A post-processing method to resolve print failure at resolution limits in additively manufactured microchannels

• Part failure from obstructions in DMLS AM microchannels characterized for AlSi10Mg and SS 316L. • CT scanning used to accurately detect obstructions and reveal internal morphology. • Chemical etching used to resolve channels with 400 µm diameter for SS 316 L and 600 µm diameter for AlSi10Mg. • Chemical flow etching technique demonstrated on failed AlSi10Mg sepentine channel of 850 µm diameter, fully clearing obstructions. • Effects of chemical flow etching on microchannel hydraulic performance measured. Additive Manufacturing is a promising technique to revitalize part design. Direct Metal Laser Sintering (DMLS) can produce solid metal parts from a powder, enabling enhanced design flexibility. Microchannel heat exchangers are a potential high value product in additive manufacturing which enable cooling of components with high energy dissipation. However, manufacturing of small features such as microchannels using DMLS comes with limitations such as large surface roughness relative to traditional manufacturing. The roughness can be generally categorized into two types: partially sintered powder and dross or sagging from unsupported surfaces. In addition to large surface roughness, DMLS has limits on the smallest internal features that can be produced. These limits are approximately 750 to 800 µm for simple self-supported features but can be as large as 1 mm for build orientations with unsupported features, high aspect ratios, and high part complexity. Such constraints limit the potential of AM to produce reliable parts. Here, we demonstrate that AM microchannel failure occurs on a stochastic spectrum, with smaller diameters and higher aspect ratios encountering increasing obstruction severity. We develop a flow etching technique to enable obstruction clearing without affecting exterior geometry. The clearing technique was demonstrated on a complex printed AlSi10Mg internal geometry with 850 µm nominal diameter. Using Computer Tomography scanning with image analysis, we show that AM microchannel obstructions have a particle matrix appearance. We use flow etching to reduce this roughness (and hydraulic pressure drop) of metal AM microchannels. We also show that the roughness has little effect on the bulk surface for the required etch time scales used to clear microchannels. Our work not only develops post processing methodologies to enable higher resolution printing of high aspect ratio channels, it identifies and characterizes fundamental mechanisms of print failure which can be used to develop future AM design guidelines.