| 1. |
- Alam, Md. Minhaj, et al.
(författare)
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Generalising fatigue stress analysis of different laser weld geometries
- 2011
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197 .- 0261-3069. ; 32:4, s. 1814-1823
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional elastic-plastic finite element analyses was carried out on a laser welded box beam in order to study the impact of the geometrical aspects of the joint type and weld root on the fatigue stress behaviour. Different experimental and hypothetical weld geometries were studied. Characteristic root shapes, measured by the plastic replica method, and critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the maximum stress. The simulation of hypothetical transition geometries facilitated the identification of trends and the explanation of part of the phenomena. However, quantitative geometry criteria were only partially suitable to describe the relations. The results have shown that the combination of throat depth, local surface radius and its opening angle determines the peak stress value and its location. Beside extended throat depths, particularly larger toe radii and the avoidance of small opening angles and of surface ripples reduces the peak stress. The explanations were developed in a generalising manner, accompanied by illustrative and flow chart description.
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| 2. |
- Johansson, Christian, et al.
(författare)
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Enhancing intra-cognitive communication between engineering designers and operators : a case study in the laser welding industry
- 2012
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Ingår i: Proceedings of the 3rd IEEE International Conference on Cognitive Communications. - Piscataway, NJ : IEEE Communications Society. - 9781467351874 - 9781467351867 ; , s. 493-497
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Konferensbidrag (refereegranskat)abstract
- In manufacturing, metal parts can be joined using a laser as a welding tool, i.e. laser welding. Despite huge amount of research over the years, the process is neither sufficiently understood nor mathematically predictable. This study aims to holistically analyze the knowledge management issues occurring in laser welding. Emerging from observations and semi-structured interviews from industry and academy, the complexity and the criticalities of the process as well as the current knowledge transfers is explained and analyzed, using a knowledge lifecycle framework as a reference. Besides enhanced awareness of the limiting issues, information and knowledge visualization, e.g. knowledge maps, is identified as a key for progress in the community. The Matrix Flow Chart is suggested as an alternative descaled map of process changes.
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| 3. |
- Kaplan, Alexander, et al.
(författare)
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Scanner analysis of the topology of laser hybrid welds depending on the joint edge tolerances
- 2011
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Ingår i: 13th NOLAMP Conference. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
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Konferensbidrag (refereegranskat)abstract
- The surface geometry after laser hybrid arc welding is an important quality criterion. What isoften called welding in a rough industrial environment can in many cases systematically bereduced to a few local conditions of the joint edge during welding, particularly depending onthe edge preparation technique. In the present study, beside the influence of surface oxidesstudied in separate publications, the conditions are reduced to the local gap width, verticalsurface position and edge mismatch. Gas cut edge conditions are compared to milling andlaser cutting. By scanning the steel edges of a 10 mm butt joint before and during hybridwelding and relating the systematic variation of the above three properties to the scannedtopology of the resulting weld, quantitative correlations are identified. By the aid of highspeed imaging, explanations for the trends can be found. Operating windows with controllabletrends can be quantitatively mapped and distinguished from instable regimes. Beside higherroughness, gas cut edges show a superimposed edge oscillation of longer periodicity, beingless visible but important. During welding, concave surface bending and gap widening alterthe initial conditions. Awareness and quantitative identification of the edge conditions isrecommended to control the welding process in a rough industrial environment.
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| 4. |
- Karlsson, Jan, et al.
(författare)
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Analysis of a fibre laser welding case study, utilising a matrix flow chart
- 2011
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 257:9, s. 4113-4122
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Tidskriftsartikel (refereegranskat)abstract
- For fibre laser welding of an eccentric corner joint, the quality of the resulting weld cross section was studied with respect to the dependence on process parameters like lateral laser beam alignment, beam inclination, focal plane position or welding speed. The complex load situation of the support beamer was simplified to bending of one corner. Due to fatigue load, the weld properties causing the peak stress are essential, in particular the top and root shape of the weld cross section. For the parameters varied, the resulting shapes were categorized into different top and root classes, determined by certain key dimensions, considering also welding defects like undercuts. The shapes are boundary conditions for Finite Element Analysis of the joint under load for quantitative comparative analysis of the maximum stress. As two high strength steel grades were joined, the hardness transition across the weld was of interest, too. High speed imaging of the weld pool surface shape provided additional information on the relation between the parameter input and quality output. The different trends identified were discussed and guidelines were derived. As the systematic documentation of results is unsatisfactory in welding, a new method was developed and applied for the first time, called the Matrix Flow Chart. It enables an illustrative view on the resulting welding trends in a combined manner and is extendable by other researchers.
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| 5. |
- Karlsson, Jan, et al.
(författare)
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Fibre laser welding for lightweight design
- 2009
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Ingår i: Congress proceedings. - Orlando, Fla. : Laser institute of America. - 9780912035598 ; , s. 1548-1557
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Konferensbidrag (refereegranskat)abstract
- Two different high strength steel grades have been welded by a fibre laser as a fillet corner joint. The purpose of the experiments is to use thinner materials of higher strength as a weight reduction strategy. The sensitivity of the welding process to the beam inclination angle, the beam positioning and the focal plane position were studied. High-speed imaging, process emission monitoring, measurement of the weld surface topography, mechanical testing and FE-analysis have been used to analyze the process and the resulting weld. The combined study by these methods gives a more comprehensive picture for studying the weld quality. The Bifurcation Flow Chart (BFC) as a new method has been applied to standardize and generalize the findings.
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| 6. |
- Karlsson, Jan, et al.
(författare)
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Observation of the mechanisms causing two kinds of undercut during laser hybrid arc welding
- 2011
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 257:17, s. 7501-7506
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Tidskriftsartikel (refereegranskat)abstract
- Two different kinds of undercut were identified when laser hybrid welding hot rolled HSLA-steel in either the as-rolled condition or with the top surface mill scale removed. The presence of mill scale on the steel surface was found to give a sharp angled undercut combined with a sharp oxide inclusion at the edge of the weld which would have the same mechanical effect as a crack in this position. Removal of the surface oxides before welding resulted in the elimination of the oxide inclusions and a more rounded undercut geometry indicative of superior mechanical properties, particularly fatigue life. The mechanisms of the formation of both types of undercut have been analysed by high speed photography and SEM.
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| 7. |
- Karlsson, Jan, et al.
(författare)
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Parameter influence on the laser weld geometry documented by the matrix flow chart
- 2010
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 5:2, s. 183-192
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Tidskriftsartikel (refereegranskat)abstract
- Three variants of fibre laser welding of corner joints where studied. In service a welded piece experiences fatigue load in a complex manner. The peak stress responsible for the fatigue life of the product is mainly determined by positioning and the geometry of the resulting weld. Some top and root shapes where identified for the joints studied. While parameter documentation is straightforward, generalization and combination of knowledge is a challenge. A new documentation method, the Matrix Flow Chart, MFC, turned out to be a powerful solution for large scale documentation, combination and generalization. Three variants of fibre laser welding of corner joints where studied. The peak stress responsible for the fatigue life of the product is mainly determined by the geometry of the resulting weld. Different top and root shape classes were identified for the joints studied. The shapes mainly depend on geometrical laser beam parameters and govern the peak stress. While parameter documentation used to be straightforward, generalization and combination of knowledge is a challenge. A new documentation method, the Matrix Flow Chart, MFC, turned out to be a promising solution for large scale documentation.
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| 8. |
- Lamas, Javier, et al.
(författare)
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The effect of fit-up geometry on melt flow and weld quality in laser hybrid welding
- 2013
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 25:3
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid laser-arc welding has a good tolerance to poor fit up as compared to simple laser welding. For a butt joint, the joint fit-up variations can be reduced to two local properties: the gap width and the vertical edge mismatch. The impact of these two properties on the resulting weld quality has been studied systematically in this paper. The original edges as well as the resulting weld surface topography have been scanned in three dimensions in order to study trends. During hybrid welding, the melt flow and the electric arc were observed at the top surface by high speed imaging to analyze the complex fluid flow phenomena.
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| 9. |
- Norman, Peter, et al.
(författare)
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Classification and generalization of data from a fibre-laser hybrid welding case
- 2010
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 5:2, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- Compared to autonomous laser welding, the amount of parameters is higher for laser hybrid welding. Consequently, empirical optimisation of these parameters is a challenge. Handling and evaluation at a higher systematic level is desired in order to enhance the ability to build research on previous knowledge. Such new approach is studied on a case with 10 mm high strength steel sheets, fibre-laser hybrid welded. Aim of the paper is to provide a method of documenting and handling data, transferable to other disciplines, to continuously build knowledge, to simplify repetition of experiments and to facilitate the start-up phase of new trials. Starting from 30 experimental results depending on 23 parameters, by the Matrix Flow Chart a guideline has been developed that filters the information through combination, priorities and quality categorization. A chart resulted where five categories of poor quality are graphically related to a high quality category which can be achieved when following the guidelines for eight main arc- or laser-parameters. The chart is a guideline suitable for extension and for exploring the limits of its validity.
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| 10. |
- Norman, Peter M., et al.
(författare)
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Mechanisms forming undercuts during laser hybrid arc welding
- 2011
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 12:1, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- That the final quality of a welded joint, using a laser hybrid arc process, is sensitive not only to the geometrical joint conditions, but also to the content of elements in the surface itself, is already known. However the description of the mechanisms forming undercut defects is still vague. In the following study two kinds of undercuts were identified. It is shown how the mill scales affects the melt motion and what mechanisms actuate the creation of the defects. The conclusion that surface oxides affect the severity of weld undercuts is straight forward but here also the mechanism is explained.
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