By Mark Norfolk on Tuesday, February 16th, 2016
Fabrisoinc has been 3D printing aluminum and copper heat exchangers for years. Because UAM is a hybrid process, all of the flow paths printed into our parts are CNC milled allowing for high accuracy and great surface finish. Recently we finished up a large program for NASA that sought to improve the state of the art with embedded channels.
In our last post, we described how the primary concern when using UAM to build heat exchangers is unsupported material. The UAM process uses several thousand Newtons of force in order to create a bond. For structures such as channel ceilings, no normal force exists to push back and enable bonding. Directly above the cavity the lack of support can cause welding discontinuities. We have recently been experimenting with many techniques to reduce or eliminate the welding discontinuities over channels.
One method that has merit for large unsupported geometry is the use of an insert panel. Intuitively the main driver of discontinuities in unsupported regions is the fact that a single UAM layer (.006”-.010”) does not have sufficient strength to support full UAM loads without deforming. How can we modify the ceiling so that it does have sufficient load carrying capacity? One possible answer is a custom fit insert. The custom insert could be designed such that it can support the applied load with minimal deflection. This method inherently leaves an unbonded zone, as UAM cannot weld thick components. However, layers directly above the insert weld with one hundred percent density. Although this method is not great for highly complex winding channels, it works great for large unsupported areas.