Study Of Activating Welding And Numerical Simulation Of Mechanism Of Weld Penetration Increased By Flux

The method and mechanism of activating welding is investigated systematically. Taking the low-carbon and stainless steel as investigation object, the influence of various mono components activating fluxes on the formation of weld, welding penetration, and welding width is investigated. The activating fluxes for A-TIG welding of low-carbon steel (FC11)and stainless steel (FS12)are fabricated, respectively, by means of cross experiment, so that the welding penetration of conventional TIG welding is doubled, and for the plates of 10mm thick the full penetration can be got in a single pass without groove preparation. The comprehensive characteristics of welded joint with such flux agree with the relevant standard for welding of low-carbon and stainless steel. Various factors such as the welding current, arc length, welding speed, flux coating thickness, and kind of gas will influence the improvement of welding penetration.On the basis of analysis of the mechanism of penetration improvement with activating flux, the activating electron-beam welding method and activating laser welding method is proposed. With the help of activating flux, the scattering electron-beam welding can make the welding penetration of conventional welding doubled. Employing the activating flux, the focusing current and bind current has influence on the improvement of penetration of electron-beam welding. The activating flux and surface activating element sulfur will have influence on the weld form of YAG laser welding, resulting in remarkable improvement of the penetration as well as the depth-width ratio of the weld in various welding conditions.The influence of coating amount of activating flux on the weld formation is investigated and the functioning range of element oxygen is clarified that, under concrete welding condition, the weld penetration will remarkably improved where the oxygen content within the weld reaches a certain critical amount, for example 160 ppm. The penetration will keep unchanged if the oxygen content is further increased.A mathematical model to describe the molten pool of 3-D GTA welding with a moving arc has been developed. The software PHOENICS is employed to perform the numerical simulation in connection with investigation of the mechanism of penetrationimprovement. The simulation result shows that, when there is no activating flux, the function of element oxygen is absent and a negative temperature coefficient of surface tension dy/ffT in the weld pool takes the prior control, driving the molten metal on the surface to flow from pool center to its edge and making the weld pool wider and shallower. In contrast, when the activating flux exists, the oxygen in the flux will have the influence on the flow pattern of the fluid in the pool. When the oxygen content reaches a certain critical value, a positive temperature coefficient of surface tension dy/3T in the weld pool will take prior control, driving the molten metal on the pool surface to flow from the pool edge to its center and forming a deep and marrow weld pool. The essential reason of penetration improvement is the change of temperature coefficient of surface tension from negative to positive one. An arc constriction will have more influence on the weld width than on the penetration depth. Increase of the voltage makes the pool surface temperature increased only, without obvious increase of penetration depth. The result of numerical simulation of weld pool form is well consistent with that of experiment.A method for testing the flow pattern of the fluid in the weld pool of A-TIG welding is designed. An experiment, in which a double thin wolfram plate is used to baffle the flow in the pool, is performed to verify the influence of activating flux on the flow direction of the fluid in the pool by means of comparing the distribution of wolfram particles around the wolfram plate in the weld. The result shows that the flow direction of fluid in the pool is oriented from the pool center to its edge when there is no activating flux, and the case is reversed when there is such flux, namely the activating flux changes the flow direction of fluid in the weld pool.