Facing COVID-19 Production Goals at Dunwoody
Dunwoody College of Technology in Minneapolis, Minnesota, has long been recognized as a leading educational institution, graduating people skilled in many areas of automated manufacturing. Students at Dunwoody are trained to perform computerized numerical control (CNC) tasks quickly and accurately.
It came as no surprise, when 3D printer manufacturer Stratasys, having a standing relationship with Dunwoody, reached out to Instructor of Machine Tool Technology, Brian Nelsen, for help in making face shield components for health professionals on the front lines of the COVID-19 pandemic.
“Of course, they can’t 3D print the clear plastic portion of the face shields,” said Nelsen. “They also had some special shapes and features that had to be machined in and around the clear plastic, so they asked if we could do the job and how many shields did we think we could do. I knew we could handle the job and provide large quantities once we were up and running.”
Working from samples provided by Stratasys, Nelsen and a few student volunteers, practicing social distancing, rolled up their sleeves and went to work. First, they designed aluminum fixtures to hold 12- x 8-inch inch polycarbonate sheets for machining. They designed and programmed the fixtures in Mastercam.
“We used the Verification tools in Mastercam to make sure we were getting what we wanted. Then we made our first fixture, put it in a CNC mill, and cut some test parts. Everything worked perfectly, so we made three more fixtures so we could put four machines into production and started making parts.”
In addition to machining the outer edge of the shield, they needed to create precision holes used for fastening the clear shield to the visor that fits around the user’s forehead. “The holes are fairly intricate,” says Nelsen. “We programmed those in Mastercam, together with the rounded corners of the shield that would go up and down toward the user’s chest without causing discomfort.” They used a pocket milling cycle for the holes and contour milling for the rounded corners.
The biggest challenge came from the polycarbonate itself. “It has a tendency to melt easily from friction,” says Nelsen. “So, we just cannot fly through it. We had to experiment with the feeds and speeds of our 1/8-inch and 3/16-inch diameter tooling. The chips are not very big, but they tend to stick to the work pieces. We changed over from our fluid cooling system to an air coolant system to get the chips out of the way so they wouldn’t heat up again and reattach to the shield.”
Once in full production mode, machining 12 to 18 shields per fixture on four Haas CNC mills with three-minute cycle times, plus setup time, Dunwoody was producing anywhere from 3,000 to 5,000 clear shields a day. This was not the end of the cooperative effort, however.
Stratasys then asked Nelsen if Dunwoody would be able to also supply the plastic visors that would attach to the clear shield. This part called for designing and producing a plastic injection mold and then making the molded part in Dunwoody’s injection molding equipment.
“We went with Mastercam again for the design and manufacture of this part. The biggest challenge in machining this mold is all the small end mill work for the features that hold the clear face shield onto the visor. One feature is so deep in the middle of the steel mold that it kind of arcs in and out of 3D space. We were able to successfully machine it in the end because we could work with Mastercam’s toolpath abilities and be able to tweak things and adjust things, so we got the job done and done well.”
Dunwoody is producing between 400 and 500 of these visors per week. The completed shields are heading to the Mayo Clinic, Children’s Hospital, and various medical firms. Stratasys and Dunwoody—and many donators of materials—have expanded productivity and skill capabilities while producing valuable PPE for medical professionals.