Change search
Refine search result
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Fedina, Tatiana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The use of non-spherical powder particles in Laser Powder Bed Fusion2021In: IOP Conference Series: Materials Science and Engineering, Institute of Physics (IOP), 2021, Vol. 1135, article id 012018Conference paper (Refereed)
    Abstract [en]

    Laser powder bed fusion (LPBF) generally involves the use of near-spherical powders due to their smooth morphology and enhanced flowability that allow for easier powder layering and laser processing. Non-spherical powders, on the other hand, are more cost-efficient to manufacture, however, the underlying mechanisms of their movement and interparticle interaction on the powder bed are still unclear. Thus, this study reports on the use of irregular iron-based powder material in LPBF, with a specific focus on particle motion and interaction behavior on the powder bed. The powder morphology, sphericity and particle size were analysed using X-ray computed microtomography and scanning electron microscopy. Based on the acquired data and by using a simplified analytical calculation, the influence of the particle shape/size on the particle movement in LPBF was established. High-speed imaging was employed to investigate the particle flow dynamics in the process zone, as well as the powder entrainment phenomenon. Particle entrainment and entrainment distances along the scanning direction were measured for near-spherical and non-spherical powders. The obtained results were compared between the powders, revealing a dissimilar particle transfer behavior. Non-spherical powder had a shorter entrainment distance partly attributed to the weaker drag force acting on these particles.

  • 2.
    Fedina, Tatiana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Spattering and oxidation phenomena during recycling of low alloy steel powder in Laser Powder Bed Fusion2021In: Materials Today Communications, ISSN 2352-4928, Vol. 27, article id 102241Article in journal (Refereed)
    Abstract [en]

    This study reports on the impact of repeated powder recycling on the degradation of low alloy steel powder in Laser Powder Bed Fusion. The average powder particle size increased slightly upon recycling due to powder agglomeration and the presence of spatters and other ejecta from the process zone. The oxygen content showed a continuous growth after each recycle, while the other chemical elements of the recycled powder remained largely unchanged. A map of ejecta classification is presented, featuring various ejecta types formed during laser processing. Ejecta of increased diameter and different shapes were observed in the recycled powder, using high-speed imaging and Scanning Electron Microscopy. The ejecta were collected after each powder recycle to enable the calculation of the ejecta mass generated during the process. The result showed a direct correlation between oxygen content in the powder and spatter/ejecta formation with the number of recycling events. It is likely that the increase in oxygen contributes to powder spattering.

  • 3.
    Fedina, Tatiana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The role of powder morphology in particle movement behavior in laser powder bed fusion with an emphasis on fluid drag2022In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 395, p. 720-731Article in journal (Refereed)
    Abstract [en]

    This study investigates the movement behavior of particles of dissimilar morphology in the powder bed in Laser Powder Bed Fusion. Gas atomized (GA) and water atomized (WA) low alloy steel powders were employed to study their motion around the laser scan path. Particle velocities, entrainment distances and denudation zones were measured for both powders using high-speed imaging. The entrainment of GA powder particles in front of the laser beam towards the process area was initiated 1.6 mm from the edge of the melt pool, whereas the distance was 0.6–0.8 mm for the WA powder. The differences in observed behavior were related to the variations in particle shape of the two types of powder. The processing of WA powder resulted in a 16% narrower denudation zone (for a low volumetric energy density) compared to GA powder. However, the denudation width difference decreased with increasing volumetric energy density, most likely due to a steeper pressure gradient in the process area which diminishes the impact of powder shape. X-ray computed microtomography was utilized to estimate the drag force acting on the powder particles of various morphologies. The results showed that the radial drag force exerted on GA powder was 64% greater than when using WA powder. Moreover, if the WA powder particles were of elongated shape the drag force decreased by almost an order of magnitude, demonstrating the importance of the particle's morphology in the process dynamics.

  • 4.
    Fedina, Tatiana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sundqvist, Jesper
    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 F.H
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A comparative study of water and gas atomized low alloy steel powders for additive manufacturing2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101675Article in journal (Refereed)
    Abstract [en]

    This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.

  • 5.
    Keskitalo, M.
    et al.
    University of Oulu, Oulu Southern Institute.
    Mentyjärvi, K.
    University of Oulu, Oulu Southern Institute.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Eriksson, Ingemar
    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.
    The influence of shielding gas on the properties of laser welded stainless steel2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan; Hans Engström, Luleå: Luleå tekniska universitet, 2013, p. 155-161Conference paper (Other academic)
    Abstract [en]

    Argon is generally used as shielding gas for laser welding. As Argon is an inert gas it doesnot have influence on the microstructure of the weld material or on the heat input of the weld,whereas nitrogen has solubility to austenite. Therefore nitrogen as an interstitial atomincreases the hardness of the weld. This has been detected when comparing the hardnessprofiles of nitrogen shielded welds of austenitic stainless steel with Argon shielded welds.Nitrogen as the shielding gas can compensate the softer structure of the weld in workhardenedand nitrogen-alloyed steels.For the duplex stainless steel grades the nitrogen additions promote formation ofaustenite in the weld, which decreases the risk of lowered toughness. In this study theinfluence of nitrogen shielding gas on the strength of the laser weld has been examined. Thestrength of laser welds of nitrogen alloyed work-hardened stainless steel seems to be slightlybetter when using nitrogen shielding gas compared to welds for argon shielding gas. It hasalso been verified that nitrogen as shielding gas decreases the risk of weak toughness of laserwelded duplex stainless steel.

    Download full text (pdf)
    FULLTEXT01
  • 6.
    Keskitalo, M.
    et al.
    University of Oulu, Oulu Southern Institute, Pajatie 5, FI-85500 Nivala, Finland.
    Mentyjärvi, K.
    University of Oulu, Oulu Southern Institute, Pajatie 5, FI-85500 Nivala, Finland.
    Sundqvist, Jesper
    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.
    Laser Welding Of Duplex Stainless Steel With Nitrogen As Shielding Gas2015In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 216, p. 381-384Article in journal (Refereed)
    Abstract [en]

    Nitrogen loss from laser welding melt pools and can have a deleterious effect on weld toughness for duplex stainless steels. This effect can be alleviated by using nitrogen as the shielding gas during laser welding. The use of Nitrogen results in increased austenite levels in the weld metal and improved toughness levels.

  • 7.
    Keskitalo, M.
    et al.
    University of Oulu, Oulu southern institute, Pajatie 5 85500 Nivala.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Mäntyjärvi, Kari
    University of Oulu, Oulu southern institute, Pajatie 5 85500 Nivala.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The Influence of Shielding Gas and Heat Input on the Mechanical Properties of Laser Welds in Ferritic Stainless Steel2015In: Physics Procedia, E-ISSN 1875-3892, Vol. 78, p. 222-229Article in journal (Refereed)
    Abstract [en]

    Laser welding of ferritic steel in normal atmosphere gives rise to weld embrittlement and poor formability. This paper demonstrates that the addition of an argon gas shield to the welding process results in tough, formable welds. Post weld heat treatment and microscopic analysis has suggested that the poor ductility of welds produced without a gas shield is, to some extent, the result of the presence of oxides in the weld metal.

  • 8.
    Kong, Choon Yen
    et al.
    TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom.
    Bolut, M.
    TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Assunção, E.
    EWF, Porto Salvo 2740-120, Portugal.
    Quintino, L.
    EWF, Porto Salvo 2740-120, Portugal.
    Blackburn, J.
    TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom.
    Single-pulse Conduction Limited Laser Welding Using A Diffractive Optical Element2016In: Physics Procedia, E-ISSN 1875-3892, Vol. 83, p. 1217-1222Article in journal (Refereed)
    Abstract [en]

    Conduction limited laser welding is commonly used in electronic and battery applications, where a high width-to-depth ratio weld is desirable. A laser beam with Gaussian or top-hat distributions is often used to produce conduction limited spot welds. Both these energy distributions result in a higher proportion of the laser beam energy being introduced towards the centre of the welded spot and consequently, a reduced penetration weld towards the circumference of the beam spot. The use of diffractive optical elements to tailor the energy distribution of the laser beam has been evaluated. An incident laser beam with an energy distribution in the shape of a ring or C-shape was projected onto the material, which results in heat propagating towards the centre, producing a shallow weld with a consistent depth of penetration across the entire overlapped joint. The results confirmed a corresponding thermal model which predicted an even distribution of heat at the joint interface.

    Download full text (pdf)
    fulltext
  • 9.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Aspects of Heat Flow in Laser Processing of Metals2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the laser was invented in 1960, its use in manufacturing industry has been growing rapidly. Laser processing of metals is based on the flow of heat that is generated by the absorbed laser beam. One outstanding aspect of laser beams is high precision along with high controllability of energy transfer, which includes creative techniques of shaping the beam and in turn the process. The thesis presents six Papers A-F on different metal processing techniques, namely welding, hardening and cutting, the latter combined with additive manufacturing. For each respective technique it was studied how desired properties can be optimized by controlled use of the laser beam and in turn of the temperature field. Addressing their different complexity of the heat transfer, various theoretical and experimental analysis methods were applied.

    Laser beam welding is usually conducted with standard beam shapes, i.e. Gaussian or top-hat like, which is not always optimal for the process. Identification of an optimised weld pool shape or temperature cycle could increase the quality of welded products or even enable new applications. Papers A and B aim to increase the knowledge for non-standard beam shapes, particularly for single-pulse conduction mode welding. Paper A presents an investigation on an industrial application where a C-shaped weld joint is desired. The sensitivity to and optimization of different C-shaped beam irradiation profiles is discussed. The analysis is mainly carried out by applying Finite Element Analysis, FEA, to calculate the heat conduction contributions, showing unexpected sensitivity in certain regimes. Paper B presents a semi-analytical model for fast calculation of the temperature field from different beam profiles. Examples include multi-spots or the misalignment sensitivity of Diffractive Optical Elements.

    In Paper C, for laser hardening of 11% Cr ferritic stainless steel the temperature field was studied to enable hardening. It was shown that single-track hardening without sensitisation could be achieved but overlapping tracks had a continuous network of ditched grain boundaries and is thereby at risk for sensitisation. The sensitised area is caused by a reheating cycle.

    The same mechanism for the same material was studied in Paper D when applying a recently developed drop deposition technique, where additive manufacturing is fed by laser cutting. The same reheating isotherm becomes critical, but here sensitisation tests show a discontinuous network of ditched grain boundaries in the added material. The solid heat-affected zone on the other hand has a continuous network of ditched grain boundaries, which implies a sensitisation risk. The continuous network is however not in contact with the surface. The tested parameters is thus not at risk for intergranular corrosion through sensitisation.

    For friction stir welding of dissimilar metals, Ti-6Al-4V with AISI 304L stainless steel, Paper E, the influence of a laser-induced preheating temperature field on the tool forces was investigated through numerical simulation. By suitable application of laser preheating, the forces acting on the tool can be substantially lowered, in a robust manner.

    The temperature field from seam welding induces a residual stress field. In Paper F, for continuous wave laser keyhole welding of high strength steel butt joints, a method is presented to identify the residual stress behaviour of laser welded sheets by measurement of the fatigue crack growth rate during testing, by deriving the crack acceleration. The analysis was confirmed by hole drilling tests and by FEA.

    The knowledge and methods of the above different experimental and theoretical studies complement each other. They contribute to further optimize certain aspects through laser-induced temperature fields, for different manufacturing techniques.

    Download full text (pdf)
    fulltext
  • 10.
    Sundqvist, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Heat conduction effects during laser welding2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the invention of the laser in 1960, its use has been growing steadily. New laser sources with high beam power and high beam quality provide potential for further growth. High quality beams can be shaped by optical tools, such as scanners or Diffractive Optical Elements, DOE, to almost any beam shape, enabling innovative laser process solutions. For welding in particular, a tailored beam can be used to control the melt pool and to optimise the temperature field and cycle. For example, joining of electrical components like battery cells becomes more common due to the shift to electrical vehicles. This is a field of applications where laser welding with a tailored beam has high potential due to the need of tightly controlled design tolerances or processing temperatures and in turn electrical and mechanical properties. The research presented in the thesis encompasses the heat flow generated from tailored laser beams, the thermal effects on the weld shape and on other quality criteria, the generated residual stress and its influence on fatigue crack propagation. For the sake of simplicity, melt flow was not considered in the calculations, which was discussed, too. The first three papers apply predictive mathematical modelling for the temperature field while the fourth paper experimentally derives the thermally induced residual stress distribution back from measured fatigue crack propagation.Paper I contains a FEM-based numerical heat flow study of a conduction mode laser welding case where a C-shaped overlap joint is desired. The quality criteria demand the welding process to be tightly controlled in terms of laser power and pulse time. Contrary to expectations, the joint geometry can significantly deviate from the laser beam C shape. As a continuation, in Paper II various quantitative indicators were derived and studied as part of the numerical simulation, in order to identify a suitable beam shape and in turn a DOE-design.Paper III presents a semi-analytical mathematical model that was developed for the heat flow in pulsed conduction mode welding for spatially and temporally shaped laser beams. As an alternative to FEM, the model is fast due to its analytical nature, which enables iterative beam shape optimization and DOE-design. By studying different beam shapes and the induced temperature fields, the potential and limits of the model were demonstrated and discussed. Paper IV is a study on residual stress that is thermally induced during the heating and cooling cycle of laser keyhole welding. Acceleration measurement of the crack propagating across the weld during fatigue testing turned out to be a suitable method to derive the residual stress distribution along the crack, including its alteration during the cracking. Comparisons with FEM-based stress analysis provide a link back to the temperature field induced by the laser, which enables optimization, e.g. by beam shaping.

    Download full text (pdf)
    FULLTEXT01
  • 11.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Eriksson, Ingemar
    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.
    Keskitalo, M.
    University of Oulu.
    Mentyjärvi, K.
    University of Oulu.
    Influence of the metallurgy on fatigue crack propagation in welded high strength steel joints2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan; Hans Engström, Luleå: Luleå tekniska universitet, 2013, p. 25-35Conference paper (Refereed)
    Abstract [en]

    A literature study of high strength steels, fatigue and fatigue assessment of welds has beenconducted and is briefly presented in this paper together with experiments on fatigue crackgrowth rates of laser welded high strength steel. It is well-known that the fatigue life ofwelded joints is heavily dependent upon the surface geometry and welding defects because ofcrack initiation from the high stress concentrations associated with these types of weldingflaws. However, the crack propagation through different weld zones of laser-welded highstrength steels and the corresponding impact from the metallurgy is not fully understood.The experiments comprise three-point bending fatigue tests on laser-welded highstrength steel with machined surfaces. Measurement of the fatigue crack propagation ratetransverse the weld and hence through the different metallurgy and hardness of the heataffected zone and of the weld can contain information on the impact of the metallurgy on thecrack propagation speed. The influence of different high strength steel grades and of differentwelding parameters on the crack propagation and fatigue life is discussed

    Download full text (pdf)
    FULLTEXT01
  • 12.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Eriksson, Ingemar
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Keskitalo, Markku
    University of Oulu, University of Oulu, Oulu Southern Institute.
    Mäntyjärvi, Kari
    University of Oulu.
    Granström, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Sundin, Karl-Gustaf
    Measuring the influence of laser welding on fatigue crack propagation in high strength steel2013In: ICALEO, 32nd International Congress on Applications of Lasers & Electro-Optics: October 6-10, 2013, Hyatt Regency Miami, Miami, FL USA, Orlando, Fl.: Laser institute of America , 2013Conference paper (Refereed)
  • 13.
    Sundqvist, Jesper
    et al.
    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.
    Sensitisation behaviour of drop-deposited 11% Cr ferritic stainless steel2018In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, p. 487-495Article in journal (Refereed)
    Abstract [en]

    For low-chromium ferritic stainless steel, a recently developed laser-driven drop-deposition technique enabled the building of three adjacent tracks on a substrate sheet of the same alloy, to study its risk for sensitisation from certain sequences of thermal cycles. The process was recorded by high-speed imaging to understand the drop-deposition mechanisms. Higher beam power resulted in a smoother track. The added layer was fully martensitic, achieving an elevated hardness of 320 HV. For a temperature peak just below austenitisation, the thermal cycle from a subsequent track affected the former track through tempering. Etching revealed a continuous region of ditched grain boundaries around the interface between the melted and heat affected zones. In the melted zone, the network became discontinuous approaching the surface, meaning that the specimen was immune to sensitisation, in contrast to transformation hardening results in the solid state. Additive manufacturing can induce manifold sequences of thermal cycles, but from the here generalized knowledge, strategies against sensitisation can be derived.

  • 14.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Analysis of inter-granular corrosion susceptibility stemming from laser-induced thermal cycles2019In: High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VIII / [ed] Stefan Kaierle; Stefan W. Heinemann, SPIE - International Society for Optical Engineering, 2019, article id 1091107Conference paper (Refereed)
    Abstract [en]

    Low-chromium ferritic stainless steel that is subjected to a second laser-induced thermal cycle is susceptible to intergranular corrosion. Precipitation of carbides and nitrides depletes the adjacent regions of chromium. For this material, despite its low carbon content of 0.007%, laser transformation hardening has achieved a considerable increase in hardness. For certain thermal conditions during overlapping of tracks the above precipitation mechanism can take place. Numerical modelling was applied to analyse the laser parameters that could be critical for precipitation to take place. The results are compared to experiments that were screened with a standardised test method. Avoiding susceptibility to intergranular corrosion when laser transformation hardening was shown to be difficult during a second thermal cycle of an overlapping pass that passes a critical though narrow temperature range. Based on this, measures to mitigate the susceptibility was introduced, in the form of heating the material above melting temperature. When melting the material, even during the first pass, corrosion behaviour changes. It is shown that the risk of corrosion can be avoided during subsequent passes. Different thermal cycles are analysed to find limits for avoiding susceptibility to intergranular corrosion. By laser treating and mapping the critical thermal cycles, the material can be used in a wider range of applications.

  • 15.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Granström, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Keskitalo, Markku
    Oulu Southern Institute, University of Oulu, Pajatie 5, Nivala FI-85500, Finland.
    Mäntyjärvi, Kari
    Oulu Southern Institute, University of Oulu, Pajatie 5, Nivala FI-85500, Finland.
    Ren, Xiaobo
    SINTEF Materials and Chemistry, N-7465 Trondheim, Norway.
    Identifying residual stresses in laser welds by fatigue crack growth acceleration measurement2015In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, no 4, article id 42002Article in journal (Refereed)
    Abstract [en]

    During laser welding, residual stresses are thermally induced. They can have strong impact on the fatigue behavior and fatigue life. A standardized measurement method for the fatigue crack growth rate was expanded to identify residual stress along the cracking path. The second derivative of the measured crack opening and in turn the crack acceleration corresponded well with distinct acceleration maxima and minima and accordingly with tensile and compressive stress, as was basically proven by numerical simulation. The method is simple and extendable. It provides valuable information, as was demonstrated for various situations.

  • 16.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sensitisation behaviour of drop-deposited 11% Cr ferritic stainless steelManuscript (preprint) (Other academic)
  • 17.
    Sundqvist, Jesper
    et al.
    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.
    Kong, Choon Yen
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Assuncao, Eurico
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Quintino, Luisa
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Blackburn, Jon
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Numerical sensitivity analysis of single pulse laser welding with a C-shaped beam2015In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, no Suppl. 2, article id S29010Article in journal (Refereed)
    Abstract [en]

    Even though Gaussian and top-hat beam profiles are suitable for most laser welding applications, for certain cases other beam distributions can be favored in terms of weld quality or performance. One promising method to generate a tailored beam shape is diffractive optical elements. A numerical model on the temperature field generated by specific beam shapes is therefore under development to iteratively identify desired beam shapes for specific applications. The present study is based on two thin steel sheets that are conduction welded in a lap joint mode by a C-shaped single laser pulse. The main aim is to ensure a specified weld width along the C-weld shape at the overlap interface between the two sheets in a robust manner. The sensitivity of main criteria like the interface weld width and phase changes at the workpiece top and bottom is studied and discussed in a systematic manner by applying a numerical heat transfer model for various parameters and conditions.

  • 18.
    Sundqvist, Jesper
    et al.
    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.
    Kong, Choon Yen
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Blackburn, Jon
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Assuncao, Eurico
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Quintino, Luisa
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Heat conduction modelling to optimize the laser beam profile for pulsed conduction mode welding2015Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 19.
    Sundqvist, Jesper
    et al.
    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.
    Shachaf, L.
    Holo/Or Ltd.
    Kong, Choon Yen
    TWI Ltd, Granta Park, Great Abington, Cambridge .
    Analytical heat conduction modelling for shaped laser beams2017In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 247, p. 48-54Article in journal (Refereed)
    Abstract [en]

    Conduction mode laser spot welding and laser spot hardening usually employ Gaussian or top-hat-like beam modes. One main requirement of these techniques is the avoidance of overheating in the centre of the laser-material interaction zone. Process flexibility can be improved by spatially and/or temporally shaping the beam, which can enable higher process quality, robustness or speed. A desired spatial beam shape can be achieved by a suitably designed diffractive optical element. However, the prediction of a suitable beam shape for a particular process can be complex. A simplified analytical heat conduction model has been developed that can rapidly calculate the temperature field and cooling behaviour for almost any spatial and temporal beam shape. The potential and limits of the model are demonstrated and discussed by calculating and analysing temperature profiles for several cases of multi-spot welding

  • 20.
    Sundqvist, Jesper
    et al.
    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.
    Shachal, L.
    Holo/Or Ltd.
    Brodsky, A.
    Holo/Or Ltd.
    Kong, Choon Yen
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Blackburn, Jon
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Assuncao, Eurico
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Quintino, Luisa
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Numerical optimization approaches of single-pulse conduction laser welding by beam shape tailoring2016In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 79, p. 48-54Article in journal (Refereed)
    Abstract [en]

    While circular laser beams are usually applied in laser welding, for certain applications tailoring of the laser beam shape, e.g. by diffractive optical elements, can optimize the process. A case where overlap conduction mode welding should be used to produce a C-shaped joint was studied. For the dimensions studied in this paper, the weld joint deviated significantly from the C-shape of the single-pulse laser beam. Because of the complex heat flow interactions, the process requires optimization. Three approaches for extracting quantitative indicators for understanding the essential heat flow contributions process and for optimizing the C-shape of the weld and of the laser beam were studied and compared. While integral energy properties through a control volume and temperature gradients at key locations only partially describe the heat flow behaviour, the geometrical properties of the melt pool isotherm proved to be the most reliable method for optimization. While pronouncing the C-ends was not sufficient, an additional enlargement of the laser beam produced the desired C-shaped weld joint. The approach is analysed and the potential for generalization is discussed.

  • 21.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kim, Kyounghak
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Bang, Hee-Seon
    Department of Welding and Joining Science Engineering, Chosun University.
    Bang, Hansur
    Department of Welding and Joining Science Engineering, Chosun University.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Numerical simulation of laser preheating of friction stir welding of dissimilar metals2018In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 23, no 4, p. 351-356Article in journal (Refereed)
    Abstract [en]

    Friction stir welding, FSW, of harder metal alloys is difficult to perform, like here dissimilar welding of titanium alloy to stainless steel in butt joint configuration. One major limitation is tool wear which can be reduced by preheating with a laser beam. A mathematical model to calculate the tool forces during FSW was developed further. The calculations show that the laser beam reduces forces at the pin and shoulder of the FSW-tool, accompanied by reduced heat generation through the tool. Within its operating limits, the process has low sensitivity on the lateral position of the leading laser beam. The model supports the understanding and optimisation of the complex interaction zone of forces and heat around the FSW-tool.

  • 22.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Manninen, Timo
    Outokumpu Stainless Oy.
    Heikkinen, Hannu-Pekka
    Outokumpu Stainless Oy.
    Anttila, Severi
    Materials and Production Engineering, University of Oulu, Oulu, Finland.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser surface hardening of 11% Cr ferritic stainless steel and its sensitisation behaviour2018In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 344, p. 673-679Article in journal (Refereed)
    Abstract [en]

    11% Cr ferritic stainless steel conforming to EN 1.4003 standard was surface hardened by a continuous-wave fibre laser beam. Both single-pass and multi-pass laser hardening was investigated. Different laser parameters were compared and their influence on hardness, microstructure, geometry of the hardened zone and sensitisation was investigated, especially for overlapping passes. The experiments showed that a surface hardness which is double that of the base material hardness was obtainable via martensitic phase transformation and high cooling rate, in spite of the low carbon and nitrogen content. This behaviour could be predicted from the chemical composition using the Kaltenhauser Ferrite Factor. Hardening at higher power levels gives more coarse-grained lath martensite but does not increase the hardness. Sensitisation was not a problem in single-pass hardening. However, the production of overlapping tracks could be detrimental to corrosion resistance in 11% Cr steel due to the formation of chromium carbides and nitrides.

  • 23.
    Sundqvist, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Samarjy, Ramiz Saeed Matti
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. University of Mosul, College of Engineering, Department of Mechanical Engineering, Mosul, Iraq.
    High-speed imaging of droplet behaviour during the CYCLAM drop-deposition technique2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 208-215Article in journal (Refereed)
    Abstract [en]

    The material in laser additive manufacturing is traditionally supplied in the form of powder or sometimes wire. A technique called CYCLAM was recently presented which is a fast and direct recycling technique which lowers the number of steps that need to be taken in typical recycling, allowing for a more circular economy. The CYCLAM technique proposes that waste metal is directly recycled through laser cutting or laser ablation of one sheet and the molten droplet is directly deposited onto a new product and can be used for additive manufacturing or cladding. The technique also can also use materials that otherwise are not available as powder or wires. Because of the novelty of the technique, it is still scarcely studied, and many aspects still needs to be understood. This paper focusses on high-speed imaging of the technique to understand the droplet behaviour. The material removal of the feeding sheet was done with Remote Fusion Cutting. Different power levels lead to different drop geometry and flight pattern of the drops where the drops at higher power are pushed further forward. The influence of the laser power on the shape of the deposited track can be seen from cross sections of the cladded track where higher power means that more power is transmitted through the feeding sheet and onto the substrate which creates a smoother surface

1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf