A comparison of manufacturing constraints in 3D topologically optimized heat sinks for forced air cooling

In this paper, the manufacturability of 3D topologically optimized (TO) heat sinks for forced-air cooling is studied for both additive manufacturing and subtractive numerical control machining. To mitigate the manufacturing difficulties which are frequently encountered when fabricating TO designs, we adopt two approaches. First, a constraint on the projected undercut perimeter is added to the standard optimization formulation to limit the number and severity of costly non-self supporting features in additive manufacturing. Second, a multi-axis machining (MAM) constraint is adopted to serve as the basis for enforcing manufacturability in a TO design for an alternative, highly-popular manufacturing modality. Locally refined nonuniform unstructured meshing and unit-cell assembly techniques for increasing the mesh and design resolution were pursued during optimization. Post-analyses were conducted in OpenFOAM for all TO and corresponding parallel-fin designs. Simulation results showed that topologically optimized heat sinks offer a 35–40% advantage in temperature performance over conventional parallel fins. A limited or non-existent compromising of thermal-hydraulic performance was necessary to enforce manufacturability. Finally, to prove the practical efficacy of the overhang angle control constraint, the AM-constrained heat sinks designs were fabricated through direct metal laser sintering in both aluminum and stainless steel.