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A three-dimensional unified model is proposed to simulate the weld pool dynamic behavior in swing arc narrow gap vertical GMA welding with allowing for swing feature of arc heat source and joint configuration. Both the moving direction of arc and its inclination are considered by transformation of coordinate system. The model can simulate the weld pool sagging process reasonably. Based on the calculated and experimental results, the mechanism of weld formation in swing arc vertical-up welding is studied. The weld pool size and the peak temperature of liquid metal are reduced largely in the case of swing arc, which leads to the faster solidification of weld pool and is the major factor responsible for suppression of weld pool sagging. Meanwhile, upward component of arc force and the enhanced support force from solidified metal bulge benefits the weakness of downward flow of liquid metal. With increasing the swing frequency, weld cross section geometry tends to be symmetrical and weld bead surface becomes smoother. When the swing frequency is higher than 0.6 Hz, the satisfied weld formation can be obtained. [ABSTRACT FROM AUTHOR]

Development of flexible forming is crucial for manufacturing three-dimensional sheet metal parts. In this paper, continuous roll forming (CRF) is investigated to improve the forming results, especially for doubly curved parts. The CRF process employs an upper flexible roll and a lower flexible roll as a forming tool, and the different forming shapes are achieved by controlling and adjusting the distribution of the roll gap between two rolls. This paper is focused on analysis of the longitudinal bending deformation in CRF process, the plane assumption for longitudinal bending analysis is discussed, and the formulation to calculate the longitudinal strain distributed over the cross-section is derived. Through a series of numerical simulation on CRF processes, the validity of the plane assumption and the other theoretical models to analyze the deformation in CRF are confirmed; the relationship between longitudinal elongation distribution and longitudinal bending deformation is discussed and the strain distribution in transverse, longitudinal, and thickness directions is presented. In addition, the CRF experiments on saddle-shaped and torus-shaped parts were carried out, and the theoretical analysis and simulation results are verified by experiments. [ABSTRACT FROM AUTHOR]

A three-dimensional transient model is proposed to investigate the weld formation during laser + metal inert gas (MIG) hybrid welding of aluminum alloy for horizontal fillet joint, which considers the coupling of keyhole, droplet, and liquid metal pool as well as the influence of joint geometry feature and welding position. An asymmetrical double-elliptic heat source is utilized to model the arc heat input and a conic heat source with increased peak heat density is used to describe the laser energy. The coordinate rotation is used to take into account the inclination of heat source and the related forces. According to the experimental and simulated results, weld formation mechanism of horizontal fillet joint is studied. At a lower laser power, the fluid flow pattern in hybrid welding is similar to that in MIG welding and a strong downward flow caused by both gravity and arc pressure occurs at the liquid metal zone of the vertical plate, leading to the accumulation of molten metal at the horizontal plate and the resultant weld asymmetry. At high laser power, a clockwise vortex appears above the keyhole. In this case, the sagging of liquid metal near weld pool surface due to effect of gravity is an important factor responsible for the asymmetry of fillet weld. Besides, with increasing laser power, the tendency of weld pool free surface sagging is enhanced to some extent and weld bead surface becomes concave. [ABSTRACT FROM AUTHOR]