Aluminium Welding Tips & Basics

Base-metal preparation: To weld aluminium, care must be taken to clean the base material and remove any aluminium oxide. Aluminium oxide on the surface of the material melts at 3,700 F where as the base-material aluminium underneath will melt at 1,200 F. Therefore, leaving any oxide on the surface of the base material will reduce penetration of the filler metal into the work piece.

To remove aluminium oxides, use a stainless-steel wire brush or solvents and etching solutions. When using a stainless-steel brush, brush only in one direction. Take care to not brush too roughly: rough brushing can further embed the oxides in the work piece. Also, use the brush only on aluminium work; do not clean aluminium with a brush that’s been used on stainless or carbon steel. If using chemical etching solutions, make sure to remove the solution from the work before welding.

To minimize the risk of hydrocarbons from oils or cutting solvents entering the weld, remove them with a de-greasing agent. Consult the de-greasing agents instructions to insure it does not contain any hydrocarbons.

Preheating...

A preheated work piece, when ally welding, can help prevent weld cracks. Preheating temperature should not exceed 230 F; use a temperature indicator to prevent overheating. In addition, placing tack welds at the beginning and end of the area to be welded will aid in the preheating effort. Welders should also preheat a thick piece of aluminium when welding it to a thin piece; if cold lapping occurs, try using run-on and run-off tabs. Aluminium is a strong conductor of heat, requiring a huge heat input when starting a weld, since much heat is lost in heating the surrounding base metal. When welding has progressed, much of the heat has expanded and pre-heated the base metal to a temperature requiring less welding current than the original cool plate. A build up of heat can often form towards the end of the weld to such a degree as to create difficult a difficult welding condition unless the current is decreased. This explains why a foot pedal current control is recommended with your AC/DC 160/200 – giving the ability to easily change the current during welding.

The Push Technique...

With aluminium, pushing the torch away from the weld pool rather than pulling it will result in better cleaning action, as well as reduced weld contamination and improve shielding-gas coverage.

Travel speed...

Aluminium welding needs to be performed "hot and fast." Unlike steel, the high thermal conductivity of aluminium dictates use of hotter amperage and voltage settings and higher weld-travel speeds. If travel speed is too slow, the work piece is at risks of excessive burn through, particularly on thin-gauge aluminium sheet.

Convex-shaped welds...

In aluminium welding, crater cracking causes most failures. Cracking results from the high rate of thermal expansion of aluminium and the considerable contractions that occur as welds cool. The risk of cracking is greatest with concave craters, since the surface of the crater contracts and tear’s as it cools. Therefore, welders should build-up craters to form a convex or mound shape. As the weld cools, the convex shape of the crater will compensate for contraction forces.

Shielding Gas...

Argon is the most common shielding gas used when welding aluminium, due to its good cleaning action and penetration profile.

Welding wire...

Select an aluminium filler wire that has a melting temperature similar to 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. The larger the wire diameter, the easier it feeds.

Wire feeder...

The Push-Pull method is a favorite for feeding aluminium wire, which employs an enclosed wire-feed cabinet to protect the wire from the environment. A constant-torque variable-speed motor in the wire-feed cabinet helps guide the wire through the torch at a constant force and speed. A high-torque motor in the welding torch pulls the wire through and keeps wire-feed speed and arc length consistent. In some shops, welders use the same wire feeders to deliver steel and aluminium wire. In this case, the use of plastic or Teflon liners will help ensure smooth, consistent aluminium-wire feeding. For guide tubes, use chisel-type outgoing and plastic incoming tubes to support the wire as close to the drive rolls as possible to avoid tangling the wire. When welding, keep the torch cable as straight as possible to minimize wire-feed resistance. Check for proper alignment between drive rolls and guide tubes to prevent aluminium shaving. Use drive rolls designed for aluminium. Set drive-roll tension to deliver an even wire-feed rate. Excessive tension will deform the wire and cause rough and erratic feeding; too-little tension results in uneven feeding. Both conditions can lead to an unstable arc and weld porosity.

Torch Types...

Aluminium tends to require a nylon/Teflon liner rather then a steel liner to prevent wire chaffing, try to restrain both ends of the liner to eliminate gaps between the liner and the gas diffuser on the torch. Change liners often to minimize the potential for the abrasive aluminium oxide to cause wire-feeding problems. Generally, when a welding current exceeds 200 Amp use a water-cooled torch to minimize heat build-up and reduce wire-feeding difficulties. TIG welding is the process most frequently associated with Aluminium welding. Many other processes can join aluminium, but lighter gauges of aluminium tend to be most applicable to the TIG process as other methods such as ARC welding could easily blow through the metal. The popularity of aluminium in automotive applications has led to the increase of the industrial use of TIG processes.

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