Burton Precision, based in Grand Rapids, Michigan, is a machine tool distributor specializing in the application of metrology and 3D printing products. The company’s involvement in manufacturing crosses a breadth of industries with technologies that have a direct effect on successful product design and manufacture.
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Most recently, a unique opportunity presented itself when the University of Michigan’s Human Submarine Team contacted Burton Precision to enlist our assistance in dealing with CAD issues related to producing a propeller for a submarine designed and built by students.
The Human Powered Submarine team competes every year in one of two races: The International Submarine Races (ISR) at the Naval Surface Warfare Center in Carderock, MD, or the European ISR in Gosport, England. In each race, the subs are timed through a 10-meter section of the race courses, which are located in the David Taylor Model Basin and the QinetiQ Ocean Basin, two massive indoor water basins used by the U.S. Navy and the Royal Navy to test new ship designs. Teams run the course one at a time, and may take as many turns as time allows over the course of the five-day competition. All of the submarines competing in the ISR are free-flooding designs. This means that there is no air inside the vehicle, so the pilot must use scuba gear to breathe during the race. The team is sponsored by the University of Michigan College of Engineering, the Department of Naval Architecture and Marine Engineering, and companies such as Burton Precision, Kaiser Aluminum, Chevron, and Ford.
The problem
This particular inquiry came via a very circuitous path. We held an open house at Burton Precision for GR Makers in Grand Rapids, which is an open community lab incorporating elements of a machine shop, a workshop, and a design studio. Members there work on projects that range from the industrial to delicate arts. It’s a unique community that focuses on enabling personal expression, providing education, and supporting entrepreneurship. We were demonstrating our metrology and 3D printing products for them when I met an individual who mentioned that his brother belonged to the Human Powered Submarine Team at the University of Michigan. The team was having problems with a point cloud file for a propeller design. More specifically, they couldn’t convert the data to a “friendly” file that they could put to a cutter path on a CNC machine to make the part. I gave him my card. They called!
Specifically, Jeremy Werner called. Werner is with the University of Michigan’s Naval Architecture and Marine Engineering Department, and he is also president of the Human Powered Submarine Team. He outlined the CAD issues they were experiencing with a propeller design program called Open Prop, which was not allowing them to export files in a format that they could use to create a toolpath. He provided us with the point cloud files, which did not include outward normal vectors. The units were in meters and arranged with 100 rows of points along the length of the prop blade, and 40 points per row (20 on either side of the blade). Ultimately, they wanted to make the toolpath in GibbsCAM.
Finding the solution
Werner and I exchanged several emails the first week seeking a solution to this dilemma, which was not as simple as a file conversion. It almost never is. He sent me an STL file that I read into Geomagic Studio Software (a 3D systems software package used on 3D printing machines) in an attempt to create a NURBS surface, which is a mathematical model commonly used in computer graphics for representing curves and surfaces.
We were dealing with low-resolution files, and an edge on the blade was giving the surface creation fits. Werner did four or five rewrites before we had a usable file. Once we had a good surface file, I asked if we could 3D-print it for him. That opened another door, which lead to further discussions about the strength of the material, testing using a scale version, and overall functionality of the 3D-printed part. The first surface files that we provided failed the initial testing in their simulator because the blade was too thin. We increased the thickness and the thicker blade passed. We then 3D-printed the propeller on a 3D Systems ProJet 3500 HDMax printer in a plastic material called Crystal.
“Burton Precision became a key player in providing a hands-on learning experience for me and all the team members involved in the scale model propeller test,” says Werner. “This kind of out-of-the-classroom training is at the core of our team’s mission statement, and everyone from outside U of M who contributes to that deserves special recognition.”
We were invited to attend the full-scale, self-propelled test of the submarine and its systems on April 22, 2014. The test was successful, as the propeller worked perfectly. We are now hoping to sell a 3D printing machine to the university.
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