An empirical equation for crack formation in the laser cutting of ceramic plates

Industrial lasers have found many applications in materials processing and manufacturing, one of which is to cut ceramic components that are difficult to cut using conventional means due to their high value of hardness and degree of brittleness. However, often one problem associated with this process is the formation of cracks that can result from the thermal stresses that are induced. This paper is concerned with the problem of cracking of ceramic plates when cut using laser beams. Based on the experimental results reported, it is argued that the most relevant operating parameters are the laser power (P) and the feed-rate of the specimens (upsilon). The material properties of interest in this study are: specific heat (c), conductivity (k) and thermal expansion coefficient (alpha). The only geometrical dimension is the thickness (t). Dimensional analysis was employed to identify four dimensionless groups. On the hypothesis that crack occurs when the tensile strain reaches the material's critical (fracture) strain, the following empirical equation was obtained, which specifies the safe region in terms of the operating power and feed-rate: P greater than or equal to 1.78 x 10(11)t(2.41)v where P is in W, t is in m, and upsilon is in m s(-1). Qualitative explanations are discussed in relation to the functional dependence of the various parameters. The identified dimensionless groups and empirical equations an of direct use to practising engineers. (C) 1999 Elsevier Science S.A. All rights reserved.