Space Station's Mobile Freezer Challenge Solved by 3D Printing
Their latest project, the Polar Unit, is one of the first of their designs to incorporate 3D printed components produced in Stratasys’ FST-compliant ULTEM™ 9085 thermoplastic material. Unlike conventional methods, 3D printing offers optimal design solutions, allowing for organic shapes and saving significant interior space within the freezer unit.
An exterior look at the front opening of the Polar Unit, which is lined with ULTEM 9085.
The primary purpose of the Polar Unit is to export biological samples to the International Space Station, with the intention of long-term testing aboard the ISS. With three current Polar freezers on deck and a goal of 14 active units scheduled for the near future, maximizing space on board the ISS is critical to daily functions.
The freezer unit’s design is unique in that it required maximum interior space to carry samples, while fitting carefully within a small locker unit. The team at UAB CBSE was challenged with the unit’s interior liner. Their initial concept using flat machined pieces of Polyether ether ketone (PEEK) proved to be insufficient for their needs, due to the inability to achieve curvature design when using this material and method.
3D printing allows users to achieve complex geometries as seen in this left duct located on the Polar Freezer.
Thermoforming the PEEK was also rejected because of inaccurate tolerances, and varying levels of sheet thickness. Furthermore, thermoforming could not produce a composite design shell that allowed for additional electrical parts needed within the interior of the freezer. Additional jigs and fixtures would be necessary to join pieces, therefore compromising overall shell space. Harnessing the power of 3D printing allowed the team to seamlessly produce the organic, complex shell structure in one build, meeting all the requirements for the interior liner.
“At first, we continued the line of thinking similar to thermoforming, in which many pieces would be 3D printed and joined together. But after some research, we realized there were 3D printers with a large enough printing volume that the entire shell could be 3D printed as a single piece. This led us to where we are now. We had to go through learning about how to design for 3D printing and what types of geometry worked well, but it has been working great.”
The inner liner was produced with Fused Deposition Modeling (FDM) 3D printing technology on the Fortus 900mc 3D Production System by Stratasys in ULTEM 9085 material. Although traditional uses of ULTEM 9085 are often subjected to high temperature environments, the high-performance thermoplastic had passed the necessary testing under freezing conditions.
FST-compliant ULTEM 9085 was the ideal material chosen for the inner shell of the freezer unit, because of its superior tensile strength and high heat and chemical resistance.
ULTEM 9085 is an ideal material for aerospace applications, because of its high heat and chemical resistance. Additionally, the engineering-grade thermoplastic delivers superior tensile strength, making it optimal against rocket vibrations during launch. According to Sealy, the Polar unit will test the long-term effects of zero gravity on biological samples, including human blood, cells and urine. Three Polar units launched in February aboard the SpaceX CR-5 Falcon 9.
As a leader in additive manufacturing within Canada, Cimetrix Solutions continues to work with some of the nations' leaders in aerospace, helping incorporate 3D printing in the design and development process for a variety of applications. For additional information on the advantages of Fortus 3D Printing, and more, please visit us at www.cimetrixsolutions.com.
Original story by Stratasys Blog