MIG

[shapelessheart]

Can anyne kindly guide me on the voltage current settings and the electrodes used in MIG weding of 25.4 mm OD 1.6mm thickness Mild Steel pipes of the chassis.
The welding man has told it is not possible unless the tubes are fishmouthed and well profiled to meet each other to 99.999 % accuracy.

So we are highly concerned that he might end up doing the whole chassis SMAW weld.

Please help!!!

[shapelessheart]

Can anyne kindly guide me on the voltage current settings and the electrodes used in MIG weding of 25.4 mm OD 1.6mm thickness Mild Steel pipes of the chassis.
The welding man has told it is not possible unless the tubes are fishmouthed and well profiled to meet each other to 99.999 % accuracy.

So we are highly concerned that he might end up doing the whole chassis SMAW weld.

Please help!!!

[Jersey Tom]

Please don't stick weld your chassis. Didn't someone ask this same kinda question not too long ago?

Good fitup is important. 99.999% accuracy means nothing. I'm a TIG guy, and you really should have as good a fitup as possible (.030" or less), but its possible to cover .060" gaps without much difficulty.

As for welding settings.. http://www.millerwelds.com/education/calculators/

[drivetrainUW-Platt]

as far as mig welding goes...
Buy a tig welder.
I compare mig welding to hot glue, just pull the trigger and point.

[SeanM]

I don't know who is doing your welding but you don't need that close a fit for mig. sure it would be best for strength if it was that close but you'd be fine with less then that. TIG needs tighter gaps and would be the best way to do a chassis. but MIG can be done relatively strong (as strong as possible with MIG) with gaps that are acutally really big.

[Landreneau]

if you can afford it, definately invest in a TIG.

in response to your question, that kind of accuracy is not necessary, but you will have to fishmouth it. any gap larger than 1/16th is often hell to weld.

as for the heat settings, you will probably have to experiment a bit. every welder has a different style. the current settings are not only dependent on the thickness of your metal

[Brian Evans]

The thing with Mig is that it's probably the easiest method for a novice to make pretty weld with very poor strength. But it's also the easiest method for a good welder to make really very good welds with excellent strength - just not very pretty. Tig, on the other hand, is harder for a novice to learn how to do but as an effect of it's process is harder to make bad welds with - you kind of either make a good weld, or you don't make a weld at all. And it lends itself to pretty welds, for those who care about pretty...

You can fill gaps with Mig almost infinitely. I have done repairs with Mig (not on chassis, BTW) where I have layered on a half inch of new material - that's a hell of a gap! In some instances of Mig welding an appropriate gap can increase penetration and create a stronger joint. The biggest fault with Mig is too little heat, so the bead sits on top of the material with little to no penetration. So if you are learning, try using as much heat as you can, get the wire speed low, and learn to control the puddle. Practice and test before you weld anything you care about.

Brian

[Crimson Racing]

Last year we used TIG for our frame. I personally can only make decent welds with a TIG. This year we have a new member who can MIG unbelievably well. If you can learn to MIG in a way that provides adequate penetration the time savings between MIG and TIG are very beneficial.

[Bill Kunst]

Okay, a few opinions:

I teach welding, and there is not a problem with the penetration that mig gives. You need to appropriately size your filler wire, the transfer mode, and the deposition rate. If you do all these, and are not getting enough penetration, then you have one heck of a piece of base metal. Try multiple pass welding.

As for the Mig's ability to do controlled penetration welding, as in 1/2" .035 wall to a 1" .095 wall tube, this is much more difficult. This is where the tig welder is going to succeed, and surpass, the mig welder. The only way that you can pull this off with a mig without significant burn through is by pulsing with an .035 wire or going to a much thinner wire. A good welder (human, not machine) can do this very easily with a tig welder with pedal control, offering instant feed back.

I am not saying that mig is bad for building chassis, just that it isn't ideal for building chassis out of the materials that most teams use. If you were doing 1.5 or 2" steel with .125 wall, mig that shit together. Don't waste time with a tig welder. But for delicate frames, tig all the way. Word of caution, heat treating should be necessary under most circumstances as the frame will have alot of stresses in it from all the welding. This is true even with a mild steel frame.

Good luck with your cars, and check out millerwelds.com and the tutorials that they have for the welding processes.
Bill

[skillet]

by heat treating do you mean stress relieving?

[Bill Kunst]

stress relieving/normalizing- either way, the use of heat to produce a "condition" in the metal (be it AL, Steel, stainless, etc.) so that the HAZ virtually doesn't exist, eliminating stresses in the welded product.

If you ever have welded a chassis and laid a weak tack weld, subsequent welding in another location probably has led to the inevitable "PING" as the tack cracks in half (its hardened). If you want this to be the condition of the entire welded vehicle, stressed and hardened in the HAZ or weld itself, then don't heat treat.

There are ways to avoid this during the welding process, one of which is to preheat the base metals. Don't get all willy nilly. The required welding power will be much lower and you will have to adapt your weld settings so as not to "burn" through.

Anyway it goes, using the correct processes to complete the project will make for a much more presentable product, and in most cases, a much more sound product.

[drivetrainUW-Platt]

We found last year that the tacks we made with the mig couldnt be welded over with the tig no matter how hot they got and how long you worked at them, not really sure why.