Why cant chromoly steel be MIG welded? I've passed on a few roll bar kits because they reguire TIG welding and I dont have TIG, just a MIG. So, am I doomed to a heavy mild steel cage? Someone clear this up for me. Inform the uninformed.

Mec

 

the small bit of chromoly i weld at work requires tig. i dunno exactly why but it's procedure on my application. do an internet search to see what you come up with.

 

One of the first things you may find is the 2008 NHRA Rulebook, page 77, that specifies that welding of 4130 chromemoly tubing "must be done by approved TIG heliarc process." Mild steel can be welded by MIG wire-feed process. There's no point in shortcutting the process if it might result in having the work rejected in the tech line. If you have no plans to enter a sanctioned race then the only thing you're risking through a less-than-spec welding job is the possibility that it might not withstand a rollover.

 

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Moly is thinner & more picky about heat. They require TIG only to control heat, get more control on penetration. At least that's what we've been told all these years.

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If all you're doing is a 6, 8 or 10 point, the weight difference (between CM or MS) will be insignificant. If you were doing a complete chassis, then you may make a fairly substantial difference.
And, you dont need a CM cage to cert for 8.5.

 

I've mig welded 4130, but it wasn't used in a structural application. I had to crank the heat up super high to get a smooth bead.

 

You can't use a mig because it will overheat the chrome moly, and make it brittle.

 

Mig welds are fairly brittle anyways. The heat on a MIG weld is quite a bit higher on the workpiece than in a TIG situation. The heat effected area will cause it to loose its temper and be of about the tensile strength of mild steel tubing. They say don't do it because of the thinner tubing's heat effected area becoming large enough to have a cage failure in an accident.

 

It can be mig welded, but depending on the application/sanctioning body you may not get certified. It's much easier to control the heat and get clean tie-ins with the tig process, which is why it's far and away the preferred method of joining thin chromoly.

 

http://www.netwelding.com/welding%204130.htm here is all you need to know about 4130 welding.

 

Alright dudes, let me inform some "weldors" giving info on this subject. First of all Chrome Moly and mild steel are not weighed out by the same wall thickness. If you have a .118 wall piece of mild steel, the comparison in Chrome Moly is .058. So comparing the weight between the two is alot more than what was said. Study before telling the world how much you think you know. Next, NHRA
has the rules that they have because of know it all people think they know how to build a race car, just ask them. Chrome Moly is an alloy, so many people just tackle it as though it were Mild steel. Concentricity is the name of the game. With Tig you can make a "key hole" and make sure your weld is super strong. Mig sucks, it's a squirt gun for kids.
Dentonarcracecars.spruz.com

 

That was some mumbo jumbo of a post. What exactly are you trying to say? What exactly in your eyes is incorrect about any of the above posts? I mean you registered just to post that Ok dood.....

 

You can keyhole and make a full pen weld with any process. Not just TIG.

 

Let's see the cars you've built. Let's see the first hundred cars that you built from scratch. Welding and all. Untill then, eata dick. You are just the jack leg I was speaking of. Call me, or pm us. My work speaks for itself, how about urs?

Denton Arc Race Cars
Dentonarcracecars.spruz.com

 

Get the sand out of your *****.

 

You didn't say anything new, you just said it in a far more jumbled and less grammatically correct fashion. And you said it 4 years too late. I could care less if you can spell words right, but coming on and telling everyone how brilliant you are while failing to put together a coherent sentence....nice try. I get what you're trying to say, you just didn't do a very good job of saying it.


Welding CM is always a hot topic. Everyone has "their" way of doing it, and "their" way is ALWAYS the ONLY way. I helped certify a certain CM process back when I worked at Chrysler(the weld lab guy wanted to build a cm frame for an airplane). It was all tigged, but we did it with no pre heat, no post heat, both pre heat and post heat, combinations of the two, different temps, ect. Then we sent them out for destructive testing. I believe there were close to a dozen samples...and every single one passed. There were differences in ductility and strength, but they all met the minimum requirements. This was on specific size, and I'm guessing the results might have been different on a larger diameter piece...but it just gives one example where there's more than one way to skin a cat.

With mig, I wouldn't suggest it. I think it's possible to do it, yes, with the right pre and post heat....but probably not a wise choice for a guy in his garage. And guys that weld for a living would know it's a better bet to tig or gas weld it.

 

I certainly do not need to prove my work quality to someone who joined just to post how incorrect others are (when you said nothing new), on a thread that was on page 160. Can you MIG weld chromoly? Sure. Would I recommend it? No.

All I said was that you can make a full pen weld with any process, not just TIG. I never said I would MIG weld chromoly together. Getting defensive over an accurate statement seems silly to me. And to bring in how many cars I have built from scratch is irrelevant. That has nothing to do with what I said.

And yes, my work also speaks for itself. But I don't need to brag about it. I wouldn't get phone calls for more jobs otherwise.

It seems like you are trolling to get traffic onto a car building site that's not a sponsor here.

Have fun with your trolling.

 

No, just replying to a stupid question. A friend showed it to me. I don't give a rats *** if it's 20 yrs ago Son. I think your Walmart type careers are getting to ya. I got the sand out of my ***** when I unburied your Mom, boy.
**** knuckles, let's see your work big mouth!

 

Thanks for the PM. Hopefully your work holds up better than the mouth you run.

 

It's an arbitrary rule set by a sanctioning body. Judging by 90% of the welders that do this kind of work, I'd rather see it MIG welded then TIG welded, but oh well, it doesn't meet the rules.

MIG is a faster process and most people that can lay down a nice looking mig bead can do it putting less heat into the weld and getting the same penetration as most that can do it with a TIG. _Both_ will cause the 4130 around the weld to harden proportionately to how much heat you put in it, and I would argue that all but the best welders will have better results with a MIG. MIG is approved for tubular structures in airframes, _without_ preheat.

As far as weight or stiffness, 10xx (mild steel) and 4130 both have the same weight and stiffness for the same size/stiffness. Chromemoly is "lighter" because of the rules again, the rules allow you to use smaller, thinner wall tubing than with mild steel. Not sure why, it is _slightly_ stronger in a normalized state (tough there acceptable tested range overlaps, so you could end up with a mild steel structure that is stronger than a 4130), but 4130 hardens around the welds making it more likely to crack durring an impact. This is the reason why most sanctioning bodies outside of dragracing do now allow 4130 in structures around the driver to prevent impaling them with the sharp ends that you get when 4130 tube cracks by a weld