A research team at Oak Ridge National Laboratory (ORNL) has developed a vacuum-assisted extrusion method that significantly reduces porosity in large-format additively manufactured polymer components. Especially when processing fiber-reinforced thermoplastics, it was possible to reduce the proportion of air inclusions by up to 75 percent. The process addresses a key challenge in large-format additive manufacturing (LFAM), in which components with dimensions in the meter range are manufactured for applications in the aerospace, automotive and toolmaking industries.
LFAM generally uses glass or carbon fiber-reinforced polymers to ensure the structural integrity of large components at a comparatively low weight. However, the rapid material deposition during extrusion often leads to the entrapment of gases between the individual strands, resulting in so-called intra-bead porosities. These impair the mechanical properties and dimensional accuracy of the manufactured components.
The new ORNL process addresses the material feed. By integrating a vacuum-assisted material hopper, the filament is degassed before extrusion, which significantly reduces the formation of cavities in the extrudate. The tests showed that a porosity of less than two percent can be achieved even with varying fiber contents.
“Using this innovative technique, we are not only addressing the critical issue of porosity in large-scale polymer prints but also paving the way for stronger composites,” said ORNL’s Vipin Kumar. “This is a significant leap forward for the LFAM industry.”
For industrial use, work is currently underway on a continuous process that converts vacuum-assisted degassing into high-throughput systems. The corresponding concept has already been registered for a patent and is to be validated in future projects.
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