The following limits can be used as safe minimum thicknesses that can be welded by various welding processes:
Gas Metal Arc Welding (also called Metal Inert Gas Welding): 1.5 mm, but can be as low as 0.5 mm with tighter control of welding current.
Gas Tungsten Arc Welding (also called Tungsten Inert Gas Welding): 0.12 mm.
Plasma Arc Welding: 0.075 mm, but can be as low as 0.025 mm.
Electron Beam Welding: foil
Laser Beam Welding: < 0.12 mm