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Publications (10 of 297) Show all publications
Bunaziv, I., Akselsen, O. M., Frostevarg, J. & Kaplan, A. F. .. (2018). Deep penetration fiber laser-arc hybrid welding of thick HSLA steel. Journal of Materials Processing Technology, 256, 216-228
Open this publication in new window or tab >>Deep penetration fiber laser-arc hybrid welding of thick HSLA steel
2018 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 256, p. 216-228Article in journal (Refereed) Published
Abstract [en]

The present investigation addresses laser-arc hybrid welding of 45 mm thick steel with variation in a wide range of process parameters. High volume fraction of acicular ferrite formed in the upper part of the weld metal regardless process parameters. Significantly lower fraction of acicular ferrite was found in the root due to substantially increased cooling rates and the inability to deliver filler wire to this region, resulting in bainite-martensite microstructures in the root. The delivery of filler wire to the root can be enhanced by increasing the air gap between the plates. Higher heat inputs reduce cooling rates in the root which create softer and ductile microstructures, at the expense of a much wider and coarser grained HAZ. The results obtained showed high fusion line and weld metal toughness at low temperature (−50 °C).

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-67696 (URN)10.1016/j.jmatprotec.2018.02.026 (DOI)000431156800021 ()2-s2.0-85042446378 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-26 (andbra)

Available from: 2018-02-20 Created: 2018-02-20 Last updated: 2018-06-11Bibliographically approved
Pocorni, J., Powell, J., Frostevarg, J. & Kaplan, A. F. H. (2018). Dynamic laser piercing of thick section metals. Optics and lasers in engineering, 100, 82-89
Open this publication in new window or tab >>Dynamic laser piercing of thick section metals
2018 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 100, p. 82-89Article in journal (Refereed) Published
Abstract [en]

Before a contour can be laser cut the laser first needs to pierce the material. The time taken to achieve piercing should be minimised to optimise productivity. One important aspect of laser piercing is the reliability of the process because industrial laser cutting machines are programmed for the minimum reliable pierce time. In this work piercing experiments were carried out in 15 mm thick stainless steel sheets comparing a stationary laser and a laser which moves along a circular trajectory with varying processing speeds. Results show that circular piercing can decrease the pierce duration by almost half compared to stationary piercing. High speed imaging (HSI) was employed during the piercing process to understand melt behaviour inside the pierce hole. HSI videos show that circular rotation of the laser beam forces melt to eject in opposite direction of the beam movement, while in stationary piercing the melt ejects less efficiently in random directions out of the hole.

Place, publisher, year, edition, pages
Elsevier, 2018
Keyword
Laser cutting, laser piercing, reliability, efficiency, fibre laser, high speed imaging
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-63492 (URN)10.1016/j.optlaseng.2017.07.012 (DOI)000414108700010 ()2-s2.0-85026484330 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-08-15 (andbra)

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-11-24Bibliographically approved
Mishra, P., Ilar, T., Brueckner, F. & Kaplan, A. (2018). Energy efficiency contributions and losses during SLM. Journal of laser applications, 30(3), Article ID 032304.
Open this publication in new window or tab >>Energy efficiency contributions and losses during SLM
2018 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, no 3, article id 032304Article in journal (Refereed) Published
Abstract [en]

Selective Laser Melting technique, SLM, requires remelting of adjacent tracks to avoid cavities and other imperfections. Usually, very conservative process parameters are chosen to avoid imperfections, resulting in a low building rate. The process efficiency relates the energy required for the generation of a new track to the laser beam power. For SLM this efficiency is determined by the process parameters, specifically hatch distance, layer depth and scanning speed, independent of the resulting process mechanisms. For SLM the process efficiency often very low, typically 2‑20%. Apart from beam reflection losses of normally 50-60%, significant energy losses result from the remelting of surrounding layers. Some areas can even experience multiple remelting cycles. Further losses originate inevitably from substrate heating. A simplified mathematical model of the track cross section and the corresponding layer overlap geometry has been developed, to analyze the different loss contributions from remelting with respect to the process parameters. The model explains why increasing the hatch distance or the layer depth proportionally increases the process efficiency. However, these increases are limited by cavity formation. The cross section of the overlapping tracks generated by SLM can be regarded as an experimental fingerprint linked to the process conditions. The track cross section geometries can significantly fluctuate, in terms of area and coordinate position. The fluctuations require additional reduction of the hatch distance or layer depth, to ensure robust, cavity-free processing. Examples are presented for stainless steel where a 180 W laser beam has led to a process efficiency of 5-11%, proportional to a hatch distance that was increased from 50 to 110 µm, for 40 µm powder layer depth, at a speed of 50 m/min.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-65948 (URN)10.2351/1.5040603 (DOI)
Note

Validerad;2018;Nivå 2;2018-06-15 (andbra)

Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-06-15Bibliographically approved
Haglund, P., Frostevarg, J., Powell, J., Eriksson, I. & Kaplan, A. (2018). Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses. Optics and Laser Technology, 100, 1-6
Open this publication in new window or tab >>Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses
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2018 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 100, p. 1-6Article in journal (Refereed) Published
Abstract [en]

Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-66009 (URN)10.1016/j.optlastec.2017.09.053 (DOI)000417669700001 ()2-s2.0-85030758159 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-10 -09 (andbra)

Available from: 2017-10-09 Created: 2017-10-09 Last updated: 2017-12-28Bibliographically approved
Sundqvist, J., Manninen, T., Heikkinen, H.-P., Anttila, S. & Kaplan, A. F. (2018). Laser surface hardening of 11% Cr ferritic stainless steel and its sensitisation behaviour. Surface & Coatings Technology, 344, 673-679
Open this publication in new window or tab >>Laser surface hardening of 11% Cr ferritic stainless steel and its sensitisation behaviour
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2018 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 344, p. 673-679Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Mechanical Engineering Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-67581 (URN)10.1016/j.surfcoat.2018.04.002 (DOI)2-s2.0-85044924333 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-04-06 (andbra)

Available from: 2018-02-09 Created: 2018-02-09 Last updated: 2018-06-11Bibliographically approved
Sundqvist, J., Kim, K., Bang, H.-S., Bang, H. & Kaplan, A. (2018). Numerical simulation of laser preheating of friction stir welding of dissimilar metals. Science and technology of welding and joining, 23(4), 351-356
Open this publication in new window or tab >>Numerical simulation of laser preheating of friction stir welding of dissimilar metals
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2018 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 23, no 4, p. 351-356Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-66366 (URN)10.1080/13621718.2017.1391936 (DOI)
Note

Validerad;2018;Nivå 2;2018-03-14 (andbra)

Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-03-14Bibliographically approved
Bunaziv, I., Frostevarg, J., Akselsen, O. M. & Kaplan, A. (2018). Process stability during fiber laser-arc hybrid welding of thick steel plates. Optics and lasers in engineering, 102, 34-44
Open this publication in new window or tab >>Process stability during fiber laser-arc hybrid welding of thick steel plates
2018 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 102, p. 34-44Article in journal (Refereed) Published
Abstract [en]

TThick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-66398 (URN)10.1016/j.optlaseng.2017.10.020 (DOI)000418970600005 ()2-s2.0-85032330245 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-06 (andbra)

Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2018-01-23Bibliographically approved
Pocorni, J., Powell, J., Frostevarg, J. & Kaplan, A. F. .. (2018). The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions. Optics and Laser Technology, 103, 318-326
Open this publication in new window or tab >>The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions
2018 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 103, p. 318-326Article in journal (Refereed) Published
Abstract [en]

Cutting fronts created by CO2 and fibre lasers in stainless steel at thicknesses between 2 mm and 10 mm have been ‘frozen’ and their geometry has been measured. Standard commercial cutting parameters were used to generate the cuts for both types of laser. The resulting three-dimensional cutting front shapes have been curve fitted as polynomials and semicircles. Various features of the cutting front geometry are discussed including the lack of correlation of the cut front inclination with either the relevant Brewster angle or the inclination of the striations on the cut edge.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-67687 (URN)10.1016/j.optlastec.2018.01.055 (DOI)000427339000041 ()2-s2.0-85041470309 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-19 (andbra)

Available from: 2018-02-19 Created: 2018-02-19 Last updated: 2018-06-11Bibliographically approved
Bunaziv, I., Frostevarg, J., Akselsen, O. M. & Kaplan, A. (2018). The penetration efficiency of thick plate laser-arc hybrid welding. The International Journal of Advanced Manufacturing Technology
Open this publication in new window or tab >>The penetration efficiency of thick plate laser-arc hybrid welding
2018 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015Article in journal (Refereed) Epub ahead of print
Abstract [en]

Double-sided fiber laser-arc hybrid welding was used to join 45 mm thick high strength steel over a wide range of parameters in order to investigate the efficiency of the process. Air gap size, I- and Y-groove type preparation, pulsed and cold metal transfer pulsed arc modes, arc-laser setup, and travel speeds were compared, and in all cases, sufficient filler material was provided to fully fill the gap. The welds were investigated using high speed imaging and cross-sectional analysis to identify penetration depths, morphology, and imperfections. Larger joint air gaps were found to contribute most to weld penetration depth. Surprisingly, increased line energy decreased penetration efficiency in most cases. The laser-arc interdistance was also investigated, revealing an arc size and melt flow dependency for achieving higher penetration depth for a leading arc. It was found that, although penetration can be optimized, solidification cracking can be a limiting factor in the application of deep penetration hybrid welding for thick steel section joining.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-68842 (URN)10.1007/s00170-018-2103-x (DOI)
Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-31
Sundqvist, J., Kaplan, A., Shachaf, L. & Kong, C. Y. (2017). Analytical heat conduction modelling for shaped laser beams. Journal of Materials Processing Technology, 247, 48-54
Open this publication in new window or tab >>Analytical heat conduction modelling for shaped laser beams
2017 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 247, p. 48-54Article in journal (Refereed) Published
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

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-63056 (URN)10.1016/j.jmatprotec.2017.04.011 (DOI)000403133400006 ()2-s2.0-85018469004 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-05-11 (andbra)

Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-02-09Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3569-6795

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