If I were to use CM4130 tubing to construct a 6 point roll cage into a bug to use for drag racing, can it be mig welded or will it have to be tig welded? Can anybody set me straight?

Thanks Dave

Current ANDRA Rulebook 2010/2011, General Regulations for Roll Bars/Cages (relating to Super Sedan/Superstreet), Section 4.4.7.4, Page 146.

".......a) ...round in section of minimum sizes as specified below, electrical resistance welded to S 1450 - 1974.........
b) ..........Tubing that does not bear CM4130 markings will not be accepted as such. All welding of CM4130 or R531 must be by the TIG process. Electrical resistance or TIG welding is recommended for mild steel tube...........

Current rulebook expires in July 2011. New book then out, costs $25inc, available from ANDRA over the phone (08) 8271 5355.

See you out there!

Mig welding chromoly tube will make the weld joint brittle.

TIG is best, but you must use the correct filler rod - manganese moly. MIG with manganese moly wire is OK, but TIG is better.

I agree with the advice above, but I know of a few of the offroad guy's use MIG regularly on CM tube with NO long term problems (probably a sign of the mammoth engineering).

yeah mig is ok on cm but shielding gas should be turned up a bit and a slow cool down of the affected area with a blow torch is recomended.

After discussing this subject only several weeks ago with a very experienced engineer in welding of chromemoly whilst I was manufacturing Bens new wheelie-bars , I would have to disagree with some of the above comments regarding the use of a mig welder .

It was explained to me that the heat associated with the welding process of a MIG welder happens far too rapidly for the chromemoly . If chromemoly is welded with a MIG , the welded area will become very brittle and the chomemoly will tear right beside the weld .

Chromemoly should be welded with a TIG for this reason .

yeah he is correct but its not just the heat, its the uncontrolled heat and feed wire that is the problem. it can be done but you need an experienced welder/fabricator with knowledge of the material. Like most Standards the spec is created for the lowest common denominator, as we all know there is more than one way to skin a cat!! If you wish there is a great welding book that is easy to read and explains most things in detail its called "The Welders Handbook"

Safe welding practises aside, you can weld the CM with a torch if you want, but if it's not TIG then ANDRA won't accept it as legal.

I have seen offroad buggy chassis welded with mig ,BUT after its finished they stick it in a bloody big oven and stress relieve it (2 days,big bucks). TIG is the only way to weld cro-mo with success, welding it with mig is so f#&*%@ tightarse its beyond belief, and just remember whos rear end is in the drivers seat

Thanks for the replies. I read the rules but understanding them requires experience or a degree in law. I don't have either and did not want to end up with a car that does not comply to the rules.
As I understand the rules, I do not require a six point cage, but better to be safe than sorry. Besides who knows whos arse will be sitting in the drivers seat. It may not be mine!

Next Question? Pros and cons of a bolt in roll bar?

Thanks again.

Bolt-in side bars were brought in by ANDRA due to pressure from sedan racers in Vic and NSW, who can't register their vehicles in those states with welded-in side bars on the cage. They're legal for unmodified chassis vehicles (again, rego constraints) down to flat-10's. As such, they are a design compromise, along the "better than nothing I suppose" lines.

Welded-in bars are structurally much stronger.