MIG Tack Welding on Tube 101

[Mike Bean]

This is in response to BM1's post about using tack welds with MIG for tube chassis.

Today I went ahead and did some test welds and this is the best I could come up with. I welded .083 channel and .095 tube mild steel with .025 solid wire. All I did was make several quick tacks one after the other.

I am looking for some input from some experienced weldors to see if they feel this type of weld I did is sound and can be used to weld up a roll cage?

My opinion is that there is plenty of heat and penetration and it should hold...

I have attached a photo of my welds from today.

Mike Bean

[hellbentrodder]

hey mike, the weld looks o.k. on the surface but i would not trust it on a roll cage. MIG welds in the short arc process can appear to tie in but really they just sort of float on the surface. check out this article for tips on tube welding.http://www.millerwelds.com/education/articles/articles70.html

[elvergon]

Well, I know you know weldingweb, so that´s the best opinions you´ll get ;) btw, It looks good, but look is not the same as strenght ;)

[Terry Skinner]

[quote=Mike Bean]

I am looking for some input from some experienced welders to see if they feel this type of weld I did is sound and can be used to weld up a roll cage? [\quote]

O.K. Mike, I will throw my two cents in but no grudges. <VBG>
The weld is too thin. It should not be concave. Take a look at:
http://www.weldingengineer.com/Discontinuities_.htm
A lot of information and nomenclature.
The tacks are giving you trouble. (Weak spot.) After everything is tacked into place take a high-speed grinder and grind the tacks down. That way you won't have that cold spot like pictured on the left. Same with the start. Cheap welding machines take a second or two to get the puddle up to temperature, which makes a hump at the start that has some porosity. Grind that out also. To test the weld cut a "coupon" out of a weld and look at the edges. Maybe even clamp it in a vice and bend back and forth until it breaks. If the break is in the weld it is not strong enough. Most of the time when using lightweight tubing like we use the welds are a lot bigger than required, which translates into more than strong enough. The only way to get the weld small enough is to go to a low voltage Tig welder. This is not Boeing so I don't think we need to be all that careful. HTH..........Terry

[Mike Bean]

Thanks for all the replies to my post. I guess I am going to have to fire up the welder and burn a few tanks of CO2 & Argon to learn how to weld tube.

I can MIG straight perfect, but this tube stuff requires constant adjustments and I think it is back to the drawing board.

I can still remember the first day I started to learn how to weld. I thought my welds were good, but now I know they were terrible. Like they say...practice makes perfect.

Mike Bean

[Terry Skinner]

[QUOTE=Mike Bean]
I can MIG straight perfect, but this tube stuff requires constant adjustments and I think it is back to the drawing board.

Maybe I can help you there. Build a rotating table. Easiest way is one half of an old car rear end. Shorten the axle to about a foot. Shorten the housing to about two foot and weld to a truck rim. Knock the lug bolts out of the axle and weld a quarter inch plate whatever diameter you want. Assemble with the truck rim laying on its side, then the axle housing sticking straight up and the plate on top. That’s it!! Be sure to connect the welder ground directly to your work. If the ground is connected to the base the welding current will run thru the bearing and make it one piece. Great for practice and small parts. HTH...........Terry

[Terry Skinner]

[QUOTE=Mike Bean]Thanks for all the replies to my post. I guess I am going to have to fire up the welder and burn a few tanks of CO2 & Argon to learn how to weld tube.QUOTE]


Performance Welding, Stock Number 21-31557, $16.95
Richard Finch’s book on welding entitled, "Performance Welding", is well-done. The book covers various aspects of different types of welding, including MIG, TIG and Oxyacetylene. It has excellent coverage on MIG and TIG welding. The author is well-known and his reputation is excellent.

can be found at: http://www.sportair.com/howto.html

HTH.........Terry

[voodoo_stepchild]

Hey Mike Im a newbie here but a welder,
Terry is absolutely correct on the weld it is too shallow. The biggest problem with a mig with thinwall is penetration. Do as terry suggested and cut a couple of samples out and bend them back and forth until it gives. I use a mig quite often on light gauge and thinwall tubing and it simply takes time. There are a lot of good videos out on the market and you can check with miller welding forums as well for info. But I will tell you how I do it just for giggles but it may not be the best way for you.


First of all I dont like my pieces that I am welding to be moving I prefer them to be stationary and I prefer to move around them instead of them revolving around me. Set your piece up where you desire and tack them in place . My particular mig I use the amperage is controlled through my wire feed instead of having a seperate amp setting like the voltage does. On thinwall material I run .045 wire at 20 volts or so and I turn my wire feed down. THIS WORKS FOR ME!!!!!!!! but it may not suit your welding style. I then grind out my tacks with a 1/8" rock and get out all the wagon wheels, perfs etc etc and start my welding. I weld 180 degrees one way and then go back to my original starting point and weld in the opposite direction. I grind out my start and stop point so I make sure and tie the weld in on both sides. Now the trick is with thinwall is in your case you have two different thickness's of metal being joined. Keep your heat (puddle) obviously on the thicker side and allow the two to begin to melt and flow. My guns I use are pretty big (600 amp) however I like to keep them at about 45 degrees side to side and about 15 degrees forward and
*******PUSH******* the gun not drag it. You have to be in front of the gun to see it so it takes a while to get used to it. Some welder like to drag the gun and step the weld in which doesnt give a good penetration because it allows the puddle to cool slightly before more filler material is added. Your weld in particular is sometimes a trick with a 90 degree vertical piece being attached to a flat base. Tack it in one spot, tack it on the opposite side 180 degrees, tack it 90 degrees from tack two and then again 180 degrees from the third tack. Grind out your tack and push the weld in. Now the weld will try and stack a little more because of you pushing the gun so you will have to try and compensate for that by allowing the weld to "sluff" down on the base metal. Practice this and it will help you tremendously.

I hope this helps a little bit and as I stated earlier there are a lot of good video on the market that can actually show you the process on the screen under the hood. Once you can see that the filler material is flowing to both sides of the pieces then you got it. Try it a few times on some scrap like you were doing and you will see it happening. Sorry my reply is so long just trying to help you out


Voodoo