In-situ analysis of microstructure development and powder aging during powder bed fusion of plastics using dielectric relaxation spectroscopy

• Applicant: Professorin Dr.-Ing. Katrin Wudy
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504676034

One of the greatest challenges in the powder bed fusion of plastics using laser-beam (PBF-LB/P) is the analysis of the microstructure development within the process. According to the state-of-the-art and current research, the in-situ analysis of the material behavior is primarily based on thermographic or imaging processes in PBF-LB/P. These methods do not allow any conclusions on microstructure development such as crystallization and aging mechanism of the polymer during the process. This challenge is addressed by the project “In-situ analysis of microstructure development and powder aging during powder bed fusion of plastics using dielectric relaxation spectroscopy”. The objective of the project is to fundamentally understand the melting and crystallization dynamics in PBF-LB/P during processing by using in-situ dielectric relaxation spectroscopy (DRS). DRS has proven to be a powerful tool for investigating phase transition areas, crystallization kinetics, moisture content, and physical and chemical aging mechanisms. This analyzing method is based on an electrical sinusoidal excitation of a polymer sample and provides detailed information on relaxation and translation phenomena. In addition, DRS is a robust and fast measurement method that has already proven its potential for in-situ monitoring in polymer processing. The latest developments in DRS sensors enable the contact-free analysis of polymer samples. This qualifies DRS as a perfect tool for implementation in the PBF-LB/P process in order to gain a deeper understanding of the microstructure formation and powder aging during processing even across several layers. Within the scope of the project, a correlation between process parameters, material-dependent process behavior, and resulting component properties is to be derived on the basis of in-situ DRS measurements. In addition to the melting and crystallization behavior, process-inherent properties of the so-called partcake powder, such as aging effects or the moisture content, will be explored to recommend further powder treatment, such as recycling of the powder, following the process without any additional measurement. In order to generate a generally valid understanding of the process, the investigations are first carried out on the well-understood material PA12, and then the findings are transferred to filled PA12 and TPU. This project represents a unique combination of materials science and additive manufacturing and answers fundamental and unresolved questions of microstructure development in PBF-LB/P.

• DFG Programme: Research Grants