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Control of the melt pool size is necessary to achieve more homogenous material properties in wire arc additive manufacturing (WAAM). The melt pool size can be measured by camera imaging or temperature field measurement. The paper aims to investigate the feasibility of using a high dynamic range two-colored pyrometric camera (Pyrocam) for melt pool size measurement in a gas metal arc welding-based WAAM process. A set of band-pass filters is identified using spectroscopy analysis to reduce the optical arc emission while the melt pool remains visible. The fusion line is identified in temperature field images, the melt pool size is measured by an automated algorithm, and the results are compared with high-speed camera images. A possible correlation between melt pool size and the grain size is examined.

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Laser powder bed fusion (LPBF) is a frequently used manufacturing process due to its advantages in lightweight construction, design possibilities and functionalization of geometry. However, the printed parts will often have to undergo time and cost expensive non-destructive testing by sophisticated methods like X-CT. Thus, there is a strong demand to identify suitable online process monitoring techniques that allow to reduce or substitute post-process NDT effort. The temperature field reacts sensitively to deviations during processing, thus online temperature monitoring is a promising approach. In the present work a spatially resolved temperature measurement, based on 2-channel-pyrometry, is used for process monitoring in LPBF. The camera system is coaxially integrated into the beam guidance of the LPBF system. The coaxial observation enables a lateral resolution better than 10 μm over the whole build-up area of 250 x 250 mm2. Single tracks were welded with different parameters and observed by the camera system to identify thermal indicators. Metallographic cross-sections of the tracks were compared with the melt pool width measured by the online observation system. The deviation was ca. 3 %. In addition, cubes of 10 mm by 10 mm by 10 mm are built up. The melt pool area is identified as useful indicator for the process behavior and for the first time the assessment of part density is demonstrated in LPBF during process by the help of a thermal monitoring system.

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