Composites Manufacturing Magazine

3-D Printed Car “Strati” Gets Ready to Rev Up

James Earle, right, an advanced materials engineer with Local Motors, and Vince Estep, lead graphic designer, test drive a 3-D printed prototype vehicle.

Local Motors and Oak Ridge National Laboratory will 3-D print an entire car at the International Manufacturing Technology Show (IMTS) in Chicago this September

Driving around in a 3-D printed car is all in a day’s work for Local Motors CEO Jay Rogers. “I’m driving it every day,” Rogers says of the vehicle, a prototype for the soon-to-be-built Strati. The Strati will be constructed on the show floor of the International Manufacturing Technology Show (IMTS) in Chicago this September using 3-D printing technology – also known as additive manufacturing or direct digital manufacturing (DDM). The technology facilitates fabrication of components from computer design to the actual part.

Approximately 90 percent of the two-person, electric Strati will be made from composites, with a single carbon fiber reinforced thermoplastic part that integrates the chassis, body and interior. Once the engine, lights and other components are added, the Strati will have a mere 20 parts – a marked contrast to traditionally manufactured cars, which can have up to 25,000 parts, says Rogers. “It’s about simplicity,” explains Rogers, who founded Local Motors in 2007 to “decomplexify” auto manufacturing and speed up innovation.

To that end, Local Motors’ products, which range from electric skateboards to motorcycles and off-road vehicles, are produced in small lots in micro-factories or “cells” that also sell and service vehicles. Peter says these “rapid products” can be changed very quickly, even unit by unit – a far cry from the weeks- to months-long shut downs that can occur to retool and retrain for year-end model changes in traditional manufacturing. Local Motors’ products also are co-created or crowdsourced – designed, developed and vetted through a community of professional and hobbyist contributors. The Strati’s design was created by automotive designer Michele Anoé of Italy, who won a contest held by Local Motors last spring.

The 3-D car project began several years ago as a quest to produce a car with a greatly reduced part count. Local Motors was already using additive manufacturing to construct its Rally Fighter off-road vehicle. The Rally Fighter, like other vehicles using DDM, is constructed from multiple 3-D printed panels that are affixed to a metal frame – in this case an extruded tubular steel frame – with fasteners and adhesives. Foam also is added to reduce noise. But Rogers wanted to go further and print a vehicle with one cohesive chassis, body and interior.

“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.

This rendering depicts the Strati two-person automobile, which will be 3-D printed this September.

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.

Once completed, the part will be milled inside and out using a Thermwood five-access router that can operate on the x, y and z planes and rotate in two directions. The remaining parts will then be attached, including a 48-volt Renault powertrain, battery, motor and battery controllers, taillights with integrated turn signals, headlights, steering wheel apparatus, wheels and an electrical wire harness. Steel fasteners will be used to affix the motor and battery.

The additive manufacturing system, which Local Motors and ORNL developed from the model already on site at the lab, is being built by Cincinnati Inc. It is a gantry-style printer that can print objects as large as 12 feet long, 6.5 feet wide and 3 feet high.

Local Motors printed the prototype vehicle at ORNL in June. Because the test printer was smaller than the one that will used to build the Strati at IMTS, the prototype was printed in multiple parts that were fastened to an aluminum sub frame. It took 30 hours to print, while the company projects the Strati will require 60 to 80 hours. Rogers says the company will likely start printing the Strati a day or so before IMTS so that it will be finished halfway through the show.

Once completed, the Strati will operate within an 80 to 100-mile range at speeds of up to 40 mph. The first customer will be the Association for Manufacturing Technology, which signed a contract for the vehicle built at IMTS. Other potential customers may have to wait a little longer: Local Motors has no plans to offer the Strati to the public immediately following the show.

The Strati is a technological leap for additive manufacturing, advancing car production from multiple parts with a metal frame to a single 3-D printed composite main body. CFRP adds rigidity and strength to the ABS plastic and combats thermal contractions, says James Earle, an advanced materials engineer with Local Motors. He adds, “This simply couldn’t be done without composites.”