Abstract

Minimal surfaces minimize the total surface area subject to some boundary or volume constraint. Soap bubbles, catenoidal soap-film surfaces and gyroids on butterfly wings are some examples in nature. In the early seventies, mathematicians discover the mathematical expressions of minimal surfaces. These surfaces were not used in product design since we couldn’t generate these designs in CAD and we couldn’t manufacture them. Recent advances in CAD systems and additive manufacturing enable designers to design and manufacture these amazing designs. Minimal surfaces such a Gyroids, Schwarz, Lidinoid, Diamond, SplitP, Neovius have remarkable properties for strength, heat transfer and manufacturability. When a volume is infilled with a minimal surface is subdivided into separate continues volumes that are intermingled. This property makes minimal surface geometries ideal for heat exchangers. In addition, at any point the angle of these surfaces measured relative to normal to the print tray is smaller than the 45 degrees and therefor these geometries can be 3D printed without supports. In order to evaluate the performance and optimize these designs a conjugate heat transfer analysis must be performed. The challenge to the simulation process is that the minimal surface geometries are not the typical B-Rep geometry but they are generated by implicit or voxel-based modelers. This presentation will demonstrate the processes to overcome these challenges with an example of an avionics heat exchanger. The hot fluid is the transmission oil and the cold fluid is the jet fuel. The steps of conceptual design, the parametric geometry generation, the real time preliminary simulation, and the final CFD validation will be presented. In designing for additive manufacturing, a “manufacturing process simulation” needs to be performed in order to evaluate the residual stress levels, the surface accessibility and the distortion sensitivity. The manufacturing process simulation dictates design changes in order to reduce residual stress and distortion. The design modifications to improve manufacturability will also be presented. The digital thread from concept to design to simulation to additive manufacturing and to postprocessing, with subtractive manufacturing, will be demonstrated. The heat exchanger has been produced using additive manufacturing and is in the process to be qualified as an end-user component.