Additive Free-Form Casting Process Combines the Advantages of 3D Printing and Injection Molding

We’ve seen all sorts of 3D printing innovations coming from the many institutes of Fraunhofer, Europe’s largest application-oriented research organization, from large-scale SLM 3D printing and a real-time autonomous 3D scanning system to a powder jet that solves issues with laser metal deposition printing.

The latest comes from the Fraunhofer Institute for Production Engineering and Automation (IPA) – researchers there have come up with a new manufacturing process that combines the best advantages of 3D printing and injection molding technologies, which they have dubbed additive free-form casting. The researchers recently completed a feasibility study on their new method during a preliminary research project, and successfully fabricated several different prototypes.

By now we know the many advantages that 3D printing has to offer – it’s faster and less expensive than injection molding for fabricating prototypes, custom-made products, and small series, and the technology also makes it possible to create integrated functionalities and complex structures.

However, we also know that the technology is not entirely without its faults.

One of the more popular additive manufacturing methods is extrusion-based 3D printing (e.g., FFF/FDM) which uses a nozzle to place print material in parallel strands. It sounds easy enough, but the process can sometimes result in weld lines and porosity issues.

“The material is not ‘full’ in the mold, as in casting,” explained Fraunhofer IPA expert Jonas Fischer in a translated quote. “As a result, the mechanical properties of the component are worse.”

It can also take quite a long time for large 3D printed components to be fully built up, and in terms of polymers, only thermoplastic materials can be processed with FFF processes – it’s not possible to print thermosets, which can be melted and formed only once, staying solid once solidified.

Fraunhofer IPA researchers sought to minimize these issues, and print with new materials, using additive free-form casting, saving on time and increasing stability. First, they 3D print the shell of the component out of water-soluble plastic polyvinyl acetate (PVA).

Then the envelope is filled automatically with the precise amount of either epoxy resin or polyurethane; the latter only takes three minutes to dry. Only after this can the component, according to Fraunhofer IPA, “be arbitrarily extended in height with the same principle.”

Once the component has cured, the mold is then removed in a water bath, resulting in a 3D printed piece that has properties not unlike an object created with injection molding.

A special dosing unit, meant for two-component materials, was installed by the researchers in their 3D printer in order to properly pour the filling material into the case. This makes it possible to complete the whole process in a single go – no interruptions necessary. Additionally, it can be completely digitized and works with resins and heat-resistant thermosets, and the process is also much quicker.

Fischer said in a translated quote, “You just have to print the envelope, leaving the rest to gravity.”

Components manufactured using additive free-form casting are much more stable, as the mold is completely filled with material, leaving no room for air bubbles, and can also result in weight savings when complex components in smaller quantities are needed.

Fraunhofer IPA’s new additive free-form casting method works for multiple industries and applications as well.

“Electrically insulating components such as sockets can be manufactured with it,” said Fischer in a translated quote. “The process is also suitable for foams and upholstery required for security elements.”

The researchers are now on the hunt for industry partners to help with future development of the process on its way to series maturity, as well as companies that have ideas on different industry areas that could use thermoset applications. Fraunhofer IPA is also in need of material manufacturers who can work with its researchers to improve properties of the two-component fixture.

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[Source/Images: Fraunhofer IPA]