| 1. |
- Rahmani Dehaghani, Mostafa, et al.
(författare)
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System identification and closed-loop control of laser hot-wire directed energy deposition using the parameter-signature-quality modeling scheme
- 2024
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Ingår i: Journal of Manufacturing Processes. - 1526-6125 .- 2212-4616. ; , s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Hot-wire directed energy deposition using a laser beam (DED-LB/w) is a method of metal additive manufacturing (AM) that has benefits of high material utilization and deposition rate, but parts manufactured by DED-LB/w suffer from a substantial heat input and undesired surface finish. Hence, regulating the process parameters and monitoring the process signatures to control the final quality during the deposition is crucial to ensure the quality of the final part. This paper explores the dynamic modeling of the DED-LB/w process and introduces a parameter-signature-quality modeling and control approach to enhance the quality of modeling and control of part qualities that cannot be measured in situ. The study investigates different process parameters that influence the melt pool width (signature) and bead width (quality) in single and multi-layer beads. The proposed modeling approach utilizes a parameter-signature model as F1 and a signature-quality model as F2. Linear and nonlinear modeling approaches are compared to describe a dynamic relationship between process parameters and a process signature, the melt pool width (F1). A fully connected artificial neural network is employed to model and predict the final part quality, i.e., bead width, based on melt pool signatures (F2). Finally, the effectiveness and usefulness of the proposed parameter-signature-quality modeling is tested and verified by integrating the parameter-signature (F1) and signature-quality (F2) models in the closed-loop control of the width of the part. Compared with the control loop with only F1, the proposed method shows clear advantages and bears potential to be applied to control other part qualities that cannot be directly measured or monitored in situ.
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| 2. |
- Ancona, Antonio, 1974-, et al.
(författare)
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Monitoring and control of directed energy deposition using a laser beam
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 612-638
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Bokkapitel (refereegranskat)abstract
- To be a successful competitor among other technologies, metallic laser-directed energy depositionusing a laser beam would benefit from the support of intelligent automation making the processrobust, repeatable, and cost-efficient. This calls for technology leaps towards robust and accuratedetection and estimation of the conditions during processing and control schemes for robustperformance. This chapter discusses how developments in sensor technology and model-basedsignal processing can contribute to advancements in in-process monitoring of directed energydeposition using a laser beam and how developments in model-based feedforward- and feedbackcontrol can support automation. The focus is on how machine vision, optical emission spectroscopy,thermal sensing, and electrical process signals can support monitoring, control and better processunderstanding. These approaches are industrially relevant and have a high potential to support amore sustainable manufacturing.
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| 3. |
- Mi, Yongcui, 1986-, et al.
(författare)
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Beam shaping with a deformable mirror for gap bridging in autogenous laser butt welding
- 2023
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Ingår i: Optics and Lasers in Engineering. - 0143-8166. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- In autogenous laser butt welding the variability of the joint gap can cause problems in terms of weld seam quality. A suitable strategy to alleviate this is to dynamically shape the laser beam instead of a circular-shaped beam with typical Gaussian or top hat distributions. Currently available systems cannot reach sufficient performance due to both the real time control system for the shape variation and the limited laser power currently manageable. In the present work, the possibility of bridging the joint gap during welding using a deformable mirror to elongate the focused laser beam from circular to transversal elliptical shape was investigated. The effect of the beam shaping on the geometry of the weld pool and of the weld cross sections was analysed, for different values of the gap in comparison with a circular Gaussian beam. It was demonstrated that the adoption of a transversal elliptical laser beam makes the welding process more stable, especially for large gaps (i.e. larger than the circular beam radius). Thanks to the beam shaping, the extension of the fused zone (in terms of the cross section area, height and width) resulted to be less sensitive to the gap's dimension; in addition, the extension of the heat affected zone and the presence of undercuts were evidently reduced.
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| 4. |
- Jadidi, Aydin, Postdoktor, et al.
(författare)
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Beam Offset Detection in Laser Stake Welding of Tee Joints Using Machine Learning and Spectrometer Measurements
- 2022
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Ingår i: Sensors. - : MDPI. - 1424-8220. ; 22:10
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Tidskriftsartikel (refereegranskat)abstract
- Laser beam welding offers high productivity and relatively low heat input and is one key enabler for efficient manufacturing of sandwich constructions. However, the process is sensitive to how the laser beam is positioned with regards to the joint, and even a small deviation of the laser beam from the correct joint position (beam offset) can cause severe defects in the produced part. With tee joints, the joint is not visible from top side, therefore traditional seam tracking methods are not applicable since they rely on visual information of the joint. Hence, there is a need for a monitoring system that can give early detection of beam offsets and stop the process to avoid defects and reduce scrap. In this paper, a monitoring system using a spectrometer is suggested and the aim is to find correlations between the spectral emissions from the process and beam offsets. The spectrometer produces high dimensional data and it is not obvious how this is related to the beam offsets. A machine learning approach is therefore suggested to find these correlations. A multi-layer perceptron neural network (MLPNN), support vector machine (SVM), learning vector quantization (LVQ), logistic regression (LR), decision tree (DT) and random forest (RF) were evaluated as classifiers. Feature selection by using random forest and non-dominated sorting genetic algorithm II (NSGAII) was applied before feeding the data to the classifiers and the obtained results of the classifiers are compared subsequently. After testing different offsets, an accuracy of 94% was achieved for real-time detection of the laser beam deviations greater than 0.9 mm from the joint center-line.
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| 5. |
- Elefante, Arianna, et al.
(författare)
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Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal
- 2019
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Ingår i: Optics and Laser Technology. - : Elsevier BV. - 0030-3992 .- 1879-2545. ; 109, s. 178-185
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Mi, Yongcui, 1986-, et al.
(författare)
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Vision based beam offset detection in laser stake welding of T-joints using a neural network
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 36, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Nilsen, Morgan, et al.
(författare)
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A study on change point detection methods applied to beam offset detection in laser welding
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 36, s. 72-79
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Nilsen, Morgan, et al.
(författare)
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Adaptive control of the filler wire rate during laser beam welding of squared butt joints with varying gap width
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 102:9-12, s. 3667-3676
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 9. |
- Nilsen, Morgan
(författare)
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Monitoring and control of laser beam butt joint welding
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Nilsen, Morgan, et al.
(författare)
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Robust vision-based joint tracking for laser welding of curved closed-square-butt joints
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 101:5-8, s. 1967-1978
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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