cjernigan

So i have all my tubing for the new downpipe and exhaust for my '99 miata. The downpipe will be 304SS with mild flanges and the rest of the exhaust will be aluminized with mild flanges. The downpipe will transition from 2.25 to 3" before the flex section and it will be 3" the rest of the way. I'm going to be using a spun metallic carsound CAT and a 5x8x14" magnaflow muffler. I bought the 304SS O2 bungs, 2-3" transition, and the flex at verocious. The tubing and flanges at CRM and the muffler/CAT from performance peddler.




With all the new stuff I figured I better start practicing my TIG welding. I went to the local exhaust shop and asked for some scrap tubing they had and got a good 3.5' piece they were throwing out. I cut up some coupons, beveled the edges to half the thickness of the tubing, and ground the aluminized coating off as good as needed for practice.

My first two tries went OK considering this is my 3rd time TIG welding anything let alone tubing but I ended up burning through in a couple spots. On my last one I didn't contaminate the tungsten or burn through and the weld came out great with good penetration from what I can tell by looking at the weld from the backside. Good enough or exhaust anyway.

-My 3rd weld with ER70 filler rod, 3/32 2% thoriated tungsten on DCSP and the switch turned to 0-125 amps with high frequency on continuous. I ended up with the pedal around 3/4 of the way depressed for good penetration. I have a long ways to go skill wise but I think I can weld up my exhaust pretty easily the way things are now.




I have never welded aluminum but decided to try it tonight. I had two options for tungsten but decided to keep the 3/32 2% thoriated on AC current just because someone told me it worked great and there was no reason to use pure tungsten balled up. So I broke the end off my tungsten and reground it to a point and then put a little flat on the end because I read that was good somewhere.

Here are some of the beads I ran, one of them was without filler but the rest i used a 3/32 filler of unknown material type. I was runnig around 18-20 CFM of pure argon.
The problem I'm having is that the weld is cracking right down the center, almost like a hot tear and I don't really understand it. I could understand if it was cracking at the end of the weld if I was leaving a shrink crater but that's not the case. My weld bead is huge and I'm not sure if I need to use a smaller electrode or if I need to grind a finer point on my tungsten. For AC welding I'm worried to grind it too fine because i'm worried i'll stress the machine too much even though its a liquid cooled torch and all.






So basically I just need some tips on welding tubing, primarily the 304SS I'll be welding for the downpipe. I plan to bevel it the same as the aluminized I welded today.
I also need to know how to keep the aluminum from cracking. I also need to know what the benefits are of using pure tungsten versus 2% thoriated.

93hatchturbo

what welder is that?

Also, add MORE filler rod. You have zero convexity(you want some hump to it). Aluminized tubing tends to be gay due to the alum content in it. Wire wheel, belt sand, flapper disk the ends where you are going to weld. It helps a ton. With the alum content, and not cleaning the metal, the weld tends to fall inside the pipe, To prevent this, less heat, more filler rod. The more filler rod you add, the cooler your weld area is. Once you get the hang of where you need your pedal at vs your heat input vs your filler rod amount.... you'll be good to go.

Smith-02

clean the aluminum with a brass wheel, used only for aluminum. 2.25" is small for a dowpipe.. too small.

cjernigan

It is an old Airco Heliwedler 250 amp with watercooled torch.


It's old as hell but it seems to work well. I don't have any instruction on tig welding but it seems to be nice compared to what I would be using considering it's this or a harbor freight TIG on my kitchen counter.

When prepping the aluminized tubing I beveled the edge of the tubing and then ground ~1/2 from the end of the tubing to remove the aluminized coating so it should have been clean. I'll try less heat and more filler rod.

The one thing I have a good bit of trouble with is keeping coordinated going around the pipe. I tried doing it with the pipe horizontal in front of me and welding coming towards me. Then decided that was retarded and didn't work well at all. So I turned it so that it aims straight out from my body and work from right to left because I'm right handed. I find that its difficult to get much of the pipe done without having to restart though. Makes it a pain in the *** having to stop and turn the pipe every 1.5-2" of welding.

I'm using a 1/16 filler rod, should I try more like a 3/32 or 1/8 (w/e is in the lab) instead?

I cleaned the aluminum well with a stainless brush dedicated for aluminum. I might try the brush and wiping it down with acetone next time as well.

The turbine outlet is just under 2.2" so I figure 2.25" tubing off the turbine housing to a 2.25-3" transition less than 1' later will work fine. The 2.25" tubing will be easy to fit in the close quarters between my turbo and the rear shelf.
The 2nd picture I posted of my tubing, flanges and other ---- shows how it will come off the turbo to the transition. I'll probably be cutting that 2.25" ubend even shorter so it won't be 2.25" for that long.

Thanks for the help guys.

93hatchturbo

Yea for a wire wheel, use a Stainless steel one and mark it, so its stricktly for whatever metal you use it on. Do not change up its use.

One other thing I forgot to mention. I always tack up in 1/4 sections or 90 degrees from eachother. I'll do 1 tack, spin 180, make sure the fit up is good, tack there, then spin 90, check pipe again, tack, then flip 180 and do my last tack.

Then you should be easily able to welder your 1/4 sections, weld 1 1/4 section, then do the weld directly opposite.

t_cel_t

first set your gas flow at about 15cfh
continuous high freq not needed on ferrous metal (steel)
get your tungsten in closer, ease up on the heat (you get better penetration with less heat if you get closer to the metal.

for the ac
tungsten doesn't need to be balled, it will do it itself. no such thing as overworking the machine from a sharp tungsten, it will just turn off if it somehow gets overworked. water cooled torches only cool the torch not the machine.
high freq continuous
way way to much heat, you should have to wait a few seconds for a pool to form and then just use enough heat to keep it molten. keep your torch very close to the metal.
when you get to the end, start easing up on your heat and keep dabbing in the same spot untill the pool is very small but keep dabbing until you are totally off the petal, then you wont have those craters at the end.
the cracks in the beginning are because you are using way to much heat.

cjernigan

Cool, thanks guys I'll take all this advice with me and let you know how things turn out.

mandrel-bends

The aluminized coating can be welded over directly. You don't need to prep the material beyond just basic cleanliness. If you grind back the coatings, your going to have rust develop more readily around your joints.

gon3r

that's what i do!

it looks like you have some contamination on the steel welds you did... make sure you sharpen your tungsten with the point facing upward into the grinding wheel as you spin it to a point, not sideways. that will help a bit with arc control. also make sure you have a wheel dedicated to tungsten only.

the most important pointer i can give you is to get quality materials from hmt sponsors like adam at racing solutions and myself. we don't sell low grade off-shore materials that are hard to weld/work with.

cjernigan

Cool, that is good to know, I will leave the coating alone then and just clean it up with a brush.

We have a dedicated grinder at school for tungsten and I did grind it with the tip facing up into the wheel. The aluminized weld does look dirty but i'm not really sure why. I might have touched my filler to the tungsten accidentally, I'll keep an eye on that though.

I actually did buy all my tubing and flanges from racing solutions though this aluminized i was messing with is from the local muffler shop so who knows where it came from originally.