Metal foams, full of tiny air bubbles like a sponge cake, are gradually making inroads in industrial applications. Lightness and high energy absorption are two demanded material characteristics. Less known is the use of open-pored variants for decorative purposes.
Interior designers can make use of an endless variety of decorative panels to realize their plans. Room dividers and suspended ceilings divide up the space in an apartment or office, but they are also expected to be more or less permeable to light, air or sound. A class of materials that meets this requirement is open-pored metal foams. A stylish effect can be achieved by filling the interconnected pores with a transparent synthetic resin or colored plastic. The closely related closed-pore metal foams are already making headway in numerous applications. Their low weight predestines them for use in light but rigid assemblies in machines with moving parts. They are used as shock absorbers in vehicles, due to their excellent capacity to convert kinetic energy into resilience and heat. As catalysts their high internal surface area is used.
The must common technique for manufacturing metal foams involves mixing metal powders with blowing agents. Now the mixture gets heated up. As it approaches melting point, the additive releases a gas which creates a mass of bubbles in the metal. Open-pored foam panels cannot be manufactured this way, because the pores extend through from one face to the other. An expanding gas would simply escape through the holes. The team at m-pore in Dresden employs a casting method. First, a mold cut in polyurethane foam is coated with wax. The cavity is filled with a heat-resistant ceramic paste. In specialist terms, this is referred to as lost wax or investment casting. When liquid metal is poured into the mold – mostly aluminum at around 700 °C –, the plastic foam burns away, leaving behind a metal “sponge” filled with pores with diameters of between one and five millimeters. The final step is to blast off the ceramic mold with a water jet.
“In order to provide a single source for development services involving the various foaming techniques and applications, we set up an alliance for cellular materials three years ago,” relates Thomas Hipke, head of the production systems department at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz. “The Verbund Zellulare Werkstoffe Sachsen consists of six active members at present, one is m-pore.” The decorative, featherweight panels are used comparatively rarely as yet. This is probably due to their relatively high price, which results from the fact that a large part of the manufacturing is done by hand. But then again, especially in matters of aesthetics, the old adage is true that “You get what you pay for. There might be cheaper options, but the result often is far less pleasing.”