Three-dimensional thermal stress analysis on laser scribing of glass

In the laser scribing of glass a thermal stress is introduced into a glass plate by means of CO2 laser irradiation. The glass plate is rapidly cooled down by water jet immediately after the irradiation. For the purpose of theoretical clarification of the factors ruling the scribable condition and the crack depth, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass plate having a thickness of 0.7 mm. Furthermore, the crack depth and the crack profile were observed for various values of the distance between the heating area and the cooling area. On the basis of the scribable conditions obtained from the experiments, a three-dimensional thermal stress analysis was conducted by a finite element method, allowing the following findings to be obtained. The scribable condition can be estimated from the maximum surface tensile stress in the cooling area and the maximum surface temperature. The crack depth in laser scribing depends on the surface tensile stress in the cooling area and the compressive stress field immediately under that area.