On the numerical modelling of laser shearing of glass sheets used to optimize production methods

Abstract

The problem of the control of the propagating crack tip during laser shearing (or zero width laser cutting of glass) is essentially one of controlling the stress field within the substrate. The glass substrate is stressed thermally using surface absorption of 10.6 μm laser radiation followed by cooling, in this case from a fine atomized waterjet. The stresses created in a large sheet, combined with the residual stresses within the glass substrate, are sufficient to propagate a subsurface flaw to form a controlled crack that gives excellent cut quality. This process has previously been studied experimentally and is successful for large plates and shapes with large radii of curvature. In order for future work to extend the process to minimize damage at the end of a cut, at the close of a profiled cut or close to the edge of the plate, it is necessary to understand the stresses that control the crack propagation and control these as the stress field changes. This work outlines an initial theoretical study of the heating and cooling cycle coupled with finite element analysis of the induced stresses to increase the understanding of laser shearing of glass. It provides a thorough description of how to perform the complex numerical studies, including how to determine the quasi-static crack tip position. The results provide levels of stresses in the immediate vicinity of the crack tip and show that thermal heating/cooling loading conditions are favourable for straight line cutting.