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  • 1.
    Ancona, Antonio
    et al.
    University West, Department of Engineering Science, Division of Production Systems. Physics Department, University of Bari ALDO MORO, Bari (ITA).
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Kisielewicz, Agnieszka
    University West, Department of Engineering Science, Division of Production Systems.
    Monitoring and control of directed energy deposition using a laser beam2023In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1., p. 612-638Chapter in book (Refereed)
    Abstract [en]

    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. 

  • 2.
    Aryal, Pradip
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsson, Håkan
    Chalmers University of Technology Mechanics and Maritime Sciences, Fluid Dynamics, SE-412 96 Gothenburg, (SWE).
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc2021In: Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21) / [ed] Huihe Qiu, 2021, article id HTFF 130Conference paper (Refereed)
    Abstract [en]

    Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20° uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow patternat 20° substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations.

  • 3.
    Aryal, Pradip
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsson, H.
    Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Comparative study of the main electromagnetic models applied to melt pool prediction with gas metal arc: Effect on flow, ripples from drop impact, and geometry2022In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 194, article id 123068Article in journal (Refereed)
    Abstract [en]

    The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs with metal transfer, in welding and additive manufacturing. Metal drop impact on the melt pool is thus included in this study. The electromagnetic force models applied in literature use either numerical solutions of Poisson equations or one of the two analytical models developed by Kou and Sun, or Tsao and Wu. These models rely on assumptions for which the effect on the melt pool predictions remains to be understood. The present work thoroughly investigates those assumptions and their effects. It has been supported by dedicated experimental tests that did provide estimates of unknown model parameters and validation data. The obtained results show that the assumptions that fundamentally distinguish these three models change the electromagnetic force, including the relation between its components. These changes, which can also be spatially non-uniform, are large. As a result, these models lead to significantly different recirculation flow pattern, thermal convection, melt pool morphology, bead dimensions, and free surface response to the metal transfer. We conclude by proposing conditions in which each of these models is suited or questionable.

  • 4.
    Elefante, Arianna
    et al.
    University of Bari, Physics Department, Via Amendola 173, 70126 Bari, Italy.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Maggipinto, Tommaso
    University of Bari, Physics Department, Via Amendola 173, 70126 Bari, Italy.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. IFN-CNR Institute for Photonics and Nanotechnologies, Physics Department, Via Amendola 173, 70126 Bari, Italy.
    Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal2019In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 178-185Article in journal (Refereed)
    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.

  • 5.
    Fang, Jingzhong
    et al.
    Department of Computer Science, Brunel University London, Middlesex, UB8 3PH Uxbridge (GBR).
    Wang, Zidong
    Department of Computer Science, Brunel University London, Middlesex, UB8 3PH Uxbridge (GBR).
    Liu, Weibo
    Department of Computer Science, Brunel University London, Middlesex, UB8 3PH Uxbridge (GBR).
    Lauria, Stanislao
    Department of Computer Science, Brunel University London, Middlesex, UB8 3PH Uxbridge (GBR).
    Zeng, Nianyin
    Department of Instrumental and Electrical Engineering, Xiamen University, Xiamen, Fujian 361005 (CHN).
    Prieto, Camilo
    AIMEN Technology Center (ESP).
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Liu, Xiaohui
    Department of Computer Science, Brunel University London, Middlesex, UB8 3PH Uxbridge (GBR).
    A New Particle Swarm Optimization Algorithm for Outlier Detection: Industrial Data Clustering inWire Arc Additive Manufacturing2023In: IEEE Transactions on Automation Science and Engineering, ISSN 1545-5955, E-ISSN 1558-3783, p. 1-14Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel outlier detection method is proposed for industrial data analysis based on the fuzzy C-means (FCM) algorithm. An adaptive switching randomly perturbed particle swarm optimization algorithm (ASRPPSO) is put forward to optimize the initial cluster centroids of the FCM algorithm. The superiority of the proposed ASRPPSO is demonstrated over five existing PSO algorithms on a series of benchmark functions. To illustrate its application potential, the proposed ASRPPSO-based FCM algorithm is exploited in the outlier detection problem for analyzing the real-world industrial data collected from a wire arc additive manufacturing pilot line in Sweden. Experimental results demonstrate that the proposed ASRPPSO-based FCM algorithm out performs the standard FCM algorithm in detecting outliers of real-world industrial data.

    Note to Practitioners

    Electric arc (which is governed by the current and arc voltage) plays a significant role in monitoring the operating status of the wire arc additive manufacturing (WAAM) process. The nominal periodic current and voltage may occasionally change abruptly due to anomalies (such asarc instability, unstable metal transfer, geometrical deviations, and surface contaminations), which would affect the quality of the fabricated component. This paper focuses on detecting possible anomalies by analyzing the current and voltage during the WAAM process. A novel clustering-based outlier detection method is proposed for anomaly detection where abnormal and normal instances are categorized into two separate clusters. A new particle swarm optimization algorithm is put forward to optimize the initial cluster centroid so as to improve the detection accuracy. The proposed outlier detection method is applied to real-world data collected from a WAAM pilot line for detecting abnormal instances. Experimental results demonstrate the effectiveness of the proposed outlier detection method. The proposed outlier detection method can be applied to other industrial applications including electrical engineering, mechanical engineering and medical engineering. In the future, we aim to develop an online outlier detection system based on the proposed method for real-time for anomaly detection and defect prediction.

  • 6.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V2013In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 46, no 2, p. 871-880Article in journal (Refereed)
    Abstract [en]

    The paper demonstrates a versatile procedure suitable for industrial implementation of temperature measurement on a hot titanium alloy. The driving force has been the need for an accurate temperature measurement during additive manufacturing using laser welding technology where Ti–6Al–4V-wire is melted. The challenges consider both industrial constraints and the varying emissivity of the surface. Measurements makes use of a narrow bandwidth spot radiation pyrometer and a calibration procedure for estimation of the surface temperature through spectral emissivity estimation. The theoretical results are validated through experiments. A number of difficulties in radiation temperature measurements for metals with varying surface properties are discussed; especially the case of surface oxidation. The uncertainty in temperature reading due to the uncertainty in the emissivity estimate is established along with a model that qualitatively describes surface oxidation. The procedure is expected to be useful for several manufacturing applications where it is important to control high temperatures.

  • 7.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Process and Product Development.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Chalmers.
    Emissivity compensated spectral pyrometry for varying emissivity metallic measurands2014In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 2, p. 025010-Article in journal (Refereed)
    Abstract [en]

    A novel method for converting electromagnetic spectral radiance information into emperature measurements is presented. It allows for varying spectral emissivity of the metallic measurand during the course of the measurement. Such variations are due to e.g. thermal oxidation or temperature dependent emissivity. Based on the assumption that emissivity changes with time and temperature in a continuous manner, it is further assumed that an emissivity estimate at one sample instance can be derived from the estimated emissivity found at the previous samples together with updated spectral information. This leads to successive recalculations of spectral emissivity together with corresponding temperature values. The proposed algorithm has been proven to give accurate temperature estimates from a measurement based on data captured by a standard UV-Vis spectrophotometer even for an oxidizing Ti-6Al-4V specimen in a temperature range between 900K and 1400K. The method however, is not limited to these wavelength- or temperature-ranges.

  • 8.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Process and Product Development.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Chalmers.
    Emissivity compensated spectral pyrometry-algorithm and sensitivity analysis2014In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 2, p. 025011-Article in journal (Refereed)
    Abstract [en]

    In order to solve the problem of non-contact temperature measurements on an object with varying emissivity, a new method is herein described and evaluated. The method uses spectral radiance measurements and converts them to temperature readings. It proves to be resilient towards changes in spectral emissivity and tolerates noisy spectral measurements. It is based on an assumption of continuous changes in emissivity and uses historical values of spectral emissivity and temperature for estimating current spectral emissivity.

    The algorithm, its constituent steps and accompanying parameters are described and discussed. A thorough sensitivity analysis of the method is carried out through simulations. No rigorous instrument calibration is needed for the presented method and is therefore industrially tractable.

  • 9.
    Jadidi, Aydin
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Physics Department, University of Bari,Bari (ITA).
    Beam Offset Detection in Laser Stake Welding of Tee Joints Using Machine Learning and Spectrometer Measurements2022In: Sensors, E-ISSN 1424-8220, Vol. 22, no 10Article in journal (Refereed)
    Abstract [en]

    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.

    Download full text (pdf)
    MDPI
  • 10.
    Kisielewicz, Agnieszka
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Physics Department, University of Bari, Bari (ITA).
    Multi sensor monitoring  of the wire-melt pool interaction inhot-wire directed energy deposition using laser beam2023In: IOP Conference Series: Materials Science and Engineering, IOP Publishing , 2023, Vol. 1296, p. 1-11, article id 012011Conference paper (Refereed)
    Abstract [en]

    This study investigates the combination of three sensors to improve in-process monitoring of the liquid bridge between the feedstock wire and melt pool in hot-wire Directed Energy Deposition using Laser Beam. The stability of the deposition process relies on the transfer of metal between the molten feedstock wire and melt pool. Therefore, monitoring the condition of the liquid bridge and the interaction between the feedstock wire and melt pool is crucial. By utilizing a laser-optics-integrated visible range optical spectrometer and electrical sensors measuring voltage and current, relevant process changes and indications of instabilities were detected. Combined information from the current sensor and the spectrometer provided a better understanding of the process and helped to identify deviations leading to unstable deposition modes.

    Download full text (pdf)
    fulltext
  • 11.
    Kisielewicz, Agnieszka
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sadeghi, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Palumbo, Gianfranco
    CNR-IFN Institute for Photonics and Nanotechnologies, Physics Department, Bari, Italy (ITA).
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. CNR-IFN Institute for Photonics and Nanotechnologies, Physics Department, Bari, Italy (ITA).
    In-process spectroscopic detection of chromium loss during Directed Energy Deposition of alloy 7182020In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 186, article id 108317Article in journal (Refereed)
    Abstract [en]

    In this work, a fast optical spectrometer was used to monitor the Directed Energy Deposition (DED) process, during the deposition of Alloy 718 samples with different laser power, thus different energy inputs into the material. Spectroscopic measurements revealed the presence of excited Cr I atoms in the plasma plume. The presence was more apparent for the samples characterized by higher energy input. The Cr depletion from these samples was confirmed by lower Cr content detected by Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The samples were also characterized by higher oxidation and high-temperature corrosion rates in comparison to the samples produced with low energy input. These results prove the applicability of an optical emission spectroscopic system for monitoring DED to identify process conditions leading to compositional changes and variation in the quality of the built material.

  • 12.
    Kisielewicz, Agnieszka
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems.
    Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 7182018In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 418-425Article in journal (Refereed)
    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.

  • 13.
    Kisielewicz, Agnieszka
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Thalavai Pandian, Karthikeyan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sthen, Daniel
    GKN Aerospace Sweden AB,Trollhättan, Sweden.
    Hagqvist, Petter
    University West, Department of Engineering Science, Division of Production Systems. Procada AB, Trollhättan.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. University of Bari, Physics Department, Bari, (ITA).
    Hot-Wire Laser-Directed Energy Deposition: Process Characteristics and Benefits of Resistive Pre-Heating of the Feedstock Wire2021In: Metals, ISSN 2075-4701, Vol. 11, no 4, p. 1-25Article in journal (Refereed)
    Abstract [en]

    This study investigates the influence of resistive pre-heating of the feedstock wire (here called hot-wire) on the stability of laser-directed energy deposition of Duplex stainless steel. Data acquired online during depositions as well as metallographic investigations revealed the process characteristic and its stability window. The online data, such as electrical signals in the pre-heating circuit and images captured from side-view of the process interaction zone gave insight on the metal transfer between the molten wire and the melt pool. The results show that the characteristics of the process, like laser-wire and wire-melt pool interaction, vary depending on the level of the wire pre-heating. In addition, application of two independent energy sources, laser beam and electrical power, allows fine-tuning of the heat input and increases penetration depth, with little influence on the height and width of the beads. This allows for better process stability as well as elimination of lack of fusion defects. Electrical signals measured in the hot-wire circuit indicate the process stability such that the resistive pre-heating can be used for in-process monitoring. The conclusion is that the resistive pre-heating gives additional means for controlling the stability and the heat input of the laser-directed energy deposition.

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    fulltext
  • 14.
    Mi, Yongcui
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Guglielmi, Pasquale
    Department of Mechanics, Mathematics and Management, Politecnico di Bari, Bari (ITA).
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Palumbo, Gianfranco
    Department of Mechanics, Mathematics and Management, Politecnico di Bari, Bari (ITA).
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Department of Mechanics, Mathematics and Management, Politecnico di Bari, Bari (ITA).
    Beam shaping with a deformable mirror for gap bridging in autogenous laser butt welding2023In: Optics and Lasers in Engineering, ISSN 0143-8166, Vol. 169, article id 107724Article in journal (Refereed)
    Abstract [en]

    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.

  • 15.
    Mi, Yongcui
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Physics Department, University of Bari, Bari (ITA).
    Conduction mode laser welding with beam shaping using a deformable mirror2022In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 148Article in journal (Refereed)
    Abstract [en]

    This study explores the possibility of tailoring the fusion zone in conduction mode laser welding using a deformable mirror for beam shaping of multi-kilowatt continuous wave laser sources. Three power density distributions were shaped and used in bead on plate welding of Ti64 plates in conduction mode at three travel speeds. The effect on melt pool free surface geometry, cross section, microstructure and hardness profiles was measured and studied. It is shown that the geometry of the melt pool can be modified using a deformable mirror. A narrower and longer melt pool or a wider, shorter and shallower one were indeed obtained forming Gaussian-elliptical power density distributions oriented along and transverse to the travel direction, respectively. The latter distribution could be a favourable option for laser beam additive manufacturing as it could improve process efficiency while reducing remelting of the previous layer. This system has also a promising potential for adaptive process control since it could change fundamentally the beam shape at a rate faster than 10 ms. 

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    Optics and Laser Technology
  • 16.
    Mi, Yongcui
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. CNR-IFN Institute for Photonics and Nanotechnologies, Physics Department, via Amendola 173, Bari, 70126, Italy.
    Vision based beam offset detection in laser stake welding of T-joints using a neural network2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 42-49Article in journal (Refereed)
    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.

  • 17.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Automation Systems.
    Monitoring of laser beam welding by a non-intrusive optical sensor system using photodiodes2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29 2015, JOM-institute , 2015, p. 1-14Conference paper (Refereed)
    Abstract [en]

    Monitoring and control of automated laser beam welding is necessary in order to increase weld quality and to optimise the process. This paper presents an evaluation of an optic monitoring system using photodiodes, integrated coaxial into the laser welding tool to monitor the optical electromagnetic emissions from the process. Three photodiodes are used, one for the visual spectra, one for the reflected laser light and one for the infrared spectra.A survey of previous research regarding monitoring of welding using photodiodes have been conducted, it indicated the need for development of a high bandwidth monitoring system able to capture the fast dynamic events of the welding process. Based on this a monitoring system was developed and the frequency components of the monitored signals was analysed. Welding experiments, using a 1 μm YAG laser on nickel-based alloy sheet metal of different thicknesses, has also been conducted in order to evaluate the correlation between monitored signals and change of parameters effecting the weld quality. Laser power and laser focus was changed during the experiments.I was shown that a bandwidth of 30 kHz for the monitoring system would be sufficient to capture the interesting components of the signals from the photodiodes. A clear correlation between signal level from the sensor monitoring the infrared spectra and weld penetration was found and also a correlation between reflected laser light and laser beam focus. High intensity peaks was found in the signal from the sensor monitoring the visual spectra. It is assumed, but not confirmed, that they show the formation plasma in the key hole.

  • 18.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Joint tracking in zero gap laser beam welding using a vision sensor2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-7Conference 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.

  • 19.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    A study on change point detection methods applied to beam offset detection in laser welding2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 72-79Article in journal (Refereed)
    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.

  • 20.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Adaptive control of the filler wire rate during laser beam welding of squared butt joints with varying gap width2019In: 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)
    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

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  • 21.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems.
    In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints2018In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 511-516Article in journal (Refereed)
    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.

  • 22.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. IFN-CNR Institute for Photonics and Nanotechnologies, Physics Department, via Amendola 173, 70126 BARI, Italy.
    Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System2017In: Physics Procedia, E-ISSN 1875-3892, Vol. 89, p. 100-107Article in journal (Refereed)
    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.

  • 23.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Physics Department, IFN-CNR Institute for Photonics and Nanotechnologies, Bari, Italy.
    Robust vision-based joint tracking for laser welding of curved closed-square-butt joints2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 101, no 5-8, p. 1967-1978Article in journal (Refereed)
    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.

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  • 24.
    Nilsen, Morgan
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. IFN-CNR Institute for Photonics and Nanotechnologies, Physics Department, via Amendola 173, 70126 BARI, Italy.
    Vision and spectroscopic sensing for joint tracing in narrow gap laser butt welding2017In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 96, p. 107-116Article in journal (Refereed)
    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.

  • 25.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hagqvist, P.
    Procada AB, Trollhättan.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    CFD-Based Feasibility Study of Laser-Directed Energy Deposition With a Metal Wire for On-Orbit Manufacturing2022In: Frontiers in Space Technologies, E-ISSN 2673-5075, Vol. 3, p. 1-13, article id 880012Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing of parts on-site in space requires investigating the feasibility ofadapting to zero-gravity and near-vacuum conditions, a technology applied today on Earthat standard conditions. While a few studies have been conducted for powder bed fusion, afeasibility study remains to be explored for direct energy deposition using a laser beam anda metal wire. This is the purpose of this study, which is conducted using a modelingapproach based on computational fluid dynamics. The simulation model developedincludes melting, re-solidification, vaporization, prediction of beam energy absorptionas a function of the local surface temperature and curvature, ray tracing, tracking of freesurface deformation and metal transfer, and wire-resistive heating. The study is carried outby starting from process parameters suited for stable on-Earth metal deposition. Theseconditions were also studied experimentally to validate the simulation model, leading tosatisfactorily results. A total of three other test cases with ambient pressure lowered downto near-vacuum and/or gravitation down to zero are investigated. It is found that,compared to on-Earth conditions, in-space conditions can induce vaporization of themetal alloy that is large enough to result in a curvature of the melt pool free surface but toosmall to lead to the formation of a keyhole. The in-space conditions can also modify theforce balance at the liquid melt bridge between the wire and the melt pool, leading to smallchanges in the curvature and temperature field at the free surface of the wire tip. Among theobserved consequences are a small increase of the melt pool length and a small elevationof the bead height. More importantly, for process control, changing to in-space conditionsmight also affect the stability of the process, which could be assessed through the width ofthe liquid metal bridge. However, by using appropriate process control to maintain acontinuous liquid metal bridge, it is concluded that direct energy deposition of metal usinga laser and a wire could be used for manufacturing metal parts in-space in a temperedatmosphere.

  • 26.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Kisielewicz, Agnieszka
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of laser-wire interaction on heat and metal transfer in directed energy deposition2023In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 205, article id 123894Article in journal (Refereed)
    Abstract [en]

    In this study, laser metal fusion with feedstock wire is addressed. We investigated how various process parameters affect the fraction of beam energy that is absorbed by the wire and the workpiece and the metal transfer from the feedstock wire to the melt pool. To perform this research, a thermo-fluid dynamic model with tracking of free surface deformation was developed to include the feeding of a solid wire and predict its melting. The fraction of beam energy absorbed by the metal was modeled as a function of local surface curvature and temperature, accounting for multiple Fresnel reflections and absorptions. The model was applied to Titanium alloy (Ti-6Al-4V) with a 1.07 μm laser and a process in conduction mode. Experiments at various wire feeding rates were conducted to evaluate the model’s ability to predict the process and a good agreement was obtained. The different parameters studied were the beam angular position, the wire angular position, the wire feed rate, and the beam-wire offset. The analysis of the simulation results gave a detailed physical understanding of the laser energy use. It highlighted that thermocapillary and Rayleigh-Plateau instabilities can contribute to the transition from continuous to drop metal transfer mode. Damping these instabilities might thus allow using a wider process window.

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  • 27.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of shaped laser beam profiles on melt flow dynamics in conduction mode welding2021In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 166, p. 1-15, article id 106957Article in journal (Refereed)
    Abstract [en]

    A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three beam shapes are studied at several welding travel speeds: a reference Gaussian profile and its elliptic elongations along and transverse to the welding travel direction. It is found that these beam shapes change not only the intensity and direction of the melt thermocapillary flow but also the flow pattern. For instance, and contrary to the other profiles, the beam shape elongated along the welding travel direction generates melt front vortices that assist metal pre-heating. It can result in deeper penetration, larger melt volume, and lower amount of thermal energy diffused into the heat affected zone. The simple elongation of a beam profile has thus a non-linear effect on the melt flow and in turn on the seam geometry as well as the temperature gradients in the heat affected zone.

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  • 28.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of Laser Beam Shaping on Melt Pool Thermocapillary Flow2020In: Proceedings of the 6th World Congress on Mechanical, Chemical, and Material Engineering (MCM'20) Prague, Czech Republic Virtual Conference – August, 2020 / [ed] Huihe Qiu, 2020, article id HTFF 125Conference paper (Refereed)
    Abstract [en]

    The effect of different shapes of laser beam power density distribution was investigated numerically with respect to the thermo-hydrodynamics of the melt pool during welding. The process addressed is conduction mode bead on plate welding of the Titanium alloy Ti-6Al-4V. A new solver based on the volume of fluid method to track the deformation of the melt free surface was developed in the OpenFOAM software. Experiments were conducted for the purpose of validating the model. In addition to the traditional cross-cut images of the weld bead, top view images of the melt pool were analysed to perform the validation along the 3-space dimensions. A good agreement between numerical predictions and experimental measurements was obtained, thus promising aconfident utilization of this simulation model when investigating the influence of beam shapes on the resulting weld seam. The effectof three different beam shapes on the melt pool velocity flow, temperature fields, and melt geometry were studied. It was found that the melt pool size was largest for an elliptical power density distribution with the major axis along the welding direction. The results also showed that the laser beam with Gaussian power density distribution resulted in the deepest penetration.

  • 29.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Mi, Yongcui
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Modelling of beam energy absorbed locally in conduction mode laser metal fusion2021In: Journal of physics. D, Applied physics, ISSN 0022-3727, Vol. 55, no 2, article id 025301Article in journal (Refereed)
    Abstract [en]

    Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach isd eveloped. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloyTi-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over awide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left afterre-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.

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  • 30.
    Rahmani Dehaghani, Mostafa
    et al.
    School of Mechatronic Systems Engineering, Simon Fraser University, Burnaby (CAN).
    Sahraeidolatkhaneh, Atieh
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Sajadi, Pouyan
    School of Mechatronic Systems Engineering, Simon Fraser University, Burnaby (CAN).
    Tang, Yifan
    School of Mechatronic Systems Engineering, Simon Fraser University, Burnaby (CAN).
    Wang, G. Gary
    School of Mechatronic Systems Engineering, Simon Fraser University, Burnaby (CAN).
    System identification and closed-loop control of laser hot-wire directed energy deposition using the parameter-signature-quality modeling scheme2024In: Journal of Manufacturing Processes, ISSN 1526-6125, p. 1-13Article in journal (Refereed)
    Abstract [en]

    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.

  • 31.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Modeling and simulation for welding automation2010Doctoral thesis, comprehensive summary (Other academic)
  • 32.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Automation Systems.
    Operator bias in the estimation of arc efficiency in gas tungsten arc welding2015In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 20, no 1, p. 128-133Article in journal (Refereed)
    Abstract [en]

    In this paper the operator bias in the measurement process of arc efficiency in stationary direct current electrode negative gas tungsten arc welding is discussed. An experimental study involving 15 operators (enough to reach statistical significance) has been carried out with the purpose to estimate the arc efficiency from a specific procedure for calorimetric experiments. The measurement procedure consists of three manual operations which introduces operator bias in the measurement process. An additional relevant experiment highlights the consequences of estimating the arc voltage by measuring the potential between the terminals of the welding power source instead of measuring the potential between the electrode contact tube and the workpiece. The result of the study is a statistical evaluation of the operator bias influence on the estimate, showing that operator bias is negligible in the estimate considered here. On the contrary the consequences of neglecting welding leads voltage drop results in a significant under estimation of the arc efficiency. © 2015, Universidade Federal de Uberlandia. All rights reserved.

  • 33.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Automation Systems.
    Operator influence on the estimation of arc efficiency in gas tungsten arc welding2013In: JOM-17 - International Conference on Joining Materials, 5-8 May 2013, Helsingør, Denmark. Proceedings / [ed] Osama Al-Erhayem, JOM-Institute , 2013Conference paper (Other academic)
    Abstract [en]

    In this paper the operator bias in the measurement process of arc efficiency in stationary direct current electrode negative gas tungsten arc welding is discussed. An experimental study involving 15 operators (enough to reach statistical significance) has been carried out with the purpose to estimate the arc efficiency from a specific procedure for calorimetric experiments. The measurement procedure consists of three manual operations which introduces operator bias in the measurement process. An additional relevant experiment highlights the consequences of estimating the arc voltage by measuring the potential between the terminals of the welding power source instead of measuring the potential between the electrode contact tube and the workpiece. The result of the study is a statistical evaluation of the operator bias influence on the estimate, showing that operator bias is negligible in the estimate considered here. On the contrary the consequences of neglecting welding leads voltage drop results in a significant under estimation of the arc efficiency.

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  • 34.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Simulation-based feedback control of welding processes2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fusion welding for joining of metals is an important manufacturing process widely used in industry, and very appreciated for its usefulness. This thesis presents a strategy dealing with the problem of designing feedback control for robotised welding. The idea is to use off-line programming where computer aided robotics for weld sequences is integrated with finite element modelling for simulations and analyses of weld processes. By this approach the design, evaluations, trials and visualisation can be made “off-line”, beside or prior to continuous production. The focus is to reduce the amount of manpower and need for physical experiments. Focuses on the results are to ensure a high quality weld with limited residual stress and deformation. Different models for two types of austenitic steels and two types of weld sources has been calibrated and validated to form a basis for this strategy. Suggestions for systematic model calibration methods have been proposed including global and local optimisation methods. Experimental work has been performed to support and verify the simulation results and the usefulness of the method. The simulation based strategy has been evaluated and proven to work successfully in two different types of applications. The method is not independent of physical experiments since it is based on models that have to be calibrated, but the experiments needed are assumed to be carried out in a simple and cost efficient way. The thesis suggests how these experiments can be performed. The use of all these technologies is assumed to form an efficient tool for the welding engineer in order to obtain high weld quality in robotised welding. The research presented indicates that the methods work well in real situations and that further work for more robust industrialisation will be beneficial for the welding community.

  • 35.
    Sikström, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Simulated Feedback Control of Metal Fusion Welding2007In: Proceedings of the ninth IASTED International Conference on Control and Applications: Montreal, Canada 2007, ACTA Press , 2007, p. 2263-2270Conference paper (Refereed)
  • 36.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation Systems.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Automation Systems. University West, Department of Engineering Science, Division of Production Systems. Chalmers University of Technology, Department of Signals and Systems,Gothenburgh, Sweden.
    Model based feedback control of gas tungsten arc welding: An experimental study2015In: Automation Science and Engineering (CASE), 2015 IEEE International Conference on, IEEE conference proceedings, 2015, p. 411-416Conference paper (Refereed)
    Abstract [en]

    In order to obtain high structural integrity and joint performance in welding a transient heat conduction model has been utilized to design a model based feedback controller.Gas tungsten arc welding of work-pieces of austenitic steel have been simulated by the finite element method. The basis for controller design is a low order model obtained from parametric system identification. The identification has been performed both on the finite element simulation and on physical welding. The low order model responses show a good agreement with both the finite element simulation result and the physical process response. An experimental study has been performed to verify the approach. This study also explores what experiments are needed for a successful design. It is shown that model based control successfully mitigates perturbations that occur during welding.

  • 37.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Process and Product Development. University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Process and Product Development. University West, Department of Engineering Science, Division of Production Systems.
    Model order reduction methods applied to a welding model2012In: Proceedings of the Institution of mechanical engineers. Part I, journal of systems and control engineering, ISSN 0959-6518, E-ISSN 2041-3041, Vol. 226, no 7, p. 972-984Article in journal (Refereed)
    Abstract [en]

    A  finite element representation modelling transient heat conduction of gas tungsten arc welding of stainless steel is used to evaluate different methods for model order reduction. The focus is on establishing a linear low-order model of the dynamic  relation between the welding current and the temperature measured by a radiation pyrometer. The objective of this low-order model is to design a model-based feedback controller and to investigate the consequences of applying feedback control of the process. Three different approaches for model reduction have been evaluated, namely the Krylov subspace method for moment    matching, balanced truncation and parametric system identification. The study provides a knowledge base for the selection of model order reduction methods when dealing with large-scale systems like finite element models of transient heat conduction, and it recommends parametric system identification. It renders sufficient approximations for controller design, no linearization of the finite element model is required, and there is no limit on degrees of freedom of the finite element model.

  • 38.
    Sikström, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Production Systems. Chalmers University of Technology, Department of Signals and Systems.
    Modelling and Simulation for Feedback Control of Welding2007In: Proceeding (567) Modelling and Simulation (MS 2007): Montreal, CanadaMay 30 - June 1, 2007, ACTA Press , 2007, p. 131-136Conference paper (Refereed)
  • 39.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering. University West, Department of Engineering Science, Division of Production Systems.
    Role of fixture forces on distortion in gas tungsten arc welding: An experimental and modelling approach2011In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 225, no 1, p. 140-148Article in journal (Refereed)
    Abstract [en]

    Simulation and experiments show that the fixture clamping force has a significant influence on the structural integrity of a welded workpiece. This understanding is of great importance for the manufacture of aerospace components with tight tolerances in the specifications. The focus in the present study is on the temperature history during welding and residual deformation; its main contribution is a demonstrator designed for evaluation of the influence of fixture clamping forces and validation of the simulation results. The demonstrator concerns a simplified situation considering gas tungsten arc welding of a nickel-based metal plate fixed by a specially designed fixture, where one side of the plate was clamped with different levels of force. The temperature history was measured during the weld sequence and deformation measurements were performed after cooling and release of the workpiece from the fixture. The results from simulation and experimentation showed good agreement. The proposed strategy is industrially competitive and has shown that the looser the fixture clamps, the smaller the residual deformation. Furthermore, the study provides a knowledge base for selection of active fixture concepts in that the fixture clamping force can be determined in advance and possibly also be subject to force control.

  • 40.
    Sikström, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Production Systems. Chalmers University of Technology, Department of Signals and Systems.
    Simulation for Design of Automated Welding2007In: EUROCON, 2007. The International Conference on "Computer as a Tool": Warsaw, Poland, 2007, IEEE Explore , 2007, p. 2263-2270Conference paper (Refereed)
    Abstract [en]

    This paper describes a promising approach where simulations were used in the design of real-time control for automated welding. A finite element method has been used for thermal modelling of gas tungsten arc welding on a simplified test object. Measurement data for model calibration and validation was acquired through thermal imaging during weld experiments on test objects of the alloy Fe-316. An optimisation scheme for inverse modelling was employed in the calibration of the distributed weld process model. Frequency weighted model reduction and parametric system identification were applied and evaluated to get a low order model of the single-input single-output dynamics between a simulated weld heat source (actuator) and a sensor. This low order model was then successfully used for controller design where the control signal was weld current and the measured output was a moving spot temperature. Finally, the closed-loop performance was evaluated by simulation of the weld process model showing improved temperature stability relative to open loop.

  • 41.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Ericson Öberg, Anna
    Volvo Construction Equipment, Arvika, Sweden.
    Prediction of penetration in one-sided fillet welds by in-process joint gap monitoring: an experimental study2017In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 61, no 3, p. 529-537Article in journal (Refereed)
    Abstract [en]

    The challenge to predict variations in penetration depth in one-sided fillet welds during robotized gas metal arc welding has been addressed by a pilot investigation of technical possibilities and limitations. The main cause for the variation in penetration depth is considered to be variation in joint gap size. Special attention has been paid in order to adopt the experimental conditions to conform to industrial welding conditions. The employed method uses in-process monitoring of joint gap size together with an empirical model relating penetration depth to gap size in order to predict this depth. The gap size estimates are based on image information from two cameras, one visual and one infrared. The results, that are evaluated off-line, confirm the development of a real-time method providing technical solutions that are industrially tractable. The results also pinpoint areas of further improvements towards increased robustness and reduced estimation uncertainties.

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  • 42.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ericsson, Mikael
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Integration of finite element analysis and computer aided robotics for advanced programming of robotized welding2009In: ASM Proceedings of the International Conference: Trends in Welding Research / [ed] S.A. David, T. DebRoy, J.N. DuPont, T. Koseki, and H.B. Smartt, ASM International, 2009, p. 454-460Conference paper (Refereed)
    Abstract [en]

    This paper describes a promising approach where finite element analysis is combined with computer aided robotics in off-line programming of advanced robotized welding. Finite element analysis is used to find an optimized weld power signal based on weld trajectories obtained from computer aided robotic simulations. The weld power signal is calculated by applying feedback control in the finite element simulation. This optimization ensures a full penetration weld while the total specific thermal energy input is minimized in order to mitigate unwanted residual stress and distortion. The objective with this approach is to support the design of robotized welding and significantly reduce the number of costly trials in physical implementations. The relevance of this paper is a useful method for off-line optimization of robot trajectories and varying process parameters.

  • 43.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ericsson, Mikael
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Niklasson, Kjell
    University West, Department of Engineering Science, Division of Process and Product Development.
    Tools for simulation based fixture design to reduce deformation in advanced fusion welding2008In: Intelligent Robotics and ApplicationsLecture Notes in Computer Science Volume 5315,  2008: First International Conference, ICIRA 2008 Wuhan, China, October 15-17, 2008 Proceedings, Part II / [ed] Youlun Xioun, Springer, 2008, Vol. 5315 LNAI, no PART 2, p. 398-407Conference paper (Refereed)
    Abstract [en]

    The traditional fusion welding and fixture simulations are performed using advanced finite element simulation tools, commonly used are e.g. MSC.Marc, ANSYS, ABACUS and COMSOL Multiphysics. These simulations are made one at a time and separately due to heavy calculation load for each case. Such an approach does not give a full description of the integrated work piece and fixture behaviour. We propose a strategy to decrease the computational time and solve the problem accurately enough for industrial needs. Focus of the simulation result is on residual deformation. The work piece is a simplified component composed by metal sheets, and rigid and loose clamping was investigated. Simulation results give the size of forces and deformations in the clamped edge. Deformation measurements are performed using 3D-scanning of the work piece after cooling and released from fixture, same situation as in the FE-simulations. The proposed strategy has shown to be useful and is industrially competitive due to reduced engineering manpower, computation time, and need for practical experiments. The strategy is to use full off-line programming where computer aided robotics for weld sequencies is integrated with finite element modelling in order to obtain weld parameters and fixture design.

  • 44.
    Sikström, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Ericsson, Mikael
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science.
    3D-Scanning for Weld Distortion Measuring2006In: Instrumentation and Measurement Technology Conference, 2006. IMTC 2006. Proceedings of the IEEE, IEEE conference proceedings, 2006, p. 2132-2137Conference paper (Refereed)
    Abstract [en]

    Optical three dimensional scanning for weld distortion measurements have been performed for validation, inspection, general visualization and documentation of a robotized welding process. The planning, preparing and processing of the weld is done in a simulation-based concept where computer aided robotics software simulations are integrated with finite element analysis simulations with the objective to reduce global geometrical deformation during welding. The off-line programmed robot paths were used as an input for finite element calculations of temperature fields and distortion in the work piece. In order to validate the finite element model 3D-scannings have been performed before and after every single welding sequence. This paper describes a validation experiment with non-contact measurements of weld distortion and discusses limitations in optical 3D-scanning techniques used for this purpose

  • 45.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Heat input and temperatures in welding2013In: JOM-17 - International Conference on Joining Materials, JOM-Institute , 2013Conference paper (Refereed)
    Abstract [en]

    A key feature in welding is the energy supplied, in order to join the work pieces together. For all fusion welding methods, the supplied energy is so high that the work-piece joint surfaces are melted and fused together. The energy supplied is then transported away, mainly by conduction through the base materials. The temperature of the weld decreases and a solid joint is eventually formed. This may then undergo phase transformations and finally the weld joint reaches ambient temperature.

    The thermal history of a welded joint has a large effect on the microstructure and mechanical properties. Welding metallurgist therefore consider the cooling time t8/5 as crucial to understand the resulting properties of a joint in steel structures. The cooling time is influenced by several factors, like heat input, base material thickness, base material thermal properties, preheat an interpass temperatures etc. Regarding the heat input, the efficiency of the welding arc has for a long time been debated, i.e. how much of the arc energy really goes into the weld. Large efforts are being made to measure this very accurately.

    Another significant research field has been to measure or calculate the cooling time of welds, in particular t8/5. However, this cooling time is affected by the arc energy and by the arc efficiency.

    In a more macroscopic sense, it has been shown that the temperature of a welded structure can vary with the presence of for example internal heat sinks. Such variations may affect macroscopic properties like penetration. One way to ensure constant condition in terms of temperature could be to increase the heat input if the temperature decreases. However, how such variations affect for example the cooling rate has not been studied.The aim of the present paper is to report some experimental results regarding cooling rate in welded joints and put this into context of arc efficiency and temperature regulations and also discuss how the cooling rate may be affected in more production like welding situations.

  • 46.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Beam offset detection in laser stake welding of tee joints based on photodetector sensing2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 64-71Article in journal (Refereed)
    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.

  • 47.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Automation Systems.
    Vision systems for in‐process monitoring of laser beam welding2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015, JOM-Institute , 2015, p. 1-8Conference paper (Refereed)
    Abstract [en]

    This paper addresses the issue of evaluating an optical vision system to be integrated with a 1μm laser beam welding tool for process monitoring. The boundary conditions for the system performance and system nature imposed by the needs in industrial production is highlighted. Initial welding experiments have been executed in order to understand the applicability of the vision system. The evaluation includes considerations on the required sensor bandwidth. The need for time synchronized data is emphasized and the use of numerical algorithms for enhancing the estimation and detection performanceof the system is discussed. The results shows a good potential for the system to give robust process information to be used in monitoring and control.

  • 48.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Automation Systems.
    Eriksson, Ingemar
    GKN Aerospace, Trollhättan, Sweden.
    Optical Methods for In-Process Monitoring of Laser Beam Welding2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-9Conference 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.

  • 49.
    Sikström, Fredrik
    et al.
    University West, Department of Engineering Science, Division of Production Systems.
    Runnemalm, Anna
    University West, Department of Engineering Science, Division of Production Systems.
    Broberg, Patrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsen, Morgan
    University West, Department of Engineering Science, Division of Production Systems.
    Svenman, Edvard
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Evaluation of non-contact methods for joint tracking in a laser beam welding application2016In: The 7th International Swedish Production Symposium, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Symposium , 2016, p. 1-6Conference paper (Refereed)
    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.

  • 50.
    Öberg, Anna Ericson
    et al.
    Volvo Construction Equipment, Arvika, Sweden.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Barriers for industrial implementation of in-process monitoring of weld penetration for quality control2017In: 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)
    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.

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