most utilized materials in various industries. Aluminum is widely used in transport, packaging, food and chemical processing, architecture, energy generation, and electrical transmission. The specific alloy used for each application depends on the specific properties that are required.
There are several welding methods used around the world for welding aluminum alloys, such as laser welding, electron beam welding, friction welding, and arc welding. As the TAF factory specializes in arc welding methods for the manufacturing of its aluminum products, we are going to take a closer look at the two most famous aluminum arc welding methods - TIG (Tungsten Inert Gas welding) and MIG (Metal Inert Gas welding). It is only fair to mention that these two methods are not used exclusively for aluminum welding but can also be used to join other types of materials, e.g. carbon steel, stainless steel, magnesium, copper, titanium alloys, and many more.
TIG – Tungsten Inert Gas welding
Historical development
Modern day arc welding methods were built by Sir Humphrey Davy, London, England in 1801. He experimented and demonstrated the first electric arc between two carbon electrodes. In order to achieve that he used what can be called a predecessor to modern batteries. As for the TIG welding method itself, an American engineer Russ Meredith is considered to be its inventor. In 1942, after a series of experiments, he managed to patent the Gas Tungsten Arc Welding (GTAW) process for magnesium and steel materials.
In later years, the GTAW process, nowadays called TIG, proved to be an ideal welding process for many other materials, with aluminum standing out as the most popular. In the 1960s and 1970s, the Linde Division of Union Carbide, which had previously bought the patent for the arc welding process, started producing and selling the first GTAW equipment, such as torches, tungsten grinders, gas kits, etc. Linde torches utilized helium as the inert gas.
Following expiration of the patent, other companies contributed to further development of TIG welding equipment and the industry as a whole. The first industrial TIG welding machines weighed thousands of pounds and required a large amount of space for installation.
Modern TIG welding machines have undergone rapid development and are getting smaller and more user-friendly year after year.
Definition
Tungsten inert gas (TIG) welding is a precise and versatile process used to create high-quality welds. It joins metals using a non-consumable tungsten electrode, while protecting the welding area from atmospheric contamination with an inert gas, such as argon or helium.
How does it work?
TIG welding requires the proper equipment and knowledge for the type of metals you plan to weld. One needs a high degree of professional welding skills to properly carry out TIG welding, which is why people usually start with the simpler MIG welding process and then move on to TIG.
TIG welding is most often performed when joining pipes and thin materials together, due to its low heat output, which preserves the microstructure of the metals. It is a precise, high-quality welding technique that uses a non-consumable tungsten electrode and employs non-reactive gas, usually argon, to protect the weld area from atmospheric contamination. Argon, Helium, or a mixture of both, are mostly used as shielding gases during the welding process, thereby maintaining the clarity of the weld pool.
Basic TIG welding machines consist of a power source, welding torch, grounding cable with clamp, and gas tank with regulator. In order to start and finish the welding process, you also need a non-consumable tungsten electrode (many types are available, depending on the material to be welded), and optionally, a filler material rod. In some cases, the additional filler material is not necessary. The TIG welding process joins pieces of metal together through a welding current.
There are three options for the welding current, with each having a specific purpose and unique properties – AC, DC negative, and DC positive. An inert gas is supplied to the welding torch that flows along the welding arc to protect the metals from oxidation and from forming small circular gaps. A tungsten electrode, which has a higher melting point than most metals, is located within the welding torch. The tungsten electrode and metal create a high-temperature arc that melts the metal and a weld pool is formed. The filler material, if any, is manually added to the weld pool in order to reinforce the joint. This allows the TIG welder to have complete control on the quality and precision of the weld.
TIG in the TAF Factory
Our TIG welders are trained by certified professionals and their work is scrutinized in-house on a daily basis. Training and testing of the welders is regularly carried out by the external company, SLV Berlin. Every step of the welding process, and the welders’ qualification, adheres to TAF’s demanding standards for the manufacture of the highest quality products . As a result, TAF’s compliance with the EN ISO 9606-2 standard for welding aluminum and aluminum alloys has never been an issue.
TAF is mainly using SELCO welding machines for its TIG operations and uses 100% argon. In order to make perfect welds, it utilizes 5356 filling rod material with a 3.2 mm diameter. The most common welds for the manufacture of truss are butt welds and corner welds.
End fittings for the truss are welded by semi-automatic welding robots, where the filler material is consistently added by the machine at an optimal speed to ensure perfect weld quality. In the case of welding fittings, a mixture of argon and helium for shielding of the welding pool is used.
MIG – Metal Inert Gas welding
Historical development
As with TIG welding, the early beginnings of MIG welding go back to the same Sir Humphrey Davy of London. Both methods use the electric arc that was introduced by him in 1801. As mentioned earlier, he used carbon electrodes in his welding process. It was not until 1892, when inventors N. G. Slavianoff and C.L. Coffin introduced the world to metal electrodes. It was at this time when the real development of MIG welding took off. In the 1920s, the first real predecessor of Gas Metal Arc Welding – the GMAW method - was invented. It used a bare electrode wire, with a direct current, and did not employ a shielding gas to protect the weld. It took almost another 30 years to develop a proper GMAW welding process. It was the Battelle Memorial Institute that finally cracked the code in 1948. The process used a smaller diameter electrode, which was made of aluminum and was continuously fed to the weld. A constant voltage power source was used and the weld was protected by argon gas. From this moment on, we can talk about the industrial utilization of GMAW welding methods, of which the modern MIG welding method is a subtype. Simplicity and speed are its biggest advantages.
Definition
Metal inert gas (MIG) welding runs high voltage through a consumable metal wire electrode to heat and fuse metals under a shielding inert gas. It is a cost-effective, fast, and simple process for the reliable fabrication of metal parts.
How does it work?
MIG welding is a subtype of the GMAW welding method. The welding process can be described as joining materials together through a welding current, while the filler material is constantly fed to the welding pool through the welding torch. The electric arc melts the electrode wire, which is then fused with the base materials in the weld pool. The entire process is achieved under the shielding of an inert gas that prevents oxygen and other contaminants from reacting with the molten metal, resulting in clean, strong welds that are free from pores and defects.
The MIG welding method is used for the same types of materials as TIG and these are commonly known as non-ferrous metals. The shielding gasses that keep the weld pool clean are also the same - argon and helium.
Metal inert gas welding is suitable for both thin and thick materials and some claim that aluminum is the hardest material to weld by this method for several reasons. One of them lies in the fact that it has low heat conductivity, which means that it is hard to maintain a stable temperature throughout the welding process without either burning through the joint or failing to melt it at all.
MIG in the TAF Factory
The MIG welding method is part of the standard, daily production process at two important working areas in the TAF factory. TAF was one of the first companies in the world to implement a fully robotic welding station for the production of truss. This step was made possible by cooperation with the professionals at KUKA, manufacturer of the robotic welding station, and their assistance with development of the robotic welding process. Given the nature of robotic welding, it is almost impossible to utilize the TIG welding method. To solve the introduction of filler material by an external source would be very difficult for the robotic arm. Therefore, the choice was simple. The robotic unit works on the basis of MIG welding. This means that straight trusses are welded by the robotic unit using the metal inert gas welding method. MIG welding can also be performed on huge welding tables, where large structures with long welds are manufactured. In all cases, argon is utilized as the shielding gas.
TIG vs MIG WELDING METHOD
There has always been a debate about which one of these methods produces higher quality welds and has the biggest benefits. In the end, they both have their pros and cons. It cannot be said that one method is better than the other. We often generalize MIG welding as faster and easier to learn, while TIG welding produces higher quality welds. Of course, both of these statements can have exceptions, and the choice really depends on the project you are working on. There are several factors that should be considered when choosing the proper welding method: type of material, quantity, cost, equipment, post-processing needs, project size, etc.
Both welding methods are popular and widely used in today’s manufacturing processes. Advances in welding continue to be breathtaking and time will tell on what the future holds with its development.
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TIG
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MIG
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Pros
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Higher quality welds
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Pros
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Faster weld time
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Optional filler material
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Cheaper welding equipment
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Easy adjustability of current
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Easy to create strong welds
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Possible to weld a wide variety of materials
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Easier to weld at difficult angles
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Cons
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Requires a clean metal surface before welding begins
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Cons
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MIG welds are not as strong as TIG welds
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Slow welding process
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Harder to control the weld bead
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Requires a high level of skill and knowledge
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Inability to weld thin metals
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TIG welders are harder to train and more expensive
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Requires protection from fumes
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