Abstract
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.
Highlights
Numerous medical and optical devices are made of transparent polymers
In contrast to conventional transparent-absorbent welding, where one partner contains a laser absorbent additive [2,4,5], or an additional absorbing material is placed in the joining zone [6–9], the samples analyzed in this work are made of identical polymers and were joined directly using absorber-free laser transmission welding [10–16]
We showed that optical coherence tomography can be successfully used for threedimensional weld seam localization in absorber-free laser transmission welding of polyamide
Summary
Numerous medical and optical devices are made of transparent polymers. The manufacturing of these devices often takes place in cleanrooms and places high demands on cleanliness, precision, visual appearance, and reliability. Absorber-free laser transmission welding possesses several advantages (i.e., contactless input of energy, high precision, no adhesives and no particle formation) which enable the fulfilment of the aforementioned demands [1–3]. In contrast to conventional transparent-absorbent welding, where one partner contains a laser absorbent additive [2,4,5], or an additional absorbing material is placed in the joining zone [6–9], the samples analyzed in this work are made of identical polymers and were joined directly using absorber-free laser transmission welding [10–16]. The setup is comparable to the one described by Olowinsky [17].
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