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Shielding gas for MIG welding Aluminum

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BillMullens
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2003-12-22          71938


Folks,
As a reward for getting my professional engineer certification, I bought myself a little Lincoln 135 MIG. I'll be using it to build little toolboxes and such from sheet aluminum. The books claim that I need pure argon as a shielding gas, but at least one local shop told me I can use the CO2/Ar mix. Any experience?
Thanks,
Bill




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Shielding gas for MIG welding Aluminum

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ScooterMagee
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2003-12-22          71941


Your book is correct. For welding aluminum you should use pure argon. The CO2/Ar mix will produce a very poor quality weld (if it works at all). When welding aluminum, any oxygen in the mix will form aluminum-oxide in the weld and cause porosity and cracking. The CO2/Ar mix is used for carbon steel. ....


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yooperpete
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2003-12-22          71943


You definitely want to use pure Argon. Aluminum is one of the more difficult materials to weld and you will need the best shielding gas you can get. At our shop we use TIG for thin aluminum stuff. We particularly like TIG for filling corners and seams. You get less splatter and more uniform flow. We use MIG for thicker or none uniform sections. We also pre-heat thicker sections to improve flow. ....


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BillMullens
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2003-12-22          71944


Thanks, guys. What about using argon on thin mild steel (sheet metal)?
Bill ....


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ScooterMagee
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2003-12-22          71945


You can weld steel with pure argon, however, an Ar-CO2 or Ar-O2 mix is preferred. The oxygen improves bead appearance, wetting and penetration. The percentages in the mix can vary vastly depending on what you are welding and what appearance and penetration you are trying to achieve. There are even triple-mixes with argon, carbon dioxide and oxygen. Helium mixes are also available. ....


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ScooterMagee
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2003-12-22          71949


Welding thin metals (sheet metal) is easier accomplished by TIG welding. The TIG process provides a more precise arc control, and would allow you to fuse the edges of a box without a lot of filler metal. The tradeoff is that you cannot get the penetration that you would with MIG. But, with sheet metal you really don’t need the penetration (or heat), since it tends to distort the box. ....


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gauthier
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2003-12-22          71963


Just make it simple,argon for alu. and co2 for steel,if you are going to weld a lot of really thin steel,then you might want to think of some kind of mix,along with a small dia. wire so as to reduce heat input,but if you are just messing around,keep it simple. Richard ....


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ScooterMagee
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2003-12-23          71993


Actually, pure CO2 shielding works against you on thin metals. CO2 has a much higher thermal conductivity and voltage gradient than an Ar-CO2 mix. What this means is that pure CO2 will produce more heat and deeper penetration, which is not what you want with thin metals. For this reason a mix should be used when welding thin steels. Ar-CO2 mix is just as common as pure CO2, and readily available from any welding supply house. A mix of 75-25 Argon-CO2, or even a 50-50 mix will work best for thin sheet steel, and not adversely affect the welding of thicker steel up to 3/16”. However, pure CO2 would work better for single pass welding of 1/4” and thicker. ....


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AC5ZO
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2003-12-23          71996


I agree with most of the posters about gases. You can get by with pure CO2 for most regular carbon steel. You need pure Ar for Aluminum. You can use pure Ar for steel, but it will make the bead stand up higher than if you had used a mix such as C25 (25% CO2 in Argon).

However, I will add two more cents to this thread. There are several things that are key to MIG welds. Power supply, wire composition, gas mix, clean weld site, and welder skill all play key roles. If you get into anything beyond plain aluminum and carbon steel using short circuit MIG technique, you will find that gas mixes can make a very big difference. I mix my own gases with a four gas mixer that I built. I can dial in the proper amounts of Helium, Argon, C02, and O2 to suit my needs. O2 and CO2 are interchangable for many operations, so sometimes I connect Nitrogen to the fourth port. I never mix over three gases in a single mix.

One last thing is that if you are going to do a lot of aluminum welding, you will want a spool gun or other hand held gun that will pull the aluminum wire through the liner from the roll of wire. You can push aluminum wire through a short torch cable, but bends and long length will make for headaches when the wire stalls and starts bunching up in the feed rollers. Now, before someone gets upset and says that you don't need a spool gun, I will say that you CAN weld aluminum without one, but you have to be careful to keep the welding cable as straight as possible and fully extended from the welder. It will work, but it is not convenient or reliable for regular aluminum welding. If you need to weld aluminum only occasionally, then a spool gun is an expensive addition that you can get by without. ....


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yooperpete
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2003-12-23          72006


We use TIG for aluminum under 1/8" thick. You will always use 100%Argon on TIG for all metals.

When MIG welding, we use 100% Argon for welding Aluminum. We use a CO2 mix(75% CO2/25% Argon)for welding steel. When welding stainless we use a Tri-gas mix (90%helium/7.5%Argon/2.5%CO2). This burns a little hotter for the stainless applications.

These are industrial applications. For your home shop you may attempt combined uses. Your local gas supplier should be able to give good recommendations based on your needs.

I'd practice a little on metals before attempting aluminum. ....


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AC5ZO
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2003-12-23          72009


When TIG and aluminim get mentioned together, it requires another two cent contribution. With TIG, you need to use a constant current power supply and reverse polarity or AC on aluminum. The reverse polarity precleans the aluminum when using TIG, but overheats the TIG torch. AC is preferred, because it cleans on one half cycle and welds on both while keeping the torch cooler. The torch must be directed forward into the metal to be fused to get maximum cleaning benefit. (opposite of normal technique for steel) The power supply for a MIG welder is constant voltage and is generally not used for TIG.

Reverse polarity is the standard setup for MIG. For TIG it is only used on metals like Aluminum, Magnesium and so forth. Straight polarity (electrode negative) is the most common connection for TIG on other metals. Straight polarity can be used on MIG, but it is only common on some flux cored wires. I have never used AC current for MIG. ....


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gauthier
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2003-12-23          72042


I still say keep it simple,if you are in the fabrication business and are working really thin stuff of course you would want a gas mixture,but the man sounded to me like he was just going to play around with it at home and fix stuff,maybe I'm wrong,so use argon on alum.,and straight co2 on steel,he is probably ,[maybe wrong again],not ready for an advanced course in shielding gas,at this time. Richard ....


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BillMullens
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2003-12-23          72051


Thanks to all for the info.

Richard, you're right on about playing around at home. I can weld OK with my Lincoln 220 AC welder, but the MIG is new to me. Still, I enjoy learning about some of the mixed gases. Books will only get you so far.

I'll probably end up using argon for the thin aluminum, and flux core wire for sheet steel. And still use the big arc welder for fixing my back blade, which I seem to break every time I use it:-)

Merry Christmas,
Bill ....


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gauthier
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2003-12-24          72081


Merry Christmas to you to Bill,you need to use pure argon on all alumin.welding,thick or thin,now on steel,just plain co2 will work on most things,but if you are going to be welding stove pipe,then you may want to see what the welding gas place reccomends,above postings desribed some combos,you will also probably need to put drive rollers made for aluminum wire in your machine,a spool gun might be the thing you need,alum. wire is much more softer and easier deformed and thus doesn't feed like steel wire,your welding place should be able to set you up,just be aware of these facts,there is more then just switching gases,to go from steel to alum.,not to mention the differences in the actual welding,it doesn't change colors the same as steel for example,you got to clean the alum. oxide off with stainless wire brush before welding and its hard to see its not like rust on steel and you'll burn a hole through it in a second if your heats to high or your travel speed is not fast enough,need some scrap to practice some on,and the thinner the harder,at least untill you get some spereance. Richard ....


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AC5ZO
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2003-12-24          72088


Richard, I agree with you about keeping it simple, but the soup of information was getting a bit thick. When the subject of TIG is mixed in, it gets even more complicated and I thought that some clarification would help. Welding is not something that someone is going to learn in five minutes or from the CTB.

One added benefit that I might mention about using pure CO2 for steel is that the bottle size can be much smaller than with mixed gases. CO2 comes in liquid form in the bottles, so a 20# bottle will weld a lot of metal for a hobbyist. If you use Argon or any of the mixed gases, a small tank will only last two or three hours of torch time.

Bill, you would get pretty good results from your Lincold AC outfit with a manual (gas valve in the handle) TIG torch on Aluminum. Again, Ar gas is the right gas. In general, your welding supply place can provide the help that you need, but if they told you to use Ar/CO2 mix on aluminum, I would suggest speaking with a different technician.

There are quite a few people here that know this subject, so you can usually get some good advice.

Happy Holidays to all. Mike ....


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gauthier
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2003-12-24          72094


AZC,Sounds good to me,I wasn't asking for any advice though,I was giving it. sorry,Mike,you were talking to Bill about the advise part weren't you. Richard ....


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ScooterMagee
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2003-12-30          72690


Okay, time for a history lesson :) ....


Link:   The History of Welding

 

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