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Welding Aluminum

Posted: Sat Jan 23, 2010 7:34 pm
by welder
Follow the rules of thumb offered here for selecting welding equipment, preparing base materials, applying proper technique, and visually inspecting weldments to ensure high-quality gas-metal-and gas tungsten-arc welds on aluminum alloys.
Even for those experienced in welding steels, welding aluminum alloys can present quite a challenge. Higher thermal conductivity and low melting point of aluminum alloys can easily lead to burnthrough unless welders follow prescribed procedures. Also, feeding aluminum welding wire during gas-metal-arc-welding (GMAW) presents a challenge because the wire is softer than steel, has a lower column strength, and tends to tangle at the drive roll.

To overcome these challenges, operators need to follow the rules of thumb and equipment-selection guidelines offered here...

Base-metal preparation: To weld aluminum, operators must take care to clean the base material and remove any aluminum oxide and hydrocarbon contamination from oils or cutting solvents. Aluminum oxide on the surface of the material melts at 3,700 F while the base-material aluminum underneath will melt at 1,200 F. Therefore, leaving any oxide on the surface of the base material will inhibit penetration of the filler metal into the workpiece.
To remove aluminum oxides, use a stainless-steel bristle 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 imbed the oxides in the work piece. Also, use the brush only on aluminum work-don't clean aluminum with a brush that's been used on stainless or carbon steel. When using chemical etching solutions, make sure to remove them from the work before welding.
To minimize the risk of hydrocarbons from oils or cutting solvents entering the weld, remove them with a degreaser. Check that the degreaser does not contain any hydrocarbons.

Preheating: Preheating the aluminum workpiece can help avoid weld cracking. 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 aluminum when welding it to a thin piece; if cold lapping occurs, try using run-on and run-off tabs.

The push technique: With aluminum, pushing the gun away from the weld puddle rather than pulling it will result in better cleaning action, reduced weld contamination, and improved shielding-gas coverage.

Travel speed: Aluminum welding needs to be performed "hot and fast." Unlike steel, the high thermal conductivity of aluminum dictates use of hotter amperage and voltage settings and higher weld-travel speeds. If travel speed is too slow, the welder risks excessive burnthrough, particularly on thin-gage aluminum sheet.

Shielding Gas: Argon, due to its good cleaning action and penetration profile, is the most common shielding gas used when welding aluminum. Welding 5XXX-series aluminum alloys, a shielding-gas mixture combining argon with helium - 75 percent helium maximum - will minimize the formation of magnesium oxide.

Welding wire: Select an aluminum 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. Obtain wire that is 3/64- or 1/16- inch diameter. The larger the wire diameter, the easier it feeds. To weld thin-gage material, an 0.035-inch diameter wire combined with a pulsed-welding procedure at a low wire-feed speed - 100 to 300 in./min - works well.

Convex-shaped welds: In aluminum welding, crater cracking causes most failures. Cracking results from the high rate of thermal expansion of aluminum 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 tears 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.

Power-source selection: When selecting a power source for GMAW of aluminum, first consider the method of transfer -spray-arc or pulse.
Constant-current (cc) and constant-voltage (cv) machines can be used for spray-arc welding. Spray-arc takes a tiny stream of molten metal and sprays it across the arc from the electrode wire to the base material. For thick aluminum that requires welding current in excess of 350 A, cc produces optimum results.
Pulse transfer is usually performed with an inverter power supply. Newer power supplies contain built-in pulsing procedures based on and filler-wire type and diameter. During pulsed GMAW, a droplet of filler metal transfers from the electrode to the workpiece during each pulse of current. This process produces positive droplet transfer and results in less spatter and faster follow speeds than does spray-transfer welding. Using the pulsed GMAW process on aluminum also better-controls heat input, easing out-of-position welding and allowing the operator to weld on thin-gage material at low wire-feed speeds and currents.

Wire feeder: The preferred method for feeding soft aluminum wire long distances is the push-pull method, 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 push and guide the wire through the gun at a constant force and speed. A high-torque motor in the welding gun 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 aluminum wire. In this case, the use of plastic or Teflon liners will help ensure smooth, consistent aluminum-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 prevent the wire from tangling. When welding, keep the gun cable as straight as possible to minimize wire-feed resistance. Check for proper alignment between drive rolls and guide tubes to prevent aluminum shaving.
Use drive rolls designed for aluminum. 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.

Welding guns: Use a separate gun liner for welding aluminum. To prevent wire chaffing, try to restrain both ends of the liner to eliminate gaps between the liner and the gas diffuser on the gun.
Change liners often to minimize the potential for the abrasive aluminum oxide to cause wire-feeding problems.
Use a contact tip approximately 0.015 inch larger than the diameter of the filler metal being used - as the tip heats, it will expand into an oval shape and possibly restrict wire feeding. Generally, when a welding current exceeds 200 A use a water-cooled gun to minimize heat buildup and reduce wire-feeding difficulties.

Re: Welding Aluminum

Posted: Sat Jan 23, 2010 7:41 pm
by welder
TIG Welders

TIG welders are designed for the Gas Tungsten Arc Welding process (GTAW), which is commonly referred to as the Tungsten Inert Gas process (TIG welding). The TIG process derives the heat for welding from an electric arc established between a non-consumable tungsten electrode and the part to be welded. Filler metal, if used, is manually feed into the weld puddle when TIG welding.

The TIG welding process requires an air- or water-cooled torch to hold the tungsten electrode and is connected to the TIG welder. The TIG welding process also requires an external shielding gas, typically argon, helium, or a mixture of the two to protect the molten metal and electrode from atmospheric contamination.

High quality welds can be produced with TIG welders. The TIG welding process also has all position welding capability and is excellent on very thin materials. Additionally, a TIG welder makes welds that have outstanding appearance and clean-up is fast and easy since there is no slag and essentially no spatter.

The Function of TIG Welders

TIG welders and the TIG welding process are capable of producing very high quality welds in almost all metals and alloys. However, TIG welding produces the slowest metal deposition rate of all the arc welding processes and thus would not be used where a high deposition rate is required. TIG welders and the TIG welding process are also especially well suited to welding thin materials where the requirements for quality and finish are exacting. To make the most of the advantages offered by TIG welders and TIG welding, a highly experienced and skilled operator is necessary.

Re: Welding Aluminum

Posted: Sat Jan 23, 2010 7:44 pm
by welder
MIG Welders

The Gas Metal Arc Welding process (GMAW), commonly referred to as the Metal Inert Gas process (MIG welding), is an arc welding process which incorporates the automatic feeding of a continuous, consumable wire electrode that is shielded by an externally supplied gas. Process control and function are achieved through three basis elements of equipment: the gun and cable assembly, wire feed unit and MIG welder. The wire feeder and MIG welder may be combined into one unit. Shielding gas for the MIG welding process is typically carbon dioxide, a mix of argon and carbon dioxide or an argon/oxygen mix.

The MIG welding process produces high quality welds, has all position welding capability, and can be used on materials of various types and thicknesses. Additionally, clean-up is fast since there is little to no slag and low spatter.

The Function of MIG Welders

The MIG welding process is North America’s most popular. Operator appeal and weld appearance are excellent with MIG welders and the MIG welding process. Good MIG welding technique will yield excellent results. The properly made finished weld has no slag and virtually no spatter.

The MIG welding process can be used on a wide variety of material types – mild steel, low alloy steel, aluminum, stainless steel – and on a wide range of material thicknesses.

A wide variety of metal transfer modes exist in the MIG welding process including axial spray, globular, short circuiting, pulsed spray and Surface Tension Transfer® (STT®). Some of these modes may require specialized MIG welders and/or specific shielding gas mixtures.

Re: Welding Aluminum

Posted: Sat Jun 07, 2014 6:27 pm
by kmorin
Welder put this set of explanations up a few years past and they're good descriptions of the basics involved in welding aluminum boats.
BUT.. the times are a changing.

the cost of welding, mainly the cost of argon, is about to go up: a lot. Here's my reasoning.

Argon is a tiny fraction of the atmosphere, meaning its around us all the time but not a lot of it one place- gases diffuse sort of evenly regardless of the global climate hoax adherents' reliance on you not understanding basic chemistry and physics: Ozone is not diffused! (??)

Argon plants, that is places that 'make' argon- don't. They collect argon, and because it's less than one (0.93%) percent of all the gas around us, by running air through a 'sieve' sort of device these plant can collect one specific gas and bottle it. What justifies collecting all this 'air' and keeping the various purified parts? Well, for the most part collecting and separating oxygen pays for most of the other gases collected by the same type but different layers of these molecule sieves.

So why does that matter? Steel making uses most (90+%) of the oxygen collected or 'purified' from the atmosphere, and that industry is seriously on the decline due to current socialist take over of society moving us back toward "the mule and dirt floors" while proclaiming its all "for the good of the children" and other silly things easily shown to be fraud and deceit- but requiring at least high school* levels of chemistry and physics knowledge and literacy to comprehend. (*circa 1955-70)

As the 'anti-US'/Frank Marshal Davis Jr. of Chicago crowd moves us backward toward a mule and dirt floors, the steel industry is being shut down along with coal, and that means there is much lowered need for huge oxygen plants and that is where argon is collected as by-product. I think argon is going to go through the roof, and so will the cost to weld our favorite boat building material.

Anyway, my speculation is that argon and other inert gases, now collected and purified as more or less byproducts of larger industrially justified processes, will increase in cost as the planned program of civilization's technological recession is realized by the 'progressives'. (irony intended) ie. progress is back to the mule and cholera as "organic" features of 'Gaia' worship.

Gotta love the 'greenies' and their worship of ignorance!

rant off :soap:

Kevin Morin