In-process determination of laser beam absorption coefficient for laser-assisted turning processes

Modeling of the laser-assisted machining (LAM) process requires an accurate estimate of the surface absorption coefficient. In addition to the laser type and material properties, this parameter is dependent on the state of the process in terms of surface quality, texture, oxidation state, and temperature change during the machining process. In this article, two methods are presented for calculating this coefficient based on the surface temperature obtained from measurement by a pyrometer and an analytical model of the process. In the first method, the pyrometer is fixed on a lathe bed while in the second method, a co-moving pyrometer is used. Temperature measurements in both methods are compared with the results of the analytical model which is developed based on Green’s function approach. Both of the methods are tested for AISI 304 stainless steel samples, and the absorption coefficient is determined for several material and machining conditions. The values determined agree with each other and with values reported in other research works. In addition, the results show that the absorption value is not totally independent of the machining conditions, i.e., for accurate applications, it would be advantageous to determine this coefficient per machining case utilizing the proposed method.