Measuring laser absorption coefficient during laser additive manufacturing of 316L stainless steel and Ti-6V-4Al alloys

There have been considerable modeling efforts aimed at studying the thermal response and residual stresses produced during Laser Powder Deposition. However, there has been little published on quantifying the laser energy transfer during the powder deposition. The energy transfer measurement is critical for producing accurate estimate of the thermal response and residual stresses produced. An accurate energy input is required when modeling. This input is dependent on the magnitude of the laser energy absorbed during the LPD process. Spectral absorptivity of metal surfaces is described in the literature but not for the LPD process. It appears that the powder increases the laser absorption coefficient by reducing reflection losses. A simple calorimeter has been built for the purpose of measuring absorbed energy during the LPD process. The laser absorption coefficient has been measured as a function of laser fluence and powder density.There have been considerable modeling efforts aimed at studying the thermal response and residual stresses produced during Laser Powder Deposition. However, there has been little published on quantifying the laser energy transfer during the powder deposition. The energy transfer measurement is critical for producing accurate estimate of the thermal response and residual stresses produced. An accurate energy input is required when modeling. This input is dependent on the magnitude of the laser energy absorbed during the LPD process. Spectral absorptivity of metal surfaces is described in the literature but not for the LPD process. It appears that the powder increases the laser absorption coefficient by reducing reflection losses. A simple calorimeter has been built for the purpose of measuring absorbed energy during the LPD process. The laser absorption coefficient has been measured as a function of laser fluence and powder density.