Plate butt welding with V-shaped groove is a welding technology deepened on the basis of flat lay welding, and it is also a basic welding technology that welding operators must master. If it is difficult to penetrate into the root of the weldment, it is necessary to make a single V-shaped groove or a double V-shaped groove, and use multi-layer welding or multi-layer multi-pass welding (Figure V and double V multilayer welding) to make the welding meet higher technical requirements.
The shape of the molten pool is shown in Figure Drill bottom pass and weld pool. when the bottom bead is made for the flat welding of the single V-shaped groove. From the cross-section, the molten pool is large at the top and small at the bottom, and the balance is mainly maintained by the upward component force of the surface tension of the liquid metal on the back of the molten pool to support the molten metal from leaking. Therefore, the operator must adjust the welding torch angle, swing amplitude and welding speed appropriately and flexibly according to the changes in the assembly gap and the temperature rise of the weldment during the welding process, keep the diameter of the molten hole unchanged as much as possible, and maintain a straight and uniform back welding. road. Therefore, it is necessary to carefully and carefully observe the situation in the welding process, and constantly sum up experience, in order to master and improve the operation technology of single-sided welding and double-sided forming.
The preparation for butt flat welding of V-shaped groove mainly includes the preparation of workpiece, welding wire, CO2 gas, welding machine and auxiliary tools.
1) The workpiece The workpiece is made of two low-carbon steel plates suitable for welding, and its size standard is 300 mm X 100 mm x 12 mm. If there is no steel plate with a thickness of 12 mm, you can also choose a steel plate with a thickness of about 10 mm for training.
2) Welding wire and CO2 gas
When welding, choose H08Mn2SiA welding wire, the diameter of the welding wire is 1.0 mm, and the surface of the welding wire should be cleaned before use; the purity of CO2 gas should reach 99.5%
3) The welding machine and auxiliary tools are semi-automatic CO2 gas shielded welding machine for welding. The main auxiliary tools include wire brushes for cleaning weldments, chisels, files, grinders and slag hammers used in the welding process for finishing weldments.
Since the butt flat welding of V-shaped groove requires multi-layer welding in the groove, it is very difficult to weld. The focus of welding is on the bottoming of the root. Improper operation can easily cause welding defects such as burn-through and slag inclusion. Defects such as slag inclusion, lack of fusion, and pores will also appear between each layer. Therefore, special attention should be paid to the selection of welding process parameters and the correct operation method before welding of V-groove butt flat welding.
It should be noted that a gap of 2.5mm should be reserved when the workpiece is assembled, which is conducive to the penetration of the weldment. When spot-fixing both ends of the weldment, the length of the weld should be about 10 mm (15 to 50 mm if it is a medium-thickness plate), and the spot weld should not be too high, as shown in Figure Locate the length of the weld ; , In order to prevent the deformation after welding, there should be 1°~2° of anti-deformation when the weldment is assembled amount, as shown in Figure Reserve inverse deformation.
Assembly and tack welding The assembly gap and tack welding of the workpiece with a plate thickness of 12mm are shown in Figure Assembly and positioning welding of workpiece with plate thickness of 12mm. The amount of reverse deformation of the workpiece can be carried out with reference to the method shown in Figure Plate thickness is 12mm butt flat welding reverse deformation.
The Butt weld welding parameters of butt flat welding with a plate thickness of 12 mm can be selected by referring to Table 5-3. There are two sets of commonly used parameters recommended here for reference only. The first group of parameters uses φ1.2 mm welding wire, which is difficult to master during welding, but has good applicability; the second group uses φ1.0 mm welding wire, which is easier to master, but because the application of φ1.0 mm welding wire is not very common, the applicability Very poor and limited use.
(1) Welding torch angle and welding method. When welding, the left welding method is adopted, and the welding level is three layers and three passes. Figure 5-22 shows the torch angle and arc position for butt flat welding.
(2) The placement of the weldment position. Before welding, check the reasonable clearance during assembly and whether the reserved anti-deformation is suitable, and the clearance is small.One end should be placed on the right side.
(3) Bottom welding. After adjusting the welding parameters of the bottom bead, start the arc on the side of the groove about 20mm to the left of the pre-welding point at the right end of the weldment. After the surface of the tack weld and the groove surface are fused to form a molten pool, start welding to the left to make the bottom bead. The welding gun swings slightly laterally along both sides of the groove, and controls the arc to burn 2~3mm away from the bottom edge. When the diameter of the melting hole at the bottom of the mouth reaches 4 ~ 5mm, it is transferred to normal welding. The following should be noted when welding the bottom bead:
①The bottom layer adopts crescent-shaped swing welding (Fig.The way the welding torch swings-a). When the welding torch swings, it moves slightly faster in the center of the welding seam, and it needs to stop for 0.5~1s when it swings to both sides of the welding seam. If the groove gap of the weldment is large, the reverse crescent-shaped swing of the appropriate forward and backward movement should be performed while swinging laterally, as shown in Figure The way the welding torch swings-b. This swing can prevent the arc from directly aligning with the gap, which can prevent the generation of burn-through defects.
②Because the arc is always aligned with the center line of the weld bead and makes a small lateral swing in the groove (Fig.The transport of the electrode at the root of the weld), and stops a little on both sides of the groove, the diameter of the melting hole should be larger than the gap of the assembly by 1 ~2mm. Therefore, the welding hole should be carefully observed during welding, and the lateral swing amplitude and welding speed of the welding torch should be adjusted according to the change of the gap and the diameter of the welding hole, and the diameter of the welding hole should be kept as constant as possible to ensure the reverse weld with uniform width and height.
③Rely on the dwell time of the arc on both sides of the groove to ensure good fusion on both sides of the groove, so that the junction between the two sides of the bottom bead and the groove is slightly concave, and the surface of the bead remains flat, as shown in Figure Lay bottom pass.
④When welding the bottom bead, the height of the nozzle should be strictly controlled, and the arc must burn 2-3 mm from the bottom of the groove to ensure that the thickness of the bottom layer does not exceed 4 mm.
4. Butt weld Filler welding. After debugging the process parameters of the filler layer, start welding the filler layer at the right end of the weldment. The lateral swing of the welding torch is slightly larger than that of the bottom layer. Pay attention to the fusion on both sides of the weld pool. Make sure that the surface of the weld bead is flat and slightly concave, and the height of the filling layer is 1.5~2 mm lower than the surface of the base metal. It is not allowed to burn the edge of the groove during welding.
5. Butt weld Cover welding. After debugging the process parameters of the cover layer, start welding from the right end, pay attention to the following matters:
①Maintain the height of the nozzle, the edge of the welding pool should exceed the edge of the groove by 0.5 ~ 1.5 mm, and prevent undercut.
②The horizontal swing of the welding torch should be slightly larger than that of the filling welding, and the welding speed should be kept as uniform as possible, so that the appearance of the welding seam is beautiful.
③The arc crater must be filled when the arc is stopped, and the arc length of the arc should be short to prevent the occurrence of arc crater crack defects.
6.The method of filling the crater. When the welding is about to be terminated, the processing method of filling the arc crater can be carried out with reference to several methods shown in Figures-Several treatment methods for filling welding pits.