Radiometric temperature measurement for metal additive manufacturing via temperature emissivity separation

IF 11.1 1区 工程技术 Q1 ENGINEERING, MANUFACTURING
Ryan W. Penny, A. John Hart
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Abstract

Emission of blackbody radiation from the meltpool and surrounding area in laser powder bed fusion (LPBF) makes this process visible to a range of optical monitoring instruments intended for online process and quality assessment. Yet, these instruments have not proven capable of reliably detecting the finest flaws that influence LPBF component mechanical performance, limiting their adoption. One hindrance lies in interpreting measurements of radiance as temperature, despite the physical link between these variables being readily understood as a combination of Planck’s Law and spectral emissivity. Uncertainty in spectral emissivity arises as it is nearly impossible to predict and can be a strong function of wavelength; in turn, this manifests uncertainty in estimated temperatures and thereby obscures the LPBF process dynamics that indicate component defects. This paper presents temperature emissivity separation (TES) as a method for accurate retrieval of optically-measured temperatures in LPBF. TES simultaneously calculates both temperature and spectral emissivity from spectrally-resolved radiance measurements and, as the latter term is effectively measured, more accurate process temperatures result. Using a bespoke imaging spectrometer integrated with an LPBF testbed to evaluate this approach, three basic TES algorithms are compared in a validation experiment that demonstrates retrieval of temperatures accurate to ±28 K over a 1000 K range. A second investigation proves industrial feasibility through fabrication of an LPBF test artifact. Temperature data are used to study the evolution of fusion process boundary conditions, including a decrease in cooling rate as layerwise printing proceeds. A provisional correlation of temperature fields to component porosity assessed by 3D computed tomography demonstrates in situ optical detection of micron-scale porous defects in LPBF.
基于温度发射率分离的金属增材制造辐射测温技术
激光粉末床熔融(LPBF)过程中熔池和周围区域黑体辐射的发射使得该过程对一系列用于在线过程和质量评估的光学监测仪器可见。然而,这些仪器尚未被证明能够可靠地检测影响LPBF组件机械性能的细微缺陷,这限制了它们的采用。尽管这些变量之间的物理联系很容易被理解为普朗克定律和光谱发射率的结合,但将辐射度的测量结果解释为温度是一个障碍。光谱发射率的不确定性出现,因为它几乎不可能预测,并且可能是波长的强函数;反过来,这显示了估计温度的不确定性,从而模糊了指示组件缺陷的LPBF过程动力学。本文提出了温度发射率分离(TES)作为一种精确反演LPBF光测温度的方法。TES同时计算温度和光谱发射率的光谱分辨辐射测量,并有效地测量后一项,更准确的过程温度结果。使用集成LPBF测试平台的定制成像光谱仪对该方法进行了评估,并在验证实验中比较了三种基本TES算法,验证了在1000 K范围内精确到±28 K的温度检索。第二次研究通过制造LPBF测试工件证明了工业可行性。温度数据用于研究融合过程边界条件的演变,包括随着分层印刷的进行冷却速率的降低。三维计算机断层扫描评估了温度场与组件孔隙度的临时相关性,证明了LPBF中微米级多孔缺陷的原位光学检测。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Additive manufacturing
Additive manufacturing Materials Science-General Materials Science
CiteScore
19.80
自引率
12.70%
发文量
648
审稿时长
35 days
期刊介绍: Additive Manufacturing stands as a peer-reviewed journal dedicated to delivering high-quality research papers and reviews in the field of additive manufacturing, serving both academia and industry leaders. The journal's objective is to recognize the innovative essence of additive manufacturing and its diverse applications, providing a comprehensive overview of current developments and future prospects. The transformative potential of additive manufacturing technologies in product design and manufacturing is poised to disrupt traditional approaches. In response to this paradigm shift, a distinctive and comprehensive publication outlet was essential. Additive Manufacturing fulfills this need, offering a platform for engineers, materials scientists, and practitioners across academia and various industries to document and share innovations in these evolving technologies.
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