{"title":"Radiometric temperature measurement for metal additive manufacturing via temperature emissivity separation","authors":"Ryan W. Penny, A. John Hart","doi":"10.1016/j.addma.2025.104904","DOIUrl":null,"url":null,"abstract":"<div><div>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 <span><math><mrow><mo>±</mo><mn>28</mn></mrow></math></span> 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.</div></div>","PeriodicalId":7172,"journal":{"name":"Additive manufacturing","volume":"110 ","pages":"Article 104904"},"PeriodicalIF":11.1000,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Additive manufacturing","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2214860425002684","RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, MANUFACTURING","Score":null,"Total":0}
引用次数: 0
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 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.
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.