Altogether, I've been working on this project for about a year now, so this post will contain a summary of sorts.
After having the idea, I built a first version based on the basic electronics knowledge I knew (I studied Mechanical Engineering, so not too much more than the basics of wiring up robots, no high voltage experience, etc) combined with a basic understanding of how TIG welding works.
Needless to say, it didn't work at all. The flyback transformer I was using for the high voltage arc starter worked, but the high current power supply didn't push any electricity through the arc.
After a while, I found a set of free plans on the internet for a home made tig welder. Using them as a starting point, I came up with a design for a pulsed tig welder powered by a bank of capacitors, and built it. This second version had no capability to sense or control the current flowing through it. However, after a couple months balancing my last semester of classes and iterating on the project, it started to work. It made lots of loud exploding noises, melting little craters in random pieces of steel I pointed the electrode at.
After that version, the next step was to add current control. For consistent melting of metal bits together, consistent welding performance is needed. And for that, precise current control is needed. To do this, the second version was chopped up, and a microcontroller (stm32f4), current sensor, and mosfet array were added. Thanks to the high voltage arc starter interfering with everything, this took a couple of months.
After finally getting current readings and being able to do current control, I assembled my X-Y table and threw together an arduino program to move it around, and wrote some code for a PC to control both the arduino and the stm32f4.
That's where the project is right now: the pulsed tig welder works, and I have a working X-Y table.
-some more work on the control algorithm
-zip tie / tape argon line to electrode (I've got a tank and regulator, not shown in pictures)
-run both systems (xy table, welder) together to print a layer or two