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A study on the accuracy of thermography-based temperature measurement in powder-fed directed energy deposition

: Kledwig, Christian; Hofer, Markus; Reisacher, Martin; Brückner, Frank; Bliedtner, Jens; Leyens, Christoph

Fulltext ()

Procedia CIRP 95 (2020), pp.35-41
ISSN: 2212-8271
Conference on Electro Physical and Chemical Machining <20, 2021, Online>
Journal Article, Conference Paper, Electronic Publication
Fraunhofer IWS ()
directed energy deposition; laser metal deposition; laser cladding; thermal imaging; temperature distribution; process monitoring

Due to continuous development and increasingly deep understanding of the additive process, directed-energy deposition (DED) is becoming more and more interesting for industrial use. However, both the number of influencing factors and the process complexity, still require well-trained operators who can monitor and understand the machine tools. In order to facilitate the operators and to enable longer unattended processes, higher process safety, reliable monitoring systems and closed-loop controller are required. For example, despite a large number of investigations, the monitoring and control of the temperature distribution within the work piece still poses a big challenge.
This study focusses on workpiece temperature measurement using a thermal imaging camera that observes the entire machining area. In order examine the measurement error caused by different viewing angles (φ = 0 … 75°), object temperatures (T = 333 … 1073K), surface conditions (welded and milled) and materials (316L, Inconel 718 and CuAl10) commonly used in DED, several approaches were followed using a thermal camera.
It was found that surface condition and material cause the greatest measuring errors (up to +325K |−453K).). However, the measuring errors can be significantly reduced by suitable selection of the emissivity, so that it is possible to measure even the milled CuAl10 surface at a known viewing angle with a measuring error of +13.3% |−10.9%.