Aluminum: Guide for Welding Aluminum GMAW

Andrea
Andrea
Aug 26, 2017 · 5 min read
aluminum (אלומיניום)

Follow the general rules that are detailed for the selection of welding equipment, base metal preparation, appropriate technical application and visual inspection of the welds to ensure high quality welding of aluminum alloys. Even for those experienced in welding steels, aluminum alloys may present a challenge. Higher thermal conductivity and low melting point of the aluminum alloys can lead to perforation unless the welders follow the prescribed procedures. In addition, feeding of the aluminum wire during GMAW welding presents a challenge because the wire is softer than steel, has a lower strength, and tends to become entangled in the take-up roller. To overcome these challenges,

Preparation base metal: To weld aluminum (אלומיניום),operators should be careful to clean the base material and remove any aluminum oxide and oil contamination from cutting oils or solvents. The aluminum oxide on the surface of the material is melted at 110 ° C while the aluminum of the base material will melt at 650 °. Thus, if any oxide particles are left on the surface, the base material will inhibit the penetration of the filler metal into the work piece. To remove aluminum oxides, use a stainless steel bristle brush or corrosive solutions. When using the stainless steel brush, brush in one direction only. Be careful not to brush too hard: strong brushing can encrust the oxides in the work piece. Also, use this brush only on the aluminum piece, do not use a brush that has been used in stainless steel or carbon steel. When using corrosive solutions, be sure to remove them from the part before welding. To minimize the risk of hydrocarbons from cutting oils or solvents entering the weld, remove them with a degreaser. Check that the degreaser contains no hydrocarbons.

Preheating: Preheating the aluminum part can help prevent cracking in the weld. The preheat temperature should not exceed 110 °, use a temperature indicator to prevent overheating. In addition, the placement of welding points at the beginning and at the end of the area to be welded will aid in the preheating effort. Welders should also preheat a thick piece of aluminum when welding to a thin piece.

Push technique: With aluminum, push the gun from the welding bath, this technique provides a better cleaning action, the contamination is reduced and the protection gas coverage improves.

Travel speed: Aluminum welding needs to be done “fast and hot.” Unlike steel, the high thermal conductivity of aluminum dictates the use of amperage and voltage settings with more heat and higher travel speeds. If the speed of movement is too slow, the welder rises to excessive perforation especially in thin aluminum sheet.

Protective gas: Argon gas, due to its good cleaning action and penetration profile, is the most common protection gas used in aluminum welding. In 5XXX Series aluminum alloy welding, a mixture of argon protection gas in combination with helium — 75 percent maximum helium — will minimize the formation of magnesium oxide.

Welding wire: Select an aluminum filler wire having a melting temperature similar to that of the base material. The more the operator can narrow down the melting range of the metal, the easier it will be to weld the alloy. Get wire 1.2 or 1.6 mm in diameter. The larger the diameter of the wire, the easier the feed will be. For soldering a fine material, a 0.035-inch wire is well combined with a pulsing procedure at a low feed rate — 250 to 760 cm / min.

Convex welds: In aluminum welding, most failures are cracking in the crater. The results of cracking are the high thermal expansion rate of aluminum and the considerable contractions that occur when welding is cooled. The risk of cracking is greater in concave craters. Therefore, welders must accumulate craters to form a convex shape or mound. As the weld cools, the convex shape of the crater will compensate for the force of the contraction.

Selection Current source: When selecting a current source for aluminum GMAW welding, first consider the arc-spray transfer method or press. Constant voltage (cc) and constant voltage (CV) machines can be used for arc-spray welding. The arc-spray draws a small stream of molten metal and sprays through the arc from the wire to the base material. For thick aluminum requiring current greater than 350A, cc produces optimum results.

Pulse transfer is generally performed with an invertec power supply. Newer power supplies have built-in pulsed procedures based on wire filler type and diameter. During the pulsed GMAW, a drop of the filler metal from the wire is produced to the work piece at each press. This process produces droplet transfer and positive results in fewer projections and faster tracking speeds than transfer-spray solder. Using the aluminum pressed GMAW process also gives better control of the heat input, which facilitates welding in position and allows the operator to weld thin materials at low feed speeds and currents.

Winder: The preferred method for feeding aluminum wire over long distances is the push-pull method, which employs a winder where the wire is protected from the environment. The constant speed of the drive motor in the bobbin helps to push and guide the wire through the gun with a constant force and speed. The gun pulls the wire and maintains the feed rate of the wire and the arc length constant.
In some workshops the operators use the same wire and aluminum wire winders. In this case, the use of plastic liners will help ensure a smooth and consistent feeding of the aluminum wire. For guide tubes, use chisel type on incoming and outgoing plastic tubes to support the wire as close as possible to the trailing rollers to prevent tangles. When welding, keep the gun cable as straight as possible to minimize the strength of the wire feed. Check the alignment between the drive rollers and guide tubes to prevent thread wear.

Use the rollers designed for aluminum. Adjust the tension of the drive rollers to provide a feed rate of the wire. Excessive tension will deform the wire and cause rough and erratic feeding; Low voltage will result in an irregular power supply. Both conditions can cause an unstable arc and porosity in the weld.

Welding Guns: Use a separate gun guide for welding aluminum. To avoid wire chafing, try to control both ends of the coating to eliminate the differences between the coating and the gas diffuses in the gun. Change coatings often to minimize the possibility that aluminum oxide may cause feeding problems. Use a nozzle about 0.38mm larger than the diameter of the filler wire being used — as the nozzle heats up, it will expand into an oval shape and possibly restrict the feed. Generally, when a current exceeds 200 A, use a water-cooled gun to minimize heat build-up and reduce wire feeding difficulties.

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