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Vision and spectroscopic sensing for joint tracing in narrow gap laser butt welding
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0002-8771-7404
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0001-5734-294X
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0001-5608-8636
University West, Department of Engineering Science, Division of Production Systems. IFN-CNR Institute for Photonics and Nanotechnologies, Physics Department, via Amendola 173, 70126 BARI, Italy. (PTW)ORCID iD: 0000-0002-6247-5429
2017 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 96, p. 107-116Article in journal (Refereed) Published
Abstract [en]

The automated laser beam butt welding process is sensitive to positioning the laser beam with respect to the joint because a small offset may result in detrimental lack of sidewall fusion. This problem is even more pronounced incase of narrow gap butt welding, where most of the commercial automatic joint tracing system fail to detect the exact position and size of the gap. In this work, adual vision and spectroscopic sensing approach is proposed to trace narrow gap butt joints during laser welding. The system consists of a camera with suitable illumination and matched optical filters and a fast miniature spectrometer. An image processing algorithm of the camera recordings has been developed in order to estimate the laser spot position relative the joint position. The spectral emissions from the laser induced plasma plume has been acquired by the spectrometer, and based on the measurements of the intensities of selected lines of the spectrum, the electron temperature signal has been calculated and correlated to variations of process conditions. The individual performances of these two systems have been experimentally investigated and evaluated offline by data from several welding experiments where artificial abrupt as well as gradual excursions of the laser beam out of the joint were produced. Results indicate thata combination of the information provided by the vision and spectroscopic systems is beneficial for development of a hybrid sensing system for joint tracing.

Place, publisher, year, edition, pages
2017. Vol. 96, p. 107-116
Keywords [en]
Laser beam welding, Joint tracing, Butt joints, Optical spectroscopy, Vision sensor, Hybrid sensing
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-10639DOI: 10.1016/j.optlastec.2017.05.011ISI: 000405051800015Scopus ID: 2-s2.0-85019735734OAI: oai:DiVA.org:hv-10639DiVA, id: diva2:1071077
Funder
Vinnova, 2014-05227Knowledge Foundation, 2010/0283EU, FP7, Seventh Framework Programme, FP7/2007-2013
Note

Ingår i lic. avhandling

Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2019-05-23Bibliographically approved
In thesis
1. Optical detection of joint position in zero gap laser beam welding
Open this publication in new window or tab >>Optical detection of joint position in zero gap laser beam welding
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents an experimental study on how to track zero gaps between metal sheets to be joined by laser beam butt welding. Automated laser beam welding is gaining interest due to its ability to produce narrow and deep welds giving limited heat input and therefore less distortions compared to other processes, such as arc-welding. The automated laser beam welding process is however sensitive to how the high power laser is positioned with regards to the joint position. Deviations from the joint position may occur due to inaccuracies of the welding robot and fixturing, changes in joint geometry, process induced distortions, etc. Welding with an offset from the joint position can result inlack of sidewall fusion, a serious defect that is hard to detect. This work develops and evaluates three monitoring systems to be used during welding in order to be able to later control the laser beam spot position. (i) A monitoring systemis developed for three different photo diodes, one for the visual spectrum of the process emissions, one for the infrared spectrum, and one for the reflected highpower laser light. The correlation between the signals from the photodiodes and the welding position relative to the joint is analysed using a change detection algorithm. In this way an indication of a path deviation is given. (ii) A visual camera with matching illumination and optical filters is integrated into the laser beam welding tool in order to obtain images of the area in front of the melt pool. This gives a relatively clear view of the joint position even during intense spectral disturbances emitted from the process, and by applying animage processing algorithm and a model based filtering method the joint positionis estimated with an accuracy of 0.1 mm. (iii) By monitoring the spectral emissions from the laser induced plasma plume using a high speed and high resolution spectrometer, the plasma electron temperature can be estimated from the intensities of two selected spectral lines and this is correlated to the welding position and can be used for finding the joint position.

Place, publisher, year, edition, pages
Trollhättan: University West, 2017. p. 64
Series
Licentiate Thesis: University West ; 2017:15
Keywords
Laser beam welding, Optical sensors, Joint tracking
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10684 (URN)978-91-87531-50-7 (ISBN)978-91-87531-49-1 (ISBN)
Supervisors
Available from: 2017-02-10 Created: 2017-02-09 Last updated: 2017-02-10
2. Monitoring and control of laser beam butt joint welding
Open this publication in new window or tab >>Monitoring and control of laser beam butt joint welding
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser beam welding is one important technology in automated production. It has several advantages, such as the ability to produce deep and narrow welds giving limited heat induced deformations. The laser beam welding process is however sensitive to how the high power laser is positioned with regards to the joint position. Therefore, to achieve a seam without defects, the joint position needs to be measured and controlled. The laser beam welding process is also sensitive to variations in joint gap width. Costly joint preparations are required to achieve the tight fit up tolerances needed to produce high quality welds. However, the demand on joint preparation can be somewhat relaxed by allowing the joint gap width to vary and controlling the process. One way of doing this is to control the filler wire feed rate based on joint gap width measurements.This thesis presents experimental studies on how to track closed-square-butt joints and also how to handle varying square-butt joints in laser beam welding.

Different optical sensor systems are evaluated for their performance to estimate the joint position and the joint gap width. The possibility of detecting beam offsets is studied by using sensors systems based on a photo diode and on a spectrometer. Estimations of the joint position, to be used for closed loop position control, is studied by using a camera and external LED illumination. Variations in joint gap width is evaluated using a spectrometer, a camera and a laser profile sensor. Experimental results show that both the photodiode system and the spectometer system is able to detect beam offsets and that the beam position can be estimated with sufficient accuracy when welding closed-square-butt joints. It is also shown that the joint gap width can be estimated by the selected sensor systems and that the estimates can be used for controlling the wire feed rate in order to obtain a constant weld geometry and avoid defects related to the gap width.

Place, publisher, year, edition, pages
Trollhättan: University West, 2019. p. 84
Series
PhD Thesis: University West ; 27
Keywords
Laser beam welding, Optical sensors, Joint tracking, Varying gap
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-13650 (URN)978-91-88847-23-2 (ISBN)978-91-88847-22-5 (ISBN)
Public defence
2019-02-05, F104, Albertsalen, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2019-03-15 Created: 2019-02-28

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Nilsen, MorganSikström, FredrikChristiansson, Anna-KarinAncona, Antonio

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