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Project enabled validation of process-structure-property models for as-deposited material and complex parts
MWIR spectrometer and high-resolution thermal imager process monitoring data for melt pool thermal emission spectra and near-field temperature distribution, which was collected track-by-track and associated with scan path position.
Measurement of melt pool thermal emission spectra during Laser Powder Bed Fusion (LPBF) is highly challenging due to the small size of the melt pool, high-scan velocity, and complex scan path. The measurement is degraded or confounded by multiple transient physical phenomena (e.g., surface angle, melt pool orientation in the zig-zag scan path, laser plume), affecting the accuracy and reliability of melt pool temperature measurement. This temperature data offers valuable insight into additive manufacturing (AM) process stability, process health, and material and product quality. Attaining a successful method to measure the melt pool temperature, while compensating for the various transient phenomena, offers substantial benefit to the AM process, material, and validation of integrated computational materials engineering (ICME) models, as well as for product qualification and certification.
The objectives of this project were to demonstrate a method to measure the melt pool emission spectra routinely, accurately, and in near-real-time during LPBF processing of reactive metals (e.g., Ti-6Al-4V); compensate for transient phenomena that affected the accuracy of temperature measurement; collect measurement data track-by-track for all layers and associate with scan path position in near-real-time; and create a pathway for the utilization of melt pool thermal spectra to validate process parameter selection, process repeatability and consistency, and feedforward process control.
The technical approach for this project included, the fabrication of off-axis optical hardware and algorithms to track the laser position on the build platform and provide a dynamic field of view (FOV) for in-situ sensing for high-resolution, simultaneous, mid-wave Infrared (MWIR) data collection using the spectrometer and thermal imager.
This project successfully collected simultaneous, high-resolution, in-situ MWIR spectrometer and thermal imager data anywhere on the build platform and validated the accuracy of measurement of gray body temperature in-situ, as well as the ability to compensate for the surface angle, roughness, and oxidation.