Researchers at the Department of Energy’s (DOE) Manufacturing Demonstration Facility (MDF) at Oak Ridge National Laboratory (ORNL) recently worked with Whirlpool Corporation to print and machine a mold used to make refrigerator doors. The process took a single day, unlike the conventional casting process for the tool that can take as long as 14 weeks.
The mold is used to reinforce the plastic liner, or the interior part of the door that holds shelving, during the injection of insulating foam on the production line. During this process, liquid foam is injected into the refrigerator door between the outer metal case and the inside plastic liner; the foam expands into every nook and cranny of the door and solidifies. If the liner is not held firmly in place by a mold, it is prone to warping that could prevent a proper fit for shelving.
To accommodate various configurations of a full refrigerator product line, appliance makers typically need many such molds, noted engineer Brian Post of the Manufacturing Systems Research group at ORNL.
“This was a nice application for additive manufacturing,” Post said. “The surface finish requirements were not that high, and the mold needed to withstand an environment of only about 100 degrees [Fahrenheit] and less than 5 psi of pressure. It was a nice jumping-off point for further research.”
Indeed, after three molds were printed, Whirlpool successfully tested them on a production line. The doors produced using the 3D printed molds were found to be within specifications. Two of the molds were printed with 100% infill, resulting in a solid interior; the third was printed at 50% infill with a mesh-like structure on the interior. All used a carbon fiber acrylonitrile butadiene styrene (ABS) material comprising 20% carbon fiber by weight.
Another advantage Post noted is the ease of re-machining additively manufactured molds if they do not come out perfectly the first time.
‘Great opportunities’ in tooling, appliance manufacturing
The demonstration project could inform further appliance research in the additive manufacturing space, including: the use of new high-temperature materials like polyphenylene sulfide (PPS) – a semi-crystalline polymer; creating watertight molds that could withstand the use of cooling liquids in the production process; and even printing the door liners themselves, Post said.
“We see great opportunities for additive manufacturing in the tooling industry, and for further work in appliance manufacturing where we can make big impacts, fast,” Post said. For example, the cost of producing custom refrigerators could be reduced by additively printing appropriate parts or molding.
The DOE’s Advanced Manufacturing Office (AMO) and Whirlpool jointly funded the demonstration project as part of the MDF’s Technology Collaborations Program.
The MDF, supported by the DOE AMO, is focused on solutions to lower production costs, help create new products and jobs, and to reduce life-cycle energy and greenhouse gas emissions in the US manufacturing space. --by Stephanie Seay