As the authors welded with a small focus distance in a small area, the shielding gas performed the following new functions: heat removal, optics shielding, and liquid metal shielding. Therefore, the gas usually used in laser welding (He, N2, Ar, or a mixture) was compared, with and without a small percentage of oxygen. The benefit influence of a small percentage of oxygen has been demonstrated for the three aimed points, but also an important and beneficial effect on the weldshape has been show; i.e., with the same welding speed value and the same welding energy value the weld penetration can be increased from 0.5 mm up to 2 mm (only by optimization of the gas composition with a small amount of oxygen).
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