Thermal analysis of laser welding for ITER correction coil case

Abstract:

This paper presents the simulation results of 3D finite element analysis (FEA) of laser welding processes for the ITER correction coil case welding; predicts the temperature distribution and compares it with the experimental result to evaluate the impact to the properties of winding pack during the welding process.A specimen of coil case was modeled and simulated by using specialized welding simulation software SYSWELD, Modeling used austenitic stainless steel 316LN as the specimen material and a 3D Conical Gaussian was used as a heat source model. A plate sample was welded before the FE modeling in order to obtain the laser welding parameters and the Gaussian parameters of molten pool. To verify the simulation results, a coil case sample was welded using laser welding with welding parameters that matched the model, and the corresponding temperature values were measured using thermocouples. Compared with the FEA results, it was found that the FEA temperature distribution shows good agreement with the experimental measurements and the laser welding process will not harm the winding pack.

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Parametric study in similar ultrasonic spot welding of A5052-H32 alloy sheets

Abstract:

Ultrasonic spot welding (USW) is a solid-state joining process highly applicable to lightweight alloy materials with high diffusivity rates in the melt state. To improve the understanding of the USW process and to enhance the weld strength in similar Al alloy welding, this work focused on a parametric study using some process parameters such as vibration amplitude and welding time. Experiments were conducted using lateral-drive USW machine operating in time control mode. Weld quality of USWed joint was analyzed based on the weld strength obtained by lap-shear tests and the fracture pattern subsequently characterized. Mixed fracture pattern of shear and pull-out exhibited a higher lap-shear failure load, while solely shear and pull-out was a distinct fracture pattern in lower lap-shear failure load. Shorter welding time was needed for higher vibration amplitude to generate enough temperature and to prevent over welding. Joint microstructures revealed that longer welding time produced over welding which gave short but intensified weld interface waviness, resulting to a shorter fracture path. The horn and anvil tip surface patterns influenced on the variation in temperature rise measured at the weld part and the extent of part marking/sticking. The temperature rise measured on the weld surface was useful to determine over welding condition. Weldability map of USWed Al alloy sheets could be constructed from the results of weld strength and fracture type, and an effective welding energy input was determined from welding process parameters combination.

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Effects of a paraxial TIG arc on high-power fiber laser welding

Abstract:

In this study, the effects of a paraxial tungsten-inert gas (TIG) arc on the high-power fiber laser welding process were investigated by measuring plume behavior, plume temperature, weld depth, and the particles in the plume. The experimental results indicated that when DLA (i.e. the distance between the laser beam and arc) was less than 8 mm, the slender plume similar to the shape of the focused laser beam was eliminated, and the weld depth was increased by around 20%. Moreover, both the vertical and horizontal temperatures of the hybrid welding plasma were much higher than that of the plume. In addition, in the space near the laser beam, the size and density of the particles were significantly reduced. Further analysis indicated that the paraxial TIG arc could eliminate the slender plume by reducing the density and size of particles in the plume during high-power fiber laser-arc hybrid welding; therefore, it can reduce the negative effects of the plume on the welding process while improving laser energy utilization and the weld depth.

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Welding of stainless steel using defocused laser beam

Abstract:

Type 321 stainless steel has a wide range of applications, including welded constructions. Common arc welding has disadvantages because of low speed and higher heat input that result in significant residual stresses and strains. The alternative to arc welding is laser welding that allows elimination of these negative effects. The results of research on welding of stainless steel with a defocused laser beam are presented and discussed in this paper. It was assumed that the use of defocused laser beam would increase volume of the weld pool that in turn would reduce requirements for preparation of edges and the gap between work pieces. Attention was mainly paid to metallurgical processes of the weld pool formation, depending on the welding conditions. Microhardness of the selected sample was measured, 2D-imaging,metallographic studies, quantitative evaluation of phase components of various zones of the weld pool were conducted. The obtained results prove that the use of the defocused beam allows obtaining quality welded joints, and this technique has also positive influence on the stability of the keyhole, and on the phase composition of the weld metal.

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Influence Of Welding Sequence On Welding Deformation And Residual Stress Of a Stiffened Plate Structure

Abstract:

An important consideration in the safe and efficient manufacture and operation of marine structures is the possible distortion,and consequential induced residual stress, owing to welding.This paper deals with welding simulation of a stiffened plate structure with longitudinal and transverse stiffeners using a thermal elasto-plastic FE method.Shell elements with section integration features are adopted to model the plate and stiffeners and solid elements to model the local detail of weld line region.Linear constraint equations are established between degrees of freedom of the shell and solid elements.Welding parameters of heat input, welding speed and welding sequence are considered in the analysis.A typical fillet-welded joint is studied and the thermal and mechanical results are compared with experimental values.Six welding sequences are simulated.The results demonstrate the specific influences of the different welding parameters on residual distortion and stress in a stiffened plate structure.

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Dual beam method for laser welding of galvanized steel: Experimentation and prospects

Abstract:

Laser welding of zinc-coated steel sheets in lap configuration poses a challenging problem, because of the zinc vapours spoiling the quality of the weld. In continuation to the earlier work, the novel solution of dual laser beam method for lap welding of galvanized steel sheets is discussed here in view of the recently obtained observations and ensuing concerns. In this method the precursor beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The metallurgical analysis of the welds is encouraging showing absence of zinc in the welded area. In the current work on this technique, new experimental results have been obtained verifying the earlier observations. Along with this, the possibility of using a transversely split-up beam for the welding purposes with this approach is discussed and analyzed in this paper. This new technique is expected to be very useful in prospective industrial applications requiring higher welding throughput along with the needed quality.

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Effect of jig constraint position and pitch on welding deformation

Abstract:

Quantitative study on jig constraint effect on welding deformation was carried out. Welding deformation in a square plate with bead welding under a non-constraint free condition and a jig constraint condition was investigated by experiment. A 3D thermal elastic–plastic FEM program was employed to simulate the transient temperature and deformation occurred in the welding. It is observed that welding angular distortion has been greatly reduced by the jig constraint, and a good agreement was confirmed between simulation and experiment. Three-direction jig constraint and normal direction jig constraint were defined based on typical constraint types in practical engineering. Two parameters a and b, which represent the pitch between two jigs in the welding direction and the distance from the weld line, respectively, were focused. Effect of jig constraint on longitudinal shrinkage, transverse shrinkage and angular distortion were discussed in details.

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Arc Welding Procedures on Steels for Molds and Dies

Abstract:

This work aims to present a method to establish arc welding procedures on steels for molds and dies. The welding of AISI P20 steel was studied. Simple and multi-pass welding were undertaken using the Tungsten inert gas process, evaluating the bead geometry, hardness distribution, microstructure and quality features after grinding, polishing and texturing. By the bead implant test and analytical heat transfer solutions, multi-pass welding techniques were optimized to cause the tempering effect to the weld metal and heat affected zone by a second thermal cycle of welding. In the welding of P20 steel it is necessary to apply the double layer and temper bead techniques. The temper bead demands refined techniques to control the welding variables.

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Friction stir welding of small-dimension Al3003 and pure Cu pipes

Abstract:

Small-dimension Al3003 pipe and pure copper pipe of thin wall (Al: 1.5 mm; Cu: 1 mm) and small diameter (19 mm) were successfully joined by a developed welding method with a specially-designed friction stir welding (FSW) system. A distinctive temperature history due to heat accumulation was identified as an important feature for FSW of small-dimension pipes, leading to distinctive variations of surface condition, macro-/micro-structure along the circumferential weld seam. Hardness distribution, tensile strength, ductility and fracture modes were found to change correspondingly along the weld seam.

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A dynamic welding heat source model in pulsed current gas tungsten arc welding

Abstract:

A time-dependent welding heat source model, which is defined as the dynamic model, was established according to the characteristic of PCGTAW. The parabolic model was proposed to describe the heat flux distribution at the background times. The recommended Gaussian model was used at the peak times due to the bell-shaped temperature contour. The dynamic welding heat source was composed of these two models with a function of time. To assess the validity of the dynamic model, an experiment was conducted in which the pulsed current gas tungsten arc deposits on the plate. From the comparison of the experimental and the simulated values, it can be concluded that the dynamic heat source model, which uses the parabolic model at the background time, is more realistic and accurate under the same welding conditions.

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