Temperature history influence on laser beam absorption at laser material processing

在激光-物质相互作用期间耦合到材料中的热能的比率的知识是用于规划基于激光或激光辅助材料处理的重要因素。拟议研究项目的主要目标是在选定钢材的动态加工中耦合（散焦）激光束能量，该钢材与工业应用相关，特别是与温度历史以及相关的表面改性相关。为此目的，进行激光辐照实验，改变温度循环，同时瞬态记录光谱反射率随温度的变化。在处理之前和之后，对每个试样的表面状况进行表征。基于反射率和表面条件的结果，建立了一个依赖于温度历史的吸收行为的唯象模型。必须在保护气体气氛下以及在正常空气条件下研究吸收行为。这样就可以考虑氧化的影响。此外，表面处理（即抛光，铣削，没有处理）的能量耦合的动力学的影响进行了研究。期望的结果应该是更准确的吸收函数的数值模拟，这取决于初始表面条件和温度的历史，而不是吸收系数的标准方法是一个过程分离值的基础。这种吸收模型有很大的应用领域，例如热成形、工艺和工艺链中的变形补偿、激光辅助机械成形和冲压、热传导焊接、硬化等等。

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.