JPMuscle

I spoke with three welding shops and they all told me the same thing, Chromoly can be mig welded providing you have the right wire, easy enough. If thats the case why does every thread that ive read and cage company states out right that Chromoly cages must be Tig welded. Is there a specific reason for this the only thing i could come up with is NHRA tech mandates that chromoly be tigged. If there is no structural integrity to be lost with the mig approach and tech mandates it be tigged why?


Thanks,
-john

NRC-Motorsports

, when migging you use more amperage than necessary for this thin a tube,to get a good weld,[as the weld is ussually is bigger than necessary .and chrome moly becomes brittle when overheated,it can also go the other way and be a cold weld easier with the mig,which will not mate the materials together properly]when tigging you are heating the filler rod and edges of tube, bob

JPMuscle

so therefore mig is sufficient for mild tubing because the wall is thicker?



-john

NRC-Motorsports

the wall is thicker and most do not fit the tube[those that do mild steel] ,like they would for chrome moly so it is easier to fill the void with the mig machine, we tig everything ,be it mild steel [which we really dont use much anymore]or chrome moly, just a nicer looking product,a little more time consuming but better finish product, if you google; can i mig weld chrome moly there are lots of examples of the welds /tubing failing [in the aircraft field,which is what most welding standards are taken from]bob
ps, we need an engineer to give the technical reason,lol

JPMuscle

so aside from asthetic purposes a properly prepared and executed MIG weld with chromoly should be comparetively strong and suitable for the majority of Drag racing applications, its just not ideal?


-john

Dan / Wolfe Race Craft

iTrader: (3)

NHRA requires that all 4130 Cromoly be TIG welded.

coop5885

iTrader: (2)

no, thats what they are saying, when you mig weld the moly you can overheat it and make it brittle.

mrdragster1970

All great answers, plus better & more consistant penetration.

I think I remember long time ago hearing NHRA's reason had something to do with SFI's concern for the heat, and more control with Tig welding, a good weld will be stronger than the tube.

JPMuscle

since were on the subject whats the average going rate per stick of 4130 moly and mild steel? 20ft



-john

JPMuscle

ttt


ttt

DOTracer

This may be a very broad generalization, so bear with me.

I think that what may be part of NHRA's mandate for Tig on 4130 is this.

Any Joe Schmoe can pick up a Mig and throw down a bead. That doesn't mean it's a well executed bead with proper penetration and no cold lapping, etc. With Mig it feeds wire weather your technique is correct or not and too easy to get a cold weld with little or no penetration, yet look like a nice bead profile. It has taken me many years of critiquing my own mig welds and really trying hard to watch very closely at what I'm doing while welding with Mig.

Generally with Tig, due to the increased difficulty in performing the process, more often than not you'll see Tig done in shops doing specialty and high quality work. Tig is much easier to see your weld puddle and manipulate it before adding filler material. I think NHRA feels that if you have the skills to wed with Tig, your more than likely gonna get the proper heat and penetration due to the increased skills required to perform the weld process.

I could be wrong, but that's my take on the requirement for the NHRA Tig mandate for chromoly.

Maggie

BINGO!


It's very hard to control the heat effected area when mig weldind chromoly. As you stated it is difficult to see what is going on in the puddle with wire squirting out continually...Can good cm welds be made with a mig? Absolutely.
There may be changes coming about in the near future that will allow for easy & excellent welds on CM with a mig welder. The bi-metal, metal core alloy, and specialty flux-gas wires look to be very promising.

Shoot, I remember when TIGing chromoly was questionable. The GAS welding people certainly made some good arguments against it... Just be glad we don't have to GAS weld our cages!