When the melt is ejected from the cut kerf by an assist gas during laser fusion cutting, a fraction of it may adhere to the lower cut edge and form a burr. Adjusting the process parameters to minimize burr formation is a challenging task that becomes more and more difficult as sheet thickness increases. The burr length has significant relevance when the quality of a cut is evaluated, but the underlying mechanisms that control its formation are still not fully understood. In this paper, new results of an experimental investigation focused on identifying characteristic melt ejection regimes are presented. The experiments were conducted on 6 mm thick stainless steel sheets using a disk laser at a power of up to 10 kW. The melt flow exiting the kerf channel and the temporal formation of burr were analyzed using two high-speed cameras. The dependency of melt ejection regimes from process parameters as well as their influence on burr formation is discussed. Furthermore, the authors demonstrate that melt ejection forming a compact and stable threefold outflow is a characteristic property of a burrfree cut.
Instabilities of the melt flow dynamics at the laser cutting front lead to quality losses, due to the formation of striations at the resulting cut flank. The application of high‐speed video diagnosis has turned out to be very instructive for a well‐founded process analysis. In this way, it was found out for the first time that the melt film dynamics at the cutting front reveal characteristic frequencies that are nearly independent of process parameters. Interestingly, their local appearance correlates with the area of lowest roughness on the resulting cut flanks. This observation suggests the amplification of the characteristic frequencies in order to obtain a reduced roughness over the complete cut depth. Comprehensible rules for optimized laser beam and gas flow parameters can be determined based on the physical understanding of the origin of the characteristic frequencies.
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