Welding roll cages; aluminum welding

[pmlpml]

Happy holidays. Sorry for the long post.

I am going to purchase a hobart welder soon, I am trying to decide what to purchase. I have been trained in MIG and TIG welding, but I have used MIG welders much more than I have used TIG welders. MIG welding seems to be much easier to use. Commonly, I will be welding undercar frame and exhaust components for (automobiles), which often requires upside down welding. Also, I will be installing an NHRA legal roll bar in a race car...I'm not sure if MIG welding is an acceptable practice for this (the roll bar will be attached to the frame). Does anyone know if roll bars can be MIG welded and still be strong enough to be safe and pass safety standards? I've heard the welds are inspected using some kind of non-destructive testing method (maybe eddy-current?).

Another concern is welding for body work. I used to use an old snap-on MIG welder to weld body panels, it seemed like it did not manage the power well on low heat settings. But it was good when working with thicker metals. Are the more powerful welders typically not suitable for doing thin metal welding? Or maybe the welder I was using was of inferior quality or not setup/functioning properly?

The last thing I would like to be able to do is weld aluminum, both thick and thin. Is a MIG welder capable of welding aluminum nicely?

The Hobart MIG welders are attractive because of ease of use. Thats only my opinion. Please feel free to give me your opinion.

Thanks for your help.

[Bill (NJ)]

I am a NHRA racer myself and if you are using crome moly tubing it must be tig welded, mild steel can be mig welded. Be sure to weld all the way around the bar, even in the hard to get areas like around the roof. If it a full frame car the roll bar must be attached to the frame, for unibody cars you need flat steel plates. A great place to purchase roll bars that fit freat is from S&W race cars http://www.swracecars.com/
How fast of a car will you be running, makes a difference on how many point roll bar is rquired to have.

Good luck,
Bill

[dysfunction]

I don't know what NHRA rules state for their cage material requirements, but most cages I do are DOM and all are mig welded. I've found that it's somewhat easier to use halo designs in interior roll cages. Make sure to gusset your corners and triangulate your designs. IIRC you can weld 4130 with any process, but you have to heat treat it afterwards or you've just weakened it. I've never done it hopefully someone else can address it with practical experience. As far as welding sheet metal with a bigger welder I have no problems with my mm200, although I use it in either spot or pulse modes.

[BugEyedValiant]

NHRA calls for 1 5/8 .118 wall mild steel for a roll cage and 1 3/4 .118 wall mild steel for a rollbar. I am very familiar with NHRA rules so if you need let me know. The thicknesses for 4130 vary a lot depending on where the bar goes. Also there are a few places on the mild steel where you can go with smaller diameter tubing but the thickness is always .118.

[pmlpml]

Thanks for your responses, everyone.

Looking briefly over the NHRA/SFI rules, I'm thinking that the car will be certified to go 9.90, but no faster. The car will run 10.40's, but surely lower ET's will be in the crosshairs later.

Can someone explain the situation with the 4130 steel and heat treating? This is new to me.

Thanks for your responses!

[Mike Sherman]

pml, 4130 can be welded with ER70S-6 with GTAW, GMAW even SMAW (low hydrogen). On tube it has been proven to be effective without pre or post heat, although thicker applications may very well require it. The mild steel weld metal will have better ductility than the HAZ. This combination has been used by the LINCOLN ELECTRIC WELD TEAM on their NASCAR applications (they use GTAW). The last time I looked into this was about 5 years ago, I have been welding it this way ever since and have not heard any new information on better techniques. If anyone has new information please post your source so I can update my files.

[BugEyedValiant]

As of now, Lincoln reccomends to use the ER70S-6 as a third choice. They now say to use ER80SD-2 as a first choice, ER70S-2 as a second and the ER70S-6 as the third. The ER80SD-2 has the ductility needed and has a higher strength to closely match the 4130 tubing. It is also known as Linde 83 if you are having a hard time locating this filler.

[Mike Sherman]

Thank you. Concerning the aluminum part of your question I was in a hurry this morning so I didn't catch it the first time I read it. Aluminum can be welded very well with GMAW. Thin stuff is usually done with GTAW but does not have to be. Thicker sections are almost always done with GMAW. With practice and the proper wire and gas for each different application, mig will do almost everything (I said almost!) thick or thin that the average hobbiest needs to do. Adding a GTAW machine later on will complete your home shop. Good luck.