Speed machining for autonomous vehicles

From Italy to Saudi Arabia, the University at Buffalo in New York to the grounds at GoMomentum Station in Contra Costa, California, Local Motors’ Olli autonomous shuttle is popping up everywhere. The brainchild of Local Motors Co-founder and CEO Jay Rogers, this self-driving, co-created, largely 3D-printed vehicle aims to change the way people get from Point A to Point B and promises to change how people think about manufacturing as well.

Developing and building an autonomous vehicle isn’t without its challenges, however. Tim Novikov, advanced manufacturing engineer at Local Motors’ facility in Knoxville, Tennessee, found this out the hard way recently while attempting to machine an Olli chassis on the company’s massive hybrid additive machining center.

“I had to turn the feed rate override to its lowest setting to keep the chatter under control,” he says. “Anything faster than that and it sounded like the chassis was going to self-destruct.”

Olli, meet LSAM

The machine tools used to make the Olli are nearly as unique as the company. Local Motors’ microfactory in Knoxville is home to one of the largest 3D printers in the world, a 40ft long gantry-style Large Scale Additive Manufacturing (LSAM) machine from Thermwood Corp. Like other fused deposition modeling (FDM) 3D printers, LSAM has a deposition head that heats and extrudes plastic feedstock, building parts one layer at a time. What’s different – aside from its enormous size – is the addition of a 5-axis milling head, allowing users to print and mill on the same machine.

This technology mirrors Local Motors’ digital manufacturing strategy, which according to research and development program director Billy Hughes, drastically reduces vehicle development lead times, provides endless customization and collaboration opportunities, and allows the vehicles to be built in community-centric microfactories. It could also enhance those communities by providing good paying manufacturing jobs and easy access to fleets of environmentally friendly vehicles.

“You look at the problems with urban blight, the decline of manufacturing in the U.S., environmental concerns and sustainability, there’s far more to this than producing fleets of high-tech shuttles,” Hughes says.

Problem solvers

Those community benefits, however, require a viable way of building Olli. That’s where Sandvik Coromant US was able to help. Faced with the unacceptable chatter and productivity problems with the complex, oftentimes thin-walled Olli chassis, Novikov turned to sales engineer Matt Brazelton to reduce the 80 hours of machine time per vehicle that Olli was taking.

“We’d actually been working with Local Motors for some time on their legacy machining center, providing them with indexable ball-nose and face mill cutters, and because the composite material they’re using is quite abrasive, we also set them up with polycrystalline diamond (PCD) milling inserts,” Brazelton says. “The larger spindle interface on their new LSAM, though, provided us with several new opportunities for improvement, with chatter elimination first and foremost.”

The first change was an adapter that allowed Local Motors to convert the LSAM’s HSK-F spindle taper to use Sandvik Coromant’s quick-change modular tooling system, Coromant Capto. This increased connection rigidity significantly, reducing tool changeover and setup time, while allowing Novikov to increase feed rates. More importantly, it allowed Coromant Silent Tool milling extensions. Those additions and a custom CoroMill 390 indexable shell mill, eliminated the chatter problem, even at full feed rate.

Printed tools

Due to the extreme length needed to reach deep inside the Olli chassis, the weight of a traditional steel milling tool mounted on the end of the Silent Tool extension did not provide the desired results. Brazelton reached out to tooling engineers at Sandvik Coromant, who came back with a novel solution: a custom CoroMill 390 cutter body made of 3D-printed titanium, optimized to achieve the lowest possible moment of inertia.

“It’s funny when you think about it,” Novikov says. “Here we are making the first 3D-printed vehicles, and we’re using the first 3D-printed tools to do it. But what’s even more funny is the tool itself. It’s so lightweight it feels like a toy.”

The titanium CoroMill 390 doesn’t cut like a toy. Novikov was able to crank the feed rate override up to its programmed setting, reducing the 80-hour cycle time to roughly 5 hours, with greatly improved surface finishes and tool life.

“Before, everything vibrated so much there were gouges in the chassis wall from where it bounced back and forth against the cutter,” Novikov remembers. “It sounded like someone plucking guitar strings, only much louder.”

With Sandvik Coromant’s updated tools, he adds, “Now, it’s completely quiet, and there’s no risk of scrapping out a very expensive workpiece. Better yet, we can now reach twice as far as we could with our old tooling, so we’re able to machine more of the chassis in one operation.”

Next project

The latest Olli iteration is almost entirely 3D-printed from tough, carbon fiber composite material. With greatly improved machining conditions and the ability to operate PCD milling tools at the recommended cutting parameters, tool life and part quality are no longer a concern. Greater spindle interface rigidity allows Novikov to use larger cutting tools, further increasing productivity.

As Novikov will tell you, the best part of the improvement is the newfound ability to print and machine a complete chassis in a single shift, freeing the LSAM to crank out more Ollis, or work on any of Local Motors’ other manufacturing projects.

“The Coromant Capto system and Silent Tools have also increased the machine’s flexibility, in that we can use pretty much whatever tools are needed to get the job done efficiently, and not be limited to relatively small milling cutters and drills like we were before,” Novikov concludes. “These chassis are quite large, and we needed a way to machine them in a productive manner. That’s what Matt Brazelton and Sandvik Coromant have done for us.”

Local Motors 

Sandvik Coromant 

Thermwood Corp.