First time welding aluminum

[Sycan]

I have several aluminum headache racks for a trucking company to modify and install on the trucks, some simple to some major fabrication on each one. I picked up an old Miller tig welder since I have always wanted to try tig anyways and it would work for these projects. Needless to say I am having a difficult time figuring it out, can get it to work ok on steel but aluminum was a utter failure. I'll work with it later when the snow flies and I have lots of time, right now I have about $2,000 worth of work sitting here. Went to the welding store this morning and walked out with a Miller 211, spool gun, and cart. Put it all together and damn, it works. Not claiming these to be great but with a complete lack of scraps to practice on I only ran a handful of beads. Plus before today I never even picked up a spool gun I think its good to start fabbing on some headache racks. Was having some problems at the start of the pass and a couple times at the end as the heat seemed to too hot by the end of the weld. I guess I'm supposed to speed up as the piece gets heat in it. Also this was on 115 volt as I didn't have the right plug for my 230 volt. I'll try that tomarrow and turn it up more.

Also is there a trick to cutting aluminum on the bandsaw, the teeth were filling up with cuttings. Something to spray on the blade maybe?

 

[Superbec]

preheat...

 

[JTH]

I have the same setup as you and found it works better for me with 240V. Preheat is great idea if your working with heavy gage as pictured.

 

[MoonRise]

Preheat on aluminum is not done quite the same as preheat on steel.

With mild steel, you can preheat rather aggressively.

With aluminum, you usually do not want to preheat any hotter than 200-230 F.

Also, aluminum must be clean-clean-clean before welding (more so with TIG, but still important with MIG). No grease or oil or paint or marker or oxides. Or blue rag lint (at least I think that is blue rag lint in your Picture #2 there) either. Clean, bright shiny metal is what you weld on.

http://www.thefabricator.com/article/aluminumwelding/aluminum-workshop-guidelines-for-preheating-t6

http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/guide-aluminum-welding-detail.aspx

Next, those workpiece thicknesses look (from a picture or two) rather thick for welding with 120V input power. The welds look cold (inadequate penetration/fusion).

And you are pushing the weld puddle and not dragging, right? (looks like dragging to me).

If there's slag, then drag.

Meaning, for slag producing welding processes (SMAW or FCAW) you drag the puddle (right handed welder, hold rod in right hand and point to the left and travel to the right as you make the weld).

For GMAW, generally you want to push the puddle. Not drag it.

From the Lincoln article on aluminum GMAW:

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.

And yeah, aluminum is done hot and fast.

The start of a GMAW weld (especially on highly thermally conductive aluminum) is often cold. You may need to use start tabs or do a backstep (start weld, go the 'wrong' way traveling, then reverse travel direction to the 'right' way and do the weld) to get some initial heating into the workpiece(s)

Oh, and wrap the corners!!!!

Meaning, don't do a start/stop right on the corners. There is already enough going on there (from a stress concentration factor standpoint) without adding to things by having a start or stop going on there as well. Start the weld on the 'flat' and 'wrap' around the corner. Same with ending, go around the corner and end on the 'flat'.

Recently updated (June 2016) Lincoln Aluminum GMAW Guide:

http://www.lincolnelectric.com/assets/US/EN/literature/C8100.pdf

As to the bandsaw cutting question, cutting aluminum usually means using a coarser blade (less teeth per inch) than for cutting steel. As well as a higher blade speed. And deeper tooth gullets (to be able to clear out the aluminum swarf).

If you choose to use some lube when cutting, make sure to clean it off of the aluminum before welding.

 

[Sycan]

Awesome info, thank you. I was trying to push, but I guess I drag with steel, cause it took concentration. I went to the depot last night and made up a pigtail for my twist lock plugs I have in the shop so I can turn it up. Also going to switch to .035 wire. All info is appreciated.

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