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Design of a Microscale Selective Laser Sintering System

The NDML is developing a new microscale selective laser sintering system (μ-SLS) that uses micromirrors to achieve write speeds on the order of 300 mm/s. In conventional selective laser sintering processes a thin layer of plastic or metal powder is spread over a build platform and a laser is used to sinter together the powder particles in the desired locations. A new layer of powder is then spread over the original layer and the process is repeated to build up a three-dimensional structure. This process can be used to produce high quality parts but the minimum feature size of the SLS processes is typically on the order of a few hundred microns, which is about two orders-of-magnitude larger than the feature sizes required for building true cellular materials. This feature size is typically set by the spot size of the laser beam and the heat diffusion from the laser melt pool. In order to achieve a feature-size resolution of approximately 1 μm in the μ-SLS system, several innovative design features have been implemented. First, the μ-SLS uses ultra-fast nanosecond lasers in order to achieve precise control over the heat-affected zone of the μ-SLS powder bed. The laser is coupled to a fiber optic lens and then directed off a micro-mirror array through a 10x, long working distance objective lens. This allows each 10.8 μm by 10.8 μm pixel in the micromirror array to be focused down to a spot size of approximately 1 μm. Second, the μ-SLS replaces the microscale powders used in conventional SLS processes with a nanoparticle ink. The use of nanoparticles in the μ-SLS system is necessary because in order to build layers that are approximately 1 μm thick, it is necessary to use particles that are at least one order of magnitude smaller than the desired layer thickness. The use of the nanoparticle ink also helps to prevent agglomeration of the nanoparticles during the powder-spreading process. Finally, a one degree-of-freedom nanopositioning system with a resolution of better than 100 nm is integrated with a slot die coating system in order to precisely control the thickness of the powder layer that is spread during the build process. Therefore, through the use of (1) ultra-fast lasers, (2) a micromirror-based optical system, (3) nanoscale powders, and (4) a precision spreader mechanism, the μ-SLS system is capable of achieving build rates of approximately 1 cm3/hr while achieving a feature-size resolution of approximately 1 μm.