New aspects of melt flow phenomena through narrow kerfs

The understanding of melt flow in kerfs is still dominated by a simplified view of melt films travelling down the kerf wall. This is mainly due to the inherent problems of observing the melt flow in the experiment. High temperatures, high speed phenomena, high intensity irradiation by the laser combined with narrow and deep kerfs are factors hindering observation. Hence the assumption that shear is the main driving force in expelling the melt was not challenged fundamentally until now. However, initial computer experiments performed by the authors appear to, albeit not contradicting, but at least augmenting this understanding by adding a second melt expulsion mechanism. This second mechanism is dominated by stagnation pressure and an expansion fan at the melt edge. Circumstantial evidence is provided in the form of micrographs showing a solidification behaviour reminiscent of the melt flow observed in the computer experiment.