Prediction of powder bed thickness by spatter detection from coaxial optical images in selective laser melting of 316L stainless steel. (January 2022)

• Record Type: Journal Article
• Authors: Zhang, Weihao; Ma, Honglin; Zhang, Qi; Fan, Shuqian
• Is Part Of: Materials & design. Volume 213(2022)
• Publication Date: 2022-01
• Subjects: Additive manufacturing -- Selective laser melting -- Spatter -- Coaxial monitoring -- High-speed imaging -- Machine vision; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2021.110301
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: The hot spatters are captured by a coaxial enhanced optical imaging system with a high-speed camera. An effective image processing method is established that can estimate the quantity and trajectory of spatters . The calculated quantity of spatters is positively related to the local density of the powder. Abstract: The uniformity of a recoated powder layer affects the performance of parts manufactured by SLM directly, while it is related to the characteristics of spatters. The small spatter moves pretty fast, while the low optical transmittance in the spectrum of a hot spatter in the coaxial optical path of SLM equipment prevents clear imaging of this target with high contrast. In this study, a coaxial optical path with an enhanced optical transmittance is used for imaging the melt pool and its surrounding phenomena simultaneously. An experimental system was developed using a high-speed camera for coaxial observation of hot spatters in the SLM process. The problems of limited field of view and high measurement uncertainty of an off-axis process monitoring system are solved. For defocused and distorted spatter images, both a segmentation algorithm and an object detection method have been proposed and proved to be effective. It was found that the direction and strength of the local airflow field could be estimated via the curvature of the spatter trajectory. More importantly, the quantity of spatters detected is positively related to the amount of powder locally distributed on the baseplate, which is useful to estimate the powder bed thickness at this position.