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Evaluation of non-contact methods for joint tracking in a laser beam welding application
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0001-5734-294X
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0001-6933-375X
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0001-7748-0565
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0002-8771-7404
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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. 1-6 p.
Keyword [en]
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: urn:nbn:se:hv:diva-10147OAI: oai:DiVA.org:hv-10147DiVA: diva2:1047294
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
In thesis
1. Inductive measurement of narrow gaps for high precision welding of square butt joints
Open this publication in new window or tab >>Inductive measurement of narrow gaps for high precision welding of square butt joints
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A recent method in aero engine production is to fabricate components from smaller pieces, rather than machining them from large castings. This has made laser beam welding popular, offering high precision with low heat input and distortion, but also high productivity. At the same time, the demand for automation of production has increased, to ensure high quality and consistent results. In turn, the need for sensors to monitor and control the laser welding process is increasing. In laser beam welding without filler material, the gap between the parts to be joined must be narrow. Optical sensors are often used to measure the gap, but with precise machining, it may become so narrow that it is difficult to detect, with the risk of welding in the wrong position. This kind of problems can cause severe welding defects, where the parts are only partially joined without any visible indication. This thesis proposes the use of an inductive sensor with coils on either side of the gap. Inducing currents into the metal, such a sensor can detect even gaps that are not visible. The new feature of the proposal is based on using the complex response of each coil separately to measure the distance and height on both sides of the gap, rather than an imbalance from the absolute voltage of each coil related to gap position. This extra information allows measurement of gap width and misalignment as well as position, and decreases the influence from gap misalignment to the position measurement. The sensor needs to be calibrated with a certain gap width and height alignment. In real use,these will vary, causing the sensor to be less accurate. Using initial estimates ofthe gap parameters from the basic sensor, a model of the response can be used to estimate the measurement error of each coil, which in turn can be used for compensation to improve the measurement of the gap properties.The properties of the new method have been examined experimentally, using a precise traverse mechanism to record single coil responses in a working range around a variable dimension gap, and then using these responses to simulate a two coil probe. In most cases errors in the measurement of weld gap position and dimensions are within 0.1 mm.The probe is designed to be mounted close to the parts to be welded, and will work in a range of about 1 mm to each side and height above the plates. This is an improvement over previous inductive sensors, that needed to be guided to the mid of the gap by a servo mechanism.

Place, publisher, year, edition, pages
Trollhättan: University West, 2016. 48 p.
Series
Licentiate Thesis: University West, 14
Keyword
Eddy current, Seam tracking, Measurement, Laser beam welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10150 (URN)978-91-87531-45-3 (ISBN)978-91-87531-44-6 (ISBN)
Presentation
2016-11-28, C118, Högskolan Väst, Trollhättan, 10:15
Supervisors
Available from: 2016-11-21 Created: 2016-11-17 Last updated: 2016-11-17Bibliographically approved
2. 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. 64 p.
Series
Licentiate Thesis: University West, 2017:15
Keyword
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

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