Tig welding——V-groove butt welding
V-groove butt welding of flat plates is a commonly used welding method in tig welding, mainly including butt flat welding, butt upward vertical welding, butt horizontal welding and butt overhead welding. No matter what kind of butt method is used, preparations before welding must be carried out.
Pre-welding preparation is a necessary process for tig welding practice or welding, which mainly includes the preparation of test plates (welding parts), the selection of welding materials, pre-welding cleaning, assembly and tack welding, as well as stenciling and scribing of welding parts.
Tig welding——V-groove butt flat welding
Preparation of plates
Preparation of plates Because manual tig welding is rarely used for welding thick parts, it is mainly used for welding thin parts or bottom welding of important products. Therefore, all test plates are mostly 3~6mm thin steel plates with a size of 300mm x 100mm x6mm 60°V-shaped groove, as shown in Figure welding sheet preparation.
The material of the plate can be selected from Q235, 20g and Q345 (16Mn) steel plate according to the situation of the factory, and Q345 (16Mn) steel plate is recommended. The groove of the board must be processed by a planer or a milling machine to ensure the flatness of the board and the groove surface, and pay attention to that the groove should have no blunt edges. The board can be cut by semi-automatic gas cutting.
Selection of Welding Materials
welding wire
Use H08Mn2Si or H05MnSiAlTiZr with a diameter of 2.5 mm, cut each welding wire with a length of 800~1000 mm, and wipe the oil, rust and other dirt on the welding wire with emery cloth and cotton yarn, and use acetone to clean if necessary.
Argon
The required purity of argon is more than 99.95%. Argon. The required purity of argon is more than 99.95%
The tungsten electrode
The tungsten electrode, brand WTh-15 thorium tungsten electrode, adopts the specification of φ2.5mm x 175mm, and the end is ground into a 30° conical shape, as shown in Figure Tungsten electrode shape.
Cleaning before welding
Because argon arc welding is very sensitive to oil rust, in order to ensure the welding quality, it is necessary to pay attention to the cleaning of the plate before welding. The metal itself is shiny. The grinding range is shown in Figure Grinding area before welding
Assembly and tack welding
Tack welds are located at both ends of the test plate, the length l≤15mm, must be penetrated, and no defects are allowed. Its location is shown in Figure Tack weld.
If the tack weld is defective, the defective tack weld must be ground off and then re-welded. Remelting is not allowed to deal with the defect on the tack weld.
Stamping and scribing of test panels
The requirements for stamping and scribing are shown in Figure Stamps and baselines. The distance between the reference line and the upper edge of the groove should be recorded before welding, and the same distance should be maintained on each test plate, so that the widening of each side of the weld can be easily calculated after welding.
Operation process
- The operation of V-groove butt flat welding is first of all assembly and tack welding. In addition to the requirements of pre-welding preparation, assembly and tack welding should also refer to Table Assembly and tack welding of butt flat welding.
- Welding parameters. The welding parameters of V-groove butt flat welding can be selected by referring to Table Welding parameters for butt flat welding.
Welding points. Flat welding is the easiest welding position, and its gun holding method is shown in Figure How to hold a torch. The angle of the welding torch and the position of the filler wire are shown in Figure Torch angle and filler wire position.
The distribution of the weld bead during welding can be carried out according to three layers and three passes; the position of the test plate should be fixed in a horizontal position, and the end with a small gap should be placed on the right side.
Play the bottom
- Weld arc ignition. When making the bottom pass welding, start the arc on the positioning weld on the right side of the test plate.
- Welding. After igniting the arc, the welding torch stays in the original position. After a little preheating, when a molten pool is formed on the outside of the tack weld and a molten hole appears, the wire filling welding starts, and the welding starts from right to left. During back cover welding, the inclination angle of the welding torch should be reduced so that the arc heat is concentrated on the welding wire, a smaller welding current should be used, the welding speed and wire feeding speed should be accelerated, the droplet should be small, and the welding seam should be avoided from sinking and burning through. The filling action of the welding wire should be skillful and uniform, the filling should be regular, the movement of the welding torch should be stable and the speed should be consistent. During welding, pay close attention to the changes and interrelations of welding parameters, and adjust the angle of the welding torch and welding speed at any time. When it is found that the molten pool increases, the weld becomes wider and sags, it indicates that the temperature of the molten pool is too high, and should be reduced at this time. The angle between the welding torch and the test piece can speed up the welding speed; when the molten pool is small, it means that the temperature of the molten pool is low, and the inclination of the welding torch should be increased to slow down the welding speed.
Weld joints.
Splices are required when the welding wire runs out and needs to be replaced, or when the welding needs to be temporarily terminated for other reasons.
When the welding is stopped in the middle of the welding bead, the button switch on the welding torch can be released to stop the wire feeding. If the welding machine has the current attenuation control function, the height of the nozzle will remain unchanged. After the arc is extinguished and the molten pool is completely cooled, move the Open the welding torch; if the welding machine does not have the current attenuation control function, after releasing the button switch, pick up the welding torch slightly, wait for the arc to extinguish and the molten pool to cool and solidify until the color turns black, and then remove the welding torch. Check the quality of the welding seam at the original arc crater before the joint. If it is well protected and there is no oxide scale and defects, the joint can be directly connected; if there is oxide scale or defects, it is best to use an angle grinder to grind off the oxide scale or defects. And grind the front end of the crater into a bevel. Ignite the arc at 15-20mm on the right side of the arc crater, and slowly move it to the left. After the original arc crater begins to melt to form a molten pool and a molten hole, continue wire filling welding.
Weld arc closing. When welding to the end of the test plate, the angle between the welding torch and the weldment should be reduced, so that the heat can be concentrated on the welding wire, and the melting amount of the welding wire should be increased to fill the arc crater. Turn off the control switch. At this time, the welding current is gradually reduced, and the molten pool is also continuously reduced. The welding wire is pulled out of the arc area, but not out of the argon protection zone. After the arc is stopped, the argon gas is closed after a delay of about 10s to prevent the molten pool metal from being heated at high temperature. under oxidation.
If the welding machine has no current attenuation control function, slowly lift the welding torch at the arc end, and reduce the inclination of the welding torch. Increase the melting amount of the welding wire, and cut off the current after the arc crater is filled.
Filling layer,Filling layer, The operation steps and precautions are the same as those for the bottom bead.
When welding, the welding torch should swing laterally, generally in a zigzag motion. The swinging amplitude of the welding torch should be slightly larger than that when welding the bottom coal channel, and it should stay on both sides of the groove. Ensure that both sides of the groove are well fused and the weld bead is uniform. The weld bead of the filling layer should be about 1mm lower than the surface of the test electrode, and do not rub the upper edge of the groove.
Cover the surface layer.
When welding the bead on the surface layer of the cover, it is necessary to further increase the swing amplitude of the welding torch to ensure that both sides of the molten pool exceed the edge of the groove by 0.5~1.5mm, and the wire filling speed is determined according to the excess height of the bead.