title: Thermo-Mechanical Modeling and Simulation of Laser-Based Powder Bed Fusion of Thermoplastic Polymers
title: Thermo-Mechanische Modellierung und Simulation von Pulverbett basiertem Laserstrahlschmelzen mit thermoplastischen Polymeren
Creators: name: Soldner, Dominic
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024
Subjects: subject: Process Simulation
subject: Thermo-Mechanics
subject: Additive Manufacturing
subject: Crystallization of Thermoplastics
subject: Domain Decomposition
subject: Multi-Physics
subject: Physical and Mathematical Model Reduction
subject: Multi-Time-Stepping

description: Laser-based powder bed fusion of semi-crystalline thermoplastic polymers (PBF-LB/P) represents one additive manufacturing (AM) technique, where parts are produced in a layer-wise manner, by locally fusing powdered material using thermal energy provided by a laser beam. This allows for a high design freedom of parts and enables functional integration. In contrary to metal AM, the polymer is present as a melt on a longer time span and supported by the surrounding powder. The transition to a solid occurs during temperature-driven crystallization, which is accompanied by an increase of mechanical properties by several orders of magnitude and shrinkage. The process is thereby very sensitive with respect to temperature variations, which can lead to poor mechanical part properties, undesired deformations during the process due to inhomogeneous crystallization shrinkage, and residual stresses. Hence, a controlled thermal environment is crucial. Further, producing parts or using different materials is often accompanied by extensive experimental work in order to identify suitable process parameters. The use of numerical tools for the simulation of the manufacturing process can reduce the amount of experimental work and enable a deeper process understanding. To this end, this work presents a numerical tool for the process simulation of powder bed fusion of semi-crystalline thermoplastics by means of a thermo-chemo-mechanical continuum modeling approach at finite deformations on multi-layer scale. This includes the aforementioned increase of mechanical properties during crystallization and volumetric shrinkage. It will be shown, that crystallization can occur rather early in the process which leads to an extended crystallization model that allows to capture re-melting phenomena of partially crystallized material. Further, accounting for the typically used heating systems by means of a controlled temperature boundary condition is proposed, which increases the accuracy of the temperature computations. The multi-scale nature of the process poses additional modeling challenges for the multi-physics process model and various model reduction techniques are frequently employed in the literature to cope with the associated numerical cost. The effect on accuracy and potential savings of different reduction techniques is also investigated herein. In addition, the use of a domain decomposition technique is proposed, which allows to integrate sub-domains of the computational domain independently. Eventually, the influence of part orientation in the build chamber as well as the dependency of the temperature field on the part geometry and the resulting effect on crystallization during the process will be discussed.