A new technique to characterize and predict laser cut striations

Abstract

The quality of a laser-made cut is of the utmost importance in laser processing. Any improvement in this area would be of considerable significance, in that it would lead to an elimination of post-machining operations. Currently the mechanisms governing the laser cutting process are not fully understood, partially due to the fact that laser cutting is a highly complex thermal process. It is the aim of the authors therefore to critically investigate the dynamic phenomena occurring within the cutting front, viz. the formation of striations, and the effect they have on the resulting cutting quality. A new technique for determining the frequency of the striations formed and the depth of the periodic structure has been developed. This is the first real attempt at accurately determining this most important quality index, surface roughness. Auxiliary information such as kerf width can also be ascertained. This leads to a more complete characterization of laser cutting quality. Results have shown that both quality indices correlate well with those actually obtained. The conceptual model developed supports the sideways burning theory for the formation of striations. It is argued that more than one mechanism for stria formation could exist and, as cutting conditions change, a move from one predominant mechanism to another could occur. This technique can be used in conjunction with theoretical models undertaken previously, whereby prediction of expected cut quality prior to machine operation will be possible. This has the ability of reducing set-up times involving parameter tuning, and leads to an optimized starting solution. The feasibility of detecting striation frequency on-line is currently being assessed through different sensing techniques. This will result in direct real-time surface roughness prediction and monitoring. Results will be published shortly.