Scientists at Oak Ridge National Laboratory have developed a vacuum-assisted extrusion method that reduces internal porosity—by up to 75%—in large-scale 3D-printed polymer parts.

The paper is published in the journal Additive Manufacturing.

Large-format additive manufacturing (LFAM) enables the direct printing of meter-scale structures used in aerospace, automotive and defense tooling. But widespread adoption has been hindered by internal porosity, or voids, that weaken printed components. Reducing porosity is key to improving strength, durability and overall performance.

ORNL researchers tackled this challenge with a novel approach: integrating a vacuum hopper during the extrusion process to remove trapped gases and minimize void formation in fiber-reinforced materials. These materials are widely used in LFAM for their stiffness and low thermal expansion but often suffer from intra-bead porosity that limits part quality.

The new system reduced porosity to under 2%, even with varying fiber content.

“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.”

While the current method is designed for batch processing, ORNL has developed a patent-pending concept for continuous deposition systems, which will be the focus of upcoming research.