In situ measurement of part geometries in layer images from laser beam melting processes

Jacobsmühlen, Joschka zur; Achterhold, Jan; Kleszczynski, Stefan; Witt, Gerd; Merhof, Dorit

doi:10.1007/s40964-018-0068-9

Cited by 22 publications

(8 citation statements)

References 18 publications

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“…during optimization of scan strategy parameters. The same holds true for the applied Jaccard Index and the comparable Sørensen-Dice index [36,37] which were also used in other investigations to assess the performance of image segmentation algorithms [15,17].…”

Section: Data Comparisonmentioning

confidence: 79%

“…Due to the high contrast between molten area and powder bed, as well as the absence of disturbing reflections, the approach nonetheless returned excellent results. This highlights a huge advantage of ELO imaging over common light-optical imaging of the build surface where extensive efforts have to be made to develop robust algorithms for image segmentation [12,13,[15][16][17]. Nevertheless, in the future, more sophisticated adaptive thresholding algorithms might also be tested on ELO images to further enhance the quality of surface extraction.…”

Section: Data Comparisonmentioning

confidence: 99%

“…Large geometrical distortions were shown to be in good agreement with XCT measurements [16]. Zur Jacobsmühlen et al investigated an alternative algorithm which combined structured forests edge detection and graph cuts image segmentation [17]. He et al proposed an contour extraction method which uses phase shift information obtained from in-situ fringe projection measurement [18].…”

Section: Introductionmentioning

confidence: 99%

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Electron-optical in-situ metrology for electron beam powder bed fusion: calibration and validation

Arnold

Körner

2021

Meas. Sci. Technol.

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A major advantage of metal additive manufacturing is the possibility for tool-free production of complex shaped parts. Currently, the geometrical and dimensional accuracy of these parts can only be reliably controlled by time and cost intensive post-process inspection, e.g. using x-ray computed tomography (XCT). The current investigation demonstrates the first in-situ metrology technique for electron beam powder bed fusion (PBF-EB) using electron-optical imaging (ELO). After a calibration experiment, the approach was validated for a PBF-EB build job by comparing in-situ ELO imaging data to XCT data of an as-built part. The quantitative comparison showed a remarkable high agreement between both imaging techniques. It is demonstrated that ELO imaging is capable of making accurate predictions on the geometrical and dimensional accuracy of the as-build part. This result is the basis of new possibilities for in-situ process and quality control in PBF-EB.

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Section: Data Comparisonmentioning

confidence: 79%

Section: Data Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron-optical in-situ metrology for electron beam powder bed fusion: calibration and validation

Arnold

Körner

2021

Meas. Sci. Technol.

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“…Because of this, almost all laser PBF (L-PBF) system developers currently provide their machines with embedded powder bed cameras and, in some cases, with basic automated powder bed anomaly detection capability, albeit commonly limited to macroscopic errors [1,2]. Images acquired after the melting phase, once the solidification of the scanned area has occurred, may be used for different aims, such as detecting undesired surface irregularities in the solidified layers, as possible sources of internal and surface defects [6][7][8][9][10], or signaling possible deviations with respect to the nominal shape in the layer, as evidence of geometrical errors [11][12][13][14][15]. Alternative sensing methods have also been presented, including fringe projection combined with single or multiple cameras for surface topography reconstruction [16][17][18][19] and high-spatial-resolution scanning sensors installed onto the recoating arm [20,21].…”

Section: Introductionmentioning

confidence: 99%

In Situ Monitoring of Powder Bed Fusion Homogeneity in Electron Beam Melting

Grasso

2021

Materials

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Increasing attention has been devoted in recent years to in situ sensing and monitoring of the electron beam melting process, ranging from seminal methods based on infrared imaging to novel methods based on backscattered electron detection. However, the range of available in situ monitoring capabilities and solutions is still quite limited compared to the wide number of studies and industrial toolkits in laser-based additive manufacturing processes. Some methods that are already industrially available in laser powder bed fusion systems, such as in situ detection of recoating errors, have not yet been investigated and tested in electron beam melting. Motivated by the attempt to fill this gap, we present a novel in situ monitoring methodology that can be easily implemented in industrial electron beam melting machines. The method is aimed at identifying local inhomogeneity and irregularities in the powder bed by means of layerwise image acquisition and processing, with no external illumination source apart from the light emitted by the hot material underneath the currently recoated layer. The results show that the proposed approach is suitable to detect powder bed anomalies, while also highlighting the link between the severity of in situ detected errors and the severity of resulting defects in the additively manufactured part.

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“…Due to the complex interaction of surface structure and illumination conditions, a robust and reliable segmentation of the molten contours is a major challenge of this approach. Therefore, a large variety of advanced segmentation algorithms was developed and tested for different camera set-ups and illumination conditions [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. In PBF-EB, due to the high processing temperature and the associated incandescence of the build surface, imaging in the visible range is hardly applied.…”

Section: Introductionmentioning

confidence: 99%

Electron-Optical In Situ Imaging for the Assessment of Accuracy in Electron Beam Powder Bed Fusion

2021

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The current study evaluates the capabilities of electron-optical (ELO) in situ imaging with respect to monitoring and prediction of manufacturing precision in electron beam powder bed fusion. Post-process X-ray computed tomography of two different as-built parts is used to quantitatively evaluate the accuracy and limitations of ELO imaging. Additionally, a thermodynamic simulation is performed to improve the understanding of ELO data and to assess the feasibility of predicting dimensional accuracy numerically. It is demonstrated that ELO imaging captures the molten layers accurately (deviations <100 μm) and indicates the creation of surface roughness. However, some geometrical features of the as-built parts exhibit local inaccuracies associated with thermal stress-induced deformation (deviations up to 500 μm) which cannot be captured by ELO imaging. It is shown that the comparison between in situ and post-process data enables a quantification of these effects which might provide the possibility for developing effective countermeasures in the future.

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In situ measurement of part geometries in layer images from laser beam melting processes

Cited by 22 publications

References 18 publications

Electron-optical in-situ metrology for electron beam powder bed fusion: calibration and validation

Electron-optical in-situ metrology for electron beam powder bed fusion: calibration and validation

In Situ Monitoring of Powder Bed Fusion Homogeneity in Electron Beam Melting

Electron-Optical In Situ Imaging for the Assessment of Accuracy in Electron Beam Powder Bed Fusion

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