Laser milling of cavity in ceramic substrate by fracture-machining element technique

A new laser-machining technique based on the concept of fracture-machining element is proposed to shape a closed cavity for advanced ceramic. The material removal of the three-dimensional milling can be composed of the removal of a series of elements. The proposed fracture-machining elements are the triangular element and quadrilateral element. A focused laser is used to scribe a series of groove-cracks at the surfaces of the material. The fracture-machining elements are enclosed with the scribed lines. After the completion of the laser scribing, a defocused laser beam is applied throughout the scribed lines. The defocused laser heat generates the tensile stresses that are concentrated at the tip of groove-crack and induces the extension of the groove-cracks. The material removal is due to the linkage of the groove-cracks. The technique of the conventional laser milling requires high laser power which results in many cracks during the grooving process. The proposed technique can be employed not only for the edge milling, but also for the central cavity milling, and the laser power required is much less than that in the conventional method. The experimental material is alumina ceramic, and the laser sources are CO2 laser and Nd:YAG laser. The SEM photographs of the removed elements are obtained to analyze the micro-mechanism of the fracture process. The temperature and stress distributions are analyzed by using the finite element software ANSYS. The relationship between laser power and element size is obtained from the experimental analysis, and the phenomena are also explained from the results of stress analysis.