Estimation of melt pool size by complementary use of external illumination and process emission in coaxial monitoring of selective laser melting

Pacher, Matteo; Mazzoleni, Luca; Caprio, Leonardo; Demir, Ali Gökhan; Previtali, Barbara

doi:10.2351/1.5096117

Cited by 19 publications

(7 citation statements)

References 19 publications

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“…On the other hand, when observing directly the molten pool geometry through the use of a secondary illumination source, image processing is more complicated due to the presence of composite elements and grayscale values present in the image. Generally, the molten pool area may be identified by the localised values of black which are symptomatic of higher absorption of the illumination source [88]. Still, when the molten pool has a higher aspect ratio, this approach tends to be fallacious.…”

Section: Appendixmentioning

confidence: 99%

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

Caprio

Demir

Previtali

2020

Additive Manufacturing

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Section: Appendixmentioning

confidence: 99%

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

Caprio

Demir

Previtali

2020

Additive Manufacturing

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“…Ideally, the threshold level would be chosen such that the melt pool geometry is captured. However, this assignment is not as straightforward in practice [19]. In this work, thresholds α = {1, 100} are picked based on the empirical observations of the coaxial images, and their physical meaning is open for interpretation.…”

Section: Image Data Processingmentioning

confidence: 99%

An empirical model for feedforward control of laser powder bed fusion

Shkoruta¹,

Park²,

Mishra³

2022

Preprint

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Highlights• Laser scanning of narrow features in LPBF parts results in predictable changes in melt pool geometry as observed in coaxial melt pool images.• An empirical model of this geometry-related behavior, validated on different geometries, is presented.• A model-based feedforward controller is designed to correct for this behavior. The proposed controller reduces geometry-related deviations by a factor of two, as demonstrated experimentally.

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“…To correctly distinguish between solid heated zone and actual molten material, a proper threshold value needs to be chosen. Hard thresholding principle is defined as [29]:…”

Section: Image Analyses Algorithmmentioning

confidence: 99%

In-line monitoring of focus shift by kerf width detection with coaxial thermal imaging during laser cutting

Vasileska

Pacher²,

Previtali

2021

Int J Adv Manuf Technol

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Nowadays industrial laser cutting systems employ a fixed set of process parameters throughout the cut of the same workpiece, which results in a good compromise between maximum productivity and surface quality. The process parameters are commonly set by trial-and-error experiments carried out on different materials and thicknesses or less frequently by physical modelling. However, the final cut quality is not constant even though the process parameters are kept fixed due to degradation of the initial status of the laser cutting system. One of the common issues in the laser cutting process is the local heating of the optical components due to contamination and/or high powers commonly employed, which cause shifting of the focus position. This can worsen the cutting-edge quality, and even result with loss of cut. Therefore, the online measurement of the position of focus is a requirement for a consistent process. An empirical method used in the industrial practice for initially setting and successively examining and adjusting the focus position is to measure the kerf width of a straight-line cut performed with constant process parameters. This paper proposes an algorithm to monitor the kerf width and yield the estimated focus position in real-time during the cutting process. The kerf width is observed during the process with a coaxial camera module mounted on the laser head which monitors the thermal interaction between the laser beam and the material. An image processing algorithm was developed for extracting the kerf width from the acquired images, and the algorithm parameters were experimentally calibrated such that the extracted value of the kerf width matches with its physical measure. To understand the influence of the focus position on the cutting kerf, an experimental campaign was conducted and subsequently a regression model was fitted. The real-time monitoring and computation of the kerf width and its correlation to the focus position give the opportunity for a closed-loop control of the focus shift, that would eventually lead to a gain of process stability and repeatability.

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Estimation of melt pool size by complementary use of external illumination and process emission in coaxial monitoring of selective laser melting

Cited by 19 publications

References 19 publications

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

An empirical model for feedforward control of laser powder bed fusion

In-line monitoring of focus shift by kerf width detection with coaxial thermal imaging during laser cutting

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