Focusing on the gameplay mechanics of the welding, I think my biggest critique is the cooling part of the weld was very frustrating to learn the timing for. For certain welds, if you ever stayed in the "sweet spot" the weld decay wouldn't be fast enough for how fast the bar moved. I think using the "sweet spot" as an indicator is great, but it should ideally guide the player.
There was also some frustration where the placement of the guide had my eyes off of the welding. i think if you could get the weld to show the status, instead of the bar, that would be a huge boon to readability and playability.
I liked the concept, and its a solid submission. Well done!