Characterization of the melt flow direction and cut front geometry in oxygen cutting with a solid state laser

Laser oxygen cutting is one of the most established laser based manufacturing processes and mainly used for cutting thick metal sheets of mild steel up to a thickness of 25 mm. Besides local absorption of the laser beam, the exothermal FeO oxidation reaction of iron and oxygen provides additional heat input to the cutting process. A lack of energy input can lead to dross formation and decreased cut quality. A detailed, phenomenological description of the melt flow direction and cut front geometry can help understanding dross formation and improving the stability of the cutting process at the cutting limit. Until now, the correlation of the melt flow direction and cut front geometry in case of dross formation is not completely understood. Therefore, high speed videos and metallographic cross and longitudinal sections have been prepared and correlated to dross formation. In order to describe the transition from a quality cut with optimized energy input to a fail cut with dross formation caused by a lack of energy input, three characteristics have been identified: The melt flow direction, characterized by the angle of melt expulsion, the local cut front angle in the lower part of the cut front and the width of the cut kerf at the bottom side of the sheet.