High power diode laser marking and engraving of building materials

A Diomed 60W-cw high power diode laser (HPDL) has been used for the marking and engraving of various building materials, including; marble, granite, clay tiles, ceramic tiles, roof tiles, ordinary Portland cement (OPC) and clay bricks. Morphological and microstructural characteristics have been investigated. The basic mechanisms of marking/engraving and the characteristics of the beam absorption are discussed. The effects of material texture, colour and laser processing parameters are reported. The work shows that engraving depths of over 2mm (0.75mm for a single pass) can be achieved on marble substrates by thermal disintegration of CaCO₃ into loose CaO powder and CO₂ gas. Uniform amorphous glazed lines (1-3mm line width) of a colour different from the untreated materials can be generated on day tiles, ceramic tiles, roof tiles, clay bricks and OPC by solidification phase formation after laser melting of these materials. Effects of atmospheric conditions, for instance using O₂ and Ar gas shrouds, have been examined, with different coloured marks being observed when different shroud gases are used. To demonstrate the practical worth of the process a UMIST crest has been marked on a ceramic tile using the system. Laser beam reflectivity is found to depend not only on material composition but also its colour. Reflectivity has been found to range between 12% to 18% for the various construction materials used in the experiment, except for marble (grey) which showed over 27% reflectivity. Since the HPDL is a portable device, on-site application of these processing techniques can be realised, which would be either impossible or difficult when using other types of lasers.