6 February 2012 Through the optical combiner monitoring in remote fiber laser welding of zinc coated steels
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Thanks to the recent affirmation of the active fiber lasers, remote laser welding of zinc coated steels is under investigation with a particular emphasis on the overlap joint geometry. Due to the high power and high beam quality offered by these lasers, the remote laser welding process has become more practicable. However laser welding of lap zinc coated steels is still problematic because of the violent vaporisation of zinc. The presence of a gap between the plates allowing vapour degassing has been proven to avoid defects due to zinc vaporization. On the other hand variation in the gap value can lead to the welding defect formation. Therefore constant gap values should be ensured and deviation from the reference gap value has to be monitored during the execution of the welding process. Furthermore, the on-line monitoring of the gap values between the plates can be helpful for the on-line quality control of the welding process. The paper proposes a new monitoring solution for the measurement of the gap in remote fiber laser welding of overlapped zinc coated steels. In this solution, referred as Through the Optical Combiner Monitoring (TOCM) , the optical emissions from the welding process are directly observed through the optical combiner of the fiber laser source with spectroscopic equipment. The TOCM solution presented in the paper is integrated in an IPG YLS 3000 fiber laser source whose beam is deflected and focused by means of an El.En. ScanFiber scanning system with an equivalent focal length of 300 mm. After the definition of the right welding process conditions, spectroscopic tests are exploited to evaluate the optical emission from the welding plasma/plume. Acquired spectra are then analysed with multivariate data analysis approach in order to ensure gap monitoring. Results showed that with the proposed method it is possible to evaluate not only the gap between the plates but also the location inside the weld at which the variation occurs. Furthermore, the relationship between the gap variation and local changes in the acquired spectra is given.
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Daniele Colombo, Daniele Colombo, Bianca Maria Colosimo, Bianca Maria Colosimo, Barbara Previtali, Barbara Previtali, Daniele Bassan, Daniele Bassan, Manuel Lai, Manuel Lai, Giovanni Masotti, Giovanni Masotti, } "Through the optical combiner monitoring in remote fiber laser welding of zinc coated steels", Proc. SPIE 8239, High Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications, 82390F (6 February 2012); doi: 10.1117/12.909903; https://doi.org/10.1117/12.909903


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