Improving process stability and ductility in laser sintered polyamide
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The desire to manufacture production parts using additive manufacturing has created an increased demand on the laser sintering technology to supply this need. A significant issue in laser sintered polymers is the variability of mechanical properties from build-to-build and the inability to determine the success or failure of the production process until the production builds are complete. Interlayer ductility of parts produced in the laser sintering process has been shown to be uncontrolled and unpredictable. This research focuses on improving interlayer ductility and establishing a baseline for modeling the time-temperature-transformation of production-grade, laser-sintered polymers. The background shows that there has been a significant amount of research to map processing parameters to mechanical properties and that industry has been focused on recording processing parameters and mechanical properties as part of the quality record. The research shows trends in mechanical performance that are not adequately explained with current analytical techniques. The experimental research characterized the thermal attributes of the laser sintering process using onboard sensors, production build data, external thermal cameras, and in-situ thermocouples to map the thermal profile of a complete laser sintering build. This information, used in conjunction with an array of over 80,000 production build tensile data points, provides the basis for a thermal model for laser sintered polymers. Current laser energy models in laser sintering are incomplete and do not consider many processing parameters available in the laser sintering process, focusing primarily on the build surface temperature and the laser energy applied to the part region. A more complete thermal model must also account for the energy exposure during the build. The thermal process model is developed to integrate the thermal history during the build and cooldown cycle as a metric of success. It will be shown that improved and more predictable ductility performance is achievable, and that a thermal process model can be used to characterize the energy input required over time to achieve optimal results. Ultimately, increased reliability in laser sintered polymer parts will increase their usage in commercial applications.