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Material thickness that can be welded with Mig process on aluminum are 14 Ga. and heavier. (How heavy depends on the output capacity of the welder being used.) To MIG weld aluminum thinner than 14 Ga. (.074") either specialized pulsed MIG or AC TIG welding equipment may be necessary.- The removal of lubricants from the aluminum base material may be necessary.
This is best done with solvents. Consult with your local Miller Welding Distributor for their recommendation.
Oxide removal should be done after degreasing. This should be done with a stainless wire brush. This can be done with a hand wire brush or with a cup wire brush. If a power wire brush is used keep the RPM'S and pressures low to reduce smearing the surface of the material, which could entrap oxides and impurities under the surface. Always use a wire brush that is used on aluminum only, to keep from contaminating the base material.
Contact your local welding distributor or aluminum filler metal representative for recommendations on wire alloys that fit your application. Know the alloy of your base aluminum and what conditions the finished part will be subjected to. The 2 most readily available aluminum filler wires are ER4043 and ER5356.
Hook spoolgun to the positive stud on the power supply.
For MIG welding aluminum you need to use a 10 to 15 degree push travel angle (tip and nozzle pointed in the direction of travel). (See Figure 1)
Figure 1: Gun Techniques
Pulling or using a drag angle will produce porous, dirty welds because of lack of gas coverage.
Spray transfer is the desired mode of metal transfer for welding aluminum. The spray transfer is a very smooth transfer of molten metal droplets from the end of the electrode to the molten pool. The droplets crossing the arc are smaller in diameter than the electrode. There is no short-circuiting in spray transfer. With spray transfer the deposition rate and efficiency is relatively high. The arc is very smooth, stable, and stiff and the weld bead has a nice appearance and a good wash into the sides. In the spray transfer a large amount of heat is involved which creates a large weld pool with good penetration that can be difficult to control and can not be used on materials thinner than 14 Ga. This transfer will produce a hissing sound, and no spatter.
The short arc transfer on aluminum produces poor cleaning action, poor tie in at the edges of the weld, and large amounts of spatter and smoke.- Maintain a tip to work distance, and have the contact tip recessed approximately 1/8" inside the nozzle if possible. (See Figure 2)
Figure 2: Gun and Weld area
The reflective heat and weld puddle that is present when MIG welding aluminum is very hot. Holding the tip closer than this could lead to the wire burning back to the contact tip and other feeding problems.
The most common shielding gas for MIG welding aluminum is 100 % argon. Flow rates of 20 to 30 CFH (cubic feet per hour) are acceptable. C25 or argon CO2 mixes are not acceptable.
Avoid large weave beads on aluminum. If larger fillet welds are needed multiple pass straight beads will provide better appearance and have less chance of cold lapping, burn through, and other weld defects.
It will be necessary to increase torch travel speed as the base material becomes heated during the weld.
The skill level of the operator, joint types, fit up, and positions, as well as the welding power supply will all have great influence on the weldability of the aluminum and your success.
Burn-Through (Melt Through) Caused by Over Heating the Base Material
1. Increase travel speed. Make shorter welds.
2. Move around on part, spreading out the heat.
3. Use thicker material or change joint design or welding process to AC TIG.
4. Eliminate/Reduce gaps
1. Use push angle instead of drag technique.
2. Increase voltage to get into spray transfer.
3. Use proper base metal cleaning techniques (Stainless Steel Brush).
4. Check for proper shielding gas and wire alloy type.
Cannot Get Machine Set Correct
1. Check inside cover of welders for good starting setting and fine tune for you needs.
2. Order MIG Calculator Part # 086446 for good starting settings.
Wire burns back to contact tip during or at the end of the weld
1. Maintain a tip to work distance.
2. Check to make sure the contact tip size, drive rolls and gun liner match the wire diameter that you are using.
Wire 'Bird Nests' (piles up) in Front of Inlet Guide on Gun
1. Check and adjust drive roll tension.
2. Check to make sure drive rolls match wire diameter
3. Replace contact tip if fouled up
4. Check pressure adjustment on Aluminum spoolgun hub.
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