Friday, March 24, 2017

2017-03-23: See How We 3D Print Our Way To Better UAVs

Ben Kelley, a small GPS chip in his hand, approached Nick Woodward's desk.

"This is going to go on a vehicle, but I can't find a case for it anywhere online," he explained, handing over the chip.

"I can do that," Nick said.

Nick, an intern and recent grad of Worcester Polytechnic Institute, has many jobs around the Ai, but chief among them is what he calls "the CAD guy." Thanks to what he's accomplished in his three-year stint in the Ai, CAD (computer assisted design) and 3D printing have become a part of everyday operations– which means faster prototyping for our whole lab. Where before people would have had to go outside the Ai to get custom components designed and fabricated, Nick can whip up a quick plastic prototype in less than half a day.

"It provides us with a relatively new and unique advantage of being able to rapidly prototype multiple options for a given solution," he added. So, if he has more than one idea about how to approach a problem, he can just print up both and see which one works best. 

On occasion, Nick sends a successful prototype out to the NASA Langley printing lab because "their abilities for production are way greater than ours... you're looking at a machine the size of a queen bed and about 8 ft tall." Today though, he planned to put his creation straight from our printer onto the vehicle.

It's all measurement taking to start with. Nick uses calipers and takes down the exact dimensions of the chip, noting outlets and screw holes, while he thinks about how to create the best case for it. In less than an hour, he's got a completed first draft.

"If there are multiple parts," he said, "I make sure everything fits together as intended in simulation and then print it out."

Our tabletop printers are extruders, which means they essentially function like very precise hot glue guns– they feed a spool of solid PLA plastic into a heated tip that applies the melted plastic to the work surface in thin layers. The machines are very fast, but also very delicate. Before Nick can fire up the print, he has to make completely sure that the machine is in full working order. This includes cleaning the extruder: cranking the temperature up as high as it goes, letting it cool, and then extracting the purged excess plastic with a pair of pliers.

"What are you doing now?" I asked as he ducked his head practically inside the machine.

"Calibrating," he said. If the extruder head isn't exactly the right distance away from the work surface, or if the axes aren't tuned just right, the print will come out off-kilter. Same for if there's any dirt at all on the surface– before starting the print, Nick has to buff it several times with a paper towel.

"If there's anything between the plate and the PLA when it goes down, it can pull away from the plate mid-print and ruin the print," he explained. There are other ways of making sure your print sticks to the plate– you can rub the printing surface with a glue stick, or coat it with a layer of painter's tape– but Nick prefers to just keep the environment as clean as possible. 

Once everything is ready to go, Nick starts the print and walks away. There's nothing to do now but wait.

"Ideally, you wanna make a print that you can put on in the morning and pick up before close of day, from a prototyping standpoint," he said. The time a component takes to print is dependent on not just the size of the piece, but also the "infill"— basically, how dense the inner honeycomb structure of the print is. Lighter infill pieces print faster, but won't be as hardy. It's a balance Nick has to consider whenever he makes a new prototype.

"I had a twenty-six hour print once," he added. It was the cone and tetrahedron package delivery system he created last summer. 

Once the print is finished, Nick gently pries the pieces off the printer bed and hands them over to Ben. Here he is, assembling the case around the GPS chip.

This first draft turned out pretty well, but Nick said he's doing revisions for a second iteration.

"The inside is about two millimeters too shallow," he said, "and I need to research closing mechanisms that don't require screws." Luckily, a new and improved component is only a few minutes of CAD work and an hour of printing away.

No comments:

Post a Comment