Foaming has long been a tried and true route to reducing part weight, particularly in the vehicle manufacturing industry. The MuCell foaming process, developed and patented by Trexel, offers particular advantages in this respect. A physical process for foaming thermoplastics that uses nitrogen or carbon dioxide as blowing agents, this process has gained popularity due to, among other things, the shorter cycle times and, importantly, minimal sink marks caused by expansion of the blowing agent.
During the process, the gas is transformed into a supercritical fluid, or SCF, fed into the plastic melt toward the front of the barrel and mixed with the melt. The SCF expands during the injection process to produce a part with a mainly microcellular foam structure (<100 µm).
In combination with special mold concepts and in cooperation with partners, KraussMaffei has now succeeded in creating additional high-gloss surfaces for the components foamed using this process.
"The MuCell process has become an established technology, particularly in vehicle manufacturing and for technical components. However, the trend is clearly moving toward also using the process for premium quality surfaces in visible components," explained Paul Caprio, President of KraussMaffei Corp. in the United States.
At KraussMaffei's booth at NPE2015 (W-903), a fully electric AX 180-750 CellForm production cell with integrated LRX 50 produces foamed visible components with premium quality surfaces in piano black. This is made possible by features including inductive dynamic mold heating (DMH) from RocTool and mold expertise. The molds have special surfaces with different effects (matte, high-gloss, with punched holes), providing an impressive showing of the design options for foamed visible components.
However, the molds and mold heat-balancing are not the only critical factors for the success of the MuCell process. Special screws, plasticizing units, barrels and process control systems are also required for the process. They are an important component of the KraussMaffei CellForm technology, which was developed specifically for the MuCell process.
The high precision and shot-weight consistency of the AX 180-750 CellForm at the NPE2015 booth make it particularly well suited for the MuCell process. The machine is producing a polycarbonate panel for coffee machines. By adapting the part design specifically to MuCell, the wall thicknesses and part weight were adjusted in such a way as to achieve significant material savings with no loss of functionality. "This not only lets us keep the weight down, but also conserves resources, an important step toward greater sustainability in production," said Caprio.