I am wondering if anyone has pointers to welding resources that don't shy away from the underlying physical processes along with any mathematical rigor required. I find it easier to retain/learn information if I'm able to reason about what's going on.

Some examples might be things like

1. I can describe the difference between 6010 and 7018 Flux coatings. But what is going on chemically that leads to different penetration profiles/arc characteristics/amperage requirements for similarly sized rods?

2. I was taught that "2/3 of the heat goes to where the electrons are heading" - so why does DCEP SMAW have deeper penetration than DCEN?

3. What controls the puddle size with tig? How? More specifically, why does AC frequency have the effect on puddle size that it does? I've memorized the relationship, but can't explain why.

4. What is the gas chemistry that lead to choosing one gas over another? Why do I use 75/25 argon/CO2 for short circuit mig, but 100% argon for Tig? Or why you might change argon/co2 ratios when moving to spray transfer?

I'd love to identify sources to learn more about this stuff, but haven't been able to come across it. I've had good luck on the metallurgy side (thanks, JFLF!) , and want to better understand what's going on once I melt stuff together.

hello Timothy,
those are some pretty deep questions.

for 1 and 2, if you drill deep enough at the resources link at Lincoln and dive into the individual PDFs, you should be able to find answers https://www.lincolnelectric.com/en/Welding-and-Cutting-Resource-Center

for the physics of mig gases, https://weldreality.com/MIG_welding_gases.htm provides some interesting points but Ed Craig definitely takes a contrarian stance. still interesting reading.

hope this helps
Jody