Additive Manufacturing is Measuring Up in Buffalo
Additive manufacturing (AM) is more than one single technology. Rather, it is comprised of multiple complementary technologies that provide manufacturers with an array of choices regarding surface finish, component size, efficiency, and overall quality. Each technology has unique requirements regarding, design, materials, processing, and finishing. The quality of built components is dependent on a variety of factors, many of which can be characterized through available measurement technologies. In Buffalo, EWI’s investment in precision measurement technologies supports the entire AM process chain, from powder characterization of new materials to metrology and surface characterization for final inspection.
Many metal AM processes utilize powders of various sizes in either a powder-bed or powder-delivered approach. The size, size distribution, shape, and chemical composition of these powders largely determine final part quality. To quantify these powder characteristics, EWI employs multiple measurement and testing technologies.
The Beckman Coulter LS 13 320 MW, a laser diffraction particle size analyzer, uses polarization intensity differential scattering to characterize the powder size and distribution in a sample. This system can rapidly analyze a range of particle sizes from 0.017µm to 2000µm in under two minutes.
Scanning Electron Microscopy
EWI’s Hitachi S-3700 Scanning Electron Microscope (SEM) is equipped with a large chamber with variable pressure to image and analyze conductive as well as non-conductive materials. This system can accommodate samples up to 12 inches wide and 4 inches high. Energy-dispersive x-ray (EDX) spectroscopy and electron backscatter diffraction (EBSD) analysis allow elemental and quantitative microstructural analysis. Figure 1 shows the results from several powder analyses, illustrating various sizes, shapes, and defects.
EWI continues to evaluate powder characterization technologies and will be investing in a gas pycnometer, a hall flowmeter, and powder analyzers to characterize powder flow rate, flowability, agglomeration, and caking.
Metrology and Surface Characterization
Surface areal topography is an emerging non-contact form of metrology capable of simultaneously measuring the roughness and form of a surface. These 3D topographies are particularly useful to optimize the form and roughness of 3D-printed parts, perform in-line inspection for in-situ process optimization, characterize tool wear, provide forensic evaluation for failure analyses, and validate sealing surfaces. Several techniques are available to make these measurements, each with its own strengths and weaknesses.
Using the Wave Nature of Light
Both the Bruker Coherence Scanning Interferometry System and the Novacam Fiber-based Coherence Scanning Interferometer use the wave nature of light to measure surface topography. As light travels towards and reflects off a surface, it acquires a phase corresponding to the distance the light has traveled. By using interference to measure this phase, precise height measurements can be achieved. The Bruker system uses this method to achieve an impressive 1 nm z-resolution and can measure a 2 mm x 2 mm area in 10 seconds. The Novacam system uses this technique to measure single data points at 30 kHz at a lower z-resolution of 200 nm. It can also use an optical fiber to measure hard-to-reach areas.
The Alicona focus-variation-based system offers another method to precisely measure height. This optical system scans through the focal range while simultaneously monitoring which features are in focus. Using this method, the height of each feature can be calculated. This scanning mechanism offers a faster method of measuring area than the Bruker and can measure rougher surfaces, but is less precise. Figure 2 illustrates the surface topography of a part built with EWI’s EOS laser powder bed system. The top surface of this part is roughly 22 mm x 46 mm. Both form and roughness are visible in this 3D representation of the topographic image.
Each measurement system has strengths, weaknesses, and ideal applications. We work with customers to identify optimal measurement solutions for their specific applications and are continuing to grow our metrology capability and expertise. For example, EWI recently purchased two computed tomography (CT) systems from Nikon to complement our existing capabilities and provide the ability to scan external features, as well as internal features, structures, and defects. This capability is particularly useful for AM applications that utilize internal design features for conformal cooling and light-weighting. CT can also be used as a quality inspection tool for final verification of AM components.
About the Authors
Alex Kitt is a member of the EWI flexible manufacturing team at Buffalo Manufacturing Works in Western New York. His specialty is automation, including discrete event simulations, robotic simulation, robot programming, control, and human-collaborative robotics. Alex has additional expertise in nondestructive examination and inspection using optical techniques, and contributes to several focus areas at our Buffalo facility including machining/finishing and materials/testing.
Kenny Kort is a Project Engineer in EWI’s AM and materials testing and characterization (MTC) groups. Based at EWI’s Buffalo Manufacturing Works facility, he is responsible for the operation of the Arcam A2X electron beam melting (EBM) 3D printer, ExOne Innovent binder jetting 3D printer, Beckman Coulter LS 13 320 MW particle analyzer, and Hitachi S-3700N ultra large chamber variable pressure scanning electron microscope.