Machining a smooth surface of ceramic material by laser fracture machining technique

A new laser machining technique developed from the concept of fracture machining is proposed to produce a smooth surface of ceramic material. It involves the removal of a series of small chip-elements. A focused laser is scanned along a constant direction to generate micro-cracks on ceramic substrate, forming a fine crack network. A defocused laser is then scanned along the same path again. The laser heat generates tensile stresses that are concentrated at the tip of crack and induces the extension of the micro-cracks. Materials are removed due to the systematical linkage of the micro-cracks. The experimental material was alumina ceramic and the laser source was CO2 laser. The minimum average length of the removed chip-element is about 0.1 mm and the thickness is about 0.02 mm. The surface quality is very good and the arithmetic average surface roughness Ra is about 1.1 μm. The proposed technique can be employed for grinding ceramic surface. The laser power required is less than 50 W, which will not affect material strength. The SEM photographs of the machining surface and the acoustic emission data were obtained to analyze the micro-mechanism of the fracture machining process. Finally, the relationships between laser power, scanning speed, and chip-element size were also investigated.