Novel approach for weld depth determination using optical coherence tomography measurement in laser deep penetration welding of aluminum and steel

Mittelstädt, Christoph; Mattulat, Thorsten; Seefeld, Thomas; Kogel‐Hollacher, Markus

doi:10.2351/1.5082263

Cited by 29 publications

(12 citation statements)

References 20 publications

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“…OCT is an optical, non-contact, non-destructive, high-speed imaging method; it uses low-coherence interferometry for the high-resolution measurement of transparent or semi-transparent samples. Due to substantial improvements in ruggedness and more compact design, OCT is very well suited to in-line monitoring in an industrial environment [ 29 ]. In flow instability detection, OCT offers advantages in terms of speed and sensitivity.…”

Section: Technologies For In Situ Detection Of Interfacial Flow Instabilitiesmentioning

confidence: 99%

In Situ Detection of Interfacial Flow Instabilities in Polymer Co-Extrusion Using Optical Coherence Tomography and Ultrasonic Techniques

et al. 2021

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Co-extrusion is a widely used processing technique for combining various polymers with different properties into a tailored multilayer product. Individual melt streams are combined in a die to form the desired shape. Under certain conditions, interfacial flow instabilities are observed; however, fundamental knowledge about their onset and about critical conditions in science and industry is scarce. Since reliable identification of interfacial co-extrusion flow instabilities is essential for successful operation, this work presents in situ measurement approaches using a novel co-extrusion demonstrator die, which is fed by two separate melt streams that form a well-controlled two-layer co-extrusion polymer melt flow. An interchangeable cover allows installation of an optical coherence tomography (OCT) sensor and of an ultrasonic (US) measurement system, where the former requires an optical window and the latter good direct coupling with the cover for assessment of the flow situation. The feasibility of both approaches was proven for a material combination that is typically found in multilayer packaging applications. Based on the measurement signals, various parameters are proposed for distinguishing reliably between stable and unstable flow conditions in both measurement systems. The approaches presented are well suited to monitoring for and systematically investigating co-extrusion flow instabilities and, thus, contribute to improving the fundamental knowledge about instability onset and critical conditions.

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Section: Technologies For In Situ Detection Of Interfacial Flow Instabilitiesmentioning

confidence: 99%

In Situ Detection of Interfacial Flow Instabilities in Polymer Co-Extrusion Using Optical Coherence Tomography and Ultrasonic Techniques

et al. 2021

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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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“…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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Novel approach for weld depth determination using optical coherence tomography measurement in laser deep penetration welding of aluminum and steel

Cited by 29 publications

References 20 publications

In Situ Detection of Interfacial Flow Instabilities in Polymer Co-Extrusion Using Optical Coherence Tomography and Ultrasonic Techniques

In Situ Detection of Interfacial Flow Instabilities in Polymer Co-Extrusion Using Optical Coherence Tomography and Ultrasonic Techniques

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

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

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