Impact of Additive Manufacturing on Internal Cooling Channels With Varying Diameters and Build Directions

Abstract

The use of additive manufacturing (AM) processes, such as direct metal laser sintering, provides the design freedom required to incorporate complex cooling schemes in gas turbine components. Additively manufactured turbine components have a range of cooling feature sizes and, because of the inherent three-dimensionality, a wide range of build angles. Previous studies have shown that AM build directions influence internal channel surface roughness that, in turn, augment heat transfer and pressure loss. This study investigates the impact of additive manufacturing on channel feature size and build direction relative to tolerance, surface roughness, pressure losses, and convective cooling. Multiple AM coupons were built from Inconel 718 consisting of channels with different diameters and a variety of build directions. An experimental rig was used to measure pressure drop to calculate friction factor and was used to impose a constant surface temperature boundary condition to collect Nusselt number over a range of Reynolds numbers. Significant variations in surface roughness and geometric deviations from the design intent were observed for distinct build directions and channel sizes. These differences led to notable impacts in friction factor and Nusselt number augmentations, which were a strong function of build angle.

Variability in additively manufactured turbine cooling features

“…Gradl et al (2021) extensively reported on the part-to-part variation of different geometries including thin walls, holes, hollow and protruding cylinders. Relative geometric error decreased with increasing feature size, which is similar to results for circular channels from Wildgoose et al (2021). Regardless of the part geometry, all components from Gradl et al (2021) contained deviations from their design intent.…”

“…Similar to the film-cooling hole, the angle at which the channel is relative to the build plate impacts the resulting tolerances and geometry. Snyder et al (2015), Mingear et al (et al2019), Wildgoose et al (2021), Kamat and Pei (2019), and Kasperovich et al (2021) showed that cooling channels built perpendicular to the build plate result in the lowest surface roughness and deviation from design intent. Wildgoose et al (2021) showed that for a circular channel fabricated at different build directions, the standard deviation in hydraulic diameter increases 166% when going from a channel built perpendicular to parallel with the build plate.…”

“…Snyder et al (2015), Mingear et al (et al2019), Wildgoose et al (2021), Kamat and Pei (2019), and Kasperovich et al (2021) showed that cooling channels built perpendicular to the build plate result in the lowest surface roughness and deviation from design intent. Wildgoose et al (2021) showed that for a circular channel fabricated at different build directions, the standard deviation in hydraulic diameter increases 166% when going from a channel built perpendicular to parallel with the build plate. Kasperovich et al (2021) accounted for these differences due to build direction by altering the geometry as well as laser scan parameters to produce favorable tolerances for a range of build directions.…”

“…Build direction has been reported by many to be a dominating effect on part quality due to additional material being sintered for surfaces that are downward facing (Ventola et al, 2014). For circular cooling channels, Wildgoose et al (2021) showed that the standard deviation in hydraulic diameter increased by more than 50% when orientating a vertically built channel relative to the horizontal orientation. Similarly, Snyder et al (2015) showed that the circularity, internal surface roughness, and concentricity of a circular channel also changes as a function of build direction.…”

Optimized Inconel 718 pressure vessel manufactured with laser powder bed fusion

“…Product design optimization methods including lattice, topology and variable thickness can be digitally generated and fine-tuned based on design for additive manufacturing (DfAM) rules to suit specific AM subcategory prior physical commitments. Different studies have investigated how optimized structures including honeycombs, lattice, variable thickness, build plan, process parameters (mainly from material deposition, beam shapes or spots) influence functional properties, energy intensities and related costs of high-performance metals [7][8][9][10][11][12][13].…”