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Full penetration laser welding was carried out on a 10 mm steel plate using a 16 kW maximum power continuous wave thin disk laser. Upper surface and lower surface of molten pool were observed synchronously with two high speed CCD cameras during the welding process. The lower surface was much longer and more unstable than the upper one. A three dimensional laser deep penetration welding model in which volume of fluid (VOF) method was combined with a ray-tracing algorithm was used to simulate the dynamic coupling between keyhole and molten pool in laser full penetration welding. The calculated weld cross-section morphology and molten pool length on both upper side and lower side agree well with experimental results. Evolution of molten pool in lower side during full penetration laser welding was analyzed, periodical features of energy coupling, molten pool behavior and keyhole dynamics in laser full penetration welding were identified and discussed.
In todays automotive frame-and-body construction, laser welds are typically carried out as square butt welds in lap joints. These welds are increasingly produced by remote laser welding optics with working distances of 500 mm and more. This enables simple path programming because clamping devices are traversed over and therefore low cycle times with improved productivity is achieved. However, workpiece tolerances lead to part displacements and varying joint positions over time. These displacements have to be acted against by appropriate flange length that contain for positioning deviations. Using this concept, aspired light-weight optimisations, e.g. reducing flange length, are difficult to achieve. By using seam tracking sensors, part tolerances are automatically detected and counteracted for. In addition, joint edge detection allows constructive changes on the type of weld. Fillet welds reduce flange lengths', improve force flow and open up possibilities for visual quality monitoring. Apart from that, vertical displacements in the form of height tolerances still occur. This needs consideration by adapting the set of welding parameter to the current welding situation. In this respect, one main welding parameter is the lateral beam offset to the upper sheet. Since body-in-white welding applications mainly comprise of zinc-coated steel sheets, special requirements for the welding process are given. Especially zero-gap-welding and welding of joints with gaps larger than 0.2 mm are critical. Using a laser beam oscillation process can stabilise these situations. Approaches to finding parameter sets are presented in this paper.
The accurate prediction of the thermal energy generation and distribution in friction stir welding process is of great significance for the optimization of the process parameters and the understanding of the underlying mechanisms. In this study, a new method of integrative calculation and measurement is proposed to obtain the more reasonable values of the frictional coefficient and the slip rate, which are both used to characterize the heat generation rate at the tool-workpiece contact interfaces. A three-dimensional model is established to fully couple the energy generation, heat transfer and material flow in friction stir welding of aluminum alloys. The energy produced by both interfacial friction and plastic deformation are taken into consideration. The analysis accuracy of the thermal energy generation and distribution is improved, and the distribution features of thermal energy density in the vicinity of the tool are elucidated. The predicted peak temperature values at some locations are in agreement with the experimentally measured ones.
Welding is one of the most critical operations for the construction of reliable metal structures in everything from ships to reactor vessels. When welds fail, often the entire structure fails, and expectations on weld quality have never been higher. Any process that uses a localized heat source, such as welding, is likely to result in some distortion. The welding process of very thick metal components is not inherently stable and is barely controllable without external forces.
This paper investigates the numerical simulations of multi-kilowatt disk laser and fiber laser welding, ranging from 6 to 18 kW to study the behavior of molten pool in 20-mm-thick steel plate by using Volume-Of-Fluid (VOF) method and several mathematical models like Gaussian heat source, recoil pressure, Marangoni flow, buoyancy force, and additional shear stress and heat source due to the metallic vapor. Vortex flow pattern is observed for higher laser power except for 6-kW case, and the higher the laser power, the bigger the vortex flow pattern. Welding speed has an influence on molten pool in terms of depth of penetration and size of molten pool, but overall shape of molten pool remains the same. The reasons for the vortex flow pattern in high-power laser welding are the absorption of more energy at the bottom of keyhole, which promotes more liquid metal at the bottom, while for lower power with lower speed, the melt formation is more uniform in the thickness direction and most of the molten metal in the lower part of keyhole reaches the top of molten pool, and consequently, no vortex flow pattern is observed in the keyhole bottom.
Im Rahmen eines AiF-Forschungsvorhabens wurde die Beeinflussung des Schweißprozesses mittels generierter Wechselstrom-Magnetfelder (ACMagnetfelder) beim Laserstrahlschweißen von Aluminiumlegierungen untersucht. Das vorrangige Augenmerk galt hierbei der Entfernung von Poren sowie der Stabilisierung der Schweißnahtoberfläche zur Vermeidung von rauen Schweißnähten. Das Schweißen mit Einsatz des AC-Magneten erzeugte im Vergleich zu den Referenznähten deutlich flachere Schweißnähte mit reduzierter Porenanzahl, die typische Schuppenstruktur wurde unterdrückt. Das Magnetfeld bewirkte bei entsprechenden Parametern der magnetischen Flussdichte und der Frequenz eine Halbierung der Rauigkeit der Schweißnahtoberfläche. Neben der Oberflächenberuhigung wurde auch die Verteilung von Poren in der Schmelze beeinflusst. Es konnte nachgewiesen werden, dass bei einer geeigneten Auswahl der Parameter von AC-Magnetfeldern die Porositätsanteile in der Schweißnaht auf ein Zehntel gegenüber den Referenzschweißnähten reduziert werden können.-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Within the framework of an AiF research project, investigations were conducted into the influences exerted on the welding process using generated alternating current (AC) magnetic fields during the laser beam welding of aluminium alloys. In this respect, attention was principally paid to removing pores and to stabilising the weld surface in order to avoid rough welds. In comparison with the reference welds, welding utilising the AC magnet produced considerably flatter welds with a reduced number of pores and the typical ripple structure was suppressed. With corresponding parameters for the magnetic flux density and the frequency, the roughness of the weld surface was halved using the magnetic field. In addition to the surface stabilisation, influences were also exerted on the distribution of pores in the molten metal. It was possible to prove that, by selecting suitable parameters for AC magnetic fields, the porosity proportions in the weld can be reduced to one tenth of those in the reference welds.
Laser beam oscillation opens up new possibilities of influencing the welding process in terms of compensation of tolerances and reduction of process emissions that occur in industrial applications, such as in body-in-white manufacturing. The approaches are to adapt the melt pool width in order to generate sufficient melt volume or to influence melt pool dynamics, e.g. for a better degassing. Welding results are highly dependent on the natural frequency of the melt pool, the used spot diameter and the oscillation speed of the laser beam. The conducted investigations with an oscillated 300 µm laser spot show that oscillation strategies, which are adjusted to the joining situation improve welding result for zero-gap welding as well as for bridging gaps to approximately 0.8 mm. However, a complex set of parameters has to be considered in order to generate proper welding results. This work puts emphasize on introducing them.
MAG welding is widely used for thin sheet metal applications such as car body structures due to its ability to tolerate a fair amount of deviation of the components from the ideal shape. In MAG welding, the process window is sufficiently large to accommodate the expected component tolerances. In practice, however, quality control is an issue since most welds are produced with parameters outside of the optimum range, especially in the case of automated MAG welding. To ensure best performance, a robust real-time control law is needed that adapts critical process parameters to the changing conditions, most notably the variation in gap height. Here, the gap-dependent adaptive control algorithm for the deposition of filler material and the related energy input comes into play. With an optical sensor that is mounted in front of the torch, the system measures the actual position of the two components in real-time during the entire welding process and the controller adapts the relevant parameters accordingly using a dynamic process model. This optimization ensures that only the required filler material is used and the associated energy input is tightly controlled to assure best quality even in a fully automated welding process.
The ever larger requirements of the material selection in the range of maritime industry necessitate the application of high-tech materials. Titanium because of its excellent mechanical properties at low weight is an attractive alternative for the construction of ships. The goal of this investigation was to design a welding method for joining samples of 16 mm thick Ti3Al2.5 V. The welding experiments with a 20 kW Yb-fiber laser source and varying combinations of parameters were intended to qualify the laser beam welding process. The welding results were analyzed by non-destructive and destructive testing. In addition, the welding tests were recorded with two high-speed cameras to observe the weld pool and the vapor plume. The evaluation of the high-speed images in correlation with the results of non-destructive testing shows, that a significant improvement of process stability and weld quality can be achieved by the suppression of the vapor plume.
The objective of this study was to investigate the influence of externally applied magnetic fields on the weld quality in laser beam welding. The optimization of the process parameters was performed using the results of computer simulations. Welding tests were performed with up to 20 kW laser beam power. It was shown that the AC magnet with 3 kW power supply allows for a prevention of the gravity drop-out for full penetration welding of 20 mm thick stainless steel plates. For partial penetration welding it was shown that an0.5 T DC magnetic field is enough for a suppression of convective flows in the weld pool. Partial penetration welding tests with 4 kW beam power showed that the application of AC magnetic fields can reduce weld porosity by a factor of 10 compared to the reference joints. The weld surface roughness was improved by 50%.