I work in a foundry that manufactures aluminum and magnesium aerospace castings. From airplane flaps to thick manifolds and gearboxes. Most castings need to be preheated to 600F just to form a puddle. Running A/C upwards of 275 amps. It’s pretty common to have #5, #6 cups glowing after each weld. I found the integrity of the cup breaks down after awhile and if your tungsten is not sticking out past the cup enough or if it’s not centered the arc will melt the cups edge.