Temperature history influence on laser beam absorption at laser material processing

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The knowledge of the ratio of thermal energy coupled into the material during laser-matter-interaction is an important factor for planning of laser based or laser assisted material processing. The main goal of the proposed research project is the coupling of (defocused) laser beam energy at dynamic processing of selected steels being relevant to industrial applications with the particular regard to temperature history and thereby related surface modification. For this purpose laser irradiation experiments are to be carried out regarding varying temperature cycles while transient recording of spectral reflectivity in simultaneity with temperature. Each specimens surface condition is to be characterized prior to and after the processing. Based on reflectivity and surface condition results a phenomenological model on absorption behavior depending on temperature history is to be constructed. The absorption behavior has to be investigated under shielding gas atmosphere as well as in normal air conditions. This way it is possible to take effects of oxidation into account. Additionally, influences of surface treatment (i.e. polishing, milling, no treatment) on the dynamics of energy coupling are to be investigated. The desired results are supposed to be a basis for more accurate absorption functions for numerical simulations, which do depend on initial surface condition and temperature history instead of the standard approach of an absorption coefficient being a process detached value. There is a large area of applications for such an absorption model, for instance thermal forming, distortion compensation in processes and process chains, laser assisted mechanical forming and punching, heat conduction welding, hardening and many more.