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Welding aluminum takes different tools and different skills compared to welding steel. Here are some pointers for using a MIG on aluminum

Welding aluminum with a gas metal arc welder (MIG) has become more popular over the past few years, due in large part to the advancement of welding technology and its increasing prevalence in farm equipment components. Many of the common aluminum alloys found on farm tools and machinery are readily welded with the MIG process. However, because aluminum has certain qualities different from steel, some welding equipment, techniques and parameter settings are different. Following the recommendations below will help ensure that you achieve the desired results.

BEFORE YOU WELD

1. Make sure the power source is set for reverse polarity (DCEP).

2. You’ll want 100 per cent argon shielding gas, which is the gas generally used for MIG welding aluminum. The flow rate will range between 20 to 40 cfh.

3. Buy a roll of 0.030-inch or 0.035-inch diameter filler wire. The 0.035-inch size is preferable because the larger diameter wire will be easier to feed.

For general maintenance, the most commonly used wire types are ER4043 and ER5356. ER4043 is commonly used for non-critical maintenance work. It is adaptable to many aluminum base metals. ER5356 is a stiffer wire than ER4043 and is used when more rigid, higher strength properties are needed. Because it has a higher magnesium content, ER5356 wire has a faster melt-off rate than ER4043. For this reason, you need to feed ER5356 at a faster speed for the same diameter electrode wire.

4. A spool gun is highly recommended for welding aluminum because the softness of the material makes it difficult for the wire to travel the length of a standard gun cable without buckling and causing a “bird-nest” at the drive rolls. Pushing aluminum through a standard MIG gun cable is often compared to trying to push a wet noodle through a straw.

5. When installing the spool of wire, be sure to check both the spool tension and the drive roll tension. The spool tension should be less than that for steel wire. To check spool tension, turn the spool hub by hand. The spool hub should be able to turn freely with little resistance. The correct drive roll tension should provide an even wire feed rate, yet when pressure is applied to the wire at the contact tip (pinching the wire with a gloved hand), the wire will slip in the drive roll area.

Too much drive roll tension will deform the wire causing rough and erratic feeding through the contact tip. This can result in a burnback (the wire melting to the contact tip). Too little drive roll tension results in an uneven wire feed, which can also cause a burnback to occur.

6. When exposed to air, aluminum forms a hard, oxide layer that completely covers the aluminum surface. The melting point of this aluminum oxide is approximately 3,700F (2,040C), compared to the melting point of aluminum, which is approximately 1,200F (650C). Because of this difference in melting points, you need to remove the oxide layer prior to welding in order to obtain an acceptable weld. Brushing the area to be welded with a stainless steel wire brush (used only on aluminum) will help break up the oxide layer. The welding action will finish removing the oxide layer.

WHILE WELDING

1. When MIG welding aluminum, be sure to use a push gun technique, in which the tip of the gun is pointed in the

direction that it will travel, not toward the material just welded. The push gun technique will provide a better cleaning action during welding as well as better gas coverage for the molten aluminum.

UNLIKE STEEL, ALUMINUM WELDING REQUIRES A “PUSH” TECHNIQUE, IN WHICH THE GUN IS POINTED IN THE DIRECTION OF TRAVEL.

Tips For Welding Aluminum

2. When MIG welding aluminum we recommend having a larger gap from the contact tip to the work piece than you would for steel. In most cases a half-inch gap is recommended.

3. To insure good starts, the end of the wire should be clipped off at an angle to remove any balled end that may have formed during welding. This will help prevent stumbling, cold starts.

4. MIG welding of aluminum progresses at a faster travel rate than of steel. Due to the high thermal conductivity of aluminum, the travel speed will increase as the welding progresses. If travel speed is not increased, you could see excessive melt-through on thin aluminum parts.

5. Pause briefly to add an extra amount of filler metal at the end of the weld to make sure that the crater is properly filled. If not properly filled, the crater will be a weak point where cracking can occur. Another method for filling the crater is to alternately switch the arc off and on until the crater is filled.

MAINTENANCE

It is important to check the contact tip periodically for wear or internal arcing. If either of these issues occurs, the wire will not slide freely through the contact tip, leading to erratic wire feed and burnbacks. The contact tip is a replaceable item. Always replace it if the wire does not freely pass through.

Finally, whenever a spool of aluminum wire is taken off the welder, it should be stored in a plastic bag to protect it from dirt and moisture. This will help prevent the liner from becoming clogged when the wire is put back into use.

Following these basic guidelines and practicing these techniques will help to insure that quality welds are obtained when welding aluminum with the gas metal arc welding process.

Jon Ertmer is a product manager with Miller Electric.

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