Energy dissipation in laser-based free form heading: a numerical approach

Cold forming generally allows the fast generation of parts with very low tolerances. In addition, mechanical properties are improved, if work hardening materials are used. Transferring the cold forming process to micro range leads to a decrease in the maximum achievable upset ratio so that the forming process becomes inefficient. Therefore, a laser-based free form heading process has been developed to generate preforms which can be calibrated in a secondary cold forming step. The achievable upset ratios reach values of several hundreds instead of 2.1 which is common for single step mechanical upsetting. In this article, heat losses arising in the material accumulation process using laser-based free form heading are analyzed and discussed. For this purpose, the process is modeled within the framework of continuum mechanics and simulated by a finite element method. By using a numerical approach, a systematic study on heat losses is performed in order to identify the influence of radiation, heat transfer due to convection and thermal conduction during laser irradiation time. The simulation results, which are validated with experimental data, show that the radiation is the most important mechanism reducing the efficiency of the accumulation process.