“People would say things like, ‘Isn’t it much easier to stamp a body panel, then weld it together with something else instead of trying to make a machine that can make it all?’” recalls Rogers. “But I was inspired by additive manufacturing, so we started to search far and wide for technologies and processes and machines that could allow us to [print one part].”
The search ended 18 months ago at the U.S. Department of Energy’s Oak Ridge National Laboratory’s (ORNL) Manufacturing Demonstration Facility in Oak Ridge, Tenn., where Rogers and his team found a large-scale additive manufacturing system. “They were printing out large parts and then going back making them more accurate by milling them, and they were doing it so very quickly – way, way faster than your standard 3-D printer,” says Rogers. This past winter, Local Motors signed a cooperative research and development agreement with ORNL to advance the technology and make cars.
The Strati will be 3-D printed from acrylonitrile butadiene styrene (ABS)thermoplastic that is reinforced with polyacrylonitrile (PAN) precursor chopped strand carbon fiber. Sabic will supply the carbon fiber in pellets, which can be fed into a plastic welder’s hopper. Once in the hopper, a screw forces the pellets down into a sleeve that heats them to approximately 210 degrees Celsius. The liquid reinforced plastic is then extruded out through a .30-inch diameter nozzle. Guided by CAD drawings that have been run through a slicing algorithm, the nozzle moves along an overhead carriage to lay down .16-inch layers of material. The layers cool within a few seconds and another layer can be put down. A heated build table keeps the layers just warm enough to adhere to each other.