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Nilsen, M., Sikström, F. & Christiansson, A.-K. (2019). A study on change point detection methods applied to beam offset detection in laser welding. Paper presented at 17th Nordic Laser Materials Processing Conference - (NOLAMP17), 27 –29 August 2019. Procedia Manufacturing, 6, 72-79
Open this publication in new window or tab >>A study on change point detection methods applied to beam offset detection in laser welding
2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 6, p. 72-79Article in journal (Refereed) Published
Abstract [en]

This paper presents an experimental study where a photodiode integrated into a laser beam welding tool is used to monitor laser beam spot deviations fromthe joint, the beam offset. The photodiode system is cost effective and typically easy to implement in an industrial system. The selected photodiode is a silicondetector sensitive in the spectral range between 340-600nm which corresponds to the spectral emissions from the plasma plume. The welding application is closed-square-butt joint welding where a laser beam offset can cause lack of fusion in the resulting weld. The photodiode signal has been evaluated by two different change point detection methods, one off-line and one on-line method, with respect to their detection performance. Off-line methods can be used to guide post weld inspection and on-line methods have the potential to enable on-line adaptive control or the possibility to stop the process for repair. The performance of the monitoring system and the change point detection methods have been evaluated from data obtained during laser beam welding experiments conducted on plates of stainless steel. The results clearly indicates the possibility to detect beam offsets by photodiode monitoring.

Keywords
Laser beam welding; monitoring; photodiode; change point detection
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-14384 (URN)10.1016/j.promfg.2019.08.011 (DOI)2-s2.0-85072523021 (Scopus ID)
Conference
17th Nordic Laser Materials Processing Conference - (NOLAMP17), 27 –29 August 2019
Funder
Vinnova, 2016-03291
Available from: 2019-09-05 Created: 2019-09-05 Last updated: 2019-09-29
Nilsen, M., Sikström, F. & Christiansson, A.-K. (2019). Adaptive control of the filler wire rate during laser beam welding of squared butt joints with varying gap width. The International Journal of Advanced Manufacturing Technology, 102(9-12), 3667-3676
Open this publication in new window or tab >>Adaptive control of the filler wire rate during laser beam welding of squared butt joints with varying gap width
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 102, no 9-12, p. 3667-3676Article in journal (Refereed) Published
Abstract [en]

Adding filler wire control to autogenous laser beam welding of squared butt joints offers a means to widen up the tight fit-up tolerances associated with this process. When the gap width varies, the filler wire rate should be controlled to assure a constant geometry of the resulting weld seam. A dual mode sensing system is proposed to estimate the joint gap width and thereby control the filler wire rate. A vision camera integrated into the welding tool together with external LED illumination and a laser line projection enables two sensing modes, one surface feature extraction mode and one laser triangulation-based mode. Data from the both modes are fused in a Kalman filter, and comparisons show that the fusing of the data gives more robust estimation than estimates from each single mode. A feed-forward control system adaptively adjusts the filler wire rate based on the estimations ofthe joint gap width in front of the keyhole. The focus is on keeping the data processing simple and affordable, and the real-time performance of the sensor and control system has been evaluated by welding experiments. It is shown that the proposed system can be used for on-line control of the filler wire rate to achieve a constant weld geometry during varying joint gap widths

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Laser beam welding, Filler wire, Squared butt joints, Varying gap width, Feature extraction, Laser triangulation, Sensor fusion
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-13640 (URN)10.1007/s00170-019-03325-w (DOI)000469060700066 ()2-s2.0-85067693903 (Scopus ID)
Funder
Vinnova, 2016-03291
Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-10-16Bibliographically approved
Sikström, F. & Nilsen, M. (2019). Beam offset detection in laser stake welding of tee joints based on photodetector sensing. Paper presented at 17th Nordic Laser Material Processing Conference (NOLAMP17), 27 –29 August 2019, Trondheim. Procedia Manufacturing, 36, 64-71
Open this publication in new window or tab >>Beam offset detection in laser stake welding of tee joints based on photodetector sensing
2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 64-71Article in journal (Refereed) Published
Abstract [en]

This paper presents an experimental study where a photodetector is used in a laser beam welding tool to monitor beam deviations (beam offsets) in stake welding of tee joints. The aim is to obtain an early detection of deviations from the joint centerline in this type of welding where the joint is not visible from the top side. The photodetector used is a GaP diode sensitive in the spectral range 150-550 nm corresponding to the spectral emissions form the plasma plume during keyhole welding. The photodetector signal has been evaluated by change point detection methods with respect to their detection performance. Both an off-line and an on-line method have been evaluated. The off-line method can be used to guide post weld inspection and the on-line method has the potential to enable on-line adaptive position control and/or the possibility to stop the process for repair. The results shows that the proposed method can be used as a go/no go system and to guide post weld inspection.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Laser beam welding, tee joint, process monitoring, photodetector
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14385 (URN)10.1016/j.promfg.2019.08.010 (DOI)2-s2.0-85072518609 (Scopus ID)
Conference
17th Nordic Laser Material Processing Conference (NOLAMP17), 27 –29 August 2019, Trondheim
Funder
Knowledge Foundation
Available from: 2019-09-05 Created: 2019-09-05 Last updated: 2019-09-29
Elefante, A., Nilsen, M., Sikström, F., Christiansson, A.-K., Maggipinto, T. & Ancona, A. (2019). Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal. Optics and Laser Technology, 109, 178-185
Open this publication in new window or tab >>Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal
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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
Keywords
Laser beam welding, Joint tracking, Butt joints, Photodiode, Wavelet analysis
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-12832 (URN)10.1016/j.optlastec.2018.08.006 (DOI)000446949600023 ()2-s2.0-85051138319 (Scopus ID)
Funder
VINNOVA, 2016-03291
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2019-02-28Bibliographically approved
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2019). Robust vision-based joint tracking for laser welding of curved closed-square-butt joints. The International Journal of Advanced Manufacturing Technology, 101(5-8), 1867-1978
Open this publication in new window or tab >>Robust vision-based joint tracking for laser welding of curved closed-square-butt joints
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 101, no 5-8, p. 1867-1978Article in journal (Refereed) Published
Abstract [en]

Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser beam is positioned in relation to the joint, and existing joint tracking systems tend to fail in detecting the joint when the gap and misalignment between the work pieces are close to zero. A camera-based system is presented based on a high dynamic range camera operating with LED illumination at a specific wavelength and a matching optical filter. An image processing algorithm based on the Hough transform extracts the joint position from the camera images, and the joint position is then estimated using a Kalman filter. The filter handles situations, when the joint is not detectable in the image, e.g., when tack welds cover the joint. Surface scratches, which can be misinterpreted as being the joint, are handled by a joint curve prediction model based on known information about the nominal path defined by the robot program. The performance of the proposed system has been evaluated off line with image data obtained during several welding experiments.

Keywords
Laser beam welding, Joint tracking, Butt joints, Camera, Hough transform, Kalman filter
National Category
Materials Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13211 (URN)10.1007/s00170-018-3044-0 (DOI)
Projects
VINNOVA project VarGa
Funder
Vinnova, 2016-03291
Note

First Online: 27 November 2018

Funders: SWE-DEMO MOTOR ; [2015-06047]

Available from: 2018-12-18 Created: 2018-12-18 Last updated: 2019-05-10Bibliographically approved
Mi, Y., Sikström, F., Nilsen, M. & Ancona, A. (2019). Vision based beam offset detection in laser stake welding of T-joints using a neural network. Paper presented at Conference of 17th Nordic Laser Materials Processing Conference, NOLAMP 2019 ; Conference Date: 27 August 2019 Through 29 August 2019. Procedia Manufacturing, 36, 42-49
Open this publication in new window or tab >>Vision based beam offset detection in laser stake welding of T-joints using a neural network
2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 42-49Article in journal (Refereed) Published
Abstract [en]

This paper presents an experimental study where a vision camera integrates coaxially into a laser beam welding tool to monitor beam deviations (beam offset) in laser stake welding of T-joints. The aim is to obtain an early detection of deviations from the joint centreline in this type of welding where the joint is not visible from the top side. A polynomial surface fitting method is applied to extract features that can describe the behaviour of the melt pool. A nonlinear autoregressive with exogenous inputs neural network model is trained to relate eight image features to the laser beam offset. The performance of the presented model is evaluated offline by different welding samples. The results show that the proposed method can be used to guide post weld inspection and has the potential for on-line adaptive control. © 2019 The Author(s). Published by Elsevier B.V.

National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14473 (URN)10.1016/j.promfg.2019.08.007 (DOI)2-s2.0-85072518360 (Scopus ID)
Conference
Conference of 17th Nordic Laser Materials Processing Conference, NOLAMP 2019 ; Conference Date: 27 August 2019 Through 29 August 2019
Funder
Knowledge Foundation
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2019-10-03
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2018). In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints. Paper presented at 8th Swedish Production Symposium (SPS 2018), Stockholm, Sweden, May 16-18, 2018. Procedia Manufacturing, 25, 511-516
Open this publication in new window or tab >>In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints
2018 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 511-516Article in journal (Other academic) Published
Abstract [en]

In robotized laser welding of technical zero gap closed square butt joints it is critical to position the laser beam correct with regardsto the joint. Welding with an offset from the joint may cause lack of sidewall fusion, a serious defect that is hard to detect and gives a weak weld . When using machined parts with gap and misalignment between the parts that is close to zero, existing joint tracking systems will probably fail to track the joint. A camera based system using LED illumination and matching optical filters is proposed in this paper to address this issue. A high dynamic range CMOS camera and the LED illumination is integrated into the laser tool. The camera captures images of the area in front of the melt pool where the joint is visible and an algorithm based on the Hough transform and a Kalman filter estimates the offset between the laser spot and the joint position. Welding experiments, using a 6 kW fiber laser, have been conducted to evaluate the performance of the system. Promising results are obtained that can be used in the further development of a closed loop controlled joint tracking system.

Keywords
Laser welding, Butt joints, Joint tracking, Camera
National Category
Production Engineering, Human Work Science and Ergonomics Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12828 (URN)10.1016/j.promfg.2018.06.123 (DOI)
Conference
8th Swedish Production Symposium (SPS 2018), Stockholm, Sweden, May 16-18, 2018
Projects
VINNOVA project VarGa (2016-03291)MoRE program project Hy-Las - Hybrid sensing for understanding of laser welding technology for process control, no 608473
Funder
Vinnova, 2016-03291EU, European Research Council, FP7/2007-2013
Note

Del av specialnumret Proceedings of the 8th Swedish Production Symposium (SPS 2018) Redaktörer: M. Onori, L. Wang, X. V. Wang och W. Ji

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2019-06-05Bibliographically approved
Kisielewicz, A., Sikström, F., Christiansson, A.-K. & Ancona, A. (2018). Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 718. Paper presented at 8th Swedish Production Symposium, SPS 2018, Stockholm, Sweden, 16-18 May, 2018. Procedia Manufacturing, 25, 418-425
Open this publication in new window or tab >>Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 718
2018 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 418-425Article in journal (Refereed) Published
Abstract [en]

Experimental explorations of a spectrometer system used for in-process monitoring of the laser blown powder directed energy deposition of Alloy 718 is presented. Additive manufacturing of metals using this laser process experiences repeated heating and cooling cycles which will influence the final microstructure and chemical composition at every given point in the built. The spectrometer system disclosed, under certain process conditions, spectral lines that indicate vaporisation of chromium. Post process scanning electron microscope energy dispersive spectroscopy analysis of the deposited beads confirmed a reduction of chromium. Since the chromium concentration in Alloy 718 is correlated to corrosion resistance, this result encourages to further investigations including corrosion tests.

National Category
Metallurgy and Metallic Materials Production Engineering, Human Work Science and Ergonomics
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-13303 (URN)10.1016/j.promfg.2018.06.112 (DOI)2-s2.0-85065640848 (Scopus ID)
Conference
8th Swedish Production Symposium, SPS 2018, Stockholm, Sweden, 16-18 May, 2018
Note

Del av specialnumret Proceedings of the 8th Swedish Production Symposium (SPS 2018) Redaktörer: M. Onori, L. Wang, X. V. Wang och W. J

Funders: SUMANnext ; DigiAM

Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-10-18Bibliographically approved
Öberg, A. E. & Sikström, F. (2017). Barriers for industrial implementation of in-process monitoring of weld penetration for quality control. The International Journal of Advanced Manufacturing Technology, 91(5-8), 2427-2434
Open this publication in new window or tab >>Barriers for industrial implementation of in-process monitoring of weld penetration for quality control
2017 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 91, no 5-8, p. 2427-2434Article in journal (Refereed) Published
Abstract [en]

The research conducted sheds a light on the question why robust in-process monitoring and adaptive control are not fully implemented in the welding industry. In the research project FaRoMonitA, the possibilities to monitor the weld quality during welding have been investigated. Research conducted in this area has merely focused on technical issues investigated in a laboratory environment. To advance the research front and release some barriers related to industrial acceptance, the studies conducted in this paper have been both quantitative and qualitative in form of experiments combined with an interview study. The quality property weld penetration depth was chosen for in-process monitoring to evaluate the industrial relevance and applicability. A guaranteed weld penetration depth is critical for companies producing parts influenced by fatigue. The parts studied were fillet welds produced by gas metal arc welding. The experiments show that there is a relationship between final penetration depth and monitored arc voltage signals and images captured by CMOS vision and infrared cameras during welding. There are still technical issues to be solved to reach a robust solution. The interview study indicates that soft issues, like competence and financial aspects, are just as critical.

Keywords
Process monitoring, Gas metal arc welding, Fillet weld, Weld penetration, Quality assurance, Manufacturing, Non-destructive testing
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10520 (URN)10.1007/s00170-016-9894-4 (DOI)000404132100078 ()2-s2.0-85008477804 (Scopus ID)
Funder
Knowledge Foundation
Note

First Online: 05 January 2017

Available from: 2017-01-10 Created: 2017-01-10 Last updated: 2019-01-31Bibliographically approved
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2017). Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System. Paper presented at 16th Nordic Laser Materials Processing Conference, NOLAMP16. Physics Procedia, 89, 100-107
Open this publication in new window or tab >>Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System
2017 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, p. 100-107Article in journal (Refereed) Published
Abstract [en]

A vision and spectroscopic system for estimation of the joint gap width in autogenous laser beam butt welding is presented. Variations in joint gap width can introduce imperfections in the butt joint seam, which in turn influence fatigue life and structural integrity. The aim of the monitoring approach explored here is to acquire sufficiently robust process data to be used to guide post inspection activities and/or to enable feedback control for a decreased process variability. The dual-sensing approach includes a calibrated CMOS camera and a miniature spectrometer integrated with a laser beam tool. The camera system includes LED illumination and matching optical filters and captures images of the area in front of the melt pool in order to estimate the joint gap width from the information in the image. The intensity of different spectral lines acquired by the spectrometer has been investigated and the correlation between the intensity of representative lines and the joint gap width has been studied. Welding experiments have been conducted using a 6 kW fiber laser. Results from both systems are promising, the camera system is able to give good estimations of the joint gap width, and good correlations between the signal from the spectrometer and the joint gap width have been found. However, developments of the camera setup and vision algorithm can further improve the joint gap estimations and more experimental work is needed in order to evaluate the robustness of the systems.

Keywords
Laser beam welding; Butt joints; Varying gap width; Vision sensor; Spectroscopic sensor
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-11898 (URN)10.1016/j.phpro.2017.08.014 (DOI)2-s2.0-85037711817 (Scopus ID)
Conference
16th Nordic Laser Materials Processing Conference, NOLAMP16
Funder
Vinnova, 2016-03291
Note

Funders: People programme (Marie Curie Actions) of the European Union's 29 seventh framework progamme (FP7/2007-2013), no 608473

Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2019-05-21Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5734-294X

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