Experimental and model-based analysis of light propagation and temperature distribution in laser-based directed energy deposition of thermoplastics

• Applicant: Professor Dr.-Ing. Michael Schmidt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Coating and Surface Technology ; Plastics Engineering
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411532653

The energy input and the resulting temperature fields have a decisive influence on the reliable processability in DED-LB/P and the part properties (e.g. surface quality, mechanical properties). The increasing height of the generated structures additionally increases the complexity due to changing boundary conditions (e.g. variation of optical properties, heat accumulation). An improved understanding of laser light propagation in the DED-LB/P process is required to set suitable temporal temperature distributions in the powder jet, in the built-up polymer structures and in the substrate. The objective of this research project is to understand the interactions between the process parameters, the temperature fields and the resulting part properties in the DED-LB/P process using a thulium fiber laser (λ = 1.94 µm). Due to the high beam quality, simple and robust integration into the system technology by means of glass fiber as well as higher achievable layer thickness through volume absorption, this laser beam source represents a promising alternative to CO2 lasers in the laser material processing of polymers. To achieve this goal, the laser light propagation at a wavelength of 1.94 µm in the powder beam and in the built-up polymer structure is to be predicted quantitatively and spatially resolved using a Monte Carlo simulation. The basis for this is the optical characterization using a a double-integrating-sphere, the inverse-adding doubling method to describe the absorption as well as scattering properties and an in-situ powder jet analysis using a high-speed camera setup. The theoretical understanding of the laser-material interaction is to be used to generate a fundamental process knowledge regarding the energy and temperature distribution in DED-LB/P. Depending on the powder material (polyamide 12, polyetheretherketone) and the process parameters, the extent to which the powder particles are heated in flight or are already melted by the direct laser-material interaction is to be estimated. In addition, the temperature fields in the built-up structure and in the substrate are to be predicted. By clarifying the relationships between the process parameters, the temperature profiles and the component properties, the system technology can be designed accordingly, process limits can be quantified and DED-LB/P-specific process strategies can be derived so that components with customized functional properties are achievable. Furthermore, the knowledge acquired on laser-material interaction will provide a foundation for utilizing a thulium fiber laser in other laser-based manufacturing processes, such as laser powder bed fusion of polymers (PBF-LB/P).

• DFG Programme: Research Grants