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Ilar, Torbjörn
Publications (10 of 26) Show all publications
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
Kaplan, A., Frostevarg, J., Ilar, T., Bang, H.-S. & Bang, H.-S. (2015). Evolution of a Laser Hybrid Welding Map (ed.). Paper presented at Nordic Laser Materials Processing Conference : 25/08/2015 - 27/08/2015. Physics Procedia, 78, 2-13
Open this publication in new window or tab >>Evolution of a Laser Hybrid Welding Map
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2015 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, p. 2-13Article in journal (Refereed) Published
Abstract [en]

Laser arc hybrid welding combines the advantages but also the complex physical mechanisms of gas metal arc welding and laser keyhole welding. From manifold mainly experimental but also theoretical research results a map with versatile functions was initiated for the first time. The purpose is to survey the overall context and to facilitate navigation to the various phenomena that are shown through case studies accompanied by theoretical explanations and guidelines for optimization. Though not complete, the map enables systematic and graphical navigation to relevant publications. Based on a fundamental structure of the map, which was decided early, it is inherently extendable in the future by adding existing and new knowledge, also from other research groups, enabling evolution. The fundament of the map structure comprises gouge thickness, joint type and metal grade, in coherence with product and weld designers’ starting points. The next hierarchy level of the map offers options in the joint type as well as in hybrid welding techniques. The latter contains techniques like double-sided welding, pulse shaping management of the arc or laser, CMT arcs, tandem arcs, or remelting of undercuts. In addition to laser-arc hybrid welding, other hybrid laser techniques like multilayer hot-wire laser welding of narrow gaps or hybrid laser friction stir welding can be taken into account. At the other end of the hierarchy, the map offers via a database-like archive electronic navigation to research results like weld macrographs, high speed imaging or numerical simulation results of the welding process.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-29953 (URN)10.1016/j.phpro.2015.11.012 (DOI)000370876600001 ()2-s2.0-84965008638 (Scopus ID)3975d56a-2fb5-4d14-87a2-d31c405d9361 (Local ID)3975d56a-2fb5-4d14-87a2-d31c405d9361 (Archive number)3975d56a-2fb5-4d14-87a2-d31c405d9361 (OAI)
Conference
Nordic Laser Materials Processing Conference : 25/08/2015 - 27/08/2015
Note
Validerad; 2015; Nivå 1; 20151126 (andbra); Konferensartikel i tidskriftAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
Powell, J., Ilar, T., Frostevarg, J., Torkamany, M., Na, S.-J., Petring, D., . . . Kaplan, A. (2015). Weld root instabilities in fiber laser welding (ed.). Paper presented at . Journal of laser applications, 27(Suppl. 2), Article ID S29008.
Open this publication in new window or tab >>Weld root instabilities in fiber laser welding
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2015 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, no Suppl. 2, article id S29008Article in journal (Refereed) Published
Abstract [en]

Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole.(This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects;(a) the melt can achieve velocities which result in melt ejection from the root of the weld-which can result in intermittent penetration,(b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces-which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-9081 (URN)10.2351/1.4906390 (DOI)000350544500017 ()2-s2.0-84943599168 (Scopus ID)7a4e8354-bb8b-48f2-b34f-87a429b2b057 (Local ID)7a4e8354-bb8b-48f2-b34f-87a429b2b057 (Archive number)7a4e8354-bb8b-48f2-b34f-87a429b2b057 (OAI)
Note
Validerad; 2015; Nivå 2; 20150410 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Moradi, M., Salimi, N., Ghoreishi, M., Abdollahi, H., Shamsborhan, M., Frostevarg, J., . . . Kaplan, A. (2014). Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance (ed.). Paper presented at . Journal of laser applications, 26(2), Article ID 22004.
Open this publication in new window or tab >>Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance
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2014 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, no 2, article id 22004Article in journal (Refereed) Published
Abstract [en]

Reinforcement, undercut, and root drop-through during laser hybrid arc welding of steel were studied in dependence of gap width, welding speed, and wire feeding rate. Generalized trends were obtained through design of experiments. Most of the trends could be explained by a mass balance while some parameter impacts relied on more complex mechanisms. In particular, different levels of complexity of parameter dependencies were distinguished, ranging from monotonous behaviour to maxima and to changing signs of the trends. The findings are of high practical relevance to optimize the process with respect to the weld quality. Moreover, the potential and limits of the design of experiments method, of a mass balance, and of the matrix flow chart method are discussed.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-13283 (URN)10.2351/1.4866675 (DOI)000334336900004 ()2-s2.0-84896745062 (Scopus ID)c7b6051c-4320-46e3-aa34-8d843f77327b (Local ID)c7b6051c-4320-46e3-aa34-8d843f77327b (Archive number)c7b6051c-4320-46e3-aa34-8d843f77327b (OAI)
Note
Validerad; 2014; 20140407 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Ilar, T. & Kaplan, A. (2013). An extended feasibility study to identify laser welding and laser.arc hybrid welding business cases and business models (ed.). In: (Ed.), Alexander Kaplan; Hans Engström (Ed.), 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden. Paper presented at Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013 (pp. 217-226). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>An extended feasibility study to identify laser welding and laser.arc hybrid welding business cases and business models
2013 (English)In: 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. 217-226Conference paper, Published paper (Other academic)
Abstract [en]

The laser research group at Luleå University of Technology has, in collaboration withSwedish industries, performed more than 20 laser welding and laser arc hybrid welding casestudies during the last decade. Most of them can be considered as successful and havedemonstrated improved mechanical properties, new design opportunities and higher weldingproductivity. Nevertheless, very few of the successful case studies have resulted in anindustrial application and the number of industrial implementations is still very limited. Thereare of course several reasons, like company organisation, human factors or lack of experience,but usually it is a rational analysis based on return of investment. The case studies are alsousually limited to one component at one company without any further evaluation and analysisof other business opportunities, i.e. other components/products within the company orforming a cluster of companies in a geographic region. This paper presents an extend analysesof a number of the performed case studies with the objectives to evaluate and identifybusiness cases. Different business models, such as investigate product families for laserwelding within a company and company clusters with common laser welding resource, isevaluated and analysed.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2013
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-37846 (URN)bfd7194b-ded5-473f-9789-249431d575d8 (Local ID)978-91-7439-688-1 (ISBN)978-91-7439-689-8 (ISBN)bfd7194b-ded5-473f-9789-249431d575d8 (Archive number)bfd7194b-ded5-473f-9789-249431d575d8 (OAI)
Conference
Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013
Note
Godkänd; 2013; 20131210 (andbra)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Matti, R., Ilar, T. & Kaplan, A. (2013). Analysis of laser remote fusion cutting based on a mathematical model (ed.). Paper presented at . Journal of Applied Physics, 114(23), Article ID 233107.
Open this publication in new window or tab >>Analysis of laser remote fusion cutting based on a mathematical model
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 23, article id 233107Article in journal (Refereed) Published
Abstract [en]

Laser remote fusion cutting is analyzed by the aid of a semi-analytical mathematical model of the processing front. By local calculation of the energy balance between the absorbed laser beam and the heat losses, the three-dimensional vaporization front can be calculated. Based on an empirical model for the melt flow field, from a mass balance, the melt film and the melting front can be derived, however only in a simplified manner and for quasi-steady state conditions. Front waviness and multiple reflections are not modelled. The model enables to compare the similarities, differences, and limits between laser remote fusion cutting, laser remote ablation cutting, and even laser keyhole welding. In contrast to the upper part of the vaporization front, the major part only slightly varies with respect to heat flux, laser power density, absorptivity, and angle of front inclination. Statistical analysis shows that for high cutting speed, the domains of high laser power density contribute much more to the formation of the front than for low speed. The semi-analytical modelling approach offers flexibility to simplify part of the process physics while, for example, sophisticated modelling of the complex focused fibre-guided laser beam is taken into account to enable deeper analysis of the beam interaction. Mechanisms like recast layer generation, absorptivity at a wavy processing front, and melt film formation are studied too.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-4676 (URN)10.1063/1.4849895 (DOI)000329056800007 ()2-s2.0-84891436109 (Scopus ID)2a8887ff-52d9-4c15-83ac-114423a4e2cf (Local ID)2a8887ff-52d9-4c15-83ac-114423a4e2cf (Archive number)2a8887ff-52d9-4c15-83ac-114423a4e2cf (OAI)
Note
Validerad; 2014; 20140108 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Pocorni, J., Powell, J., Ilar, T., Schwarz, A. & Kaplan, A. (2013). Measuring the State-of-the-Art in Laser Cut Quality (ed.). In: (Ed.), Alexander Kaplan; Hans Engström (Ed.), 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden. Paper presented at Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013 (pp. 101-108). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Measuring the State-of-the-Art in Laser Cut Quality
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2013 (English)In: 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. 101-108Conference paper, Published paper (Other academic)
Abstract [en]

This paper discusses the strategy appropriate to investigating the state of the art of laser cutting from an industrial point of view. The importance of creating the samples in a high quality industrial environment is emphasised and preliminary results are presented.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2013
Keywords
Laser cutting, Cut quality, Cut edge inclination, Cut edge roughness, Dross, State of the art, Technology - Electrical engineering, electronics and photonics, Teknikvetenskap - Elektroteknik, elektronik och fotonik
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-37769 (URN)be39c34b-b884-4467-b4ef-23d2e8d7022a (Local ID)978-91-7439-688-1 (ISBN)978-91-7439-689-8 (ISBN)be39c34b-b884-4467-b4ef-23d2e8d7022a (Archive number)be39c34b-b884-4467-b4ef-23d2e8d7022a (OAI)
Conference
Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013
Note
Godkänd; 2013; 20130709 (jetpoc)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Matti, R., Ilar, T. & Kaplan, A. (2013). Modelling the cutting geometry for laser remote fusion cutting of metals (ed.). In: (Ed.), Alexander Kaplan; Hans Engström (Ed.), 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden. Paper presented at Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013 (pp. 121-132). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Modelling the cutting geometry for laser remote fusion cutting of metals
2013 (English)In: 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. 121-132Conference paper, Published paper (Other academic)
Abstract [en]

The high brilliance fibre and disc lasers that were developed during the last decade providelong range focusing that enables remote laser techniques without assist gas, including remotelaser welding and cutting. In combination with industrial robots these lasers offer industry ahighly flexible production solution, including quick positioning with scanner optics across aworkpiece. The paper presents the state of the art in the field of remote metal cutting with thefocus on analytical models and the physical process analyses. Several remote cuttingtechniques can be distinguished, in particular remote ablation cutting, remote fusion cuttingand remote gravity cutting. The three-dimensional cutting process and kerf geometry isconcluded to an extensive impact on the melted metal flow and the cutting processperformance. A semi-analytical mathematical model has been developed that enables tocalculate and analyse the cutting front with respect to absorption, heat conduction, recoilpressure and melt film flow. Beside analysing the remote laser fusion cutting process, theregimes and their transitions from remote fusion cutting to keyhole laser

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2013
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-29803 (URN)367165e2-cb6c-48ed-8166-93f033fde9db (Local ID)978-91-7439-688-1 (ISBN)978-91-7439-689-8 (ISBN)367165e2-cb6c-48ed-8166-93f033fde9db (Archive number)367165e2-cb6c-48ed-8166-93f033fde9db (OAI)
Conference
Nordic Laser Materials Processing Conference : 26/08/2013 - 28/08/2013
Note
Godkänd; 2013; 20131210 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Ilar, T., Eriksson, I., Powell, J. & Kaplan, A. (2012). Root humping in laser welding: an investigation based on high speed imaging (ed.). Paper presented at Laser Assisted Net Shape Engineering : 12/11/2012 - 15/11/2012. Physics Procedia, 39, 27-32
Open this publication in new window or tab >>Root humping in laser welding: an investigation based on high speed imaging
2012 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 39, p. 27-32Article in journal (Refereed) Published
Abstract [en]

Regular drop formation (humping) along the weld root during laser welding was studied by high speed imaging of the melt pool underneath the workpiece. The formation of droplets towards the rear of this weld pool was seen to be primarily caused by the pumping of melt from the bottom of the keyhole and the influence of gravity drawing melt into a sagging hump. This is a different process from the one which creates humps on the top surface of welds.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-32189 (URN)10.1016/j.phpro.2012.10.010 (DOI)000314404000003 ()2-s2.0-85014482318 (Scopus ID)69aa8157-6535-4b1b-9576-dbd9bba56149 (Local ID)69aa8157-6535-4b1b-9576-dbd9bba56149 (Archive number)69aa8157-6535-4b1b-9576-dbd9bba56149 (OAI)
Conference
Laser Assisted Net Shape Engineering : 12/11/2012 - 15/11/2012
Note
Validerad; 2012; 20121112 (andbra); Konferensartikel i tidskriftAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
Kaplan, A., Barsoum, Z., Alam, M. M. M., Jonsén, P., Häggblad, H.-Å. & Ilar, T. (2010). The impact of weld shape on fatigue cracking of eccentric geometry laser hybrid welds under bending load (ed.). In: (Ed.), Mustafa Kocak (Ed.), Istanbul IIW 2010: proceedings of the International Conference on Advances in Welding Science & Technology for Construction, Energy & Transportation, AWST 2010, Swissôtel "The Bosphorus", Istanbul/Turkey, from July 15 - 16. July, 2010 ; [is being held in conjunktion with the 63rd Annual Assembly & International Conference of the International Institute of Welding]. Paper presented at International Conference on Advances in Welding Science & Technology for Construction, Energy & Transportation : 15/07/2010 - 16/07/2010 (pp. 253-259). Istanbul: Ridgeview Publishing Company
Open this publication in new window or tab >>The impact of weld shape on fatigue cracking of eccentric geometry laser hybrid welds under bending load
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2010 (English)In: Istanbul IIW 2010: proceedings of the International Conference on Advances in Welding Science & Technology for Construction, Energy & Transportation, AWST 2010, Swissôtel "The Bosphorus", Istanbul/Turkey, from July 15 - 16. July, 2010 ; [is being held in conjunktion with the 63rd Annual Assembly & International Conference of the International Institute of Welding] / [ed] Mustafa Kocak, Istanbul: Ridgeview Publishing Company, 2010, p. 253-259Conference paper, Published paper (Refereed)
Abstract [en]

A butt joint of two 10 mm thick stainless steel plates, but 5 mm vertically eccentric to each other, was laser hybrid welded. The weld experiences four point bending fatigue load such that the root stress remains compressive. Thus only the stress formation at the top of the weld was studied, both by fatigue testing and by linear elastic fracture mechanics analysis. The location of the peak stress for crack initiation as well as the direction and speed of crack propagation can be well explained. Weld throat depth, weld toe radii and surface roughness compete against each other for determining the peak stress. It was also shown why occasional lack of fusion has only limited impact on the peak stress and fatigue life. Optimization of the laser beam contribution is responsible for full penetration and for avoiding lack of fusion. Optimization of the MIG-process is essential, as governing the top shape. Beside stress analysis including the topography, the propagation of the cracks along surface resolidification ripples was an indicator that surface roughness has essential impact. Several approaches were developed and studied for systematic documentation and generalization of the discovered knowledge.

Place, publisher, year, edition, pages
Istanbul: Ridgeview Publishing Company, 2010
National Category
Manufacturing, Surface and Joining Technology Applied Mechanics
Research subject
Manufacturing Systems Engineering; Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-26961 (URN)03d4143a-1fe4-4b73-b597-be0600948168 (Local ID)978-6-05-614191-1 (ISBN)03d4143a-1fe4-4b73-b597-be0600948168 (Archive number)03d4143a-1fe4-4b73-b597-be0600948168 (OAI)
Conference
International Conference on Advances in Welding Science & Technology for Construction, Energy & Transportation : 15/07/2010 - 16/07/2010
Note
Godkänd; 2011; 20110406 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-04-12Bibliographically approved
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