Investigation of the roughness variation along the length of LPBF manufactured straight channels

Conformal cooling channels, made by the laser powder bed fusion process, are a promising design strategy for optimising cooling and process control of manufacturing tools and injections moulds. The addition of internal features such as corrugations and ribs are becoming an interesting addition to the cooling channel designs. Internal surfaces of laser powder bed fusion components have an inherent process-induced roughness. The roughness may affect the flow in the channels and may affect the addition of internal features by changing the actual geometry of the channels. This work seeks to characterise the variation of the internal surface roughness along the length of seven straight channels, manufactured using the laser powder bed fusion process, by utilising X-ray CT and image analysis. The characterisation showed that the surface roughness varied discontinuously along the length of the channels and that the roughness magnitudes and roughness variations along the channel lengths were dependent on the orientation of the channels with respect to the build direction. Therefore, the actual geometries of multiple, nominally equal, embedded internal features would vary differently from nominal design, dependent on the location of the feature along the channel length and orientation in the channel.