Statistical evaluation method to determine the laser welding depth by optical coherence tomography

Boley, Meiko; Fetzer, Florian; Weber, Rudolf; Graf, Thomas

doi:10.1016/j.optlaseng.2019.03.014

Cited by 41 publications

(18 citation statements)

References 14 publications

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“…One approach for an inline depth control of the laser welding process is optical coherence tomography (OCT), which is applied for many applications in macro laser welding already [1][2][3]. For micro laser welding, only few investigations have been carried out.…”

Section: Introductionmentioning

confidence: 99%

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

et al. 2021

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The transition of the powertrain from combustion to electric systems increases the demand for reliable copper connections. For such applications, laser welding has become a key technology. Due to the complexity of laser welding, especially at micro welding with small weld seam dimensions and short process times, reliable in-line process monitoring has proven to be difficult. By using a green laser with a wavelength of λ=515, the welding process of copper benefits from an increased absorption, resulting in a shallow and stable deep penetration welding process. This opens up new possibilities for the process monitoring. In this contribution, the monitoring of the capillary depth in micro copper welding, with welding depth of up to 1 , was performed coaxially using an optical coherence tomography (OCT) system. By comparing the measured capillary depth and the actual welding depth, a good correlation between two measured values could be shown independently of the investigated process parameters and stability. Measuring the capillary depth allows a direct determination of the present aspect ratio in the welding process. For deep penetration welding, aspect ratios as low as 0.35 could be shown. By using an additional scanning system to superimpose the welding motion with a spacial oscillating of the OCT beam perpendicular to the welding motion, multiple information about the process could be determined. Using this method, several process information can be measured simultaneously and is shown for the weld seam width exemplarily.

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Section: Introductionmentioning

confidence: 99%

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

et al. 2021

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“…Interferometric techniques (including RRI) offer illumination and detection from an instrument mounted at a single location and are hence more easily integrated into mounting structures. Optical coherence tomography (OCT), an interferometric technique conceptually similar to RRI, has been widely applied to welding research [14][15][16][17], although in these implementations the ability of OCT to image structure within turbid materials [10] such as human skin is not utilised as the light cannot penetrate the metal surface. OCT can in principle achieve 0.01 mm but typically has a working range of only a few millimetres (compared to up to 10 s of cm for RRI).…”

Section: Introductionmentioning

confidence: 99%

In-process range-resolved interferometric (RRI) 3D layer height measurements for wire + arc additive manufacturing (WAAM)

Hallam

Kissinger

Charrett

et al. 2022

Meas. Sci. Technol.

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In this work a range resolved interferometry (RRI) instrument for absolute distance measurements is integrated into a wire + arc additive manufacturing (WAAM) system to provide in-process monitoring of layer height, and prospects for volume and proﬁle monitoring are discussed. Interferometry as a coherent optical technique oﬀers a straightforward in-process measurement even in the harsh welding environment, as compared to non-coherent techniques based either on laser proﬁling or camera vision systems. RRI can be accomplished at signiﬁcantly lower cost, and with higher depth of ﬁeld (up to 10s of cm) than existing optical coherence tomography based weld monitoring. In this experiment titanium feedstock was used to create a 150mm long, 13.5mm high weld-wall comprised of 11 welded layers. The RRI in-process measurements are in very good agreement with both mid-process, on-machine micrometer measurements taken by hand after each weld, and post-process laser scanning measurements of the completed wall. The high depth of ﬁeld allows direct referencing of the layer height measurements to the build plate making the measurement independent of the motion system and build plate bending, considerably lowering uncertainties. This, together with the capability for cost-eﬀective in-process measurements in harsh environments, should make the proposed approach very interesting for routine use in WAAM systems.

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“…One solution to observe the weld penetration depth inline is optical coherence tomography (OCT). OCT is an interferometric measurement technology that enables the measurement of weld penetration depth coaxially to the processing laser in a fixed optic [5][6][7][8][9][10][11][12] or scanning optic [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

“…The process noise can be caused by changes in the optical path by the vapor plume in the welding process and thermal noise [16]. To date, this issue was treated with data analysis methods such as histogram analysis [9,17], different filtering (e.g., percentile filter [9,10], Kalman filtering [14]), or kernel density estimation (KDE) [1,7]. The simplest method is the evaluation of histograms at every measurement point [17] and the extraction of the local maximum [9].…”

Section: Introductionmentioning

confidence: 99%

Algorithms for Weld Depth Measurement in Laser Welding of Copper with Scanning Optical Coherence Tomography

Will

Garcia²,

Hoelbling³

et al. 2022

Micromachines

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In-process monitoring of weld penetration depth is possible with optical coherence tomography (OCT). The weld depth can be identified with OCT by statistical signal processing of the raw OCT signal and keyhole mapping. This approach is only applicable to stable welding processes and requires a time-consuming keyhole mapping to identify the optimal placement of a singular OCT measuring beam. In this work, we use an OCT measurement line for the identification of the weld depth. This approach shows the advantage that the calibration effort can be reduced as the measurement line requires only calibration in one dimension. As current literature focuses on weld depth measurement with a singular measurement point in the keyhole, no optimal algorithm exists for weld depth measurement with an OCT measurement line. We developed seven different weld depth processing pipelines and tested these algorithms under different weld conditions, such as stable deep penetration welding, unstable deep penetration welding, and heat conduction welding. We analyzed the accuracy of the weld depth processing algorithms by comparing the measured weld depth with metallographic weld depths. The intensity accumulation approach is identified as the most accurate algorithm for successful weld depth measurement with a scanning OCT measurement line.

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Statistical evaluation method to determine the laser welding depth by optical coherence tomography

Cited by 41 publications

References 14 publications

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

In-process range-resolved interferometric (RRI) 3D layer height measurements for wire + arc additive manufacturing (WAAM)

Algorithms for Weld Depth Measurement in Laser Welding of Copper with Scanning Optical Coherence Tomography

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