The method of laser cutting using the controlled fracture technique has great potential to be used for the cutting of glass substrates. In this technique, a score wheel is used to generate a groove-crack along the cutting path in a glass surface. The glass substrate is then separated by applying a defocused laser beam throughout the scribed line for driving the groove-crack through the glass thickness. The material separation is similar to a crack extension and the fracture growth is controllable. The fracture mechanism of laser cutting with controlled fracture was studied in this paper. The experimental materials were silica glasses and the laser source was CO2 laser.
It was found that the cutting process could be divided into three stages. Stage I is fracture initiation, when the crack is initiated at the edge of the substrate. Stage II is stable fracture growth, when the crack propagation steadily follows the moving laser spot. Stage III is unstable fracture, when the crack extends close to the edge of the substrate. The signals of acoustic emission during the separation process were obtained to analyze the three different stages of the crack growth. The temperature and stress distributions were analyzed by using the finite element software ANSYS. The SEM photographs of the breaking surface were obtained to analyze the cutting quality. The relationships between laser power, cutting speed, and specimen geometry were discussed from the experimental results, and their phenomena were also explained from the results of stress analysis. It is obvious that the stress state and the extending speed of crack are strongly affected by the specimen size.