Characterization of channels made by laser powder bed fusion and binder jetting using X-ray CT and image analysis

Abstract

Metal additive manufacturing is highly suited to enhance the performance of engineering applications with sophisticated internal features and passageways. Laser Powder Bed Fusion (LPBF) is commonly used or considered for fabrication in these applications, although the resulting channels can show significant form and surface deviations, particularly due to dross-formation at overhang-areas. Binder Jetting (BJ), another additive manufacturing method that can process metals does not employ a heat source to fuse powder particles during build-up and therefore has the potential to overcome these limitations. In this study, additively manufactured circular channels with a nominal diameter of two millimeters are made by LPBF and BJ in seven different directions and are extensively analyzed depending on their orientation. The test-artifacts are made by four different state-of-the-art LPBF and BJ system manufacturers with standard parameters in 17−4PH stainless steel and with similar layer thicknesses. A novel type of X-ray Computed Tomography (CT) image analysis method for additively manufactured channels is applied in combination with commercial image analysis software. Form deviations and surface texture are characterized in accordance with ISO1101 and ISO 4287:1997. Results show a high level of precision, independently of build direction for channels made by BJ when compared to LPBF. The accuracy of BJ-channels is strongly dependent on the appropriate scaling before printing. Parallel to the build direction, LPBF-channels exhibit superior characteristics. The channels investigated in this work are categorized into ISO tolerance grades IT13−17 for LPBF and IT13−15 for BJ following ISO268−2. Based on the findings, design considerations and characteristic attributes of each process to manufacture channels are discussed within a broader context.