OCT for Process Monitoring of Laser Transmission Welding

Schmitt, Robert; Ackermann, Philippe

doi:10.1002/latj.201600030

Cited by 10 publications

(3 citation statements)

References 5 publications

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“…In addition to pure process monitoring, data volumes for AI approaches can also be recorded in this way. Spot offset compensation can be useful not only in the topographical case discussed here, but also in the application of classical OCT, e.g., for process monitoring in laser transmission welding [34]. However, further research is needed on these points.…”

Section: Discussionmentioning

confidence: 99%

Dynamic, Adaptive Inline Process Monitoring for Laser Material Processing by Means of Low Coherence Interferometry

2021

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Surface laser structuring of electrical steel sheets can be used to manipulate their magnetic properties, such as energy losses and contribute to a more efficient use. This requires a technology such as low coherence interferometry, which makes it possible to be coupled directly into the existing beam path of the process laser and enables the possibility for an 100% inspection during the process. It opens the possibility of measuring directly in the machine, without removing the workpiece, as well as during the machining process. One of the biggest challenges in integrating an LCI measurement system into an existing machine is the need to use a different wavelength than the one for which the optical components were designed. This results in an offset between the measurement and processing spot. By integrating an additional scanning system exclusively for the measuring beam and developing a compensation model for the non-linear spot offset, this can be adaptively corrected by up to 98.9% so that the ablation point can be measured. The simulation model can also be easily applied to other systems with different components and at the same time allows further options for in-line quality assurance.

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Section: Discussionmentioning

confidence: 99%

Dynamic, Adaptive Inline Process Monitoring for Laser Material Processing by Means of Low Coherence Interferometry

2021

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“…Since the upper joining material is partially transparent, a highly reflective surface for welding metal sheets to plastic [23] and internal structures with high differences in the refractive index like glass fibres or gas bubbles can be recognized [24][25][26][27]. In transparent-absorbent laser transmission welding, OCT has already been used for measuring the seam width and for detecting gaps and internal pores [22,[28][29][30][31]. If there are no errors, the interface between a properly welded transparent and absorbent partner is usually represented by an absent OCT signal [31].…”

Section: Introductionmentioning

confidence: 99%

“…In transparent-absorbent laser transmission welding, OCT has already been used for measuring the seam width and for detecting gaps and internal pores [22,[28][29][30][31]. If there are no errors, the interface between a properly welded transparent and absorbent partner is usually represented by an absent OCT signal [31]. However, because the absorbing partner contains additives, changing the optical properties compared to the transparent one, the interface of properly welded partners can be detected using an OCT with sufficient dynamic range [29].…”

Section: Introductionmentioning

confidence: 99%

Optical Coherence Tomography for 3D Weld Seam Localization in Absorber-Free Laser Transmission Welding

et al. 2022

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Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To attain sufficient absorption of laser energy without absorbent additives, thulium fiber lasers, which emit in the polymers’ intrinsic absorption spectrum, are used. Focusing the laser beam with a high numerical aperture provides significant intensity gradients inside the workpiece and enables selective fusing of the internal joining zone without affecting the surface of the device. Because seam size and position are crucial, the high-quality requirements demand internal weld seam monitoring. In this work, we propose a novel method to determine weld seam location and size using optical coherence tomography. Changes in optical material properties because of melting and re-solidification during welding allow for weld seam differentiation from the injection-molded base material. Automatic processing of the optical coherence tomography data enables the identification and measurement of the weld seam geometry. The results from our technique are consistent with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimeter.

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