The Research Of Underwater Wet FCAW Arc Characteristic And Weld Forming

Underwater welding is the way of welding in the harsh environment of the oceans,rivers and so on. Along with the developing efforts of our marine resources, especially thedeep-sea oil and gas and combustible ice resource are constantly increasing, the demand forunderwater welding is also growing increasingly urgent. When conducting underwater wetwelding, the workpiece is placed directly in water, and there are no isolation facilitiesbetween the water and arc. Arc is protected by the gas from external inputting or theproducing gas and water vapor bubble of welding materials and base metal combustion. Inthe process of welding, arc bubble is disturbed by water; because of the periodic rupture,buoyancy and other factors, the arc column often drifts, so that the arc length is changing.Meanwhile because water has the characteristic of big density, heat capacity, fast heatconduct, non-compression and the pressure also increasing with the depth of the water, basemetal is strongly cooling down in the welding process, then the welding quality is rapidlydeteriorating.For the study of arc characteristics and weld forming geometric dimensions and qualityof underwater wet welding power and a hyperbaric chamber underwater welding hardwaresystem that can simulate different depths is built, and according to the requirement of theexperiment, software platform is also designed. So it provides a guarantee of the subsequentunderwater wet welding experiment at different depths.Stable arc is the basis of good welding quality. Due to effect of the water and pressure,the arc stability of underwater wet flux cored wire welding is difficult to achieve the level ofwelding in the air, resulting the poor quality in underwater welding. Studing the effect of theunderwater welding arc stability mechanism can provide the theoretical basis for improvingthe quality in underwater welding. In this paper, as index of evaluating the arc stability, theinverse of the coefficient of variation of the welding arc voltage signal is used to study thearc stability of underwater wet flux cored wire welding in different process conditions afterexperiments. And at the same time, arc stability index is used to comparatively analyze thevoltage and current matching relations of the FCAW in shallow underwater and air. Thispaper briefly introduces the principle of regression analysis, and it is used to establish the sensitivity of the model of underwater wet welding of the arc stability, and the effect to arcstability of the wet flux cored wire welding by various influencing factors such as weldingcurrent, arc voltage, welding speed, contact-tube to workpiece distance and water depth isanalyzed. The conclusions of this article can promote the understanding of arc stabilitymechanism in underwater welding, and can provide theoretical guidance for underwater wetflux cored wire welding process optimization.In order to reduce the workload of the welding test and the developing costs, theorthogonal experimental design method is applied, and the reciprocal of the coefficient ofvariation of arc voltage is used as the evaluation of indicators and according to the actualtrial, the relatively good welding process parameters of underwater wet welding experimentfor different water depths is reasonably drawn.For analysis of the relationship between the weld geometry dimensions and impactparameters, in this paper the principle of the use of regression analysis is used to establishthe prediction models between underwater wet welding current I, arc voltage U, weldingspeed, contact-tube to workpiece distance D and water depth H with the weld width W,the penetration depth P and the reinforcement height R. And the prediction models areanalyzed by statistical tests and error analysis. Finally, according to the forecast model,sensitivity of the welding parameters is studied.Finally the appropriate welding specifications are selected, and underwater wetwelding experiments are done in different depth of water to analyze the water’s impact onthe the arc stability, weld geometry dimensions and forming quality.