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Publications (10 of 57) Show all publications
Li, P., Hurtig, K., Högström, M., Svensson, L.-E. & Scotti, A. (2018). A contribution to the study of negative polarity in GMA welding. The International Journal of Advanced Manufacturing Technology, 95(5-8), 2543-2553
Open this publication in new window or tab >>A contribution to the study of negative polarity in GMA welding
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2018 (English)In: 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) Published
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. 

Place, publisher, year, edition, pages
London: Springer, 2018
Keywords
Welding; Production; GMAW; Negative Polarity; Fusion rate; Weld bead geometry
National Category
Other Mechanical Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11817 (URN)10.1007/s00170-017-1349-z (DOI)2-s2.0-85035104454 (Scopus ID)
Projects
Maplab
Available from: 2017-11-26 Created: 2017-11-26 Last updated: 2018-03-02Bibliographically approved
Karimi Neghlani, P., Raza, T., Andersson, J. & Svensson, L.-E. (2018). Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 718. The International Journal of Advanced Manufacturing Technology, 94(5-8), 2199-2207
Open this publication in new window or tab >>Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 718
2018 (English)In: 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) Published
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)

Place, publisher, year, edition, pages
Springer London, 2018
Keywords
3D printers; Defects; Deposition; Deposits; Hardness; Microstructure, Alloy 718; Deposition Parameters; Large amounts; Laser energies; Laser exposure; Point distances; Selective laser melting; Small points, Porosity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11886 (URN)10.1007/s00170-017-1019-1 (DOI)2-s2.0-85028818109 (Scopus ID)
Note

First Online: 06 September 2017

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-02-20Bibliographically approved
Raza, T., Andersson, J. & Svensson, L.-E. (2018). Varestraint weldability testing of additive manufactured alloy 718. Science and technology of welding and joining, 1-6
Open this publication in new window or tab >>Varestraint weldability testing of additive manufactured alloy 718
2018 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, p. 1-6Article in journal (Refereed) Epub ahead of print
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.

Keywords
Weldability; Selective laser melting; Alloy718
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12077 (URN)10.1080/13621718.2018.1437338 (DOI)2-s2.0-85041916665 (Scopus ID)
Note

Published online: 12 Feb 2018

Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2018-02-26Bibliographically approved
Harati, E., Karlsson, L., Svensson, L.-E. & Dalaei, K. (2017). Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels. International Journal of Fatigue, 97, 39-47
Open this publication in new window or tab >>Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels
2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, p. 39-47Article in journal (Refereed) Published
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.

Keywords
Low Transformation Temperature Welding Consumables, Fatigue Strength, Residual Stress, Martensite Start Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10212 (URN)10.1016/j.ijfatigue.2016.12.007 (DOI)000393631300005 ()2-s2.0-85007154275 (Scopus ID)
Available from: 2016-12-05 Created: 2016-12-05 Last updated: 2017-08-23Bibliographically approved
Fahlström, K., Andersson, O., Melander, A., Karlsson, L. & Svensson, L.-E. (2017). Correlation between laser welding sequence and distortions for thin sheet structures. Science and technology of welding and joining, 22(2), 150-156
Open this publication in new window or tab >>Correlation between laser welding sequence and distortions for thin sheet structures
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2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 2, p. 150-156Article in journal (Refereed) Published
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.

Keywords
Automotive, Distortion, High strength steel, Laser welding, Welding sequence
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9678 (URN)10.1080/13621718.2016.1207046 (DOI)2-s2.0-84978705979 (Scopus ID)
Available from: 2016-12-16 Created: 2016-08-10 Last updated: 2017-11-29Bibliographically approved
Segerstark, A., Andersson, J. & Svensson, L.-E. (2017). Evaluation of a temperature measurement method developed for laser metal deposition. Science and technology of welding and joining, 22(1), 1-6
Open this publication in new window or tab >>Evaluation of a temperature measurement method developed for laser metal deposition
2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 1, p. 1-6Article in journal (Refereed) Published
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.

Keywords
Laser metal deposition, additive manufacturing, powder, Alloy 718, temperature measurement
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-8803 (URN)10.1080/13621718.2016.1169363 (DOI)000387910300001 ()2-s2.0-84978471771 (Scopus ID)
Note

Ingår i lic.avhandling

Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2018-04-11Bibliographically approved
Harati, E., Svensson, L.-E. & Karlsson, L. (2017). Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers. Engineering Failure Analysis, 79(September), 64-74
Open this publication in new window or tab >>Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers
2017 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, no September, p. 64-74Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2017
Keywords
Fatigue strength; Low transformation temperature welding consumable; High frequency mechanical impact treatment; High strength steel; Residual stress
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10923 (URN)10.1016/j.engfailanal.2017.04.024 (DOI)000405538800006 ()2-s2.0-85018745969 (Scopus ID)
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2017-12-11Bibliographically approved
Segerstark, A., Andersson, J. & Svensson, L.-E. (2017). Investigation of laser metal deposited Alloy 718 onto an EN 1.4401 stainless steel substrate. Optics and Laser Technology, 97(Supplement C), 144-153
Open this publication in new window or tab >>Investigation of laser metal deposited Alloy 718 onto an EN 1.4401 stainless steel substrate
2017 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 97, no Supplement C, p. 144-153Article in journal (Refereed) Published
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.

Keywords
Laser metal deposition, Additive manufacturing, Powder, Superalloy, Stainless steel
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11578 (URN)10.1016/j.optlastec.2017.05.038 (DOI)000409284800019 ()2-s2.0-85021979985 (Scopus ID)
Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2018-07-03Bibliographically approved
Fahlström, K., Andersson, O., Karlsson, L. & Svensson, L.-E. (2017). Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength. Science and technology of welding and joining, 22(7), 573-579
Open this publication in new window or tab >>Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength
2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 22, no 7, p. 573-579Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Taylor and Francis Ltd., 2017
Keywords
Distortion (waves); Hardness; Heat affected zone; High strength steel; Laser beam welding; Martensitic steel; Metallurgy; Metals; Sheet metal; Welding; Welds, automotive; Geometrical distortion; Good correlations; Steel grades; Thin sheet; Total energy; Weld metal; Weld widths, Steel metallurgy
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10936 (URN)10.1080/13621718.2016.1275483 (DOI)000406522500004 ()2-s2.0-85009275116 (Scopus ID)
Note

Published online: 12 Jan 2017

Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2017-08-25Bibliographically approved
Harati, E., Karlsson, L., Svensson, L.-E., Pirling, T. & Dalaei, K. (2017). Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel. Materials, 10(6), 1-14, Article ID E593.
Open this publication in new window or tab >>Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel
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2017 (English)In: Materials, E-ISSN 1996-1944, Vol. 10, no 6, p. 1-14, article id E593Article in journal (Refereed) Published
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.

Keywords
Residual stress; high strength steel; neutron diffraction; weld toe; low transformation temperature welding consumable
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-11065 (URN)10.3390/ma10060593 (DOI)000404415000027 ()28772953 (PubMedID)2-s2.0-85020406713 (Scopus ID)
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2017-12-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2560-0531

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