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Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal
University of Bari, Physics Department, Via Amendola 173, 70126 Bari, Italy.
University West, Department of Engineering Science, Division of Production Systems.ORCID iD: 0000-0002-8771-7404
University West, Department of Engineering Science, Division of Production Systems.ORCID iD: 0000-0001-5734-294X
University West, Department of Engineering Science, Division of Production Systems.ORCID iD: 0000-0001-5608-8636
Show others and affiliations
2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 178-185Article in journal (Refereed) Published
Abstract [en]

Robotized laser beam welding of closed-square-butt joints is sensitive to the positioning of the laser beam with respect to the joint since even a small offset may result in a detrimental lack of sidewall fusion. An evaluation of a system using a photodiode aligned coaxial to the processing laser beam confirms the ability to detect variations of the process conditions, such as when there is an evolution of an offset between the laser beam and the joint. Welding with different robot trajectories and with the processing laser operating in both continuous and pulsed mode provided data for this evaluation. The detection method uses wavelet analysis of the photodetector signal that carries information of the process condition revealed by the plasma plume optical emissions during welding. This experimental data have been evaluated offline. The results show the potential of this detection method that is clearly beneficial for the development of a system for welding joint tracking.

Place, publisher, year, edition, pages
Elsevier, 2019. Vol. 109, p. 178-185
Keywords [en]
Laser beam welding, Joint tracking, Butt joints, Photodiode, Wavelet analysis
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-12832DOI: 10.1016/j.optlastec.2018.08.006ISI: 000446949600023Scopus ID: 2-s2.0-85051138319OAI: oai:DiVA.org:hv-12832DiVA, id: diva2:1240300
Funder
VINNOVA, 2016-03291Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2019-02-28Bibliographically approved
In thesis
1. 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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