Fracture control of unsupported ceramics during laser machining using a simultaneous prescore

While lasers offer many advantages when machining ceramics, costly premature fractures and related damage is the tradeoff often faced by manufacturers. This tradeoff is especially apparent for higher-speed machining of complex shapes where traditional "nail-bed" supports are not always practical. To help overcome these problems, research efforts have focused on a unique method of simultaneously scoring and cutting to help control fracture. Using a customized beam delivery system, a lower-power beam simultaneously created a shallow groove or prescore directly ahead of the higher-power cutting beam. To ensure that the prescore groove is completed before fracture is likely, beam spacing was set at half of the plate width. Results for 0.59 mm thick alumina plates under exaggerated mixed-mode conditions indicated that prescoring did indeed work with markedly improved fracture surfaces when compared to traditional single-beam cuts. In fact, a complete reduction of the mixed-mode fracture was achieved with net prescore groove as shallow as 14.6 μm. Modeling via a customized finite-element algorithm that includes melting/ablation indicates that the two beams can be used in relatively close proximity of 2-4 beam diameters without any significant overlaps of the independently developing stress fields.