Modeling the selective laser melting of polylactide composite materials

The rapid manufacturing technology selective laser melting (SLM) is among others employed to build individually designed bone implants out of the bioresorbable composite material polylactide/β-tricalcium phosphate (PDLLA/β-TCP). Degradation of PDLLA, which commences at temperatures >215 °C and results in unwanted changes in resorption kinetics, has to be avoided. This is achieved by keeping the process temperatures as low as possible while still producing dense parts. Processing strategies are investigated using a thermal model of the SLM process solved with finite element analysis. A mesh refinement algorithm is implemented, reducing the computation time by a factor of approximately 5, making the full three-dimensional modeling of the SLM process possible. The thermal and optical properties of PDLLA/β-TCP are measured focusing on the absorption of laser radiation during the process. The model predicts the lowest degradation when a top hat beam profile in combination with a reduced layer thickness and the respective laser power are used. The results of the theoretical investigation are used to fabricate dense parts (density >98%) out of the material PLDLA/β-TCP.