Abrasive Flow Machining of Additively Manufactured Titanium: Thin Walls and Internal Channels

Metal additive manufacturing using Laser-Powder Bed Fusion (L-PBF) technique has enabled the metal manufacturing industry to use design tools with increased flexibility such as freeform internal channel geometries that benefit thermofluidic applications such as heat exchangers. A primary drawback of the L-PBF process is the as-built surface roughness, which is a critical factor in such surface-fluidic applications. In addition, complex internal channel geometries cannot be post-processed through traditional finishing and polishing methods, and require advanced finishing processes such as Abrasive Flow Machining (AFM). In this original study, the effects of AM design including geometrical changes at the inlets, internal channel and wall thickness of thin features are experimentally studied on Ti64 L-PBF parts. A novel surface roughness inspection technique using micro-CT data is also presented. The internal channels with larger dimensions underwent 40% improvement in surface roughness with no statistically significant change in diameter whereas the channels with smaller dimensions and bends had a 38% improvement in surface roughness accompanied by a 6% increase in diameter. While there was as much as 30% improvement in surface roughness values, the thin walls less than 0.4 mm in dimension were deformed under the AFM pressure after just 5 cycles.