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The Fraunhofer Institute for Chemical Technology ICT, based in Pfinztal, conducts research and development in the research fields of Energetic Systems and Materials, Applied Electrochemistry, Environment and Polymer Engineering, and New Drive Systems. The researchers' latest achievement is very low-density thermoplastic foams that can be molded into individual lightweight components using 3D printing. In order to be able to use foams at all in additive production processes, researchers at the Stuttgart-based Fraunhofer Institute for Manufacturing Engineering and Automation IPA had previously developed a shutter nozzle specifically suited for this purpose. For applications involving small batch sizes and individually customized components, 3D printing is often the most economical solution. Accordingly, new materials with new property profiles for additive manufacturing processes are increasingly coming onto the market. Printed foam components are one such new application. Up to now, the state of the art has been filaments loaded with chemical blowing agents that foam up during the printing process. Studies on polylactic acid (PLA) with a chemical blowing agent have shown that it can be used to produce foam components with a density of around 430 kilograms per cubic meter. Compared to the compact material, these foams have about 35 percent of the density.

Fraunhofer ICT takes a different approach

In contrast to the method described above, the filaments produced by extrusion at the Fraunhofer ICT are mixed with blowing agents in a newly developed process. The process has so far been demonstrated on the completely biobased plastic PLA, on partially biobased cellulose propionate (CP) and on the petroleum-based polystyrene (PS) commonly used in the classic thermoplastic foam sector. These materials have a wide range of applications as foams.

Increase by a factor of ten

In initial trials on commercially available 3D printers, the materials produced using the Fraunhofer ICT process have resulted in component densities of up to 52 kilograms per cubic meter, which is roughly five percent of the density of the solid material. Compared to the current state of the art, this is an increase by a factor of almost ten. The density of the foam can be easily adjusted within a wide range of values by means of pressure parameters such as temperature or feed rate. This also makes these foams interesting for very many applications from the printer. Due to the strong foaming of the component during printing to about 20 times the volume of the solid material, the volume-related printing times can also be significantly reduced compared to a printed solid material, which further increases the cost-effectiveness of foam 3D printing.

Sandwich constructions with high lightweight potential

Combined construction methods are also conceivable via the printing process. For example, the Fraunhofer ICT considers the printing of so-called sandwich structures to be possible, whereby structures consisting of thin cover layers on the outside of the component made of solid material and a foamed core in the middle of the structure could be produced in one printing cycle. Such combined structures would have very high lightweight potential, as they combine stable mechanical properties with simultaneously low component density.

Use cases particularly conceivable in the transport and traffic sector

Jonas Fischer from the Center for Additive Production (ZAP) at Fraunhofer IPA therefore initially sees possible applications in the transport and traffic sector: "In the field of mobility, lightweight solutions play an important role. Printed foam components could be used here in suitable places to save weight and thus improve the efficiency of aircraft and vehicles for road and rail," says Fischer. And printable foams could also make a difference to the freight that a freight train carries: Custom-fit packaging material could be printed for special machinery, special spare parts and other individualized products, protecting them from damage in transit. At the same time, the low weight of the packaging could reduce emissions during transport by plane, ship or truck. The foams also make possible, for example, personalized seat cushions for wheelchairs or load-bearing bicycle saddles.