Could Slower be better? Assessing Sintering Time, Temperature, and Area Tradeoffs in 3D Printing by Polymer Sintering

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3D printing (additive manufacturing) is enabling dramatic changes in design, manufacturing, and distribution. While this has created many new opportunities, the materials and the properties available with 3D printing are still much more limited than those available with traditional processes such as machining and injection molding. This award supports fundamental research to enable expansion of the range and functionality of materials used in 3D printing processes that form components by locally heating (sintering) a polymer powder (usually with a laser). As the range of available materials expands, the processes can be used more widely. The continued expansion of additive manufacturing through improved material properties, increased variety of materials, and reduced production costs, will help achieve the full benefits of additive manufacturing including low-cost customized products, faster development times, and more personalized medicine. Additive manufacturing via sintering of polymer powders has typically used a scanning laser to heat the materials quickly. The tightly focused laser creates large thermal gradients and short sintering times. Relatively few materials can densify reliably without degradation under these conditions. A single material (nylon 12) composes a large majority of all polymer-sintered components. However, a solution may be to use lower intensity light for longer time. Build rate may be maintained or improved by heating larger areas using large laser spot sizes or by sintering an entire layer with a single exposure. Longer processing times will require a transition from process characterization based on energy input to temperature history. The objective of this research is to understand the effects of sintering time, temperature, and area in polymer sintering. This will be done by modeling process outcomes based on processing temperature and time, rather than optical energy input--enabling application of viscous sintering theory to guide process development. Viscosity and sintering rates of test materials will be measured to calibrate sintering models while stiffness, strength, and viscosity measurements of heated materials will be used to identify the processing window which avoids degradation. A projection-sintering system will be developed to measure sintering outcomes (porosity, stiffness, and strength) with varying exposure time, temperature, and area. Models will be developed to identify combinations of processing time and temperature that achieve equivalent material properties. These models will be used to predict tradeoffs in material properties, build rate, and resolution between alternative machine architectures using point, line, and area-based heating methods. They will also accelerate selection and development of new polymer sintering materials.