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Publications (10 of 303) Show all publications
Siva Prasad, H., Frostevarg, J. & Kaplan, A. (2019). The stability of laser welding with an off-axis wire feed. Journal of Materials Processing Technology, 264, 84-90
Open this publication in new window or tab >>The stability of laser welding with an off-axis wire feed
2019 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 264, p. 84-90Article in journal (Refereed) Published
Abstract [en]

The concept using an off-axis filler wire during laser welding is introduced here in order to provide added process robustness considering gap width variations. Its stability is investigated with respect to gap width, welding speeds and powers. Geometry of the welds is analysed by tracing of weld cap edges and joint cross sections, connecting trends to weld parameters. High speed imaging and streak images are used to further study and describe sequences of events, including undercut formation. Formation of imperfections are found to be mainly correlated to wire feed position variations at the surface due to irregular melting of the wire tip.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-70826 (URN)10.1016/j.jmatprotec.2018.09.003 (DOI)2-s2.0-85053062410 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-09-21 (svasva)

Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2018-09-21Bibliographically approved
Näsström, J., Frostevarg, J. & Kaplan, A. (2018). Arc formation in narrow gap hot wire laser welding. Welding Journal, 97(6), 171S-178S
Open this publication in new window or tab >>Arc formation in narrow gap hot wire laser welding
2018 (English)In: Welding Journal, ISSN 0043-2296, Vol. 97, no 6, p. 171S-178SArticle in journal (Refereed) Published
Abstract [en]

Many heavy industrial applications, e.g. shipbuilding and offshore, rely on thick-section, high-quality welds. Unfortunately, traditional arc-based techniques are often found wanting due to a limited penetration depth and excessive heat-affected zone. The former is typically solved by having a wide groove filled by multiple weld passes, which is both costly and time consuming. Other processes such as autonomous laser or electron beams can join thick materials, but have disadvantages such as increased hardness and solidification cracks inside the welds. A promising in-between technique to join thick sheets is narrow gap multi layer laser welding (NGMLW), using less filler material while also offering more control of weld properties. This technique is often used with laser scanning optics and cold wire, or a defocused laser and electrically heated wire. This paper investigates the limitations of the latter during NGMLW, mainly using high-speed imaging to directly observe and explain process behavior. Increased deposition rates are wanted, but heating also consequently needs to be increased for proper bead fusion. Arc occurrences are found to be the cause of instabilities. They are observed occasionally even at low voltages, but more frequently at higher outputs, and then are also more disruptive to the process.

Place, publisher, year, edition, pages
American Welding Society, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-70165 (URN)10.29391/2018.97.015 (DOI)000435429400018 ()2-s2.0-8504937533 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-07-26 (inah)

Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2018-08-09Bibliographically approved
Volpp, J., Prasad, H. S. & Kaplan, A. (2018). Behavior of heated powder particles on solid surfaces. Paper presented at 8th Swedish Production Symposium, SPS 2018, Stockholm, Sweden, 16-18 May 2018.. Procedia Manufacturing, 25, 365-374
Open this publication in new window or tab >>Behavior of heated powder particles on solid surfaces
2018 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 365-374Article in journal (Refereed) Published
Abstract [en]

Powder particles applied through a powder nozzle as used e.g. in laser additive manufacturing or cladding processes are heated during their flight through the laser beam. The heating process and the interaction of the particle with the solid substrate were modeled in this work. In addition, the particle interaction with the solid substrate was observed using high speed imaging. At a high temperature and a high speed of the particles, the heat conduction into the base material is not fast enough to solidify the particles due to the short interaction time with the substrate.

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-70242 (URN)10.1016/j.promfg.2018.06.105 (DOI)
Conference
8th Swedish Production Symposium, SPS 2018, Stockholm, Sweden, 16-18 May 2018.
Note

Konferensartikel i tidskrift;2018-08-07 (andbra)

Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2018-09-11Bibliographically approved
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
Keywords
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 selective laser melting. Journal of laser applications, 30(3), Article ID 032304.
Open this publication in new window or tab >>Energy efficiency contributions and losses during selective laser melting
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 Other Materials Engineering
Research subject
Manufacturing Systems Engineering; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-65948 (URN)10.2351/1.5040603 (DOI)2-s2.0-85048655783 (Scopus ID)
Note

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

Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-06-28Bibliographically 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)000437391300077 ()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: 2018-07-25Bibliographically approved
Bunaziv, I., Akselsen, O. M., Frostevarg, J. & Kaplan, A. (2018). Laser-arc hybrid welding of thick HSLA steel. Journal of Materials Processing Technology, 259, 75-87
Open this publication in new window or tab >>Laser-arc hybrid welding of thick HSLA steel
2018 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 259, p. 75-87Article in journal (Refereed) Published
Abstract [en]

A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modelling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.

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-68544 (URN)10.1016/j.jmatprotec.2018.04.019 (DOI)000437814500008 ()2-s2.0-85045563495 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-04-30 (andbra)

Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2018-08-08Bibliographically 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)000435470000009 ()2-s2.0-85032491421 (Scopus ID)
Note

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

Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-07-26Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3569-6795

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