| 1. |
- Ilar, Torbjörn, et al.
(författare)
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An extended feasibility study to identify laser welding and laser.arc hybrid welding business cases and business models
- 2013
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Ingår i: 14th NOLAMP Conference. - Luleå : Luleå tekniska universitet. - 9789174396881 - 9789174396898 ; , s. 217-226
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
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| 3. |
- Ilar, Torbjörn, et al.
(författare)
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Modelling, simulation and analyses of systems with breakdown imposed scrapping
- 2009
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Ingår i: Journal of Simulation. - : Informa UK Limited. - 1747-7778 .- 1747-7786. ; 3:2, s. 107-113
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that, for many manufacturing processes (such as welding and injection moulding), a machine breakdown will result in the scrapping of a component, and goes on to explain the effect that this can have on process simulation models. Breakdown-related scrapping events are ignored by commercially available process simulation packages and this reduces their usefulness in decision support. This paper explains the different types of breakdown/scrapping dynamic possible and clearly demonstrates the scrapping dynamics effect on one of the major performance measures in LEAN-based manufacturing systems, namely the Overall Equipment Effectiveness. The paper also demonstrates the effect on model accuracy of a miss interpretation of part scrap behaviour or none deliberately simplified modelling of part scrap. This uncertainty in model accuracy will reduce the usefulness of the simulation model as a decision support tool.
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| 4. |
- Ilar, Torbjörn, et al.
(författare)
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Root humping in laser welding : an investigation based on high speed imaging
- 2012
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 39, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Ilar, Torbjörn, et al.
(författare)
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Simulation of production lines : The importance of breakdown statistics and the effect of machine position
- 2008
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Ingår i: International Journal of Simulation Modelling. - 1726-4529. ; 7:4, s. 176-185
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates the importance of choosing the correct values and statistical distributions for breakdown frequency and duration when simulating production line productivity. Statistical distributions with a wide range tend to reduce the productivity of the line but this trend can be disrupted by poor choice of mean values for the variables in question. Also, it is demonstrated that the productivity of a production line can be improved simply by re-arranging the order of unreliable machines in the line. If the line consists of similar or exchangeable machines, productivity can improved if the most unreliable machines are placed towards the end of the line. The paper also demonstrates the risks of reduction of the standard deviation to obtain a more deterministic model.
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| 6. |
- Ilar, Torbjörn, et al.
(författare)
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Simulation of production lines involving unreliable machines : the importance of machine position and breakdown statistics
- 2007
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Konferensbidrag (refereegranskat)abstract
- This paper demonstrates the importance of choosing the correct statistical distributions for breakdown frequency and duration when simulating production line productivity. Statistical distributions with a wide range tend to reduce the productivity of the line. Also, it is demonstrated that the productivity of a production line can be improved simply by re-arranging the order of unreliable machines in the line. If the line consists of similar or exchangeable machines, productivity can improved if the most unreliable machines are placed towards the end of the line.
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| 7. |
- Ilar, Torbjörn, et al.
(författare)
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The effect of process interruption and scrap on production simulation models
- 2007
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Ingår i: CARV 2007. - : CARV. - 9780978318703
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Konferensbidrag (refereegranskat)abstract
- This study shows that, for many manufacturing processes (such as welding and injection moulding), a machine breakdown will result in the scrapping of a component, and goes on to explain the effect that this can have on process simulation models. Breakdown related scrapping events are ignored by commercially available process simulation packages and this reduces their usefulness in decision support. This paper explains the different types of breakdown/scrapping dynamic possible and provides equations which can be used to describe them in future generations of simulation software. This work clearly demonstrates the scrapping dynamics effect on one of the major performance measures in LEAN based manufacturing systems, namely the Overall Equipment Effectiveness.
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| 8. |
- Kaplan, Alexander, et al.
(författare)
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Evolution of a Laser Hybrid Welding Map
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 78, s. 2-13
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Kaplan, Alexander, et al.
(författare)
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The Impact of Weld Shape on Fatigue Cracking of Eccentric Geometry Laser Hybrid Welds under Bending Load
- 2010
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Ingår i: Proc. of the Int. Conf. on Advances in Welding Science and Technology for Construction, Energy and Transportation, AWST 2010, held in Conj. with the 63rd Annual Assembly of IIW 2010. - Istanbul : Ridgeview Publishing Company. - 9786056141911 ; , s. 253-259
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Matti, Ramiz, et al.
(författare)
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Analysis of laser remote fusion cutting based on a mathematical model
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 114:23
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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