CO2 gas shielded welding, flat butt welding, single-sided welding, double-sided forming operation process

【Summary Description】 Features of semi-automatic CO2 welding. When the plate is welded, the molten pool is in a suspended state, and the metal liquid is easy to fall under the action of gravity. During the process, the angle, swing amplitude and welding speed of the welding torch must be adjusted in time according to the changes in the assembly gap and the temperature of the molten pool to control the size of the molten hole and ensure the uniform weld on the back of the sample. 2. the welding operation process. 1. Preparation before welding. (1) The test piece is processed by using the normal strength ship structural steel Class B test piece with a thickness of 10mm. The processing size is 300mm × 150mm × 10mm, the bevel processing angle is 300±10mm, and no blunt edge is left, as shown in Figure 3-1 below. Semi-automatic CO2 welding is very sensitive to rust and oil prevention, so it is necessary to clean the 20mm range around the groove before welding, and use an angle grinder to polish the metallic luster. (3) See Table 3-5 for the dimensions of the test piece group and the positioning of the welding blank. The two ends of the specimen are positioned welded, and the length of the positioning weld is 10~15. The welding wire and welding parameters used in the positioning welding are the same as those used in the formal welding. After the tack welding, grind both ends of the tack welding into inclined surfaces with an angle grinder to remove the spatter on the groove. (4) Welding parameter selection B plate butt flat welding semi-automatic CO2 welding welding parameter selection is shown in Table 3-6. Table 3-6 Selection of welding parameters. 2. Welding. Place the test piece flat on the workbench with enough space on the back, place the end with the smaller gap as the starting end on the right, and use the left welding method for welding. (1). Semi-automatic CO2 gas shielded welding, single-sided welding, double-sided forming, backing welding, using filaments, small current welding, and molten droplets are transferred in the form of short circuit. In order to avoid spatter caused by low short-circuit voltage, the end of the welding wire should be cut into a bevel shape with pointed nose pliers before starting the arc to reduce the short-circuit contact area and start the arc smoothly. At the same time, pay attention to the length of the wire. Generally, the arc is started at about 10mm. If the length is too long, it is easy to increase the resistance and heat, causing the wire to burst, and the arc cannot be smoothed. The arc position shall be at the top of the slope of the tack weld, see Figure 3-2. (2). Bottom welding. When the bottom layer is welded, the angle between the welding torch and the weldment is shown in Figure a, and the extension length of the welding wire is 20~25mm. After the arc is ignited, the welding torch runs along the root of the groove without pressing the arc. The welding torch swings slightly laterally at the root and pauses on both sides of the cut. During welding, pay attention to observe the size of the weld hole. The diameter of the weld hole is 0.5~1mm larger than the groove gap. Adjust the transverse swing range and welding speed of the welding torch according to the change of groove spacing and weld aperture. When the gap between the groove and the weld hole increases, the transverse swing of the welding torch should be widened to ensure uniform weld formation on the back. During the welding process, the end of the welding wire should always be burned in the front half of the molten pool, and the welding wire should not be separated from the molten pool. In addition, the nozzle height should be strictly controlled. That is, the operating line of sight cannot be blocked, and the gas protection effect is good. During welding, the arc burns at a distance of 2~3mm from the root of the groove to keep the thickness of the female weld at about 4mm. Semi-automatic CO2 gas shielded welding does not need joints. Generally, it can be completed continuously at one time. If it cannot be completed at one time, the arc should be polished and then arc. The welding method is the same as the above method. From the above analysis of the welding process, it can be seen that the operation points of CO2 semi-automatic welding single-sided welding double-sided welding are: when backing welding, attention should be paid to the swing mode of the welding torch, the position of the welding torch corner arc in the groove and the influence of the melting hole. The angle of welding torch should be controlled within a certain range. If the back angle of welding torch is too small, it will not only destroy the protective atmosphere, but also easily make the liquid metal flow forward, hinder the formation of molten hole, so that the back weld can not be formed. The back angle of the welding torch is too large, which not only affects the operation line of sight, but also makes the end of the welding wire out of the molten pool and extends to the back of the sample through the groove gap, causing the welding process to be interrupted. The welding torch swing method should be appropriate to effectively control the size of the molten pool and prevent the liquid metal from falling through the groove gap. During flat welding, the small amplitude transverse swing method should be adopted, and the arc should be suspended on both sides of the groove to control the temperature rise of the molten pool. During the welding process, attention should be paid to controlling the size of the weld hole so that it is always greater than the gap between 0.5~1mm on both sides of the groove to obtain uniform and smooth back weld formation. (3). Filling welding. Before welding the filling layer, the welding slag and spatter on the surface of the bottom weld shall be cleaned to prevent pollution and affect the quality. The angle and lateral swing mode of the welding gun are the same as that of the master welding, and the extension length of the welding wire can be slightly greater than 1~2mm. During welding, pay attention to the even swing of the welding torch in place, and pause on both sides of the groove to ensure smooth welding seam. At the same time, it is conducive to full melting of the edges on both sides of the groove without slag inclusion defects. In the welding process, attention should be paid to controlling the welding speed to ensure that the thickness of the weld is appropriate and the filling layer and the underlying metal are well fused. After the filling layer is welded, the weld surface shall be 1~1.5mm away from the specimen surface, and the groove edge shall not be damaged. (4) Cover welding. In front of the welding cover, the welding slag and metal spatter on the surface of the welding seam of the filling layer shall be removed first, the uneven part of the joint shall be leveled with an angle grinder, and the spatter around the conductive nozzle and nozzle shall be removed. The angle and swing mode of the welding gun are the same as that of filling welding, but the swing amplitude of the welding gun should not be too large, otherwise the welding wave thickness and undercut phenomenon are easy to occur. When the welding gun swings, both sides of the groove shall be evenly and slowly to prevent the concave. The welding process can be completed continuously. When the welding is interrupted, the gas should be delayed to avoid oxidation of the molten pool at high temperatures.

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