Engineers map the physics behind defects in laser-cut metal foils

<p>The geometrical process conditions of thin foils in laser cutting result in higher local surface tension forces, increasing the susceptibility to dross attachment. Drop-like dross formation patterns and modes in laser cutting of 100 μm thin stainless steel foils were investigated using high-speed imaging and run length analysis. Laser power and cutting speed significantly influenced dross formation. Three distinct dross patterns were identified: an alternating side pattern, single-sided formation, and irregular formations on both sides. These patterns, observed via bottom-view high-speed imaging, correspond to the three melt flow modes A, S, and I respectively, each associated with different line energy regimes. Mode S tends to occur at low line energy, with about 3 ms duration until drop completion, while Mode A is more likely at high line energy, with about 18 ms completion time. A run length was introduced, where analysis revealed up to 36 consecutive dross deposits within the single-sided formation pattern. The preferred movement of the melt, either to the one or to the other cut edge, is based on details of the complex fluid mechanics, which could partially be explained, aided by high-speed imaging. Occasional drop merging events were observed during single-sided formation when molten dross remained in contact with a newly formed drop before solidification. Dross diameter and kerf width were measured, as key criteria for controlled laser cutting. These findings offer new insights into how process parameters govern dross behavior in thin-sheet laser cutting, aiming to keep one side dross-free.</p>