Welding ChromeMoly with MIG

**Gavin Newman** · 18th August 2010, 02:57 PM

Can any of the experts shed any light on whether it's practicable to weld CrMoly tubing in a race chassis with the MIG process. We currently use brazing successfully but it's been suggested that MIG could be used instead. Do we need special wire and/or heat treatment?

The application is for a Superkart chassis which needs to flex unlike a race-car chassis which is triangulated to be rigid. As such the joints will have a lot of twisting and bending forces acting on them and shock loads as the kart rides over saw tooth kerbs at 160kph+.

Given that it's going to be my backside in the seat an inch off the track I want to be sure that the welds will hold. I've used MIG for 20+ years and did trade training in the 1980s but have always used the MIG on mild steel only.

**NewLou** · 18th August 2010, 03:24 PM

I wouldnt touch it with a mig.............

Id Tig it

N if my life depended on it i'd get the job done by someone who really knows what their doing!

Check these out:

Miller - Best Practices for TIG Welding of 4130 Chrome-Moly Tubing In General Motorsports and Aerospace Applications

http://ezinearticles.com/?Chrome-Mol...ong&id=1414397

Tig Welding 4130 Tubing

Hope this helps ................

Regards Lou

**Woodwould** · 18th August 2010, 03:45 PM

I used to MIG all my CM front suspension arms and rear semi-trailing arms, but they were fairly meaty .083" wall tube. I would always turn up the amps to get more heat into the welds and ensure they cooled slowly.

Anything made from .065" or under, I would always TIG.

**Gavin Newman** · 19th August 2010, 02:16 PM

Thanks for the responses fellas. Graham Collins, do you have an opinion?

**RicB** · 21st August 2010, 06:04 PM

I have twenty + years experience in Aircraft maintenance and I can assure you chrome molly should only be TIG welded. MIG will do the job but produces a hard weld that will fracture under the constant stresses involved in the type of vehicles usually associatedwith CM.

**catweaselmusic** · 21st August 2010, 06:45 PM

Hi Gavin, Co- moly tubing. 4140. Reynolds 531 etc. can be welded with mig or gas with mild steel filler rod but my favorite is with nickel bronze and an oxy torch. BUT.. the torch must be adjusted to a neutral flame and never over heat the steel. I have sucessfully repaired E type Jaguar tubular front chassis, a job the experts say cannot be done. Be warned though the cooling process is critical with any method. A tip is to prepare a sheet of layers of kitchen foil big enough to fully wrap the joined area. The foil should be lightly screwed up and opened out. Do this three or four times to build up a multi layed pad ready for wrapping the heated area. The screwing up provides air gaps in the pad to assist insulation, this is an alternative to using messy dry lime. The instant the torch or welder is removed from the job the pad is wrapped around the hot area. Make sure that you work in a draught free zone. If electric welding try preheating the area welding then wrapping. Hope this is of some help. Bob Antolik

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