https://weldingweb.com/vbb/showthread.php?709519-MIG-welding-aluminum-tubing&highlight=spool+gun

 

All-in-All the TIG will be a "nicer" weld but, MIG is used structurally all the time I think. I mean, look at big trucks, they're Migged all the time...

Cost is the biggest factor, not only in the equipment (although good Mig rigs, especially those made with Aluminum welding in mind, cost as much as their Tig counterpart) but, without the Tig consumables and "post flow" gas consumption on short welds, cost much less to run too.

 

Structural vs non structural, I won't argue.

I think (I say I think because somebody will say I'm wrong) That structural welds are usually best in thicker stock (1/8" and thicker) with spool gun. TIG is best for thinner stock.

I'm absolutely NOT an expert in spool gun use. I've owned one for my Millermatic 252 several years, haven't plugged it in. I'm very happy with TIG & the advantage of spool gun is speed. I've never built anything where speed was the most critical factor.

That said, Miller has a recent offering of a MIG welder "optimized" for thin aluminum. You will NOT like the price.

 

Burb,
the question could be restated:"will MIG welds, instead of TIG welds, in aluminum; hold my project to the limits of my designed extrusions for my camper extension?"

If you choose inadequate scantlings of aluminum structure for your project they won't hold the load regardless if they are MIG or TIG welded. So, choosing 1/16" thick by 3/4" angles to hold a 200lb load wont support the load regardless of how you weld the frame elements.

However, if you use 2x2x1/4" 6061 aluminum angles to hold the same load? You could MIG or TIG and carry the wt.

If you select adequate scantlings (cross section dimensions) of extrusions, plate or sheet; that will (if welded correctly) hold the loads implied by a vehicle carrying some cantilever (?) load in your design:

The answer is Yes. MIG will fuse the adequately sectioned modulus parts well enough to hold the load, even in the dynamic of vehicle traffic movement.

To test your ability to design and weld (any) this structure; use the 'bend/break' technique on your practice welds and you'll confirm if the joints (MIG OR TIG) are adequate for the loads.

cheers,
Kevin Morin
Kenai, AK

 

Aluminum welds TIG or MIG do not have the strength in terms of tensile, or bend that tempered aluminum stock will have. Heat treating after welding is beyond the capability of most of us. Design for welds placed where the lesser strength is not a problem. Imagine a bicycle. Joints are placed where strength is less critical & reinforced with combining more than two members. Same is true of roll cages.

 

Thanks for the input guys. Sorry I don't have any drawings yet, but had a little down time last week and starting to plan this project. The camper I have in the truck sits even with the back bumper (no rear overhang) and it also sits up on a pair of 2x8's in the bed to provide bed rail clearance. I was thinking of adding a frame under the camper of 1.5" x 1.5" square tube (essentially replace the 2x8's) and having it cantilever out the back about 18" or so. The truck bed is 4' wide, so probably 3 pieces extending out with some cross pieces, etc. Also wanting to add a rack below for generator storage.

I was originally thinking steel, but it would add a lot of weight...not worried about weight in the truck, but weight on the camper jacks when lifting the camper to remove it from the truck. AL also has the plus of corrosion resistance.

I couldn't afford a Millermatic 211 after I took my welding classes, and at current prices that situation hasn't changed LOL. I did see this Hobart 210MVP with spool gun at Northern for $1030 with free shipping and thought this might be a good first project to learn how to MiG AL and also an excuse to buy a new welder...from what I can see you really need 220v to MiG AL correctly. http://https://www.northerntool.com/shop/tools/product_200722096_200722096

I get that TiG would produce a better looking weld but equipment is very pricey for a hobby guy like me. I looked into brazing with MAPP gas but you can't get the joint strength that you need with brazing, especially with the vibration hanging off the back of a 3500 truck....last thing you want is to get where you're going and see the busted rack where your $1000 Honda generator used to be....

 

Aluminum welding is not a cheap hobby by any stretch of the imagination. Gotta pay to play.

 

Gotta tell ya I was shocked beyond belief as a vintage car client wanted to prove out a Harbor Freight Titanium mig welder with a spool gun for alum last Friday. Said it just was too finicky and was burning holes in his alum body panels. With rolling eyes I says bring it in and I will see if I can find any defects. Well the door chart was off by 10% and when I tuned from 14.5 volts it I could spoolgun 18gauge alum sheet at 13 volts with 4043 .035 wire.

Worked pretty darn good. I recommended 5356 wire and I guess it is doing the job. Only other thing I noticed is is was really not able to get into spray and was kind of short arcing probably because of the inductance control. Who knows but I was surprisingly impressed at what I could weld, and the client was stoked.

 

I have that same welder - Handler 210MVP with the spool gun. I didn't have high hopes, but I have been pleasantly surprised by how well it has worked. I would go that route for what you are looking to build.