| 1. |
- Adolfsson, Stefan, et al.
(författare)
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On-line quality monitoring in short : circuit gas metal arc welding
- 1999
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Ingår i: Welding Journal. - New York,N.Y. : American welding society. - 0043-2296. ; 78:2, s. 59S-73S
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problems involved in the automatic monitoring of the weld quality produced by robotized short-arc welding. A simple statistical change detection algorithm for the weld quality, the repeated Sequential Probability Ratio Test (SPRT), was used. The algorithm may similarly be viewed as a cumulative sum (CUSUM) type test, and is well-suited to detecting sudden minor changes in the monitored test statistic. The test statistic is based on the variance of the weld voltage, wherein it will be shown that the variance decreases when the welding process is not operating under optimal conditions. The performance of the algorithm is assessed through the use of experimental data. The results obtained from the algorithm show that it is possible to detect changes in weld quality automatically and on-line.
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| 2. |
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| 3. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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A look at the optimization of robot welding speed based on process modelling
- 2007
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Ingår i: Welding Journal. - 0043-2296. ; 86:8, s. 238-244
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Tidskriftsartikel (refereegranskat)abstract
- Simulation tools to search for optimal process parameters are of great interest to reduce the number of experiments and thereby reduce cost and production time. In this paper, robot simulation has been used in combination with finite element simulations to optimize robot speed in order to minimize distortion while keeping complete joint penetration. In an earlier work performed by the authors, a finite element model was developed to predict heat transfer and residual stresses of parts with complex shapes. An interface between a robot simulation model and a finite element analysis model was also constructed. In this paper, an iterative method for robot speed optimization has been developed using MATLAB. The algorithm is designed to maintain complete joint penetration while maximizing productivity by utilizing the fastest weld speed. The method makes it possible to optimize the heat input to the component and thereby minimize component deformation for parts with complex shapes. The system was evaluated on stainless steel plates with varying thicknesses. Robot weld paths were defined off line and automatically downloaded to the finite element software where the optimization was performed. Simulations and experimental validations are presented.
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| 4. |
- Ion, John, et al.
(författare)
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Process diagrams for laser beam welding of carbon manganese steels
- 1996
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Ingår i: Welding Journal. - 0043-2296. ; 75:7, s. 225-
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Tidskriftsartikel (refereegranskat)abstract
- Diagrams are presented which illustrate the ranges of process variables that can be used to produce acceptable laser welds in carbon manganese steels. The most practical type uses axes of beam power and welding speed. An empirical operating window is displayed, which describes the limits of full joint penetration welding for a particular steel and plate thickness. Theoretical contours of heat-affected zone (HAZ) hardness, established using analytical models, are also displayed on the diagram. Appropriate combinations of laser beam power and welding speed can thus be selected. A more comprehensive diagram uses axes of carbon equivalent and absorbed laser beam energy, on which theoretical HAZ hardness contours are displayed. The effects of changes in steel composition and welding variables on HAZ hardness can thus be assessed. Model results agree well with experimental data, as well as more sophisticated predictive methods. The diagrams provide guidance on the selection of steel composition and beam parameters during the initial stages in the development of procedures for laser welding of carbon manganese steels.
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| 5. |
- Jonsson, Mikael, et al.
(författare)
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Simulation of tack welding procedures in butt joint welding of plates
- 1985
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Ingår i: Welding Journal. - 0043-2296. ; 64:10, s. 296-301
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Tidskriftsartikel (refereegranskat)abstract
- The influence of tack welding procedure on change in root opening was investigated. This change during the first part of welding depends on the order in which the tack welds are made. It is also affected by the starting position of the welding arc. These effects were studied in seven theoretical analyses - three cases where the tack welding procedures differed and four cases where the temperature fields at the beginning of the butt joint welding differed. The material investigated was a fine-grain steel with a yield stress of 360 MPa (52,200 psi) at room temperature. The filler material was ESAB 1. 2/12. 51 (AWS ER70S-6).
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| 6. |
- Jönsson, Pär, et al.
(författare)
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Influence of oxygen additions on argon-shielded gas metal arc welding processes
- 1995
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Ingår i: Welding Journal. - 0043-2296. ; 74:2, s. 48-
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Tidskriftsartikel (refereegranskat)abstract
- It has been observed experimentally that small additions of oxygen to the argon shielding gas affect the general operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxygen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophysical transport and thermodynamic properties caused by the oxygen addition. Therefore, it is concluded that the addition of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxides initiates arcing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the electrode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.
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| 7. |
- Jönsson, Pär, et al.
(författare)
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Power characteristics in GMAW: experimental and numerical investigation
- 1995
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Ingår i: Welding Journal. - 0043-2296. ; 74:3, s. 93s-102s
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Tidskriftsartikel (refereegranskat)abstract
- The voltage and power distributions in gas metal arc welding (GMAW) were studied both experimentally and numerically. The principal voltage drop takes place in the arc, which also constitutes the dominant power contribution. Within the arc, the dominating voltage contributions are from the arc column and the cathode fall, while the anode fall and the electrode regions are less significant. The power input to the arc column increases with both increasing current and increasing arc length. These results indicate that it is critical to control the arc length in order to control the power input to the system.
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| 8. |
- Näsström, Jonas, et al.
(författare)
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Arc formation in narrow gap hot wire laser welding
- 2018
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Ingår i: Welding Journal. - : American Welding Society. - 0043-2296. ; 97:6, s. 171S-178S
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Sigler, D. R., et al.
(författare)
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Improving aluminum resistance spot welding in automotive structures
- 2013
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Ingår i: Welding Journal. - 0043-2296. ; 92:6, s. 64-72
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Tidskriftsartikel (refereegranskat)abstract
- The majority of automotive body shop welding consists of resistance spot welding (RSW) steel sheet due to its inherently low cost and high speed. With the introduction of aluminum, it is desirable to continue using RSW as the joining process. However, the presence of insulating oxide layers on the aluminum alloy material surface presents significant problems in obtaining consistent spot welding processes. If dressing fails to completely remove the pits, it will cause the electrode surface to deteriorate more rapidly, which in turn will eventually lead to unacceptable welds. Macrodeformation of the electrode, which commonly happens in steel spot welding, does not occur for aluminum spot welding because the nugget temperatures are much lower. However, circular protrusions on the MRD electrode with their small cross sections can be susceptible to deformation or flattening during use.
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| 10. |
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