Tig Versus Mig welding Aluminum

[Harold in CR]

Please excuse my ignorance. I never went to college or trade schools. I am NOT trying to start an argument, or disagree with any pro or certified aluminum welder person.

My story: after being involved with Treasure Hunting, in salt water conditions, I put together my own boat. We use "Propwash" blowers, that corral the thrust of water produced by a boat engine to drive the boat. IF a boat can do 40 MPH, then, you have that much thrust to deflect down to blow away the sand on the ocean floor.

Yeah, this IS getting to a point. We used a giant PVC elbow, installed in an aluminum frame using 6061-T6 channel and angle.

All we had was a 120V 140 Miller MIG welder, and used plain aluminum welding wire, on the spool. NO flux on the wire. We DID use Argon, and, we scuffed up the aluminum to "clean it".

Now, we also did many repairs to aluminum blowers and winch supports on up to 60' boats. That's a LOT of power.

We also built approx 20 of these blowers from scratch, and, never had 1 fail. THEY were built using a TIG welder.

My questions are, Were we extremely lucky to make all this work without failure ? How is it possible to weld without that TIG welder, and do a pretty decent job laying beads and not having failure ?

I am after info re: Tig versus Mig on aluminum. I don't expect to do mods on bicycle frames, BUT, I have a plan on building an Aluminum frame WITH Aluminum headpost, and would greatly appreciate straight talk. Theory is great, but, I learned to weld without theory classes.

PLEASE don't get uppity or feel like I'm talking down to anyone that responds. Just try to help me-US understand what I did wrong and still have very good results.

 

[Ben Wilson]

A decent MIG will weld aluminium fine, but it works better on thick material. Unless you are an extremely talented welder you will have real troubles controlling the power on thin tube like a bike frame.

 

[parajared]

I love my mig welder, and mig most everything that needs welding. When it comes to aluminum though Tig is the way to go. Tig is more precise; you get less blobs, ripples, and splash. It takes longer, and you have to focus harder, but you get better welds with tig.

 

[Harold in CR]

Thanks guys. We also have a Tig welder. I am just trying to see what all the fuss is about for us hobby types that want to build using aluminum. I won't have a TIG down here, just the Mig.

Super light, very thin Aluminum is not what I want to use. That requires more equipment and training.

 

[Drunkskunk]

When I asked a freind once what the diffrence was, he tolde me TIG is a Scalple, MIG is a butcher Knife, Flux Core Wire fed is a rusty bucher knife in the hands of a drunk, and Stick welding is Psychopath with an Axe.
Beer fueled that conversation, but his point was TIG is for fine work or hi-precision welds

 

[Harold in CR]

Quite the analysis, but, have to agree with that last part. We used -used aluminum pipe to build diver access ladders, and jib cranes for lifting artifacts from the ocean, all with the Mig. We welded SS tubing for our production items with the Tig. Brazed a bunch of galvanized stuff, also. Mig was more for portable work, especially on the boats, at the docks.

Never tried flux core for Aluminum, but, my Son is supposed to find a GOOD flux core wire and ship it with the welder. Only real problem we had, was, aluminum or oxide powder build up in the liner and would stop feeding smoothly. THAT was a REAL problem. Had 3 liners we kept cleaning and they all got progressively worse.

 

[liveforphysics]

MIG can burn through filthy surfaces to get the filler wire into the base material. It has very poor control of the depth of your melted area, but it's very very fast and can burn through dirty contaminated surfaces to make a sorta-OK weld that will work fine for most non-structural things.

TIG needs really good surface prep with aluminum, the difference between welding brand new clean materials and old contaminated materials is huge.

If you're making a bicycle from aluminum, personally I wouldn't waste my time. Welded un-heat-treated aluminum is buttery crack-prone garbage. Unless you're going to use all the right alloys (filler rod alloy matters) and processes to make heat-treatable after you've built it, you're way better off using CroMo, and can make a lighter bike that will last a lifetime, and it's easy to weld or braze.

 

[Harold in CR]

Thanks Luke.
My problem, as well as many on the ES is, age. We don't see so pretty good, anymore. It's tough on us old guys to see where we are laying the bead.

I agree, Cro-Mo is probably best, but, I don't think it's readily available here. John doesn't use it.

I have an idea for an all aluminum box frame and headpost. Just needs the BB and swingarm tube MAYBE welded into the box tube. Have to get some and experiment, first. There will be minimal welding required, and, it will only be to stop movement of parts, NOT to be the structural weld, so to speak.

I have some pretty rough rocky sections of road leading away from and to my house. I need to be sure to have enough strength in the frame to not shake apart, crack and fail, and, to haul stuff. It will be my Pick up E-bike.

I started this thread for those that think Tig is the only way to weld aluminum. I realize it's not the BEST, but, it CAN work very well in the right situation.

Thanks for the info. Really appreciate it, Harold

 

[heathyoung]

I do like the analysis of the different welding technologies. Stick welding especially

Liners - best for this is teflon, don't use steel liners - use a nozzle that is larger than the wire size since aluminium wire tends to expand a lot more - and as you said, argon shield, cannot use argon + CO2! Most of the problems I have had using al wire in a mig are due to wire feed, creating pretty bird's nests inside the wirefeed unit (aaarg!) - Good for thick work, non-structural and works much better if you prep the surfaces properly.

 

[liveforphysics]

I only use a spool gun if I've got to MIG aluminum for some reason.

It has about 6in of nearly straight tube to push the wire through that way.

 

[Harold in CR]

Yes Luke. Spool gins are nice. My little putsy Miller don't have that option.

I never do much Aluminum since we bought the antique Hobart stand up welder. My Son, with the good eyes, did all that. Now, he needs glasses.

As I said before, this thread is mostly for the guys that don't know much about welding Aluminum. John said somewhere, he didn't know you could Mig Aluminum.

Thanks for all the input, guys. Maybe this helps someone. 8)

 

[Zen_Shenron]

I used to fabricate large cantilever gates from aluminum using a mig welder.
It worked well but the material was quite thick.
Also as Luke said a spool gun will make mig welding a lot less of a pain in the arse.
The problem being the soft aluminum wire tends to kink up inside the feed line, where as the spool gun moves the spool of wire to close to the welding tip making kinks and bird nest type clogs less likely.
Here is a link just for example of some spool guns for those who are wondering what they are.
http://www.millerwelds.com/products/gunstorches/spool-guns/

 

[marty]

Any body braze steel bicycle frames? Would brazing take less skill then MIG, TIG and stick?

I did some sheet metal auto body repair with MAP gas and brazing rods. Seemed real easy.

 

[John in CR]

Ebikes have motors and they're for riding not carrying, so steel is fine, even regular old steel like is used on the vast majority of the millions and millions of motorcycles sold every year. We can have better triangulation and don't have to design for the same speeds so they don't need to be heavy like a motorcycle frame. A few pounds difference is really nothing for local sales. For export then weight becomes a selling point and less weight ships cheaper too, but it needs to be cromo, not AL. Even the motorcycle makers had real trouble with AL and they have the many millions in R&D.

If 4130 end up impossible here, which I doubt, then 4140 is as good for all practical purposes and is easily sourced and therefore cheaper. It just requires heat treatment afterward...an electric assisted concentrated solar oven sounds like a fun project.

A purpose built bike needs enclosed battery space, so that's an opportunity to save weight by using just enough steel for enough strength and then carbon fiber panels to create the enclosure and add rigidity along with greatly increasing perceived value. I'd like to see a discussion of the practicality of using just enough steel to avoid all potential for catastrophic failure and then use a carbon/aramid blend to give the bike all it's rigidity while keeping weight low for the extra perceived value.

I just don't trust aluminum for our extra weight and speeds, because it gives no warning before failing unlike steel. Thick aluminum won't save weight. How about a stainless steel ebike if you want all metal? You know and have access to wood, so don't forget that for parts of a bike too like the battery enclosure or at least a dash panel for CA, etc. An ebike wouldn't get any more green that with some of that teak you planted yourself, it's it the best wood period for outdoor use? I think very little teak could easily add $100 of perceived value to an ebike.

Sorry, couldn't resist my typical off topic wanderings.

John

 

[parajared]

If you choose to do a steel build, DOM steel is like 20 times easier to work with, and much cheaper than cromo. I built an aircraft out of DOM because the slightly heavier weight didn't overule the more trustworthy welds, higher tensile strength and cheaper cost.

Also Marty,
I find brazing to be pretty tough. The job involves melting metal in just the right place in attempt to get the fill to melt into the joint. Anyone can braze, but getting a braze to come out looking clean and also effective takes a practiced hand. Brazing is awesome because you can braze a piece of aluminum to a piece of steel, but you will never get the strength of an actual weld.

 

[iamsofunny]

I have done a lot of testing with 6061. The post weld heat treatment is 400F for 1 hour. Pretty easy. It greatly affects the weld strength. However, since I use .125 tubing as versus mtb frames which use between .06-.09 and I weigh 140lb I didn't bother to heat treat my frame. I put 3 gussets at the head tube. The most important gusset connects the head tube to the downtube. Most frames break there or in the middle of the top tube or middle of the down tube because the thin tubing bends after a large dropoff landing (which I never do) and once it bends past a certain point it snaps. The thicker wall reduces the bending. Also, gussets and frame design help.

Really though, not many 140lb riders break frames. A 280lb guy will require double the frame wall thickness but everyone rides stock bikes that really aren't strong enough.

Oh yea, and if you are thinking of using Al 1000 3000 4000 or 5000 series, forget it. The frame will just bend.

 

[John in CR]

If you choose to do a steel build, DOM steel is like 20 times easier to work with, and much cheaper than cromo. I built an aircraft out of DOM because the slightly heavier weight didn't overule the more trustworthy welds, higher tensile strength and cheaper cost.

Thanks parajared, being an untrained metal noob I never even heard of DOM steel. If it's good enough for NASCAR, then it's good enough for me, and since it's widely used in industry it should be easy to source and fairly cheap down here. Is there any way to tell the difference just by looking at it. Are there any numbers I should look for or other names, because going into a supplier here without a variety of names and descriptions is always better since it could be called something totally different in Spanish.

Any suggested sizes and wall thickness you could recommend?

John

 

[liveforphysics]

If you choose to do a steel build, DOM steel is like 20 times easier to work with, and much cheaper than cromo. I built an aircraft out of DOM because the slightly heavier weight didn't overule the more trustworthy welds, higher tensile strength and cheaper cost.

DOM just means Drawn Over Mandrel. All the decent cro-mo tubing, including what I made my bike from is DOM, but it has nothing to do with the alloy or strength or any properties at all really, other than the inside and outside will be smooth with a pretty consistent wall thickness. Manacoti pasta tubes are DOM tubing.

A decent alloy for general stuff is 1020 steel if you're not fussy about having it be as strong as possible, you can get it in DOM if you want a nice smooth surface and inside finish. 4130 is really very common tubing, and about 20-50% stronger than most everything else.


Here is a chart with some common cheap steel tubing options compared. All of these weld and cut equally easy.

1010
ERW tube (the ERW means electrically resistive welded tubing seam)
Tensile 45
Yield 32
Rockwell RB55

1020
DOM tube (this means it was drawn over a mandrel after getting resistively welded up)
Tensile 80
Yield 70
Rockwell RB80

4130
DOM tube
Tensile 100
Yield 90
Rockwell RB90