An axi-symmetric transient model was used to calculate melt front movement with temperature and flow fields during deep penetration (keyhole) stationary laser welding. The keyhole was assumed to be a cylindrical hole with the boiling temperature at the boundary. The solution was obtained by finite difference methods with the aid of a coordinate transformation technique to immobilize the liquid-solid interface. The important findings were that the vapor flow in the keyhole and the surface tensions force at the top surface play a major role in giving the upper part of the weld a nail head shape.
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