CO2 laser cleavage of chemically strengthened glass

It is necessary to strengthen glass surfaces to protect mobile electric devices from unexpected scratches and breakages, and various strengthening methods are available to this end. However, strengthened glass is difficult to cut and finish owing to the high compressive stress on the glass surface. In this work, chemically strengthened glass was separated using a fracture control technique. The initial crack for the crack propagation was generated through a thermal shock induced by laser beam irradiation, and the thermal stress distribution inside the strengthened glass was simulated via a finite element analysis. In addition, the influence of the laser conditions on the cleavage characteristics was evaluated experimentally, and a groove was fabricated via a short-pulsed laser to improve the quality of the cleaved surface. The thermal stress induced by the laser beam irradiation was affected by the stress distribution inside the strengthened glass, and the depth of the initial crack was required to exceed that of the compressive stress layer to realize the crack propagation through laser beam irradiation. The minimum energy density required for the thermal stress cleavage decreased with the increase in the initial crack depth, and the energy density required for the thermal stress cleavage was large when the compressive stress on the surface was high. The compressive stress layer on the surface helped reduce the lateral crack at the tip of the initial crack, and the tensile stress inside the specimen helped realize high-quality cleavage. In addition, the groove fabricated using the short-pulsed laser acted as the initial point for the crack propagation and helped prevent the thermal damage induced by the laser beam irradiation applied as the heat source.