In fused filament fabrication (FFF) 3D printing, a thin spray of material is deposited, or extruded, in successive layers to create a fused physical object of a specific design. Originally designed for use with simple plastic filaments, this field is continually advancing. For example, new material feedstocks can improve the mechanical properties or introduce stimuli-responsive features in the final parts. However, some new or experimental materials can be too fragile or do not flow suitably for extrusion with current hardware. In addition, no commercially available FFF printing nozzles can effectively combine and extrude two different filaments into blends with efficiency and precision. Until now.

A new mixing extruder developed by PNNL enables FFF printers to efficiently mix dissimilar polymer filaments at the time of printing to yield homogeneous prints. The PNNL extruder successfully mixes a wide range of ratios of polymer materials with different attributes: conductive and insulating; soluble and insoluble; flexible and rigid filament; and in some cases, dissimilar melting points and composition. In addition, specialized filaments containing metal-organic frameworks results in parts with extremely high surface area post printing. Large surface area composite parts are useful for building absorption/detection-based devices, such as those intended for catalysis, gas capture, or selective chemical sensing applications.

PNNL’s mixing extruder uses an auger bit that rotates within the heated chamber of the extruder's hot end. This design produces the shear forces necessary to induce mixing of the molten plastics. The rotating auger bit also acts as a secondary driving mechanism to assist with extruding highly viscous or soft filaments. The design allows for rapid screening and fine tuning of material properties in final parts, including strength and flexibility. This combination of properties is otherwise difficult to acquire through traditional composite formulation and subsequent 3D printing cycles.

Applicability

The PNNL mixing extruder can yield greater material strength and flexibility for a variety of manufacturing processes. When used with specialized filaments containing chemically-responsive particle fillers, the ability to tune the dispersion and concentration of the active component may be attractive for absorption/detection applications. The extruder is a drop-in design for current fused filament 3D printers with minimal modifications and may be controlled using standard software.