Fraunhofer's new 4D printing technology can shrink printed objects by up to 63%.    

Contributed by Lily Manolis Sherman

Thanks to the 4D printing technology developed in the CPM cluster of Fraunhofer's outstanding programmable materials, the printed polymer changes shape in a predefined way when heated. The shape of printed objects varies greatly: they can shrink by as much as 63%. Fraunhofer researchers predict that in the future 4D manufacturing technology can be used to produce parts that only exhibit specific behaviors after having a predefined shape, such as the fastener industry in the assembly of components in medical technology, mechanical engineering, automobiles and aerospace.

It is said to be very popular now. According to reports, D printing has many advantages as an additive manufacturing technology. For example, products and prototypes can be individually designed and quickly available. A team of researchers at Fraunhofer CPM has significantly expanded their revenue by using so-called 4D printing to produce printed objects. This technology adds a time dimension or 1D to the space dimension or 3D. In this way, objects can be printed with shape memory polymers, which can change their shape at a later point in time when exposed to heat-and in a very remarkable way: a rod-shaped sample about 4 cm in length Shrink as much as 63%.

It is also possible to perform a specific curvature in a targeted manner. Thorsten Pretsch of the Fraunhofer Institute for Applied Polymers IAP said that he is coordinating the project at Fraunhofer CPM. “We started with relatively simple rod geometries, but in the end we were able to produce more complex hollow cylinders. Samples of solid and hollow rectangular parallelepiped shapes. For all the geometries we studied, we specified the desired material behavior in advance." There are generally two ways to adjust the response to temperature increases. The first is the choice of materials-in this case, researchers have developed a new type of TPU with shape memory properties. The team also showed that the findings of 4D printing can also be transferred to another thermoplastic polymer: they use bio-based PLA to produce shrinkable printed objects. The second possibility lies in the clever management of the printing process. "The key is that we let the material have almost no time to cool down during the printing process. As a result, severe internal stress is stored in the material. The subsequent shrinkage effect is very obvious," Pretsch said. In short, the selection of materials, processing temperature and printing speed can not only be used to adjust the shrinkage behavior, but also can be used to adjust the bending state. The first step of the project is to develop materials and transfer research results from TPU to PLA. The second step is to develop a demonstrator-a door opener that retracts on the door handle so that it can be operated with the elbow without touching it by hand. Disassembly is simple: by reheating; the door opener is separated from the handle, leaving no residue. When the object to be printed is no longer needed, it can be ground and reprocessed into filaments, which can be used for 4D printing at least again. "This concept is holistic and future-oriented. As far as the cradle-to-cradle approach is concerned, we have gone through the entire product cycle-from monomer selection and polymer synthesis to 4D printing of the demonstrator and its mechanical recycling," Pretsch concluded. Four Fraunhofer Institutes contributed their expertise: Fraunhofer IAP synthesized shape memory polymers, further developed 4D printing technology, and carried out mechanical recycling. Linda Weisheit from Fraunhofer Institute for Machine Tools and Forming Technology IWU developed the concept of 4D material programmable stiffness. The Fraunhofer Institute for Industrial Mathematics ITWM conducted mathematical simulations to design the demonstrator. “For example, we studied how the force is distributed when the door opener is loaded. We also want to find out which design is better in terms of material consumption,” explains Heiko Andrä. The actual test was carried out at the Fraunhofer Institute for Material Mechanics IWM. “For example, the question here is what torque will be generated when the door opener is loaded,” explains Tobias Amann.

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