42 Focus | Additive manufacturing includingmicroporous and tiny hollow structures, the smallest of which was 40 µm in size. Themetal patterns on these parts were very specific, and could be precisely controlled to produce 3D circuit boards and sensors with complex metal topologies. This approach also needed a new type of 3D printer. It uses a 5.5 in, 405 nm70Wultraviolet parallel light source with a light intensity of 85MW/cm2 and a light uniformity of 98%. During the printing process, different slice thicknesses and single-layer exposure times are used. Photopolymer AM Another additive technique is photopolymer AM (PAM). This uses digital light processing (DLP) with two lasers at different frequencies to cure photosensitive materials and curb the associated over-curing. That enables components to be fabricated with higher resolution and greater precision than existing PAM technologies. Rather than using a single laser, this DLP2Curb process uses the first laser to cure the photopolymer, while the second prevents the material from overexpanding into the surrounding area. This can increase both the accuracy and the resolution in three dimensions, and allows faster printing. The technique is still being developed, with testing of how the process works and how different materials behave under different conditions. This will involve creating a digital twin that will simulate how tweaks made to the process or material will change the outcome. In the second part of the development, interferometric and ultrasonic monitoring systems will analyse the materials in real time to characterise PAM, providing data for AI to optimise and enhance the printing process. Using a singlewavelength to cure polymers while printing is already complex. Adding a second escalates that complexity, but theML can enhance the accuracy. Conventional ML calculations take time and aren’t fast enough for real-time control yet, but the digital twinwill providemore data to speed up the AI algorithms. ML is also being used for real-time detection of keyhole pores that occur in a common AM technique called laser powder bed fusion (LPBF). LPBF usesmetal powder and lasers to 3D-print metal parts, but porous defects remain a challenge, and they can come fromdeep and narrow depressions which are the keyholes. The formation and size of a keyhole is a function of laser power and scanning speed, as well as thematerials’ capacity to absorb the laser energy. If the keyhole’s walls are stable, it enhances the surroundingmaterial’s laser absorption and improves manufacturing efficiency. If, however, the walls are wobbly or collapse, the material solidifies around the keyhole, trapping the air pocket inside the new layer. That makes the material more brittle and more likely to crack under environmental stress. A combination of synchrotron X-ray imaging, near-infrared imaging June/July 2023 | Uncrewed Systems Technology This self-healing laminate is created by 3D-printing a pattern of thermoplastic healing agent onto the reinforcement material and embedding thin ‘heater’ layers in the composite (Courtesy of North Carolina State University) Researchers are developing alloys that are optimised for use with ceramics to 3D-print components for hypersonic flight (Courtesy of University of Arizona)
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