Melt depth prediction during the high power diode laser treatment of selected building materials

The development of an accurate analysis procedure for many laser applications, including the surface treatment of building materials, is extremely complicated due to the multitude of process parameters and materials characteristics involved. A one-dimensional analytical model based on Fourier’s law, with quasi-stationary situations in an isotropic and inhomogeneous workpiece with a parabolic meltpool geometry being assumed, was successfully developed. This model, with the inclusion of an empirically determined correction factor, predicted high power diode laser (HPDL) induced melt depths in clay quarry tiles, ceramic tiles and ordinary Portland cement (OPC) that were in close agreement with those obtained experimentally. It was observed, however, that as the incident laser energy density increased (> 15 W mm−1 s−1/2), the calculated and the experimental melt depths began to diverge at an increasing rate. It is believed that this observed increasing discrepancy can be attributed to the fact the model developed neglects sideways conduction which, although it can be reasonably neglected at low energy densities, becomes significant at higher energy densities since one-dimensional heat transfer no longer holds true.