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  Techniques of Aluminum Welding During GMAW  
 
November 22, 2018

GMAW (gas metal arc welding), also known as MIG (metal inert gas) or MAG (metal active gas), is an automatic or semi-automatic arc welding method in which a consumable and constant wire electrode is fed, via a welding gun. With GMAW, a direct current power of constant voltage is commonly used. Sometimes, constant current systems and alternating current are also used. At  Xinxiang Aluminum, we provide complete aluminum fabrication services and understand the challenges that come with welding aluminum alloys.
As a leading custom aluminum fabricator, we recommend following the rules closely when it comes to GMAW. From preparing the base material, choosing welding equipment, applying the correct techniques to inspecting weldments, every process must be carried out carefully to make sure that top-notch quality gas tungsten-arc and gas-metal welds on aluminum alloys. The low melting point of aluminum alloys and higher thermal conductivity can lead to burnthrough if welders do not follow the prescribed procedures. Another issue that our fabricators have to overcome is the softness of aluminum welding wire, along with its lower column strength when compared to steel. However, you can easily beat such challenges by following the guidelines given below.
# Prepare the Base Metal
In order to fabricate aluminum, you must properly clean the base material, and get rid of any hydrocarbon contamination from cutting solvents or oils and aluminum oxide. This is crucial as the base-material aluminum will melt at 1,200 F while the aluminum oxide on the surface will melt at 3,700 F. Therefore, if you fail to remove all traces of oxide from the surface of the material, the filler metal will be inhibited from penetrating the workpiece. You can make use of solvents or a brush made of stainless steel bristle wire and etching solutions to eliminate aluminum oxides. As for minimizing the risk of hydrocarbons, you can use a degreaser.
# Preheat the Aluminum Workpiece
In order to prevent the weld from cracking, we heat the aluminum workpiece beforehand during our aluminum welding process. Our welders always preheat at 230 F, and they make use of a temperature indicator to avoid overheating. You may also choose to place tack welds at the end and the beginning of the area that is about to be welded to aid in the preheating process. When preheating a thick aluminum piece into a thin piece, we usually make use of run-off and run-on tabs that prevents cold lapping.
# Push the Gun Away
With aluminum, you must not pull, but push the gun away from the weld peddle. This results in reducing weld contamination, better cleaning action and enhanced shielding-gas coverage.
# Control the Travel Speed
The travel speed needs to be controlled by custom fabricators when welding aluminum. It must be welded hot and fast. Aluminum is not like steel, and its thermal conductivity dictates the use of voltage settings, hotter amperage and a higher weld-travel speed. In case the travel speed is slow, you risk excessive burnthrough, especially on the thin-gauge aluminum sheet.
# Select the Right Shielding Gas
In GMAW, solid-wire electrodes are used, and they need a shielding gas that will safeguard the molten weld puddle from atmospheric impurities, particularly nitrogen and oxygen. For aluminum fabrication, we make use of argon as it boasts a good penetration profile and cleaning action. Also, it is the most common shielding gas. To prevent the formation of magnesium oxide when fabricating aluminum alloys, you can make use of a mixture of shielding gas combining helium and argon.
# Choose the Correct Welding Wire
You need to carefully select a welding wire, and the most commonly used is an aluminum filler wire. This wire has a melting temperature that is quite similar to the base metal. Thanks to our years of experience in this industry, we have realized that the more we narrow-down the melting range of the metal, the easier it gets to weld the aluminum alloy. Also, we use wires with a large diameter as it is much easier to feed.
# Use Convex-shaped Welds
When it comes to aluminum fabrication, the most failures are caused due to cracking of the crater. The crater cracks as a result of aluminum’s high rate of thermal expansion and the contractions that occur when the welds cool down. With concave craters, the risk of cracking is much higher as the surface cracks and also tears as it cools. This is why our welders build craters to form a mound or convex shape. When the weld cools down, the shape of the crater is going to compensate for all the forces of contraction.
# Choose Power-source Wisely
You must at first choose the type of transfer before selecting the power source for GMAW of aluminum. There are two types of transfer, namely, spray-arc and pulse.
The spray-arc takes an extremely small stream of molten material and sprays it to the base material from the electrode wire, across the arc. For this type of transfer, we use constant-voltage (cv) and constant-current (cc) machines. The latter is a better option if you want to weld thick aluminum with welding current exceeding 350 A.
For pulse transfer, we use an inverter power supply. During pulsed GMAW, with each pulse of current, a droplet of filler metal shifts to the workpiece from the electrode. This procedure is useful if you are looking for positive droplet transfer, and faster follow speeds, as well as, less spatter when compared to spray-transfer aluminum fabrication. The fact that the pulse transfer better controls heat input, allows you to weld on the thin-gage material at low currents and wire-feed speeds, besides facilitating anti-gravity or out-of-position welding.
# Get consistent wire-feeding
If you want to feed soft aluminum wire long distances, the push-pull procedure is the most suitable and favored method. In this process, an encompassed wire-feeder cabinet protects the wire from the environment. In order to push and steer the wire into and out of the gun at a continuous speed and force, a constant-torque variable-speed motor is used. The wire is pulled through a high-torque motor in the aluminum fabrication gun and keeps arc length, as well as, the wire-feed speed consistent.
To get consistent and smooth aluminum-wire feeding, you can make use of Teflon liners or plastic. You can use plastic incoming and chisel-type outgoing pipes to support the wire in close proximity to the drive rolls, which stops the wire from getting entangled. While fabricating aluminum, you can keep the gun cable as straight as you can and reduce the wire-feed resistance. This may lead to aluminum shaving, which can be checked by carefully examining the alignment between guide tubes and drive rolls.
You have to make sure that the drive-roll tension is perfect to deliver a homogenous wire-feed rate. For this, use only those drive-rolls that are meant for aluminum. Also, always remember that with too little tension, the feeding can get uneven, while the wire can get deformed and lead to erratic and rough feeding if the tension is very high. Thus, it can be said that both the aforementioned conditions can cause weld porosity and an unsteady arc.
# Check Wire-feeding Problems Through Welding Guns
Aluminum fabrication should be executed through a separate gun liner. We get rid of gaps between the gun’s gas diffuser and the liner, by restraining either end of the liner, and stop wire chaffing. When we encounter wire-feeding issues caused due to abrasive aluminum oxide, we address the problem by frequently altering liners. You can make use of a contact tip, which is about 0.015 inches bigger than the filler metal’s diameter and expands into an oval shape with heat, perchance moderating the feeding. With the welding current crossing 200 A level, you may use a water-cooled gun to reduce heat accumulation and decrease wire-feeding problems.
At Xinxiang Aluminum, we strive to fabricate aluminum during GMAW in such a way that the ultimate product is high in quality. Adhere to our measures and make easy aluminum fabrication possible.

 
 

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