Challenges in Inspecting Internal Features for SLM Additive Manufactured Build Artifacts

Additive manufacturing (AM) is a process where the component is built layer by layer using powder or wire precursors. AM is a new and developing technology offering advantages over conventional subtractive machining in terms of design optimization and weight reduction and enabling the creation of complex internal and external features that are impossible to achieve with conventional subtractive machining. AM technologies continue to be the subject of rapid development and, consequently, the geometrical repeatability and mechanical properties of AM parts are still the subject of research. X-ray computed tomography (XCT) is a nondestructive inspection method that can be utilized in characterizing and measuring the internal defects/features of metallic AM components and is becoming the go-to tool for AM metrology. This paper presents several challenges associated with the inspection of the internal features and defects. The parts utilized in the present study were a 10-mm aluminum (AlSi10Mg) AM artifact/sample manufactured using a Renishaw AM250 (Renishaw, UK) selective laser melting (SLM) AM system. The sample contains several “designed-in” internal features, varying in size from 50 µm to 1 mm, and located between 50 µm and 5 mm from the outer surfaces of the component. The features were designed as geometric features (spheres, cylinders, prisms, and helical prisms). A Nikon XTH 225 (Nikon Tring, UK) industrial XCT was used to analyze the internal features' location, form, and volume. The results from the XCT were compared to the prebuild slicing software to attempt to identify the cause of the variation from design. The sample was then physically sectioned to confirm the actual variation of the features from the design intent. After sectioning, the defects were characterized/verified using an Alicona G4 (Alicona, Graz) focus variation instrument. Data processing, surface determination processes, and defect analysis were carried out using VG Studio Max 3.1 (Volume Graphics, Heidelberg). The focus of this study is on identifying the limitations in designing, building, and characterizing micro internal features in AM SLM components.