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Optical detection of joint position in zero gap laser beam welding
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0002-8771-7404
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. , 64 p.
Series
Licentiate Thesis: University West, 2017:15
Keyword [en]
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: urn:nbn:se:hv:diva-10684ISBN: 978-91-87531-50-7 (print)ISBN: 978-91-87531-49-1 (electronic)OAI: oai:DiVA.org:hv-10684DiVA: diva2:1073199
Supervisors
Available from: 2017-02-10 Created: 2017-02-09 Last updated: 2017-02-10
List of papers
1. Optical Methods for In-Process Monitoring of Laser Beam Welding
Open this publication in new window or tab >>Optical Methods for In-Process Monitoring of Laser Beam Welding
2014 (English)In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, 1-9 p.Conference paper (Refereed)
Abstract [en]

This paper addresses the issue of evaluating and selecting optical sensors to be integrated with a 1μm laser beam welding system. The method used for this evaluation is mainly a survey of relevant research litterature. The result of this work is a matrix showing the different methods and distinct features related to relevant process conditions that can be estimated or detected with respective methods. This evaluation also includes considerations on the required sensor bandwidth in relation to inertia and time constants in the physical process.

Keyword
Optical methods, process monitoring, laser beam welding
National Category
Engineering and Technology Production Engineering, Human Work Science and Ergonomics
Research subject
ENGINEERING, Mechatronics
Identifiers
urn:nbn:se:hv:diva-6854 (URN)978-91-980974-1-2 (ISBN)
Conference
The 6th Swedish Production Symposium
Available from: 2014-10-15 Created: 2014-10-15 Last updated: 2017-02-09Bibliographically approved
2. Evaluation of non-contact methods for joint tracking in a laser beam welding application
Open this publication in new window or tab >>Evaluation of non-contact methods for joint tracking in a laser beam welding application
Show others...
2016 (English)In: The 7th International Swedish Production Symposium, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Symposium , 2016, 1-6 p.Conference paper, (Other academic)
Abstract [en]

The use of automated laser welding is a key enabler for resource efficient manufacturing in several industrial sectors. One disadvantage with laser welding is the narrow tolerance requirements in the joint fit-up. This is the main reason for the importance of joint tracking systems. This paper describes anevaluation of four non-contact measurement methods to measure the position, gap width and misalignment between superalloy plates. The evaluation was carried out for increased knowledge about the possibilities and limitations with the different methods. The methods are vision-, laser-line-,thermography- and inductive probe systems which are compared in an experimental setup representing a relevant industrial application. Vision is based on a CMOS camera, where the image information is used directly for the measurements. Laser-line is based on triangulation between a camera and a projected laserline. Thermography detects the heat increase in the gap width due to external heat excitation. Inductive probe uses two eddy current coils, and by a complex response method possibilities to narrow gap measurement is achieved. The results, evaluated by comparing the data from the different systems, clearly highlights possibilities and limitations with respective method and serves as a guide in the development of laser beam welding.

Place, publisher, year, edition, pages
Lund: Swedish Production Symposium, 2016
Keyword
Joint tracking, Gap width, Misalignment, Inductive coil, Thermography, Laser line, Vision sensor
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10147 (URN)
Conference
7th Swedish Production Symposium, Lund, Sweden, October 25-27, 2016
Note

Ingår i lic.uppsats

Available from: 2016-11-17 Created: 2016-11-17 Last updated: 2017-02-09Bibliographically approved
3. Joint tracking in zero gap laser beam welding using a vision sensor
Open this publication in new window or tab >>Joint tracking in zero gap laser beam welding using a vision sensor
2016 (English)In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, 1-7 p.Conference paper, (Refereed)
Abstract [en]

The paper describes a robust vision sensor system that can find very narrow gaps between metal sheets to be butt welded together. The use of automated laser beam welding is seen as a key enabler for efficient manufacturing by enabling narrow and deep welds with a limited heat affected zone and low thermal distortion of the welded components. It is sensitive to positioning the laser beam with respect to the joint position. Even a small off-set from the actual joint could result in detrimental lack of fusion. The system comprises a CMOS camera with optic filters integrated in the welding optics and appropriate LED illumination of the work piece. By analysing the spectral emissions during welding, illumination and matching optic filters have been chosen in a spectral range where the process disturbances are relatively low. In this way it has been shown possible to detect the joint position even during harsh welding conditions. Preliminary results from the first experiments show promising results, however more tests will be performed using different weld geometries etc. to verify the robustness of the algorithm.

Place, publisher, year, edition, pages
Lund: Swedish Production Academy, 2016
Keyword
Laser beam welding, joint tracing, narrow gap, butt weld
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10162 (URN)
Conference
7th Swedish Production Symposium (SPS), Lund, Sweden, October 25-27, 2016
Available from: 2016-12-07 Created: 2016-11-23 Last updated: 2017-02-09Bibliographically approved
4. Vision and spectroscopic sensing for joint tracing in narrowgap laser butt welding
Open this publication in new window or tab >>Vision and spectroscopic sensing for joint tracing in narrowgap laser butt welding
2016 (English)Article in journal (Other academic) Submitted
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.

Keyword
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:nbn:se:hv:diva-10639 (URN)
Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2017-02-09Bibliographically approved

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Citation style
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Output format
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