Material qualification for medical 3D printing

• Applicant: Professor Dr.-Ing. Elmar Moritzer
• Subject Area: Plastics Engineering ; Polymeric and Biogenic Materials and Derived Composites
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549355155

The Plastic Freeforming process is an additive manufacturing process which combines a plasticizing unit known from injection molding with a novel deposition mechanism. The machine principle results in significant residence time in the dosing volume which has proved to have a negative influence on the mechanical properties. Additionally, it is expected that decomposition products are induced by the resulting thermal degradation which is critical especially for medical applications such as cranial implants. Until now, it has not been quantified to what extend thermal degradation takes place in the Plastic Freeforming process. Another topic is that the size and distance between the discharged droplets must be defined precisely to achieve reliable and reproducible mechanical properties. This is done during material qualification. As the current procedure for the qualification of materials is based on a subjective assessment of the parameters, a reproducible method for material qualification is currently not given. This project has three main objectives. The first is the combination of the analysis of thermal degradation mechanisms in the Plastic Freeforming process with the calculation of the residence time to predict the probability of decomposition products occurring in the final part by developing a model-based software tool. The second is the development of a reproducible software-based method for material qualification to achieve consistent mechanical properties independent from machine and operator. The third objective is to merge the results of the previous two objectives into a software suite which is capable of being integrated into existing manufacturing execution systems (MES). To reach the objectives, the mechanisms of the thermal degradation in the Plastic Freeforming process are analyzed and modeled by identifying the occurring thermal degradation by measuring the decrease of the molar mass of the material at different temperatures and points in the plasticizing unit. Parallel, the chronological build process is simulated by developing a suitable software tool which considers the part geometry and the process parameters. Hereby, the residence time is derived from the simulations. Accompanying, tests are performed to identify the existence of decomposition products which will be considered in the model. Thus, the software tool can predict the existence of decomposition products in the final part. For the material qualification, among others, the influence of material viscosity on the droplet size is analyzed. Also, the placement of the droplets depending on the part geometry is analyzed and a model is derived to be able to calculate a precise starting point for the experimental validation of the parameters. For the experimental validation a standardized procedure is developed. Finally, the software tools are integrated into MES to enhance traceability of material for the Plastic Freeforming process.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partners: Professor Dr.-Ing. Clemens Holzer; Professorin Ute Schäfer, Ph.D.; Professor Dr. Wolfgang Vorraber