welding aluminum pipe???

[red2rider]

I work at a plastics manufacturing co and we're getting ready to build a manifold with 2in pipe for drawing resin into the plant from our silos. Each pipe that comes in will have 4 2in lines hooked to it to create the manifold. My question is that I'm new at aluminum welding and am going to try to do this to save the company a bunch of money for having this done from outside labor. We have 2 welders. A Miller Tig, And another, I forget the name, Mig that was set up at one time with an aluminum welding gun. I would like to use the mig as I think it would do this pretty quickly. It's a 250 size mig. From all my work with aluminum doesn't it have to be preheated before migging?? And what's the best way to go about this?? I can tig it, but it will take so long, and might not be the prettiest thing when done. I mig, and tig really good with steel. This aluminum is still pretty new to me. I can tig it somewhat but I thought mig might be a bit easier with better results.

Thanx
RandyB..
auto painter and restoring on the side.
Proud owner of a Black 67 chevelle prostreet 468 roller motor.
6:90's in the 1/8th. and a show car to boot.

[ASKANDY]

Red-
Before deciding whether to MIG or TIG this project, ask yourself:
1 Does this need to hold pressure of any amount?
MIG may be harder to make a water tight weld if you are not proficient at it.
TIG will give you a more precision weld.
2 How thick is the tubing?
It may take a machine of high amperage to do the job. Preheating can help if you are using a machine of smaller amperage.
3 Can you weld it in the shop and take it to location or does it have to be on site?
A weld in a closed environment without the possibility of wind blowing shield gasses away will be much better.
4 Do you know the base metal material?
You will need to know this to pick the best filler for either MIG or TIG.
Remember, If you MIG this, always PUSH the gun not drag. The pushing action will help clean the Aluminum and give you a better weld.

Sounds like a big project. Good luck!

Andy

p.s.
nice car, how 'bout a picture next time.

[red2rider]

Well Andy it'll be for vacuum not pressure. The pipe is very thin like exhaust pipe. I'm doing all the work in our shop so no problem with the wind. I was told that a mig gun would be too hard with such a thin pipe, so I;ve been practicing tigging. We bought a ole joint jigger for peicing the pipe together. I'm starting to get this tigging thing down but my welded seams are so wide, like a 1/2 inch or better. I just can't seem to get it to pull together like you can with steel. I'm preheating both peices and slightly heating my filler rod in the process. As it comes up to temp I dab the rod into it but it creates a big drop. By the time I get the drop to flow out it looks like it's gotten foreign material in it. So what I'm doing now is preheating and and melting the rod in a long bead and then coming back to melt it all in. For some reason it comes out a bit cleaner. Can you help me with the procedure just a bit or give me some pointers. The tig is a Miller 250. I'm using the foot pedal and my amperage setting is at 125 and 100% argon.

I really appreciate the help, I did buy a welders handbook but it gives very little insight on tigging.

Randy Brooks.
I'll post some pics on my site when I can but for now
You'll just have to see the 70SS I just sold.

https://www.angelfire.com/ky2/mycars