Thermographic measurements of the commercial laser powder bed fusion process at NIST

Abstract

Measurement of the high-temperature melt pool region in the laser powder bed fusion (L-PBF) process is a primary focus of researchers to further understand the dynamic physics of the heating, melting, adhesion, and cooling which define this commercially popular additive manufacturing process. This paper will detail the design, execution, and results of high speed, high magnification in-situ thermographic measurements conducted at the National Institute of Standards and Technology (NIST) focusing on the melt pool region of a commercial L-PBF process. Multiple phenomena are observed including plasma plume and hot particle ejection from the melt region. The thermographic measurement process will be detailed with emphasis on the ‘measurability’ of observed phenomena and the sources of measurement uncertainty. Further discussion will relate these thermographic results to other efforts at NIST towards L-PBF process finite element simulation and development of in-situ sensing and control methodologies.

Metal additive-manufacturing process and residual stress modeling

“…Figure 19 shows a typical thermal history for powder bed processes as predicted by the micromodel. The cooling rate reaches 1.5 million degrees per second and is in agreement with thermographic images and temperature histories reported by Lane et al [81]. The cooling rate is much higher than those measured for the traditional manufacturing process.…”

Application of finite element, phase-field, and CALPHAD-based methods to additive manufacturing of Ni-based superalloys

“…To validate our FEA thermal model, we compared its surface temperature prediction against in situ thermographic measurements. Details of the thermographic measurement setup were published in [45], and data used for the single-track comparison given here are described in [51]. The same thermal camera settings used in [45,51] were used here: 40 µs integration time, and 1350 nm to 1600 nm spectral range.…”

“…As described in [45], thermographic imaging of laser scans on metal powder produces highly stochastic temperature fields with localized gradients due to the varying surface structure and emissivity, which inhibit true temperature measurement. In contrast, scans on flat plates of bulk metal result in smooth temperature gradients, and single-line scans create steady-state melt pools that simplify comparisons to FEA simulations.…”

Ultrafast X-ray imaging of laser–metal additive manufacturing processes

“…Various imaging methods have previously been used to study LPBF processes in situ (Everton et al, 2016). The majority of these studies have used high-speed visible-light (Matthews et al, 2016;Ly et al, 2017;Scipioni Bertoli et al, 2017;Trapp et al, 2017;Bidare et al, 2017Bidare et al, , 2018 or thermal imaging (Pavlov et al, 2010;Furumoto et al, 2013;Lane et al, 2016;Fox et al, 2017). High-speed visible-light imaging was used to study particle entrainment and denudation (Matthews et al, 2016), spatter formation (Ly et al, 2017), and laser-melt-pool interactions (Scipioni Bertoli et al, 2017).…”

“…High-speed visible-light Schlieren imaging was also used to study the metal-vapor jetting generated due to evaporation of the material underneath the laser beam (Bidare et al, 2017(Bidare et al, , 2018. Two-color pyrometry (Pavlov et al, 2010;Furumoto et al, 2013), in-line thermal imaging (Fox et al, 2017) and off-axis thermal imaging (Lane et al, 2016) have been used to monitor the melt-pool temperature during the build process. The melt-pool geometry has also been studied using in-line coherent imaging (Kanko et al, 2016).…”