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  • 1.
    Azar, Amin S.
    et al.
    SINTEF Mat & Chem, Oslo, Norway.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Nyhus, Bård
    SINTEF Mat & Chem, Oslo, Norway.
    Effect of crystal orientation and texture on fatigue crack evolution in high strength steel welds2015In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, p. 95-104Article in journal (Refereed)
    Abstract [en]

    In the present study, electron backscattered diffraction is used to analyze the fatigue crack evolution in a high strength steel weld that was loaded cyclically in the plastic regime. Three prominent regions of a fatigue crack are investigated separately: crack tip, crack trajectory and crack initiation. Taylor and Schmid factors are mapped with respect to the defined loading matrix. Possible effective mechanisms are proposed based on the local plasticity properties like lattice rotation and misorientation. The analyses of the crack tip and trajectory regions show that although the critical resolved shear stresses in some regions are low, small deformation resistance of these regions can compromise the dislocation immobility and cause local fracture. It is shown that if the crack grows transgranularly, at least one side of the crack may show low lattice rotation or strain equivalent values, which indicates the relaxation of elastic stresses after fracture. The crack initiation is determined to be dominantly controlled by transcrystalline mechanism of initiation that takes place under plastic loading conditions. It is also shown that the secondary < 123 >11 (1) over bar type of slip systems were the most activated under such loading conditions. (C) 2015 Elsevier Ltd. All rights reserved.

  • 2.
    Dalaei, K.
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Karlsson, B.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Svensson, L. E.
    University West, Department of Engineering Science, Division of Production Engineering.
    Stability of shot peening induced residual stresses and their influence on fatigue lifetime2011In: Materials Science and Engineering A, Vol. 528, no 3, p. 1008-1015Article in journal (Refereed)
    Abstract [en]

    Mechanical surface treatment methods such as shot peening may improve the fatigue strength of materials. In this study, the effect of shot peening on strain controlled constant amplitude fatigue loading of a near pearlitic microalloyed steel was investigated. The stress amplitudes throughout the whole lifetime were followed, in addition to detailed recording of stress-strain hysteresis loops, particularly at small cycle numbers. The detailed relaxation of residual stresses and the changes in full width of half maximum (FWHM) of the X-ray peak at the surface and in depth as function of the number of cycles and plastic strain were recorded. By these techniques, the onset as well as the rate of relaxation of residual stresses could be followed at different strain amplitudes. Pronounced increase in lifetime of the shot peened specimens tested at total strain amplitude smaller than 0.3% (corresponding to 0.034% plastic strain amplitude) was achieved. This coincides with reasonably stable residual stresses at the surface and in depth. © 2010 Elsevier B.V.

  • 3.
    Ericson Öberg, Anna
    et al.
    Chalmers Tekniska Högskola.
    Hammersberg, Peter
    Chalmers Tekniska Högskola.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    The right evaluation method - an enabler for process improvement2013Conference paper (Other academic)
    Abstract [en]

    This paper aims at describing the procedure where an alternative evaluation process was developed to support the improvement of both welding and weld quality evaluation. Welded structures are important when striving for reduced fuel consumption due to vehicle weight. Hence good control of the fabrication process is critical to keep welding performance on target, avoiding waste in terms of added weight and overproduction. The resulting distribution of weld weight has shown to be an important control parameter in the sense of keeping cost down.

    To identify the causes for deviations between actual and theoretical weld weight, information about the weld was needed. The currently used evaluation method showed not to be capable of giving the information needed. It was necessary to know the throat size as well as weld geometry. The current evaluation method introduced more variation due to the measurement than the actual fabrication process itself, leading to drift of process target and overproduction.

    To fulfil the need of information, that different functions within the company had, a PULL-approach was used. The information need, information presentation and sequence were outlined for each information receiver individually. An alternative measurement method was developed and named WIA – Weld Impression Analysis. The method consists of two parts; creating the replica and analysing the shape in an image analysis program.

    The method was tested to see if it was capable of delivering accurate and precise measurements, satisfying repeatability and reproducibility requirements for this particular situation. A thorough measurement system analysis was carried out. The measurement system assigned 98.98% of the total variation to part-to-part variation corresponding to long-term process variation. The variation that stems from taking the impressions and preparing them was as well investigated, also showing satisfying results. Finally it was investigated if the impressions reflect the true shape of the welds accurately. The results showed a tendency of slightly higher cross sectional areas in the range of 0-3 %. This however indicated that the accuracy of the measurement system was sufficient for its purpose.

    The PULL-approach generated a sufficient method which enabled the possibility to perform process improvement and gain large production cost savings.

  • 4.
    Ericson Öberg, Anna
    et al.
    Material- och Tillverkningsteknik, Chalmers.
    Johansson, Martin
    Holm, Erik
    Hammersberg, Peter
    Material- och Tillverkningsteknik, Chalmers.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    The Influence of Correct Transfer of Weld Information on Production Cost2012In: 5th Swedish Production Symposium 2012, SPS12: 6-8 nov 2012, Linköping / [ed] Mats Björkman, Linköping, 2012, p. 295-302Conference paper (Other academic)
    Abstract [en]

    This study aims at identifying the causes for deviations between actual and theoretical weld weight. Previous performed studies have shown examples of up to 40% extra weld consumables used in some cases. One consequence is of course higher production cost but it can also give increased weight leading to higher fuel consumption and decreased payload. An interesting aspect is that generous margins on specific production measures dilute important feedback of process variation information preventing and prolonging structural root cause analysis.

    The causes for the observed deviations can heritage from several areas, both technical and within the information handling. The investigation shows that single components of the information structure and system, such as unsuitable demands as well as incapable evaluation methods, significantly influences the reliability of the entire manufacturing process. The common factor concerning when problems occur, seems to be the ability of correct information transfer between different functions in the organisation preventing the mismatch to appear in the interface. Suggestions for improving this situation include cross functional agreements as well as new measuring methods.

  • 5.
    Fahlström, Karl
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Swerea KIMAB in Kista.
    Andersson, O.
    Volvo Cars in Torslanda & KTH in Stockholm, Sweden.
    Melander, A.
    Swerea KIMAB in Kista, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Correlation between laser welding sequence and distortions for thin sheet structures2017In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 2, p. 150-156Article in journal (Refereed)
    Abstract [en]

    Thin ultra-high strength steel shaped as 700 mm long U-beams have been laser welded in overlap configuration to study the influence of welding sequence on distortions. Three different welding directions, three different energy inputs as well as stitch welding have been evaluated, using resistance spot welding (RSW) as a reference. Transverse widening at the ends and narrowing at the centre of the beam were measured. A clear correlation was found between the weld metal volume and distortion. For continuous welds there was also a nearly linear relationship between the energy input and distortion. However, the amount of distortion was not affected by a change in welding direction. Stitching and RSW reduced distortion significantly compared to continuous laser welding.

  • 6.
    Fahlström, Karl
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. University West, Department of Engineering Science, Research Environment Production Technology West.
    Andersson, Oscar
    Volvo Cars, Torslanda, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength2017In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 7, p. 573-579Article in journal (Refereed)
    Abstract [en]

    Geometrical distortions occur while welding, but the understanding of how and why they occur and how to control them is limited. The relation between the weld width, weld metal volume, total energy input, width of hard zone and distortions when laser welding three different thin sheet steels with varying strength has therefore been studied. Weld metal volume and total energy input show a good correlation with distortion for one steel at a time. The best correlation with the when including all three steel grades was the width of the hard zone composed of weld metal and the martensitic area in the heat affected zone. © 2017 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute.

  • 7.
    Fahlström, Karl
    et al.
    Swerea KIMAB.
    Andersson, Oscar
    KTH Royal Institute of Technology.
    Todal, Urban
    Volvo Car Corporation.
    Melander, Arne
    Swerea KIMAB.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Distortion Analysis in Laser Welding of Ultra High Strength Steel2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-9Conference paper (Refereed)
    Abstract [en]

    Due to increased demands on reduced weight in automotive industries, the use of ultra high strength steels (UHSS) has increased. When laser welding UHSS sheets, heating and cooling of the material will cause geometrical distortions and may cause low joint quality. 700 mm long U-beam structures of 1 mm thick boron steel simulating structural pillars in body-in-white constructions have been welded along the flanges with different welding speeds to investigate distortions and weld quality. The results show that final distortions appear in the range of 0-8 mm. FE simulation methods have also been presented which generally predict the distribution of welding distortions.

  • 8.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg.
    Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, p. 39-47Article in journal (Refereed)
    Abstract [en]

    Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.

  • 9.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Dalaei, Kamellia
    ESAB AB, Gothenburg.
    The relative effects of residual stresses and weld toe geometry on fatigue life of weldments2015In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, p. 160-165Article in journal (Refereed)
    Abstract [en]

    The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. A moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.

  • 10.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Pirling, Thilo
    Institut Max von Laue-Paul Langevin, 6 rue Jules Horowitz, BP156, F-38042 Grenoble, France.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg, Sweden.
    Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel2017In: Materials, E-ISSN 1996-1944, Vol. 10, no 6, p. 1-14, article id E593Article in journal (Refereed)
    Abstract [en]

    Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.

  • 11.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Automation Systems.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Non-destructive measurement of weld toe radius using Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection methods2014In: Proceedings of First International Conference on Welding and Non Destructive Testing (ICWNDT2014), 2014, p. 1-8Conference paper (Refereed)
  • 12.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers2017In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, no September, p. 64-74Article in journal (Refereed)
    Abstract [en]

    Fatigue improvement techniques are widely used to increase fatigue strength of welded high strength steels. In this paper high frequency mechanical impact (HFMI) and a Low Transformation Temperature (LTT) filler material were employed to investigate the effect on fatigue strength of welded 1300 MPa yield strength steel. Fatigue testing was done under fully reversed, constant amplitude bending load on T-joint samples. Fatigue strength of LTT welds was the same as for welds produced using a conventional filler material. However, HFMI treatment increased the mean fatigue strength of conventional welds about 26% and of LTT welds about 13%. Similar distributions of residual stresses and almost the same weld toe radii were observed for welds produced using LTT and conventional consumables. HFMI increased the weld toe radius slightly and produced a more uniform geometry along the treated weld toes. Relatively large compressive residual stresses, adjacent to the weld toe were produced and the surface hardness was increased in the treated region for conventional welds after HFMI. For this specific combination of weld geometry, steel strength and loading conditions HFMI treatment gave higher fatigue strength than LTT consumables.

  • 13.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    The measurement of weld toe radius using three non-destructive techniques2014In: Proceedings of The 6th International Swedish Production Symposium 201416-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The three non-destructive methods Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection were employed to measure the weld toe radius of fillet welds. All three methods could be used succesfully but results are dependent on evaluation procedure. The results show that the weld toe geometry cannot be considered uniform and varies along the weld. It was also found that the measured weld toe radii do not vary significantly with minor variations ofthe surface profile orientation.

  • 14.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of HFMI treatment procedure on weld toe geometry and fatigue properties of high strength steel welds2016In: Procedia Structural Integrety, Vol. 2, p. 3483-3490Article in journal (Refereed)
    Abstract [en]

    The effects of high frequency mechanical impact (HFMI) treatment procedure on the weld toe geometry and fatigue strength in 1300 MPa yield strength steel welds were investigated. In this regard first the effect of three or six run treatments on the weld toe geometry was evaluated. The fatigue strength and weld toe geometry of as-welded and HFMI treated samples was then compared. Fatigue testing was done under fully reversed, constant amplitude bending load. When increasing the number of treatment runs from three to six, the weld toe radius and width of treatment remained almost constant. However, a slightly smaller depth of treatment in the base metal and a somewhat larger depth of treatment in the weld metal was observed. HFMI treatment increased the fatigue strength by 26%. The treatment did not increase the weld toe radius significantly, but resulted in a more uniform weld toe geometry along the weld. A depth of treatment in the base metal in the range of 0.15-0.19 mm and a width of treatment in the range of 2.5-3 mm, were achieved. It is concluded that the three run treatment would be a more economical option than the six run treatment providing a similar or even more favourable geometry modification.

  • 15.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Widmark, Mattias
    Material Technology, Volvo Group Trucks Technology, Gothenburg, Sweden.
    Effect of high frequency mechanical impact treatment on fatigue strength of welded 1300 MPa yield strength steel2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, p. 96-106Article in journal (Refereed)
    Abstract [en]

    High frequency mechanical impact (HFMI) is a recent post weld treatment method which can be employed to increase the fatigue strength of welded components. In this paper the fatigue strength of as-welded and HFMI treated fillet welds in a 1300 MPa yield strength steel was compared. Fatigue testing was done under fully reversed, constant amplitude bending load. Finite element analysis was used to calculate the stress distribution in the weld toe region to permit evaluation of the fatigue data with the effective notch stress approach. As-welded samples showed a mean fatigue strength of 353 MPa and a characteristic fatigue strength of 306 MPa. HFMI treatment increased the mean fatigue strength by 26% and the characteristic fatigue strengths by 3%. The weld toe radii in as-welded condition were large. HFMI only increased the weld toe radii slightly but resulted in a more uniform weld toe geometry along the weld. A depth of indentation in the base metal in the range of 0.15–0.19 mm and a width of indentation in the range of 2.5–3 mm, were achieved. Maximum compressive residual stresses of about 800 MPa in the longitudinal and 250 MPa in the transverse direction were introduced by HFMI treatment, adjacent to the weld toe. The surface hardness was increased in the entire HFMI treated region. It is concluded that the increase in fatigue strength is due to the combined effects of the weld toe geometry modification, increase in surface hardness and creation of compressive residual stresses in the treated region.

  • 16.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2016In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 21, no 5, p. 339-350Article in journal (Refereed)
    Abstract [en]

    Comprehensive models of heat transfer require specification of the total amount of heat received by the workpiece. The objective of this work was to critically examine the use of a water-cooled stationary anode calorimeter to obtain both arc efficiency and total heat input into the workpiece. For simplicity and clarity, this last quantity is called the gross heat input. The effects of current, material type and water flow rate on the calorimeter performance were determined experimentally. Some measures for reducing errors in calorimetry were evaluated. Improvements were made to reduce heat losses from the top surface of the test coupon and boost heat removal from the opposite surface. A sensitivity test was conducted to estimate the effect of measurement inaccuracies. The results demonstrate the effectiveness of calorimetry for measuring gross heat input in arc welding.

  • 17.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015, JOM-institute , 2015, p. 1-19Conference paper (Refereed)
    Abstract [en]

    A comprehensive model on heat transfer in welded plates is able to calculate the amount of heat losses from the surfaces. A model demands as input parameter the amount of heat delivered to the plate, independently of any loss (called here gross heat input for clarity). However, the great discrepancies among the results of calorimetric measurements have left many researchers skeptical about using this parameter in modeling as absolute term. The objective of this work was to assess the use of a water-cooled stationary anode calorimeter to obtain not only arc efficiency, but also gross heat input. A series of tests was carried out to determine the effect of current, material type and water flow rate on the calorimeter performance, as well as to evaluate some measures for reducing the calorimeter intrinsic errors. Finally, a sensitivity test was conducted to estimate the effect of measurement inaccuracies on the absorbed heat and arc efficiency values. The results showed that this calorimetric approach is a simple way for measuring gross heat inputs in arc welding. Nevertheless some improvement to reduce heat losses from the top surface and boost heat sinking from the opposite surface of the test coupon must be applied. This calorimeter is, on the other hand, highly sensitive to the parameter measurements, leading to errors up to ± 0.09 in arc efficiency determination if the instrument is not properly calibrated and installed.

  • 18.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 7182018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 94, no 5-8, p. 2199-2207Article in journal (Refereed)
    Abstract [en]

    A systematic matrix with 25 samples, using five different point distances and five laser exposure times, depositing 75-μm-thick layers of Alloy 718 has been studied. The work has concentrated on defects formed, hardness of the deposits, and the microstructure. Relatively large amount of defects, both lack of fusion and porosity, was found in several of the specimens in the deposits. The defects were never possible to fully eliminate, but a significant decrease, mainly in the lack of fusion, was seen with increasing laser exposure time. The gas porosity on the other hand was not affected to any larger degree, except for the lowest laser energy input, where a slight increase in porosity was seen. A small increase in hardness was noted with increasing laser energy input. The width of the deposited beads increased with increasing laser energy, while the depth of deposits was more or less constant. However, for the lowest combination of point distance and laser exposure time, quite deep and narrow beads were formed. A comparison was made with deposition of 50-μm-thick layers, with quite similar laser energy input, but with some variation in detailed deposition parameters. It was found that the 75-μm-thick layers contained less lack of fusion, particularly for small point distances. The amount of porosity was also less, but that did not vary with deposition parameters.© 2017 The Author(s)

  • 19.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of dilution on properties of high strength steel weld metals2014In: Biuletyn Instytutu Spawalnictwa W Gliwicach: Rocznik 58, 2014, p. 65-71Conference paper (Refereed)
  • 20.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Efficient welding of high strength steel2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

     Producing welds with properties matching those of the steel is a challenge at high strength levels. The present study investigated how cooling rates and dilution affects strength and toughness when welding steels with yield strengths of 777 MPa and 1193 MPa. Overmatching weld metal strength was achieved for the less strong steel and weld strengths >1000 MPa were recorded for the stronger steel. Fracture in transverse tensile testing was always located in base material or HAZ. Low dilution, rapid cooling and single pass welding contributed to higher strength. Impact toughness was higher for lower strength and low dilution.

  • 21.
    Li, Peigang
    et al.
    ESAB AB, Gothenburg, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Högström, Mats
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology.
    A contribution to the study of negative polarity in GMA welding2018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 95, no 5-8, p. 2543-2553Article in journal (Refereed)
    Abstract [en]

    GMAW using the electrode with negative polarity (DCEN) has been frequently suggested as a potential means of increasing production capacity. The objective of this work was to further study the performance of negative polarity in GMAW of carbon steels. In this project phase, bead-on-plate welds were carried out in flat position to assess the effect of different potential shielding gas compositions on bead geometry, finishing and spattering. The characteristics were compared with DCEP at the same current, but depositing the same volume of material per unit of length (more industrial related comparison). The arc length was kept the same by adjusting voltage to reach shortest arcs, yet with suitable non short-circuiting metal transfer mode. An approach to measure bead convexity was also proposed and assessed. The results showed that DCEN is feasible as a means of increasing GMAW production capacity. However, to become DCEN applicable with GMAW, the results suggest an Ar based blend with around 6.5 % of O2 is the most appropriate shielding gas, as much as that there is a demand for a standard electronic controlled power source able to work in constant current mode. 

  • 22.
    Li, Peigang
    et al.
    University West, Department of Engineering Science.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Factors influencing fusion of spatter to the base metal during tandem GMAW2012In: Proceedings of The 5th International Swedish Production Symposium: 6th-8th of November 2012 Linköping, Sweden / [ed] Mats Björkman, Linköping, Sweden, 2012, p. 233-239Conference paper (Refereed)
    Abstract [en]

    Tandem gas metal arc welding (tandem GMAW) is, as a high productivity welding method of manufacturing process, utilized broadly in modern Swedish industry. Spatter is more or less an inevitable flaw in GMAW, especially for the high efficiency processes. Recently, spatter was found as a potential source of cold laps, which negatively influences fatigue life. The main objectives of this paper are to investigate the spatter/base metal interface and identify the primary factors for formation of cold laps.

    Tandem GMAW was performed in a sealed chamber filled with either pure argon or pure dioxide. Cross sections of spatter and base metal were prepared and evaluated by Light optical microscopy and Scanning Electron Microscopy (SEM) with an attached Energy Dispersive Spectroscope (EDS).

    Mn-Si oxides were found to enhance the lack of fusion occurrence in the spatter/base metal. The oxide of Mn and Si mostly came from oxidation of the droplets in the welding process. Spatter diameter and spatter distance was evaluated with respect to lack of fusion in spatter/base metal interface for welds using pure Ar shielding gas. From this it was concluded that temperature is another important factor for lack of fusion formation in the spatter/base metal interface.

  • 23.
    Li, Peigang
    et al.
    University West, Department of Engineering Science.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Factors influencing fusion on spatter to the base metal during tandem GMAW weldingArticle in journal (Refereed)
  • 24.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Influence of oxides on cold lap formation in tandem GMAW2012In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, ISSN 1362-1718, Vol. 17, no 8, p. 643-648Article in journal (Refereed)
    Abstract [en]

    The connection between the formation of cold laps and the presence of Mn‐Si oxides was studied. The underlying purpose is to understand the fundamental mechanisms of cold lap formation and to avoid it. Tandem gas metal arc welding (GMAW) was used to produce welded specimens in two different shielding gases (pure Ar and pure CO2) with base metal S355 MC (EN-10149-2) and wire G3Si1 (EN ISO 14341-A). Cross-sections of welds in the cold lap location were evaluated by light optical microscopy and scanning electron microscopy combined with energy dispersive spectroscopy. The results showed that the Mn‐Si oxides significantly enhanced cold laps formation, especially the overlap type cold lap formation. The Mn‐Si oxides originated from oxidation of the droplets. These oxides transfers to the surface of the weld pool at the weld toe, where they contributed to the formation of the cold laps.

  • 25.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Influence of preheating temperature on cold lap formation in tandem GMAW2013Conference paper (Other academic)
    Abstract [en]

    A cold lap is defined as a type of micro-lack of fusion in ISO standard (ISO 6520-1:2007) and have been found to influence fatigue properties of welds significantly. In the present study, the main purpose was to investigate the influence of preheating temperature on cold lap formation in tandem GMAW, both with respect to dimensions and occurrence probabilities.

    Three different preheating temperatures were applied and cross-sections of welds were evaluated by light optical microscopy. The results showed that the cold lap occurrence frequency is a function of base metal temperature. However, the base metal temperature does not have a significant influence on cold lap depth.

  • 26.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Study on temperature influence on lack of fusion formation in spatter/base metal interface2014In: Advanced Materials Research, ISSN 1662-8985, Vol. 875 - 877, p. 1421-1428Article in journal (Refereed)
    Abstract [en]

    In the development of modern welded structures with longer life-time and/or higher load-carrying ability, fatigue properties are becoming more and more important. A lot of researches have been done to investigate which factors can elongate the fatigue life of weldments. Cold lap defects, were found to be important initiation sites of the fatigue failure in 1990s. In the ISO standard, cold lap is referred to as a type of micro-lack of fusion. Previous study found that most of the cold laps in GMAW process are formed in spatters. In this paper the interface of spatter/base metal was cut, polished and investigated by conventional metallographic methods. The aim is to reveal the influence of temperature on cold lap formation. In the experiments, different pre-heating temperatures of the parent plate were used in tandem GMAW. Results showed linear empirical relationship between the temperature of the parent plate and the amount of lack of fusion in the spatter/base metal interface.

  • 27.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science.
    Cold laps - micro-lack of fusion defects in steel arc welds: a reviewManuscript (preprint) (Other academic)
  • 28.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Klement, Uta
    Department of Materials and manufacture, Chalmers University.
    Characterization of cold lap defects in tandem arc MAG welding2012In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 56, no 9/10, p. 20-25Article in journal (Refereed)
    Abstract [en]

    The objective of this investigation was to classify and characterize the small lack of fusion defects, called cold lap, located at the weld toe. Since the defects are very small (0.01–1.5 mm) and difficult to detect by NDT methods, a better understanding of the formation mechanism is required to be able to avoid their formation. The investigation consisted of two parts. Firstly, a study was made on the type and frequency of cold laps. Three types were identified, namely “spatter cold lap”, and “overlap cold lap” and “spatter-overlap cold lap”. No relation between type or frequency of cold laps and the welding parameters could be established. Secondly, the interface between spatter and the base material was investigated using optical and scanning electron microscopy, to better understand the cold lap formation mechanism. Manganese-silicate particles were found in the interface located in such a way that they may assist cold lap formation.

  • 29.
    Li, Peigang
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Klement, Uta
    Chalmers University of Technology, Materials and Manufacturing Technology.
    Characterization of cold lap defects in tandem arc MAG welding2013In: Rivista Italiana della Saldatura, ISSN 0035-6794, Vol. 65, no 5, p. 761-769Article in journal (Refereed)
    Abstract [en]

    The objective of this investigation was to classify and characterize the small lack of fusion defects, called cold lap, located at the weld toe. Since the defects are very small (0.01-1.5 mm) and difficult to detect by NDT methods, a better understanding of the formation mechanism is required to be able to avoid their formation. The investigation consisted of two parts. Firstly, a study was made on the type and frequency of cold laps. Three types were identified, namely "spatter cold lap", and "overlap cold lap" and "spatter-overlap cold lap". No relation between type or frequency of cold laps and the welding parameters could be established. Secondly, the interface between spatter and the base material was investigated using optical and scanning electron microscopy, to better understand the cold lap formation mechanism. Manganese-silicate particles were found in the interface located in such a way that they may assist cold lap formation.

  • 30.
    Manvatkar, V.
    et al.
    The Pennsylvania State University, University Park, PA.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    DebRoy, T.
    The Pennsylvania State University, University Park, PA.
    Cooling Rates and Peak Temperatures during Friction Stir Welding of a High Carbon Steel2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 94, p. 36-39Article in journal (Refereed)
    Abstract [en]

    Friction stir welding can potentially avoid post weld heat treatment for the welding of high carbon steels. Although control of both peak temperature and cooling rate has been suggested to achieve this goal, the current literature does not provide any help to select appropriate welding variables. In order to address this problem, here we present a set of easy-to-use maps of both the cooling rates and the peak temperatures for various welding conditions during friction stir welding of a high carbon steel.

  • 31.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, L. E.
    University West, Department of Engineering Science, Division of Welding Technology.
    A review of the effect of selective laser melting process parameters and its influence on microstructure, defects and strength in the iron-nickel based superalloy Alloy 7182016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-8Conference paper (Refereed)
    Abstract [en]

    This review presents a basic insight into the powder-bed fusion process selective laser melting (SLM), with focus on the microstructure and mechanical properties of the iron-nickel based superalloy Alloy 718. The microstructures and mechanical properties of SLM components are highly affected by the process parameters. Laser power, scanning speed, powder layer thickness and hatch distance, are the primary process parameters which can be adjusted in order to influence the microstructure and minimize potential defects. SLM-manufactured Alloy 718 generally produce a columnar microstructure which is a result of epitaxial formation and dendritic grain growth in the build direction (perpendicular to the substrate). Gas porosity, lack of fusion and residual stresses are process induced problems observed in SLM-manufactured Alloy 718. The microstructure of the as-manufactured Alloy 718 is susceptible to microsegregation of Nb and Mo as well as to subsequent non-equilibrium phase transformation. A post-process heat treatment of as-manufactured Alloy 718 is required in order to improve general mechanical properties and to relieve the residual stresses. The tensile strength, yield strength and hardness of heat treated SLM-manufactured Alloy 718 are comparable to that of wrought material.

  • 32.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Varestraint weldability testing of additive manufactured alloy 7182018In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 23, no 7, p. 606-611Article in journal (Refereed)
    Abstract [en]

    The weldability in terms of susceptibility towards hot cracking of selective laser melted (SLM) Alloy 718 was investigated and wrought Alloy 718 was used as reference material. Varestraint testing was carried out by means of investigating the weldability in three conditions; (1) SLM as-built, (2) hot isostatic pressing at 1160°C at 105MPa for 3h and (3) wrought Alloy 718 in the mill-annealed condition. The material exhibited intergranular cracking in all three conditions; however,theSLMHIPedconditionhadanincreasedmagnitudeofcracksusceptibilityatallstrain levels.TheincreasedsensitivityoftheHIPedmaterialwasduetothesignificantlylargergrainsize incomparison.TheSLMas-builtconditionshowedthesamedegreeofcrackingasthewrought material.

  • 33.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Uddeholms AB, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB, Hagfors, Sweden.
    Högman, Berne
    Uddeholms AB, Hagfors, Sweden.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel2016In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 12, no 1 December, p. 1609-1618Article in journal (Refereed)
    Abstract [en]

    The effects of austenitization and tempering temperatures for a 5 wt% Cr cold work tool steel are studied with an aim of understanding the influence on microstructure and mechanical properties. Microstructures are characterized with scanning electron microscopy and light optical microscopy. Retained austenite contents and martensite start temperatures are measured by X-ray diffraction and dilatometry, respectively. Hardness, impact toughness, and compressive yield strength are also determined. When the austenitization temperature is increased from 1020 or 1050 to 1075 °C, followed by tempering at 525 °C, significant hardness is gained while there is no increase in compressive yield strength. Higher austenitization temperatures also produce larger amounts of retained austenite. At the same time, the impact toughness is reduced due to coarsening of the martensitic microstructure. When the steel is tempered at 200 °C, a higher impact toughness and a higher volume fraction of retained austenite are observed. Retained austenite is not found after tempering at temperatures of 525 °C or above. It is concluded that the best combination of mechanical properties is achieved by austenitization at 1020 or 1050 °C followed by tempering at 525 °C.

  • 34.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Uddeholms AB, SE-683 85, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB, SE-683 85, Hagfors, Sweden. .
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effects of Austenitisation Temperature and Multiple Tempering on the Microstructure and Impact Toughness of a 5 wt. % Cr Cold Work Tool Steel2016In: 10th TOOL Conference, Tool, conference proceedings, 10th TOOL Conference , 2016, p. 1-10Conference paper (Other academic)
    Abstract [en]

    The microstructure and properties of a 5 wt.% Cr cold work tool steel were studied after austenitisation at 1020°C, 1050°C or 1075°C followed by single, double and triple tempering treatments at 525°C. The microstructures were investigated with scanning electron microscopy and X-ray diffraction and phase transformations were studied by dilatometry. Furthermore, hardness and Charpy un-notched and V-notched impact toughness testing was performed and results were correlated to observed microstructures. With higher austenitisation temperature, the martensite and bainite start temperatures were lowered resulting in microstructures containing a higher volume fraction of retained austenite. Retained austenite transformed into martensite on cooling from the tempering temperature. Specimens that were austenitised at 1050°C or 1075°C and tempered twice contained fresh martensite. Applying a third tempering was therefore required to guarantee a fully tempered microstructure. The second tempering resulted in an increase of the un-notched impact energy while the third tempering did not have a pronounced effect. A triple tempering procedure could be preferable when austenitising at high temperatures to avoid undesirable fresh martensite in the tool microstructure.

  • 35.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Medvedeva, Anna
    Uddeholms AB, S-68385 Hagfors, Sweden.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 11, p. 5233-5243Article in journal (Refereed)
    Abstract [en]

    Retained austenite transformation was studied for a 5 wt pct Cr cold work tool steel tempered at 798 K and 873 K (525 degrees C and 600 degrees C) followed by cooling to room temperature. Tempering cycles with variations in holding times were conducted to observe the mechanisms involved. Phase transformations were studied with dilatometry, and the resulting microstructures were characterized with X-ray diffraction and scanning electron microscopy. Tempering treatments at 798 K (525 degrees C) resulted in retained austenite transformation to martensite on cooling. The martensite start (M-s) and martensite finish (M-f) temperatures increased with longer holding times at tempering temperature. At the same time, the lattice parameter of retained austenite decreased. Calculations from the Ms temperatures and lattice parameters suggested that there was a decrease in carbon content of retained austenite as a result of precipitation of carbides prior to transformation. This was in agreement with the resulting microstructure and the contraction of the specimen during tempering, as observed by dilatometry. Tempering at 873 K (600 degrees C) resulted in precipitation of carbides in retained austenite followed by transformation to ferrite and carbides. This was further supported by the initial contraction and later expansion of the dilatometry specimen, the resulting microstructure, and the absence of any phase transformation on cooling from the tempering treatment. It was concluded that there are two mechanisms of retained austenite transformation occurring depending on tempering temperature and time. This was found useful in understanding the standard tempering treatment, and suggestions regarding alternative tempering treatments are discussed. (C) The Author(s) 2017.

  • 36.
    Rehan, Arbab
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Dept. of Material Technology, Uddeholms AB, Hagfors, Sweden.
    Medvedeva, Anna
    Uddeholms AB.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Retained austenite transformation during heat treatment of a 5wt.% Cr cold work tool steelManuscript (preprint) (Other academic)
  • 37.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Economical Viability of Laser Metal Deposition2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Reports on large economic savings using Additive Manufacturing (AM) has been found in literature when exploiting the positive capabilities of AM. This paper evaluates the economic potential of, the AM method, laser metal deposition (LMD) in production of add-on features compared to conventional manufacturing methods. This is done by theoretical case studies, which explore factors critical to the cost of manufacturing a jet engine flange. LMD has the potential to be an economical viable alternative to conventional manufacturing methods when the manufactured component has a high buy-to-fly ratio, the component is small and complex, if the operator time can be kept to a minimum, and/or when the design freedom of LMD can be capitalized into lighter and more efficient components.

  • 38.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Evaluation of a temperature measurement method developed for laser metal deposition2017In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 1, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Measuring temperatures in the material during laser metal deposition (LMD) has an inherent challenge caused by the laser. When thermocouples are radiated by the high intensity laser light overheating occurs which causes the thermocouple to fail. Another identified difficulty is that when the laser passes a thermocouple, emitted light heats the thermocouple to a higher temperature than the material actually experience. In order to cope with these challenges, a method of measuring temperatures during LMD of materials using protective sheets has been developed and evaluated as presented in this paper. The method has substantially decreased the risk of destroying the thermocouple wires during laser deposition. Measurements using 10 mm2 and 100 mm2 protective sheets have been compared. These measurements show small variations in the cooling time (∼0.1 s from 850°C to 500°C) between the small and large protective sheets which indicate a negligible effect on the temperature measurement. © 2016 Institute of Materials, Minerals and Mining.

  • 39.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Evaluation of the effect of process parameters on microstructural characteristics in laser metal deposition of Alloy 7182015In: Journal of optics and laser technologyArticle in journal (Refereed)
  • 40.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of Heat Input on Grain Structure in Thin-Wall Deposits using Laser Metal Powder Deposition2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. -7Conference paper (Refereed)
    Abstract [en]

    Laser metal deposition (LMD) is an additive manufacturing method which is used to deposit material directly onto a metal surface layer upon layer until a final component is achieved. The material used in this study is the nickel iron based superalloy Alloy 718. There is a strong thermal gradient associated with this method which generally produces columnar grains growing in the build-up direction. The preferred solidification orientation of the FCC matrix is in the (001) direction which makes it possible to build directionally solidified structures with epitaxial grains growing through the layers. In this study LMD with powder as additive has been used to build thin walled samples, multiple layers high. The main objectives of this research are to assess the influence of the heat input on the grain structure in LMD builds and evaluate how the morphology and texture of the grains are affected by the changes in process parameters. Two different parameter sets are compared where a high and a low heat input have been used. The two samples with different heat inputs have been evaluated using a scanning electron microscope coupled to an electron back scatter diffraction detector in order to obtain quantitative grains size measurements as well as crystallographic information. It was shown that the grain structure was considerably affected by the heat input where the high heat input produced a strong texture with columnar grains growing in the build-up direction. With a low heat input the grains became finer and, although elongated, the grains became more equiaxed.

  • 41.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Investigation of laser metal deposited Alloy 718 onto an EN 1.4401 stainless steel substrate2017In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 97, no Supplement C, p. 144-153Article in journal (Refereed)
    Abstract [en]

    This paper focuses on how process parameters affect the deposition of Alloy 718 onto an EN 1.4401 stainless steel substrate in terms of secondary phase formation, dilution and hardness. A columnar solidification structure with elongated grains growing in the direction normal to the substrate was observed for all parameters. In the interdendritic regions, phases with a high content of Niobium were identified. Scanning Electron Microscopy imaging and Energy Dispersive Spectroscopy measurements revealed these phases to most likely be Laves phase and Nb-carbides. Temperature measurements indicated no significant aging in the deposits. Considerable enrichment of iron was found in the initially deposited layers due to dilution from the substrate. The increased content of iron seemed to aid in forming constituents rich in niobium which, in turn, influenced the hardness. The highest mean hardness was noted in the sample with the lowest area fraction of Nb-rich constituents.

  • 42.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Review of Laser Deposited Superalloys Using Powder as an Additive2014In: 8th International Symposium on Superalloy 718 and Derivatives: Conference Proceedings / [ed] Ott, E., Banik, A., Andersson, J., Dempster, I., Gabb, T., Groh, J., Heck, K., Helmink, R., Liu, X. & Wusatowska-Sarnek, A, Hoboken, NJ, USA: John Wiley & Sons, 2014, p. 393-408Conference paper (Refereed)
  • 43.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    University of Manitoba, Department of Mechanical Engineering,Winnipeg, R3T 5V6, Canada.
    Effect of Process Parameters on the Crack Formation in Laser Metal Powder Deposition of Alloy 7182018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 10, p. 5042-5050Article in journal (Refereed)
    Abstract [en]

    Cracking in Alloy 718 using laser metal powder deposition has been evaluated in this study. It is found that the material is susceptible to cracking when the laser power is high, the scanning speed is high and the powder feeding rate is low. Almost all the cracks are located close to the center of the deposited wall and propagates in the normal direction to the substrate. Evidence of liquation are found at the cracked surfaces and since all cracks reside in regions which are reheated several times, the cracks are determined to mostlikely be heat affected zone liquation cracks. The influence of respective process parameter was evaluated using a design of experiment approach. It is shown that, when the powder feeding rate is incorporated as avariable, the heat input is not a suitable indicator for the hot cracking susceptibility in laser metal powder deposition of Alloy 718. A combinatory model using the power ratio together with the heat input is therefore proposed.

  • 44.
    Segerstark, Andreas
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    University of Manitoba,Department of Mechanical Engineering, Winnipeg, R3T 5V6, Canada.
    Microstructural Characterization of Laser Metal Powder Deposited Alloy 7182018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 142, p. 550-559Article in journal (Refereed)
    Abstract [en]

    A microstructural study of Laser Metal Powder Deposition (LMPD) of Alloy 718, using a low (40 J/mm) and high (100 J/mm) heat inputs (HIs) was performed. The microstructure was characterized in as-deposited condition as well as after a standard heat-treatment, using optical microscope (OM), scanning electron microscope (SEM) and Transmission Electron Microscope (TEM). Laves, MC-carbides, γ' and γ'' are observed in the interdendritic areas of both conditions. However, the dendritic core only consists of γ-matrix. The high HI condition shows a slightly larger Primary Dendrite Arm Spacing (PDAS) as compared to the low HI condition. Additionally, the particle size of the Nb-rich constituents in the interdendriticregions (Laves-phase and Niobium carbide) are larger in the high HI sample. After heat-treatment, the Laves phase dissolves and is replaced by δ-phase in the interdendritic regions, while γ', γ'' and MC-carbideremain in the interdendritic regions. However, the γ'' precipitates seems to be less developed in the dendritic core as compared to the interdendritic regions, especially in the high HI sample. This can be attributed to a heterogeneous distribution of Nb in the microstructure, with a lower Nb content in the dendritic core as compared to close to the interdendritic regions.

  • 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.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West. GKN Aerospace Sweden.
    Pérez Caro, Lluís
    IUC, Olofström, Sweden.
    Odenberger, Eva-Lis
    IUC, Olofström, Sweden.
    Oldenburg, Mats
    Luleå University of technology, Luleå, Sweden.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Comparison of forming, welding and heat treatment simulations in LS-DYNA and MSC Marc2016In: Proceedings of 10th International Conference on Trends in  Welding Research & 9th International Welding Symposium of Japan Welding, American Welding Society (AWS) & Japan Welding Society (JWS) , 2016, p. 660-663Conference paper (Refereed)
    Abstract [en]

    The manufacturing of components for aero engine structures from a flat sheet to the final shape usually requires several steps that may introduce residual stresses and shape distortions in the part. Depending on the magnitude, sign and distribution with respect to the stresses induced by the service load, the remaining stresses may affect the service life of a component, especially when submitted to cyclic loading. Nowadays, several types of software that have the ability to predict the residual stresses and the final shape of a component subjected to various process steps are available. However, literature shows a lack of comparison studies among different software tools for multi-step simulations of a manufacturing process. In this study, the manufacturing process chain of an aerospace component including forming, welding and heat treatment in the nickel-based superalloy 718 is modelled and simulated using the two finite element software codes LS-DYNA and MSC.Marc. The results from the displacement of the blank in the punch stroke direction, the equivalent plastic strain and the von Mises stress are compared between both FE codes. The displacement of the blank after forming is slightly higher in LS-DYNA compared to MSC.Marc, as well as the equivalent plastic strain and the von Mises stress values. This tendency is also observed after trimming and welding. It can also be noted that the distribution of both strains and stresses on the trimmed and welded parts varies between the two compared codes, presumably due to the choice of different solver options, explicit and implicit.

  • 47.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Simulation and validation of forming, edge milling, welding and heat treatment of an alloy 718 componentManuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes finite element simulations of a manufacturing process chain consisting of forming, weld preparation by milling, laser welding and stress relief heat treatment of an alloy718 aero-engine part. The work also includes experimental validation with optical measurements of the part after each process step. Approximation and discretization errors were avoided by keeping the same mesh and constitutive model. The results show that the remaining stresses affect the subsequent manufacturing process step and therefore, simulation of the process chain is essential. The accuracy with respect to the geometry showed relatively good agreement between measurement and simulation.

  • 48.
    Steffenburg-Nordenström, Joachim
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Simulation and Validation of Forming, Milling, Welding and Heat Treatmentof an Alloy 718 Component2017In: International Journal of Materials Forming and Machining Processes IJMFMP), ISSN 2334-4563, Vol. 4, no 2, p. 15-28Article in journal (Refereed)
    Abstract [en]

    This paper describes finite element simulations of a manufacturing process chain consisting of

    forming, weld preparation by milling, laser welding and stress relief heat treatment of an alloy 718

    aero-engine part. The work also includes experimental validation with optical measurements of the

    part after each process step. Approximation and discretization errors were avoided by keeping the

    same mesh and constitutive model. The results show that the remaining stresses affect the subsequent

    manufacturing process step and therefore, simulation of the process chain is essential. The accuracy

    with respect to the geometry showed relatively good agreement between measurement and simulation.

  • 49.
    Svensson, Lars-Erik
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Increasing fatigue life using Low Transformation Temperature (LTT) welding consumables,2013In: 2nd Swedish conference on design and fabrication of welded structures: Conference proceedings / [ed] Zuheir Barsoum, Stockholm, 2013, p. 49-64Conference paper (Other academic)
  • 50.
    Svensson, Lars-Erik
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Ohlsson, A. R.
    SSAB AB, Oxelösund, Sweden.
    Stemne, D.
    SSAB AB, Oxelösund, Sweden.
    Gustafsson, M.
    ESAB AB, Göteborg, Sweden.
    Bengtsson, P.
    AGA Gas AB, Stockholm, Sweden.
    Strength and Impact Toughness of High Strength Steel Weld Metals: Influence of Welding Method, Dilution and Cooling Rate2015In: Proceedings of IIW International Conference, High-Strength Materials: Challenges and Applications, 2-3 July 2015, Helsinki, Finland, Helsingfors, 2015, p. 1-9Conference paper (Refereed)
    Abstract [en]

    Producing welds with properties matching those of the steel is a challenge at high strength levels. The present study has investigated how the choice of welding method affects weld metal mechanical properties through effects on dilution and cooling rate. Butt welds were produced in 12 mm plates in 777 MPa and 1193 MPa yield strength steels. Conventional arc welding methods including manual metal arc, gas metal arc welding, rapid arc welding and submerged arc welding were used as well as laser-gas metal arc hybrid welding. Filler materials with nominal yield strengths between 810 and 1000 MPa were used. Cooling times between 800 C and 500 C were varied between 5s and 15s and measured by insertion of thermocouples into the weld pool.High quality welds were produced efficiently with all welding methods even though dilution varied between 3%, for manual metal arc welding, to 73% for laser-hybrid welding. Low dilution, rapid cooling and single pass welding contributed to higher strength. Overmatching weld metal strength was achieved for the less strong steel and weld yield strengths of >1000 MPa were recorded for the stronger steel. Fracture in transverse tensile testing was always located in base material or HAZ. Impact toughness was higher for lower strength and low dilution. Results are discussed relating choice of welding method and cooling rate to weld metal properties for different steel strength levels.

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