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  • 1. Engström, Hans
    et al.
    Norman, Peter
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    DATLAS: a new approach for monitoring the laser welding process2007In: 11th NOLAMP Conference: 11th NOLAMP Conference in Laser Processing of Materials ; Lappeenranta, August 20 - 22,2007 / [ed] Veli Kujanpää, Lappeenranta: Lappeenranta University of Technology Press, 2007Conference paper (Refereed)
  • 2.
    Engström, Hans
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Karlsson, Jan
    Hybridsvetsning av lastbilskomponenter med 15 kW fiberlaser och MAG2010Report (Other academic)
  • 3. Eriksson, Ingemar
    et al.
    Norman, Peter
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Basic study of photodiode signals from laser welding emissions2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Photodiodes are commonly used to monitor laser welding as a cheap, rugged, online method to get an indication of changes in the process, particularly the occurrence of defects. However, the correlations between the signal characteristics and the process are usually empirical and not fully understood. In this basic study we try to obtain a better understanding of the generation of the signals from the laser welding process. By synchronising high speed imaging with photodiode signals in three wavelength spectra, we attempt to identify the contributions from different geometrical domains and temporal events, particularly from the weld pool surface, the keyhole opening and the escaping metal vapour flow. It is particularly valuable to study dynamic behaviour during pulsed laser welding. A quantitative estimation is difficult, but , with the help of high speed photography and modelling, clear correlations between different dynamic events and signal changes can be identified.

  • 4.
    Forsman, Tomas
    et al.
    Luleå tekniska universitet.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ämnesskarvning med laser minskar bilens vikt2002In: Svetsen, ISSN 0039-7091, no 3, p. 30-31Article in journal (Other academic)
  • 5.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lamas, Javier
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Yañez, Armando
    Centro de Investigacións Tecnolóxicas, Universidade da Coruña, Ferrol.
    Scanner analysis of the topology of laser hybrid welds depending on the joint edge tolerances2011In: 13th NOLAMP Conference: 13th Conference on Laser Materials Proce Nordic Countries 27 - 29 June 2011 / [ed] Einar Halmøy, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2011Conference paper (Refereed)
    Abstract [en]

    The surface geometry after laser hybrid arc welding is an important quality criterion. What isoften called welding in a rough industrial environment can in many cases systematically bereduced to a few local conditions of the joint edge during welding, particularly depending onthe edge preparation technique. In the present study, beside the influence of surface oxidesstudied in separate publications, the conditions are reduced to the local gap width, verticalsurface position and edge mismatch. Gas cut edge conditions are compared to milling andlaser cutting. By scanning the steel edges of a 10 mm butt joint before and during hybridwelding and relating the systematic variation of the above three properties to the scannedtopology of the resulting weld, quantitative correlations are identified. By the aid of highspeed imaging, explanations for the trends can be found. Operating windows with controllabletrends can be quantitatively mapped and distinguished from instable regimes. Beside higherroughness, gas cut edges show a superimposed edge oscillation of longer periodicity, beingless visible but important. During welding, concave surface bending and gap widening alterthe initial conditions. Awareness and quantitative identification of the edge conditions isrecommended to control the welding process in a rough industrial environment.

  • 6.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Eriksson, Ingemar
    Analysis of the keyhole and weld pool dynamics by imaging evaluation and photodiode monitoring2009In: Proceedings of LAMP2009: The 5th International Congress on Laser Advanced Materials Processing ; LPM2009, the 10th International Symposium on Laser Precision Microfabrication ; HPL2009, the 5th International Symposium on High Power Laser Processing ; Kobe, June 29 - July 2, 2009 ; [congress program & technical digest], Tokyo: Sumitomo Corp. , 2009Conference paper (Refereed)
    Abstract [en]

    Process monitoring of laser welding defects by commercial systems based on photodiodes has high potential, but improved understanding is desirable for more systematic industrial use. The signal is generated from spectrally filtered emissions or reflections from the dynamic welding process. Improved knowledge on the cause of the signal was achieved by accompanying high speed imaging. Numerical evaluation of the images and subsequent modelling provided additional information to judge the potential and limits of commercial photodiode sensors. For welding with a 3 kW Nd:YAG-laser, a 15 kW fibre laser or a 14 kW CO2-laser, various joint cases were studied with respect to defects like craters, spatter, blowholes, underfill, root drop-out, lack of penetration, lack of fusion or pores. From the findings a more general theoretical description of the links between the welding process, the defect mechanism and the generated signal was initiated.

  • 7.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Soldatov, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Eriksson, Ingemar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fang, Shaoli
    Baughman, Ray
    Incorporation of CNT-yarns into metals by laser melting of powder2012In: 31st International Congress on Applications of Lasers and Electro-Optics (ICALEO) Proceedings, Laser institute of America , 2012, p. 1239-1246Conference paper (Refereed)
  • 8. Kaplan, Alexander
    et al.
    Westin, Elin
    Outokumpu Stainless, Avesta Research Center.
    Wiklund, Greger
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Imaging in cooperation with modeling of selected defect mechanisms during fiber laser welding of stainless steel2008In: Congress proceedings: ICALEO, 27th International Congress on Applications of Lasers and Electro-Optics : October 20 - 23, 2008 Pechanga Resort & Casino, Temecula, CA, USA / [ed] Yongfeng Lu, Orlando, Fla: Laser institute of America , 2008, p. 789-798Conference paper (Refereed)
    Abstract [en]

    Fiber laser welding of stainless steel was studied for different joint configurations and gaps. The higher focusing capability of fiber lasers compared to traditional Nd:YAG and CO2 lasers creates different, usually smaller, keyhole and melt pool geometries. These geometrical aspects, accompanied by a different laser energy redistribution, are essential for the weld pool dynamics and the resulting joint, with or without defects. Typical defects identified during fiber laser welding were spatter, humping, or lack of material at the top or root. High-speed imaging enables observation of the geometry and motions of the melt pool surface and keyhole during welding. This is illuminated by an additional diode laser permitting spectral filtering and also the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena that are difficult to measure, such as effects inside the melt volume or the impact of surface tension forces on dynamic melt motion. For recorded melt surface motion images, in particular, the corresponding surface tension forces and other mechanisms can be estimated by cooperative complementary modeling, enabling to draw conclusions. This advanced method was carried out for the different joint and defect cases studied, resulting in an illustrated theoretical description of the observed physical phenomena.

  • 9.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Rubin, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lamas, Javier
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Yañez, Armando
    Universidade da Coruña, Ctr Invest Tecnol.
    Observation of the mechanisms causing two kinds of undercut during laser hybrid arc welding2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 17, p. 7501-7506Article in journal (Refereed)
    Abstract [en]

    Two different kinds of undercut were identified when laser hybrid welding hot rolled HSLA-steel in either the as-rolled condition or with the top surface mill scale removed. The presence of mill scale on the steel surface was found to give a sharp angled undercut combined with a sharp oxide inclusion at the edge of the weld which would have the same mechanical effect as a crack in this position. Removal of the surface oxides before welding resulted in the elimination of the oxide inclusions and a more rounded undercut geometry indicative of superior mechanical properties, particularly fatigue life. The mechanisms of the formation of both types of undercut have been analysed by high speed photography and SEM.

  • 10.
    Lamas, Javier
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Yañez, Armando
    The effect of fit-up geometry on melt flow and weld quality in laser hybrid welding2013In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, no 3Article in journal (Refereed)
    Abstract [en]

    Hybrid laser-arc welding has a good tolerance to poor fit up as compared to simple laser welding. For a butt joint, the joint fit-up variations can be reduced to two local properties: the gap width and the vertical edge mismatch. The impact of these two properties on the resulting weld quality has been studied systematically in this paper. The original edges as well as the resulting weld surface topography have been scanned in three dimensions in order to study trends. During hybrid welding, the melt flow and the electric arc were observed at the top surface by high speed imaging to analyze the complex fluid flow phenomena.

  • 11.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Advanced process monitoring and analysis of machining2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Milling is a processing technology massively applied in the metal manufacturing industry. The continuous demand for higher productivity and product quality asks for better understanding and control of the machining process. A better understanding can be achieved through experimental measurement and theoretical simulations and modelling of the process and its resulting product. In particular process monitoring and control is desirable for automated control and optimization of the process and in turn of productivity and product quality. However, due to the high complexity of the process, in particular of the interaction system/process/product, the above goals have only partially been achieved today, to a limited, unsatisfactory extent. The here presented research addresses the above needs and their progress by developing and starting to implement and study a highly sophisticated sensor and analysis platform for machining with the objectives of (i) advanced measurement and analysis of the milling process and (ii) advanced process monitoring and control. For a certain highly advanced high speed machining centre a comprehensive concept has been developed for the integration different kinds of sensors to the system. In particular the complex concept takes into account sophisticated analysis, research and development through the cooperation between different experimental and theoretical methods. The present thesis presents the developed platform concept. Due to the complexity of this sensor and analysis platform and its early stage of development, the here presented research work focuses on the implementation and investigation of selected sensors and analysis methods. Paper I screens and discusses the possibilities of the applied machining centre for sensor integration, particularly aiming at process monitoring. From the large variety of relevant sensors, particularly promising turned out to be acoustic emission sensors, force sensors, accelerometers, temperature sensors and optical sensors. Their potential and limitations are discussed. The specific concept developed for the addressed high speed machining centre is described in Paper II. Force sensors measuring the spindle force components, flexible accelerometers measuring the vibrations at almost any desired spindle or product location and Laser Doppler Vibrometry (LDV) for non-contact measurement of vibrations turned out to be the most promising sensors, to be implemented and studied in more detail in the following. Moreover, the concept recommends the cooperation of the sensors with modelling, simulation and analysis at different levels. Experimentally, the simulation of a static load to the spindle or even oscillating load through a magnetic shaker was realised in order to simulate the processing conditions for measuring and characterizing the spindle behaviour. The LDV- measurement enables precise identification of spindle oscillations at different locations. A particular challenge is the identification of stable operating points at high rotational speeds through stability lobes. For this purpose the vibrations of a certain complex, thin walled aerospace structure were measured by LDV and in good agreement simulated by FEA for different machining process stages in order to derive stable lobe areas. Beside implementation and first testing of the above mentioned methods, the paper describes and discusses possible concepts for a closed loop control of the process. In Paper III the LDV method is for the first time and successfully applied for measuring the fee-running rotating spindle of a high speed machining centre. In particular the roundness of the dummy tool applied was measured at high accuracy during rotation, as verified by mechanical measurement. Moreover, the LDV permits the measurement of misalignment of other geometrical and kinematical imperfections of the spindle rotation. Paper IV describes in more detail the verification of FEA through LDV for the complex aerospace structure, presented in Paper II. Both, vibrations of the unconstrained and of the clamped workpiece are studied. Moreover, the workpiece vibration characteristics was studied at four different machining stages, starting from aluminium stock and ending in a thin walled structure after removal of 97% of the material. In particular the corresponding stability lobes were predicted by the aid of the FEA, compared with modal analysis and with selected milling experiments. When machining a monolithic structure that reduces it's volume to such an extent gives several problem: Clamping of a thin walled structure is hard due to its flexibility, The changing dynamics of the workpiece has the affect that prediction of the vibrational properties is very hard to realise and finally the milling is hard because of the fact that the walls of the structure bends when a force is applied from the milling tool. Paper V discusses the suitability of different sensors for process monitoring, by applying them on-line during machining experiments for steel and aluminium, each at three different feed rates. The signals of force sensors in three dimensions arranged below the workpiece, of accelerometers in two directions mounted at the spindle housings and of LDV spotting the tool fixture ring were acquired on-line. The six signals were analysed, extracting mean values that were compared to the achieved surface roughness for the six different milling conditions. From evaluation of the stability of the signal and its coherence with the surface roughness trends the suitability of each sensor was discussed. While the sensors lateral and vertical to the feeding direction were not suitable, the sensors measuring in feeding direction were most promising, in particular the accelerometer and the corresponding LDV. The context between the roughness, process and sensor signals is discussed. Summarizing, a sophisticated sensor and analysis platform concept was developed. Selective sensors and methods have been implemented and studied with the purpose of system characterization, process understanding and process monitoring. The promising results encourage for continuation of this research programme.

  • 12. Norman, Peter
    Aktivitet: Measurement Science and Engineering2008Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Titel: Measurement Science and Engineering Undertitel: Measurement Science and Engineering

  • 13.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Process monitoring and analysis of laser welding and of milling2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Defects during fabrication of a part can implicate large costs for the manufacturer. In industry they use several types of measurement platforms/sensors to try to make the process more stable and detect when a defect is happening or has happened. The systems used mainly focuses on setting an upper and lower level where the signal from the sensor should be held within to withhold a satisfactory product quality. This thesis investigates two different processes, laser welding and milling and their accompanying defects. Although they are not equal process wise (mechanical and thermal) they share some similarities when using sensors for the detection/diagnostic of a defect. In some cases even the same sensor can be used for both processes. A platform for monitoring and control of milling was implemented, that was also done with the laser welding process. Both processes are described and explained. The milling process has been simulated with the crucial points laid on the vibration and force components acting on the work-piece and tool giving data on how to run the machine-tool. The process was monitored using piezoelectric force transducers, accelerometers and a Laser Doppler Vibrometer (LDV). The data was analyzed using both in-house developed and commercial software. The laser welding process has been simulated with respect to the melt pool surface radiation and the oscillations of the keyhole and melt-pool edges. It was observed with a high-speed camera, monitored with photodiodes and analyzed with commercial hardware/software systems. The aim of this work is to gain knowledge in why and how a defect arises, how it is represented in a sensor signal and if this knowledge can help industry in becoming more self-confident in using commercially available monitoring systems for defect analysis and monitoring. The work as a whole, over the last five years, consists of sixteen papers where seven have been chosen to be included in the thesis.

  • 14.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bäckström, Mikael
    Luleå tekniska universitet.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A sophisticated platform for characterization, monitoring and control of machining2006In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 4, p. 847-854Article in journal (Refereed)
    Abstract [en]

    The potential for improving the performance of machine tools is considerable. However, for this to be achieved without tool failure or product damage, the process must be sufficiently well understood to enable real-time monitoring and control to be applied. A unique sophisticated measurement platform has been developed and applied to two different machining centres, particularly for high-speed machining up to 24 000 rpm. Characterization and on-line monitoring of the dynamic behaviour of the machining processes has been carried out using both contact-based methods (accelerometer, force sensor) and non-contact methods (laser Doppler vibrometry and magnetic shaker) and numerical simulation (finite element based modal analysis). The platform was applied both pre-process and on-line for studying an aluminium testpiece based on a thin-walled aerospace component. Stability lobe diagrams for this specific machine/component combination were generated allowing selection of optimal process parameters giving stable cutting and metal removal rates some 8-10 times higher than those possible in unstable machining. Based on dynamic characterization and monitoring, a concept for an adaptive control with constraints based machine tool controller has been developed. The developed platform can be applied in manifold machining situations. It offers a reliable way of achieving significant process improvement

  • 15.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Engström, Hans
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Correlation between photodiode monitoring and high speed imaging of the dynamics causing laser welding defects2008In: Congress proceedings: ICALEO, 27th International Congress on Applications of Lasers and Electro-Optics : October 20 - 23, 2008 Pechanga Resort & Casino, Temecula, CA, USA ; [includes] Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference / [ed] Yongfeng Lu, Orlando, Fla: Laser institute of America , 2008, p. 829-837Conference paper (Refereed)
    Abstract [en]

    Today merely a few monitoring systems for in-process detection of laser welding defects are commercially available. Despite a trend towards cameras, industrially more robust is still a photodiode, measuring in an optically filtered spectral window either the thermal emissions from the melt and vapour or the laser beam reflections. The monitoring rule for each application is identified empirically through correlations between the signal dynamics and welding defects, as the linking mechanism is non-trivial and therefore hardly understood. Thus the method does not provide a systematic guideline to detect a certain welding defect.The here presented approach studies the context between the photodiode signal, the welding defects and the vapour, melt pool, keyhole and temperature dynamics. Simultaneous laser-illuminated high speed imaging is compared to photodiode monitoring at three spectral windows in order to identify through simultaneous timing any linking dynamics in a qualitative manner. Supportive methods are emission modelling and thermal imaging. Several cases of joints, materials and defects were studied to develop an illustrated theoretical description of the defect-signal correlations.

  • 16.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Engström, Hans
    Kaplan, Alexander
    State-of-the-art of monitoring and imaging of laser welding defects2007In: 11th NOLAMP Conference :: 11th NOLAMP Conference in Laser Processing of Materials ; Lappeenranta, August 20 - 22, 2007 / [ed] Veli Kujanpää, Lappeenranta: Lappeenranta University of Technology Press, 2007Conference paper (Refereed)
  • 17. Norman, Peter
    et al.
    Engström, Hans
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Theoretical analysis of photodiode monitoring of laser welding defects by imaging combined with modelling2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 19Article in journal (Refereed)
    Abstract [en]

    On-line process monitoring of laser welding defects by detecting characteristic changes of the process emissions via photodiodes has high potential but, due to the complex process, lack of directly interpretable and thus controllable correlations. Deep analysis of the process by high speed imaging in combination with modelling enables one to discuss the correlations between the signal and the process, as was demonstrated for quasi-steady state conditions and for transient phenomena. Despite improved knowledge through the study, several uncertainties like the emissivity, the keyhole radiation characteristics and the temperature field need to be identified more accurately for a complete theoretical description of the signal causes.

  • 18. Norman, Peter
    et al.
    Eriksson, Ingemar
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Monitoring laser beam welding of zinc coated sheet metal to analyze the defects occurring2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    During laser welding of overlapping zinc-coated steel sheets typically blowouts as a defect can occur. They can be crucial to the mechanical performance and to the optical appearance of the product. In the present research approved regions are compared to regions where the blowouts are in majority. Time-dependent radiation is captured with a commercial photodiode monitoring system in three different wavelengths ranges, 400-600 nm, 1100-1800 nm and 1064 nm, corresponding to metal vapour emissions, surface temperature emissions and reflected laser light, respectively. Accompanying high speed imaging as well as mathematical modelling of the process emissions was carried out, enabling combined analysis. Different gap widths and laser beam positions were studied. From imaging, surface elevations of the melt indicate a Zn-bubble formation that travels to the rear part of the melt pool before it breaks through, often completely separated from the keyhole. The escaping vapour ejects melt and causes a significant crater, if not flooded with melt again. Although this violent surface event is clearly visible, it was hardly found in the temperature sensor signal. The separate mechanisms that can be responsible for the lack of contribution of the dynamic blow-out formation to the emissions generating the photodiode signal are discussed, e.g. melt surface geometry changes, drops, temperature and emissivity changes, the role of the Znvapour and the detection area of the sensor. This study demonstrates that obvious defects can sometimes be hard to detect on-line.

  • 19.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Engström, Hans
    Modelling of the impact of melt surface dyanmics on a photodiode monitoring signal in laser welding2007In: Congress proceedings: 2007 ICALEO, 26th International Congress on Applications of Lasers & Electro-Optics : October 29 - November 1, 2007, Hilton in the Walt Disney World Resort, Orlando, FL, USA ; [including] Laser Materials Processing Conference, Laser Microprocessing Conference [and] Nanomanufacturing Conference / [ed] Yongfeng Lu, Laser institute of America , 2007Conference paper (Refereed)
    Abstract [en]

    Today merely a few monitoring systems for inprocess detection of laser welding defects are commercially available. Despite a trend towards cameras, the industrially most powerful concept is still a photodiode with optical filter, measuring thermal emissions from the melt surface and from the plasma or laser beam reflections. The monitoring rule for each application is identified empirically through temporal correlations between dynamic signal changes and obtained welding defects. The mechanisms behind are widely not understood. Thus the method does not provide a systematic estimation of success for identifying a certain welding defect. The here presented research approach studies the context between welding defects, the physical mechanisms behind, particularly the dynamics of melt pool, plasma and temperature field, and the photodiode signal. Numerical simulation results of the thermal emissions from the weld pool and keyhole dynamics and their non-linear conversion into a voltage signal are presented. An essential outcome is the sensitivity of the sensor signal to certain sub-mechanisms of the motion for judging under which conditions they can be monitored. Various results are discussed for simplified hypothetic cases as well as for observed weld pool dynamics of practical relevance.

  • 20.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Karlsson, Jan
    Classification and generalization of data from a fibre-laser hybrid welding case2010In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 5, no 2, p. 69-76Article in journal (Refereed)
  • 21.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Svenningsson, Inge
    AB Sandvik Coromant, Sandviken.
    Study of a sensor platform for monitoring machining of aluminium and steel2007In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 18, no 5, p. 1155-1166Article in journal (Refereed)
    Abstract [en]

    Being able to measure and monitor the forces applied and the resulting vibrations is important to be able to understand and control the process of milling, which is a highly interrupted process based on many variables. The present work concerns analysis of signals gathered during shoulder milling of toughened steel 2541-3 and aluminium alloy 7010. The signals acquired are force in three dimensions and accelerometer in the two horizontal dimensions. Moreover, a laser Doppler vibrometer is applied. The correlations of the analysed signals of the different sensors with the surface roughness were studied. While the signal stability and correlation were unsatisfactory for several sensors, the three sensors measuring along the feed direction were most suitable to monitor the increase of the machined surface roughness with increasing feed rate

  • 22.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Mechanisms forming undercuts during laser hybrid arc welding2011In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 12, no 1, p. 201-207Article in journal (Refereed)
    Abstract [en]

    That the final quality of a welded joint, using a laser hybrid arc process, is sensitive not only to the geometrical joint conditions, but also to the content of elements in the surface itself, is already known. However the description of the mechanisms forming undercut defects is still vague. In the following study two kinds of undercuts were identified. It is shown how the mill scales affects the melt motion and what mechanisms actuate the creation of the defects. The conclusion that surface oxides affect the severity of weld undercuts is straight forward but here also the mechanism is explained. Keywords: laser; hybrid; welding; mill scale; oxides; defects; undercut

  • 23.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Karlsson, Jan
    Kaplan, Alexander
    Monitoring undercut, blowouts and root sagging during laser beam welding2009In: Lasers in Manufacturing 2009: proceedings of the Fifth International WLT-Conference Lasers in Manufacturing, LIM 2009 : Munich, Germany, June 15th - 18th, 2009 / [ed] Andreas Ostendorf, Stuttgart: Gabler Verlag/GWV Fachverlage GmbH, 2009Conference paper (Refereed)
    Abstract [en]

    Using a 14 kW CO2-laser, 12mm thick cold-formed steel S420MC has been welded to a machined shaft pivot made of 25CrMo4 steel as part of a truck rear axel. A photodiode-based, on-line process monitoring system has been applied for detecting defects. However, the occurrence of certain defects, namely undercut, blowouts and root sagging is often not detectable from the sensor signal. The time dependent signal is collected from emissions from the melt pool surface as well as from the plasma plume. Based on the evaluation of high speed images, an explanation of the potential and limitations of detection of these defects has been generated. Although preliminary conclusions have been drawn, uncertainties regarding emissivity and the keyhole and plasma radiation characteristics require further studies.

  • 24.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Legge, David
    Bäckström, Mikael
    Opportunities, problems and solutions when instrumenting a machine tool for monitoring of cutting forces and vibrations2003In: Laser metrology and machine performance, VI: [Sixth International Conference on Laser Metrology, Machine Tool, CMM and Robot Performance] / [ed] Derek G. Ford, Southampton: WIT Press, 2003, p. 557-567Conference paper (Refereed)
    Abstract [en]

    The ability to monitor the behaviour of machine tools and cutting processes is important both from a research perspective as well as in industrial applications such as adaptive control, condition monitoring, process optimization and quality control. The division of Manufacturing Engineering at Lulea University of Technology has been carrying out research in the area of high speed and multi axis (5-axis) machining since the mid 1990s. This European and nationally funded research, much of it carried out with Nottingham University and Sandvik Coromant, as well as in manufacturing companies in Sweden and the UK, has focused on understanding the possibilities offered by 5-axis/high-speed machining, as well as understanding the machining process. This initially empirical work has become more qualitative through the development of an instrumented machine tool test bed based on a 5-axis Leichti Turbomill equipped with a 24,000 rpm spindle and fast controller. The machine installation costs approximately 1.000.000 USD. The instrumentation that has been implemented includes piezo-electric force transducers in the machine table whilst ongoing work will move the research focus towards monitoring vibration in the workplace for which accelerometers and acoustic emission sensors will be used. The work presented will highlight the problems and solutions involved in creating the present test bed as well as indicating future research directions and challenges

  • 25.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Svenningsson, Inge
    Kaplan, Alexander
    Monitoring of the machining process for aluminium and steel2006In: Proceedings, 10th International Research/Expert Conference, Trends in the Development of Machinery and Associated Technology: TMT 2006, 2006Conference paper (Refereed)
  • 26.
    Norman, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Janiak, P.
    Swerea KIMAB AB.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Comparison of 22MnB5-steel with and without AlSi-coating during laser hybrid arc welding2011In: 13th NOLAMP Conference: 13th Conference on Laser Materials Processing in the Nordic Countries 27 - 29 June 2011 / [ed] Einar Halmøy, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2011Conference paper (Refereed)
    Abstract [en]

    22MnB5/Usibor1500 is a hot-dip aluminized manganese-boron steel grade that is used withinthe car manufacturing industry and as lasers are increasingly used for welding of the car bodythe amount of research concerning laser welding of this material follows. For thicker materialthe laser hybrid arc welding process has grown to a well-known tool to increase productivity,but for thinner materials the advantages are less obvious. In the present research the melt pooland wire drop transfer was observed with a high speed camera. Differences between welding,with and without the coating were clearly visible and are described and discussed in the paper.The resulting welds were examined microscopically and chemically to unveil the compositionof the material. It is aimed to avoid possible brittle inter-metallic phases directly during theprocess, hence by skipping the usual additional manufacturing step of removing the AlSicoatingin advance.

  • 27. Powell, John
    et al.
    Lamas, J.
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Yañez, A.
    Centro de Investigacións Tecnolóxicas, Universidade da Coruña, Ferrol.
    The sensitivity of hybrid laser welding to variations in workpiece position2011In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 12, no 1, p. 188-193Article in journal (Refereed)
    Abstract [en]

    High speed imaging has been used to analyze the sensitivity of the Hybrid laser welding process to variations in the laser-arcworkpiece geometry along the axis of the laser beam. The welding process was found to be stable within a certain range of workpiece positions. Outside of this range the process became unstable. If the workpiece was too close to the laser/arc combination, the two energy sources did not supplement each other sufficiently. If the workpiece was too far away the droplets from the arc interfered with the laser-keyhole interaction.

  • 28.
    Rantatalo, Matti
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Göransson, Bo
    SKF Nova, Göteborg.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Milling machine spindle analysis using FEM and non-contact spindle excitation and response measurement2007In: International journal of machine tools & manufacture, ISSN 0890-6955, E-ISSN 1879-2170, Vol. 47, no 7-8, p. 1034-1045Article in journal (Refereed)
    Abstract [en]

    In this paper a method for analysing lateral vibrations in a milling machine spindle is presented including finite element modelling (FEM), magnetic excitation and inductive displacement measurements of the spindle response. The measurements can be conducted repeatedly without compromising safety procedures regarding human interaction with rotating high speed spindles. The measurements were analysed and compared with the FEM simulations which incorporated a spindle speed sensitive bearing stiffness, a separate mass and stiffness radius and a stiffness radius sensitive shear deformation factor. The effect of the gyroscopic moment and the speed dependent bearing stiffness on the system dynamics were studied for different spindle speeds. Simulated mode shapes were experimentally verified by a scanning laser Doppler Vibrometer (LDV). With increased spindle speed, a substantial change of the eigenfrequencies of the bearing related eigenmodes was detected both in the simulations and in the measurements. The centrifugal force that acted on the bearing balls resulted in a softening of the bearing stiffness. This softening was shown to be more influential on the system dynamics than the gyroscopic moment of the rotor. The study performed indicates that predictions of high speed milling stability based on 0 rpm tap-test can be inadequate.

  • 29.
    Rantatalo, Matti
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tatar, Kourosh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser doppler vibrometry measurements of a rotating milling machine spindle2004In: Eighth International Conference on Vibrations in Rotating Machinery: 7 - 9 September 2004, University of Wales, Swansea, UK, Bury St Edmunds: Professional Engineering Publishing Ltd , 2004, p. 231-240Conference paper (Refereed)
    Abstract [en]

    Finding an optimum process window to avoid vibrations during machining is of great importance; especially when manufacturing parts with high accuracy and/or high productivity demands. In order to make more accurate predictions of the dynamic modal properties of a machining system in use, a non-contact method of measuring vibrations in the rotating spindle is required. Laser Doppler Vibrometry (LDV) is a non-contact method, which is commonly used for vibration measurements. The work presented consists of an investigation into the use of LDV to measure vibrations of a rotating tool in a milling machine, and the effects of speckle noise on measurement quality. The work demonstrates how the axial misalignment and the roundness of a polished shaft can be evaluated from LDV measurements. © IMechE 2004.

  • 30.
    Rantatalo, Matti
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tatar, Kourosh
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Non-contact measurements of tool vibrations in a milling machine2004In: Nordic vibration research, 2004Conference paper (Other academic)
  • 31.
    Svoboda, Ales
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Tatar, Kourosh
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bäckström, Mikael
    Luleå tekniska universitet.
    Integrated approach for prediction of stability limits for machining with large volumes of material removal2008In: International Journal of Production Research, ISSN 0020-7543, E-ISSN 1366-588X, Vol. 46, no 12, p. 3207-3222Article in journal (Refereed)
    Abstract [en]

    High-speed machining of thin-walled structures is widely used in the aeronautical industry. Higher spindle speed and machining feed rate, combined with a greater depth of cut, increases the removal rate and with it, productivity. The combination of higher spindle speed and depth of cut makes instabilities (chatter) a far more significant concern. Chatter causes reduced surface quality and accelerated tool wear. Since chatter is so prevalent, traditional cutting parameters and processes are frequently rendered ineffective and inaccurate. For the machine tool to reach its full utility, the chatter vibrations must be identified and avoided. In order to avoid chatter and implement optimum cutting parameters, the machine tool including all components and the work piece must be dynamically mapped to identify vibration characteristics. The aim of the presented work is to develop a model for the prediction of stability limits as a function of process parameters. The model consists of experimentally measured vibration properties of the spindle-tool, and finite element calculations of the work piece in (three) different stages of the process. Commercial software packages used for integration into the model prove to accomplish demands for functionality and performance. A reference geometry that is typical for an aircraft detail is used for evaluation of the prediction methodology. In order to validate the model, the stability limits predicted by the use of numerical simulation are compared with the results based on the experimental work.

1 - 31 of 31
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