• Blunt, Liam
• Racasan, Radu
• Bills, Paul
• Tawfik, Ahmed

Abstract

<p>Additive manufacturing (AM) is recognized as a core technology for producing high-value components. The production of complex and individually modified com-ponents, as well as prototypes, gives additive manufacturing a substantial advantage over conventional sub-tractive machining. For most industries, some of the current barriers to implementing AM include the lack of build repeatability and a deficit of quality assurance standards. The mechanical properties of the components depend critically on the density achieved. There-fore, defect/porosity analysis must be carried out to verify the components’ integrity and viability. In parts produced using AM, the detection of unfused powder using computed tomography is challenging because the detection relies on differences in density. This study presents an optimized methodology for differen-tiating between unfused powder and voids in additive manufactured components, using computed tomogra-phy. Detecting the unfused powder requires detecting the cavities between particles. Previous studies have found that the detection of unfused powder requires a voxel size that is as small as 4 µm³. For most applica-tions, scanning using a small voxel size is not reason-able because of the part size, long scan time, and data analysis. In this study, different voxel sizes are used to compare the time required for scanning, and the data analysis showing the impact of voxel size on the detection of micro defects. The powder used was Ti6Al4V, which has a grain size of 45–100 µm, and is typically employed by Arcam electron beam melting (EBM) machines. The artifact consisted of a 6 mm round bar with designed internal features ranging from 50 µm to 1400 µm and containing a mixture of voids and unfused powder. The diameter and depth of the defects were characterized using a focus variation micro-scope, after which they were scanned using a Nikon XTH225 industrial CT to measure the artifacts and characterize the internal features for defects/pores. To reduce the number of the process variables, the measurement parameters, such as filament current, accel-eration voltage, and X-ray filtering material and thick-ness were kept constant. The VGStudio MAX 3.0 (Vol-ume Graphics, Germany) software package was used for data processing, surface determination, and de-fects/porosity analysis. The main focus of this study is to explore the optimal methods for enhancing the detection of pores/defects while minimizing the time taken for scanning, data analysis, and determining the effects of noise on the analysis.</p>

Topics

• density
• impedance spectroscopy
• pore
• surface
• grain
• grain size
• tomography
• void
• porosity
• electron beam melting