Roughness Investigation of SLM Manufactured Conformal Cooling Channels Using X-ray Computed Tomography

Abstract

Conformal cooling channels are becoming one of the next big steps in the fabrication of moulds and tools. Mass flow rate and heat transfer are affected by the surface roughness in the cooling channels. The freeform shape of conformal cooling channels makes it difficult to evaluate the internal roughness with respect to classic planar techniques. This work presents a fitted-ellipse method to evaluate internal surface features of helical cooling channels. The investigated cooling channel was made from maraging steel 300 and manufactured with the selective laser melting process. X-ray computed tomography and image analysis were utilized in order to generate a freeform nominal surface by fitting ellipses to the reconstructed surface. The nominal surface was compared to the reconstructed surface and resulted in a point cloud of deviation values. The deviation values were used as input for deviation plots, inner area and volume estimations together with estimations of classic area surface parameters, according to ISO 25178-2:2012. Results showed that the internal surface features were highly orientation dependent, with extreme roughness observed on the downward facing surface of the cooling channel. The arithmetical mean height and average maximum height of the total inner surface were estimated at Sa = 13.7 μm and Sz20 = 251 μm, respectively. The mass distribution was positively skewed, the root mean square height was Sq = 21.8 μm and the peaks observed on the surface were characterized as spiked. The obtained results suggested that the proposed method could evaluate the internal features of a helical cooling channel efficiently and qualitatively, while giving realistic quantitative estimations of the surface roughness characteristics.

Characterization of 3D metal printed cutting tool with transpiration cooling channels

“…This is because the angle at which the channels are built in the middle regions is very steep (>45°), resulting in overhangs and step effects. This dimensional deviation occurring due to the build angle is confirmed by [21][22][23][24]31]. This trend in the dimensional deviation of channels 7, 8 and 9 follows the same pattern as in Design 1-B, which is similar in free-form.…”

“…Channels 1, 2, and 3 made a steeper angle (>45°) to the build platform (z axis) than the other channels, whose angles are 30°−50°. This dimensional deviation occurring due to the build angle is confirmed by [21][22][23][24]31]. All the channels till the top are circular in profile, which complies with the intended design.…”

“…The first row of channels made a steeper angle (>45°) than the other channels with angles of 30°−50°. This dimensional deviation occurring due to the build angle is confirmed by [21][22][23][24]31]. The dimensional deviation in the built channel is mainly due to the adhesion of unsintered powder particles at the profile edges, decreasing the diameter and the step effect caused due to steeper angles causing overhangs.…”

“…Significantly the same channels are affected even at the top position, with the dimensions achieved being 360 μm (deviation −28%), 376 μm (deviation −25.6%) and 312 μm (deviation −37.6%). This deviation is mainly due to the angle at which it is printed, and the trend it follows is confirmed by [21][22][23][24]31]. The free-form path's angle is severe (>45°) for channels 7, 8 and 9.…”

“…XRμCT scanning revealed 90°channels had the least deviation from the design, while deviation increased as build orientation angle decreased. XRμCT scans are conducted on AISI-1.2709 conformal cooling channels [24] produced through LS technique which melted the material on the build surface. Results revealed XRμCT's usefulness in measuring freeform-shaped internal micro channels.…”