Questions from someone new to steel TIG

I have been doing a lot of practice with steel recently. Last year I did the TI course at UBI and before that some welding classes at the local tech school. I have been slowly getting a TIG set up put together. I have worked on some other projects with thicker stock before working on thinner tubing.
Steel seems to take the heat differently than TI does. I feel like it will take as much heat as you want to give it and then melt a hole before you can blink whereas while at UBI the TI seemed to be much more predictable. I have welded a practice frame that I then cut up for more practice tubing as I wasn't happy with the results (lots of holes that were filled and dimensions got funky). I feel like I have started to get a good weld sequence and getting better puddle control and am looking to improve my skills as I feel like I am hitting a bit of a plateau. In the pictures my stops are on major axis which I have gathered isn't the best for frame longevity but I have a habit of stopping just short of overlapping so I have been trying to over compensate.
What I am becoming more concerned with is the interior sides of the tubing where the welds are. I seem to be building up some material on the backsides which doesn's seem like the best for finish work or weld quality. With other steel that I have welded this doesn't happen as I have mostly worked on thicker material. At UBI we back purged everything as that is the only way you should weld TI. I ordered a dual flowmeter and other parts to set up a back purge system as I feel like a back purge system would help with this.
The tubing is all whatever True temper Henry James had on clearance a while ago. The sections that I have been welding on are in between the butts so they are pretty thin (at least for me).
My current welding settings/ setup is:
75A peak, 1.2 PPS (I have a maxstar 210 which doesn't let me set the background % etc), 1/16 ceriated tungsten, #8 nozzle with lens. Filler is .045 ER70-S2. Argon flow is ~15-18 CFH with 4s of post flowEverything has been sanded with 80 grit emery paper then 3M pads and 91% isopropyl inside and out. I have also been cleaning the filler with the 3M and Isopropyl.
Any assistance, criticism or wisdom would be greatly appreciated.
Thank you
Matt Hill
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Matt,

A few quick suggestions...

Back purging is an important step for clean, consistent steel fabrication on thin tubes. Though not as critical to the strength of the weld as it is with Titanium, back purging steel prevents impurities on the back side of the weld from forming and being drawn into the join. For purity sake, use it.

Looking at your bead profile, a couple things jump out.

- Work in defined sections; practice moving your torch smoothly over the section without power, focusing on turning your wrist to maintain proper electrode angle. Dry run a few times before lighting up, knowing how far your bead will travel and where your defined start and stop points are.
- Get rid of the pulse. To get a feel for laying a consistent bead with proper penetration, run with straight power and focus on watching the puddle, filling the keyhole consistently with the same amount of filler. Once you develop a foundation of muscle memory for both your torch and filler hands, you can move to pulse to reduce the HAZ.
- Pick up the pace. Much of the burn through and sunken puddle you are experiencing is because you using too much heat and moving slowly. Gotta find a rhythm and really focus on bringing your hands, pace, and heat control together.

Keep at it, you've made a solid start!

cheers,

rody

Rody
Thank you for the help. I have done some more practice this morning. I did this piece with the same machine settings just without the pulse on. I did make two holes on corners of the wings area (if that would be the proper nomenclature) and I filled those for the practice. On the acute areas I definitely see the benefit of moving faster as those sections saw a lot less "junk" on the backside. I have also been adding my filler by using laywire and kind of pushing it into the puddle as I go to get the material in there.

Matt Hill

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Matt,

The issue with using a lay wire technique is that the filler is artificially cooling the puddle and consistently blocking your view of how the base material is reacting to your torch angle, heat input, and travel rate. Get that wire out of there...you need to practice visualizing what's going on and dabbing the keyhole.

Lay wire has it's place in thin wall fabrication, but it comes long after you have a solid understanding and mechanical aptitude for creating proper joins.

Keep at it!

rody