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High-temperature calibration methods in additive manufacturing involve the use of advanced techniques to accurately measure and control the temperature of the build material during the additive manufacturing process. Infrared cameras, blackbody radiation sources and non-linear optimization algorithms are used to correlate the temperature of the material with its emitted thermal radiation. This is essential for ensuring the quality and repeatability of the final product. This paper presents the calibration procedure of an imaging system for in-situ measurement of absolute temperatures and temperature gradients during powder bed fusion of metal with laser beam (PBF-LB/M) in the temperature range of 500 K–1500 K. It describes the design of the optical setup to meet specific requirements in this application area as well as the procedure for accounting the various factors influencing the temperature measurement. These include camera-specific effects such as varying spectral sensitivities of the individual pixels of the sensor as well as influences of the exposure time and the exposed sensor area. Furthermore, influences caused by the complex optical path, such as inhomogeneous transmission properties of the galvanometer scanner as well as angle-dependent transmission properties of the f-theta lens were considered. A two-step fitting algorithm based on Planck's law of radiation was applied to best represent the correlation. With the presented procedure the calibrated thermography system provides the ability to measure absolute temperatures under real process conditions with high accuracy.
thermal diffusivity measurements by the laser flash method in the temperature range
from 23 °C to 3000 °C. The main objective was to assess the variability and coherency
of thermal diffusivity measurements performed at ultra-high temperatures at
the European level. Three refractory materials (molybdenum, tungsten and isotropic
graphite IG210) were selected for this inter-laboratory comparison, due to their high
melting point. The disk-shaped specimens needed were machined from the same
blocks of materials in order to reduce any potential scattering of results between
participants due to inhomogeneity effects.
The homogeneity of the sets of specimens was studied by the pilot laboratory (LNE)
before launching the comparison process. Thermal diffusivity measurements were
then carried out by the seven participants on the three materials during two successive
thermal cycles up to the maximum temperatures that can be reached by the
devices used. The analysis of results showed a good agreement between the participants
for temperatures above 400 °C, with relative deviations within the uncertainties
of measurement and lower than ± 4 % for molybdenum, ± 5 % for isotropic
graphite and ± 9 % for tungsten.
HIMERT: A pan-European project for development of metal-carbon eutectics as temperature standards
(2002)
A concerted international project to establish hig-temperature fixed-points for primary thermometry
(2007)