Abstract
Additive manufacturing (AM) allows for the fabrication of complex metallic specimens which are otherwise very difficult or impossible to create using traditional manufacturing methods. For multi-phase heat spreaders such as vapor chambers, complex internal geometry lends itself well to AM as new design features can be realized. The internal geometries of vapor chambers frequently involve several thin pillars, which act as wicking structures and support a small internal cavity in which the phase change of a liquid, usually water, provides a means to effectively ‘spread’ a high heat flux throughout a larger area. In this case study, Laser Powder Bed Fusion (L-PBF) AM was utilized to create a series of aluminum alloy (AlSi10Mg) support pillars of fixed height with varying filet angles and build orientations (0°, 10°, 20°, 30°, 40°, 50° and 60° from the normal surface) to determine effects on surface roughness and resolution. Surface-to-water contact angles were measured on rinsed, un-polished surfaces, and microscopy was employed to obtain images demonstrating surface roughness profiles. This was done on both heated and unheated surfaces. Results clearly demonstrate that the surface roughness of upward and downward-facing surfaces during L-PBF depends on build orientation. The observational findings of this experiment showed that the surface roughness on surfaces representing horizontally oriented faces decreased as the printing orientation increased. This indicates that one must be cognizant of printing orientation for the L-PBF of capillary structures. A change in surface roughness as a result of printing orientation effects the heat transfer within an enclosed space due to a change in contact angles between the liquid and the heated surface. The results of this study will aid in future design considerations of heat pipes for their additive manufacture via current L-PBF technology.
