Local Motors and Cincinnati Inc. made history earlier this month when they 3D printed an entire Strati EV on the show floor at IMTS in Chicago. A lesser-known story focuses on the material used to accomplish this feat, and that’s what SABIC has revealed to Design News.
The Strati car was 3D printed with SABIC’s LNP STAT KON AE003. This is a carbon fiber-reinforced compound based on the company’s CYCOLAC resin, an ABS (acrylonitrile butadiene styrene) material, and contains 15% carbon fiber, Tony Cerruti, marketing director Americas for SABIC Innovative Plastics, told us. STAT-KON AE003 was selected for its high stiffness, as well as its high strength-to-weight ratio, its extrudability, and low coefficient of thermal expansion (CTE). These characteristics minimize any potential warping during the 3D printing process to ensure good performance, as well as good appearance, of the car’s large-format printed parts.
“In the 3D printing process, warpage frequently occurs because the material starts shrinking immediately after it is deposited,” said Cerruti. “By the time the second layer is extruding on top of the first layer, the first layer has had sufficient time to shrink. Because the two layers adhere together, the first layer restricts the shrinkage of the second layer.” Too high a CTE can cause stress to build up in the part, warping its long sections.
CYCOLAC resin was used as the base material for printing the car parts on Cincinnati Inc.’s BAAM (Big Area Additive Manufacturing) machine because it has a proven record of success in traditional 3D printing extrusion processes, said Cerruti. “In general, amorphous thermoplastics like CYCOLAC resin perform well in 3D printing processes because they shrink less than crystalline thermoplastics as they cool.”
In a composite, CYCOLAC resin acts like a glue, while the carbon fiber increases mechanical strength and reduces the shrinkage. Carbon fiber’s high strength-to-weight ratio compared to other thermoplastic additives also lowers CTE significantly. To work properly, CYCOLAC must adhere well to the carbon fiber reinforcement, and also acts as a glue between the printed layers.
A range of SABIC materials has been used previously in 3D printing applications, including CYCOLAC, ULTEM, LEXAN, and LNP resins and compounds, said Cerruti.
To provide materials and processing expertise, SABIC worked closely with both Cincinnati Inc. and Oak Ridge National Laboratories (ORNL) to select and validate the right materials for the 3D-printed car, as well as determining equipment specification and processing. As we told you last spring, advanced materials research pioneer ORNL partnered with Local Motors to develop the technology needed to 3D print an entire production model car, and also with Cincinnati Inc. to develop a huge, fast commercial 3D printer, which resulted in BAAM. The machine prints polymer components 200 to 500 times faster and 10 times larger than today’s additive manufacturing machines.
By Ann R. Thryft