Absorbance determination of a powder bed by high resolution coaxial multispectral imaging in laser powder bed fusion

[Display omitted] •Coaxial images at PBF-LB resolving a 114 mm × 114 mm powder bed at 5.12 μm/pixel.•Performed in-situ particle detection down to Ø = 20 µm.•Implementation of a method and setup to correct coaxial images for 6 wavelengths.•Absorbance determination of powders using coaxial multispectral imaging in PBF-LB/M.•20 different absorbance spectra and measurements of PBF-LB powders are presented. This study presents an approach for in-situ monitoring of laser powder bed fusion. Using standard laser optics, coaxial high-resolution multispectral images of powder beds are acquired in a pre-objective scanning configuration. A continuous overview image of the entire 114 × 114 mm powder bed can be generated, detecting objects down to 20 µm in diameter with a maximum offset of 22–49 µm. Multispectral information is obtained by capturing images at 6 different wavelengths from 405 nm to 850 nm. This allows in-line determination of the absorbance of the powder bed with a maximum deviation of 2.5% compared to the absorbance spectra of established methods. For the qualification of this method, ray tracing simulations on powder surfaces and tests with 20 different powders have been carried out. These included different particle sizes, aged and oxidized powders.