| TIG welding is one of the most widely used welding techniques in modern manufacturing,especially in the manufacture of important components such as boilers,pressure vessels and pressure pipes.It is the most important welding method for backing welding in single-sided welding method.In actual production,the backing welding is usually used need a reserved gap,and the gap plays a crucial role in ensuring penetration and good formation on the back.Therefore,it is of great significance to study the butt welding process of the reserved gap can realize the quantitative analysis of the whole welding process,understand the welding heat process and the dynamic behavior of the molten pool flow field,and deeply understand the heat transfer and mass transfer of the weld pool,and then understand the impact of the gap on the welding process and welding quality by using the numerical simulation method.A numerical analysis model of three-dimensional transient mass transfer heat transfer of TIG welding pool with reserved butt gap was established.By introducing the control functions of arc heat flow and arc pressure,an arc heat and arc pressure model with adaptive changes of free surface deformation of the molten pool during TIG welding with reserved butt gaps is established.The complex effects of the butt gap and the surface deformation of the molten pool on the arc heat flow and the arc pressure distribution are simplified,and the conservation of the total heat input and the conservation of the total arc pressure after a small amount of arc passing through the gap are considered.The calculation mesh was divided by ICEM CFD software,and the simulation calculation was performed by ANSYS FLUENT software.The weld pool interface is tracked by the VOF method and solved by the PISO algorithm.The welding process with no reserved gap and reserved gap of 0.4mm,0.6mm and 0.8mm is simulated.The welding process are also simulated with the welding current 60A,65A and 70A respectively while the gap is 0.6mm.The fluid flow of liquid metal from the liquid metal formation,fusion to filling gap,and the temperature:field-flow field characteristics of the cross section,longitudinal section and upper surface of the bath are quantitatively analyzed.According to the TIG welding process experiment of the reserved gap,the shape of the weld cross section were measured,and the established numerical analysis model was verified by compared the measured shape and calculated shape of weld cross section.The welding heat process under different reserved gaps and different welding currents was compared,and the influence of gap changes on the temperature field and fluid flow field of the molten pool was analyzed.The results show that the upper surface of the molten pool after fusion shows two kinds of flow tendency:the liquid metal of the molten pool flows backwards and forms a backflow behind the molten pool;the liquid metal at the front end of the molten pool exhibits a forward flow-backward flow period.But the amount of metal flowing to the back of the molten pool is small,and the promotion of penetration is limited.The arc can directly act on the abutting faces of the workpieces on both sides through the gap,so that the workpiece in front of the molten pool can be directly heated by the arc in the thickness direction,which greatly promotes the melting of the back surface of the workpiece.As the reserved gap increases,the liquid metal required to fill the gap also increases,the maximum sag of the molten pool is large,and the surface area on the molten pool is smaller.After the metal on the upper surface of the workpiece is melted,it will quickly flow to the lowest point of the molten pool by gravity,bringing more heat into the gap.When the butt gap is small,the lower surface of the molten pool is less sagged,and after the metal on the upper surface of the workpiece is melted,the velocity in the middle of the gap is smaller,and a large reflux is formed at the boundary of the molten pool to bring the heat to the boundary of the pool. |
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