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Thread: Welding aluminum: how different is it from steel?

  1. #1
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    Default Welding aluminum: how different is it from steel?

    I ask, because I did use a spool gun in class once, and it was so wildly different from steel that I got essentially no knowledge from using it.

    What I came away from it were the following (which are clearly not true, since I have seen aluminum welds that look just like steel):

    Aluminum does not develop a puddle

    If you loiter at all, trying to get a puddle, you will just blow away all the filler and part of the base.

    When I used the spool gun in class..... in one try there was zero weld material placed.... literally ZERO..... the joint was just a burned-looking area with nothing at all deposited, apparently it was all burned away. That time I had tried to develop a puddle etc, as if it was steel.... THAT did not work, had a brighter-than-the-sun arc, but what happened to the material, I have no idea.

    Trying again, I just pulled the trigger and zipped along the joint.....saw nothing, just literally whipped the arc down a 4" joint in about a second. That time I got a rather decent looking weld, but to this day I have no idea how, or why, it worked better than the first. I would LIKE to know, but.......

    Yes there was shielding gas.... the instructor had just a bit before done a very nice weld with no burning etc.
    1601

    Keep eye on ball.
    Hashim Khan

  2. #2
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    I've never used a spoolgun so my knowledge about your specific experiences is limited at best. I have a TIG machine. The difference in TIG welding alum (esp. Sheet, which is almost all I weld) vs steel is pretty big. I assume some or most of this translates to MIG/spoolgun:
    1. The aluminum must be extremely clean. You have to scour it with a stainless brush before welding - a dedicated brush that doesn't get used on anything but aluminum. Then clean it with acetone.
    2. Aluminum sinks heat way faster than steel. You have to move at a pace that feels too fast, to prevent turning the work into a big puddle. Or else make a series of tacks, followed by another series of tacks, and another.
    3. The plastic state between solid and liquid is almost nonexistent. It goes from solid to a dripping hole real fast. If your metal is very thin, the amp settings (and many mire parameters, with TIG) are absolutely crucial.

    I would start with the manufacturer's suggestions for wire diameter, shielding gas, amp & speed settings, traverse rate, etc. on some scrap and play with one parameter at a time until you see an improvement. Dial in your settings and then move on.

  3. #3
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    I have hundreds of hours with aluminum mig a lot of which with spool guns.

    I recommend you start with pieces at least 1/4" thick, or more. Start with just running beads. That will show you how to see and control the puddle. Then do butt joints which will show you penetration control.

    Pick a voltage then play with the feed to get a stable arc. If that's not the right 'heat' then change the voltage and play with the feed again.

    You don't need big gas flow, set it for about what you get out of TIG aluminum and adjust up if you have drafty conditions.

    The material should be clean and have most of the thick 'factory' oxides removed. Grind, brush, sand, what ever. If using grit then make sure you remove any grit.

    Practice, practice, practice!

    And make sure the contact tip is clean! You can use anti-spatter spray, the only down-side is the smoke but for most application the spray doesn't affect the weld.

    Don't expect spool gun to make TIG pretty welds. You can make good looking welds but not like TIG.

    Oh, use 4043 wire and pure argon.

    Pete
    1973 SB 10K .
    BenchMaster mill.

  4. #4
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    In my experience, the puddle is difficult to see because it forms UNDER the oxide layer. The oxide layer has a higher melting temperature than the underlying aluminum alloy that you are trying melt. That's part of the reason that you go from a solid appearance to a hole so fast. AC TIG "cleans" up the oxide which allows access to the puddle just under the surface.

    If you are not using a spool gun you should use a clean liner for your whip so that the aluminum does not pick up metal shavings from the last time that you use steel filler. I found by accident that you CAN fuse aluminum to steel. The resulting alloy in my case was a very weak and brittle joint.



    Dan
    There is a profound difference between spare parts and extra parts.

  5. #5
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    Quote Originally Posted by danlb View Post
    In my experience, the puddle is difficult to see because it forms UNDER the oxide layer. The oxide layer has a higher melting temperature than the underlying aluminum alloy that you are trying melt. That's part of the reason that you go from a solid appearance to a hole so fast. AC TIG "cleans" up the oxide which allows access to the puddle just under the surface.

    If you are not using a spool gun you should use a clean liner for your whip so that the aluminum does not pick up metal shavings from the last time that you use steel filler. I found by accident that you CAN fuse aluminum to steel. The resulting alloy in my case was a very weak and brittle joint.



    Dan
    Dan has stated the BIG DIFFERENCE!

    There is a puddle, you just can't see it.

    Try welding Coke cans.... ;-)

  6. #6
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    I have a spoolgun for my MM175 and the biggest difference in technique for me was aluminum wants a lot more stick out, like 3/4” from memory. I didn’t have much issue once I got used to that. The sound is much quieter and less slag. Dedicate flap wheels and stainless wire brushes to aluminum only for cleaning.

  7. #7
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    It occurs to me that aluminum melts considerably lower than steel, as well as with a different appearance, so the arc is that much hotter than it has to be. Probably is important to the way it gets handled. Gonna have to think more like "lead burning" than steel welding.

    I look at VPTs nice stack-o-nickels aluminum tig welds and figure THAT will take a bunch of practice......
    1601

    Keep eye on ball.
    Hashim Khan

  8. #8
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    Aluminum mig is done spray arc unlike steel which is short arc. Spray arc is smooth, sounds like spray painting. You are using spray arc when: sounds like spray painting, sharp point on wire not a ball, no white spatter on the ground, very little smoke, smooth ripples not sharp. If you don’t have all of this turn the voltage up and increase wire feed until the arc transitions into spray mode. Start with thick aluminum until you get technique as the weld speed is very fast on thin material.

  9. #9

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    I used to have to use a spool gun at my last job. It uses straight argon as the shielding gas and the flash seems much hotter than what I was used to welding steel. I spent a ton of time getting the wire un-stuck from the tip. It was always getting jammed. I never got that pretty "stack-of-dimes" I was normally so proud of with the spool gun. It was uniform, but wide separation in the ripples. I figured if I wanted pretty, I would TIG it.
    TIG requires A/C power and lots of shielding gas. The gas is to keep oxygen away long enough for the material that's hot to get below it's flash-point so it doesn't burn. Once oxygen gets to it, it burns. Aluminum likes to burn.
    I have a Miller 210 Dynasty with a ton of functions and half of them are just to be able to weld aluminum and more exotic materials properly. I'm still learning how to TIG. I've been welding for over 20 years off and on but I still have a lot of learning to go. There are cocky dudes at my job that have been welding a few months and think they are the kings. I guess we all have to go through that phase until reality puts us in our place.

  10. #10
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    Quote Originally Posted by JCByrd24 View Post
    I have a spoolgun for my MM175 and the biggest difference in technique for me was aluminum wants a lot more stick out, like 3/4Ē from memory. I didnít have much issue once I got used to that. The sound is much quieter and less slag. Dedicate flap wheels and stainless wire brushes to aluminum only for cleaning.
    First time I tried my spool gun I had horrible results. Went through about 4 tips in just the first couple minutes, the wire stuck in the tip and plugged it. THEN.... I fell back and regrouped... did some reading.... I was running the spoolgun in the same manner as doing steel..... the biggest difference is the stickout !!!! About a inch stickout is close to what you want and of course with steel its about 1/3 that amount. Once I went to the proper stickout, things improved radically.

    As for cleaning the metal... I have friends with a fab shop that constantly mig aluminum. They do not clean new extruded material at all, just weld it and it comes out fantastic. Textbook says cleaning is a lot more important than it is in the real world. Now IF the material is all corroded and nasty then yes you must clean it up but if its shiny new it should mig weld nicely as-is.

    As stated, pure argon is the correct gas for aluminum mig. IF you try it with the blend used for steel you will have zero success.

    With all the problems you describe, my bet is the stickout was your major problem and possibly the wrong gas also. Its not much more difficult than mig welding steel from what I seen. You DO move along faster too.

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