A NEW TECHNIQUE TO CHARACTERIZE AND PREDICT LASER CUT STRIATIONS

The quality of a laser-made cut is of the utmost importance in laser p rocessing. Any improvement in this area would be of considerable signi ficance, in that it would lead to an elimination of post-machining ope rations. 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 the refore to critically investigate the dynamic phenomena occurring withi n the cutting front, viz. the formation of striations, and the effect they have on the resulting cutting quality. A new technique for determ ining the frequency of the striations formed and the depth of the peri odic structure has been developed. This is the first real attempt at a ccurately determining this most important quality index, surface rough ness. Auxiliary information such as kerf width can also be ascertained . This leads to a more complete characterization of laser cutting qual ity. Results have shown that both quality indices correlate well with those actually obtained. The conceptual model developed supports the s ideways burning theory for the formation of striations. It is argued t hat more than one mechanism for stria formation could exist and, as cu tting conditions change, a move from one predominant mechanism to anot her could occur. This technique can be used in conjunction with theore tical models undertaken previously, whereby prediction of expected cut quality prior to machine operation will be possible. This has the abi lity of reducing set-up times involving parameter tuning, and leads to an optimized starting solution. The feasibility of detecting striatio n frequency on-line is currently being assessed through different sens ing techniques. This will result in direct real-time surface roughness prediction and monitoring. Results will be published shortly.