Practice Weld for new fuel rail

SCrazy

SCCoA Member
I am going to fab up some new stainless steel fuel rails for my 80lb shorty injectors and the welding will definitely be pushing my limited skills and experience to the limit.

I've been practicing a little bit but decided to attempt a more realistic weld last night. I think I cooked it a bit too much. Funny thing is I had actually turned the heat down a little bit from my practice sessions which resulted in me moving quite a bit slower and I think ultimately putting more heat into the piece.

It's been suggested to me to make a heat sink by pushing a piece of copper tubing into the stainless tube. I'm gonna give it a try and see what happens. I also haven't been back purging the tube so it's all buggered up inside.
 

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Id use a silicon bronze rod for that, Brian, the high tensile strenght isnt needed. 70s2 works but the silicon bronze is good stuff. Ive tried the turn the heat down and go slow thing, but the part still gets too hot all together. Everything I do anymore I shoot for hot and fast, really hard to do on that little stuff. Maybe try one leaving the rod in the puddle and a tiny fast weave. This will minimize pin holes. and leaving the rod in the puddle means no contamination. If you pull it out of the argon on a dab, youve oxidized the end. The stack of dimes really is pointless.

What size rod are you using?
 
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I'm using 1/16" filler, the base material is 304 and the rod is 308. I'll try laying the wire and running hot. I'm hoping that running hot with a copper tube heat sink on the backside will help.

I'm going the stainless route because I wanted the smallest possible size rail and the extrude aluminum rail stock was all much bigger than 5/8" stainless tubing.
 
I suggest using smaller rod. I use very small rod, like .043 I think.

Keeping the weld 100% pure is very difficult on stainless due to oxidation from the back side, and if you do get a pinhole it's even harder to remove later for the same reason. I don't know if you'll be able to do it without back purging.

My best suggestion is to make sure that the components fit exactly correct. Clamp them together and take the time to make a perfect fit of the two parts. If you do that and then weld quickly, you won't get any bubbling on the back side. The less starting and stopping you do the better also, although that is hard to do on a small tube.

As Corey said, since strength isn't an issue, focus on a smooth surface. A smooth surface is less likely to have a pinhole in it. Don't worry about penetration, this is going to be a surface job.
 
The big thing with SS Tig welding is to grind the tungsten to a real sharp point. It should stick out further than the tungsten welding alum. What polarity are you running?

Ken
 
Yup....it definitely likes to cool the puddle way down especially last night when I was running a lower amperage. Before when I was hotter it was a little better but still got stuck alot.
 
The big thing with SS Tig welding is to grind the tungsten to a real sharp point. It should stick out further than the tungsten welding alum. What polarity are you running?

Ken

DCEN

I think my stick out might have been about 3/8" or so on a 1/16" gas lens so it was pretty far out. Tungsten was nice and sharp at the start but by then end.....not so much.
 
DCEN

I think my stick out might have been about 3/8" or so on a 1/16" gas lens so it was pretty far out. Tungsten was nice and sharp at the start but by then end.....not so much.

Sounds like too much heat. Maybe you are keeping the tungsten too far from the puddle? Keep it close without dunking it and turn the heat down. The shorter the arc, the cooler it can run. I even use .035 Mig wire for Tig welding when doing intricate work to avoid disrupting what I'm going when adding filler.

If you fit your parts well enough you can often weld with minimal or no filler which make for nicer welds too.
 
What are you using on your gas flow too, usually see some rainbow if its shielded well, unless you really got it that hot. Are you holding the torch over for post flow?
 
I suggest using smaller rod. I use very small rod, like .043 I think.

Keeping the weld 100% pure is very difficult on stainless due to oxidation from the back side, and if you do get a pinhole it's even harder to remove later for the same reason. I don't know if you'll be able to do it without back purging.

My best suggestion is to make sure that the components fit exactly correct. Clamp them together and take the time to make a perfect fit of the two parts. If you do that and then weld quickly, you won't get any bubbling on the back side. The less starting and stopping you do the better also, although that is hard to do on a small tube.

As Corey said, since strength isn't an issue, focus on a smooth surface. A smooth surface is less likely to have a pinhole in it. Don't worry about penetration, this is going to be a surface job.


I think I can set up a little rig to back purge without too much trouble. I have the regulator for my Mig and a spare bottle. Gonna be a ~~~~ plugging the injector cups, I wonder if I could just wad up some aluminum foil and stick it in the end of the cup
 
DCEN

I think my stick out might have been about 3/8" or so on a 1/16" gas lens so it was pretty far out. Tungsten was nice and sharp at the start but by then end.....not so much.


It should stay sharp until you accidently dunk it in the puddle. At that point the tunsten is contaminated and you will have a much harder time welding. You just have to regrind it. Dave is right if the parts are fitted to a fairly close tolerance they will almost fuse together with minimum fill rod.
 
What are you using on your gas flow too, usually see some rainbow if its shielded well, unless you really got it that hot. Are you holding the torch over for post flow?

My flow rate was around 15cfm so I think it was OK and I was keeping the gas on it until it cooled. At the end of that weld the entire little machined injector cup was glowing cherry red.

I think my arc length was pretty short at least until my hand was a little out of position before stopping and moving, the torch angle made for a little longer arc.
 
I think I can set up a little rig to back purge without too much trouble. I have the regulator for my Mig and a spare bottle. Gonna be a ~~~~ plugging the injector cups, I wonder if I could just wad up some aluminum foil and stick it in the end of the cup


Alum foil will likely melt right out. You dont want a dead tight seal if you are back purging, you just need to have the gas flowing inside to displace air

ken
 
My flow rate was around 15cfm so I think it was OK and I was keeping the gas on it until it cooled. At the end of that weld the entire little machined injector cup was glowing cherry red.

I think my arc length was pretty short at least until my hand was a little out of position before stopping and moving, the torch angle made for a little longer arc.

I think you want to be able to maintain the gas coverage until its done glowing. Are you doing the whole joint in one pass? Maybe let it cool to the touch after re positioning, before you light up on it again.
 
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