08 Apr A new simulation improves the use of polyurethane foams
A research team at Fraunhofer ITWM, together with colleagues from the Department of Lightweight Structures and Polymer Technology at TU Chemnitz, have developed the first ever simulation for composite materials like polyurethane foams, used for car seats, mattresses and insulation materials
Polyurethane foams (PU) play a big role in our everyday lives, even if we are generally not aware of them. Predicting the properties of foams and characterizing them is very complex, because experimental analyses often lead to false parameters. Fraunhofer researchers are now able to simulate the foaming behavior and reliably characterize the material. This also works with composite materials in which the plastic foams are combined with textile structures.
In a car seat, for example, some areas are meant to be harder and others softer. Manufacturers achieve this by injecting foams with different characteristics against each other. They use liquid polymer blends as their starting materials, which are injected into a suitable mold: a rapid but complicated chemical process begins. Within a few seconds, the two liquid emulsions transform into a complex polymer foam. But how exactly do the two different substances foam? Do they have the required properties, and do they spread as intended into their proper zones? “Instead of starting with chemistry and experimentally determining all parameters such as reaction rates and viscosity in many independent experiments, we do two or three simple experiments – such as foaming in beakers,” explains Konrad Steiner, head of department at Fraunhofer ITWM.
“We simulate these experiments one to one on the computer. These experiments serve to establish the model parameters needed for the FOAM simulation tool, which calculates foaming behavior based on simulations. The results are robust and reliable for the specific application.” Instead of determining each characterizing parameter separately in an individual experiment, which can lead to imprecise values, researchers can now quickly obtain reliable data for the foaming process with a minimum of effort.
“Manufacturers usually work with three or four different foams – for new products, they generally just change the combination of foams and the end geometries,” says Steiner. Once the Fraunhofer researchers have characterized a PU foam through simulation, this provides a good starting point for new products. Manufacturers can input the foam data they receive into the FOAM simulation tool and simulate for each new product and each new geometry how the foam mass and heat should be transported during the foaming process. In the case of a car seat, they can find out exactly how to inject the two foams against each other to achieve the desired zone properties at the right places.
The simulation methodology for identifying parameters and simulating foam with the FOAM tool has been established, and several projects are already underway with various customers. The researchers have already validated and tested the results on components and established that they match up very well with reality.