A research team from the Center for Additive Production (ZAP) at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA has now presented a solution. It has developed a shut-off nozzle that automatically interrupts the material flow at predefined points: the extruder motor transports the plastic filament to the nozzle, which is closed by a spring mechanism. Shortly above the nozzle, the filament passes a heating element. The plastic melts, becomes liquid and collects in a cavity inside the nozzle. At a certain internal pressure, the melt pushes a hollow needle, through which the filament itself was previously conveyed, and thus the spring upwards. The nozzle opens and the plastic flows out of it.

Additively manufactured rigid foam components

The material flow is stopped when the conveyor unit no longer transports material towards the heating element. "The remaining melted plastic in the nozzle is still being compressed. The cavity empties, the pressure decreases, the spring pushes the hollow needle back down and closes the opening of the nozzle," explains Jonas Fischer from ZAP, who played a key role in the development of the patent-pending shut-off nozzle.

So far, the researchers have only printed foams with a very low density, which the Fraunhofer Institute for Chemical Technology ICT in Karlsruhe had previously developed, with their sealing nozzle. It is conceivable that these foams could be used in the near future to additively manufacture substructures for seating, insulation, packaging or lightweight structures, for example. The shut-off nozzle is also suitable for low-viscosity plastics such as polyamide. However, initial test prints are still pending.

A model of the sealing nozzle will be on display at Formnext in Frankfurt. In addition to Fraunhofer IPA and Fraunhofer ICT, the furniture manufacturer Rolf Benz from Nagold was also involved in the research project "BioxXprint - the bio-foam printer for graded structures" (funding code: 031B0860C), in which the shutter nozzle for 3D printers was developed. The project was coordinated by the Institute of Wood Technology in Dresden. The research project was scheduled to run for two years and ended in August 2022. The Federal Ministry of Education and Research funded it with 250,000 euros.

Hall 11.0, Stand D51