Gas tungsten arc welding basic operation technology includes arc initiation, welding and joint, wire filling and arc closing, etc. The following problems should be paid attention to during welding:
(1) Keep the correct gun posture, adjust the welding gun Angle and nozzle height at any time, not only reliable protection effect, but also easy to observe the molten pool.
(2) Pay attention to the changes in the shape and color of the tungsten pole after welding. If the tungsten pole is not deformed during welding and the extreme part of tungsten after welding is silver white, it indicates that the protection effect is good; If tungsten is blue after welding, the protection effect is poor; If the extreme part of the tungsten is black or lumplike, it means that the tungsten pole has been polluted. Most likely, there is a short circuit in the welding process, or there is a lot of splash, so that the head becomes an alloy. This section of tungsten pole must be ground off, otherwise it is easy to clamp tungsten.
(3) Wire feeding should be evenly, and can not be stirred in the protected area to prevent air involvement.
Gas tungsten arc welding adopts arc ignition device, such as high frequency oscillator or high voltage pulse generator, to ionize argon and ignite the arc. The advantages are that the tungsten electrode can directly ignite the arc at the welding spot without contacting the workpiece, and the loss of the tungsten extreme head is small. Arc starting welding quality is high, will not produce tungsten clamping defect without arc starting device, can use pure copper plate or graphite plate as arc starting plate. The arc starting plate is placed on the welding groove, or on the edge of the groove, and the tungsten pole is not allowed to contact the arc starting plate or the groove surface directly.
To prevent deformation caused by thermal expansion of the workpiece during welding, ensure the distance between positioned welds. You can choose from Table Gas tungsten arc welding-6. The positioning weld will be part of the weld, must be welded firmly, not allowed to have defects, if the weld requires single-sided welding double-sided forming, then the positioning weld must be welded thoroughly must be welded according to the formal welding process requirements welding positioning weld, if the formal weld requires preheating, slow cooling, positioning welding before preheating, after welding to slow cooling.
The positioning weld can not be too high, so as not to weld to the positioning weld joint difficulties, if you encounter this situation, it is best to lower the positioning weld, both ends of the grinding slope, in order to weld a good joint. If cracks, pores and other defects are found on the positioning weld, the positioning weld should be polished off and rewelded, and remelting is not allowed to repair.
Before welding, the relative position of the welding parts is fixed to ensure the correct geometry and size of the whole structural parts. The welding operation is called positioning welding, commonly known as spot solid welding. The formation of positioning welding is relatively short, not removed in the welding process, but the part of the formal weld is retained in the weld, so the quality of the positioning weld, the appropriate position, length and height, will directly affect the quality of the formal weld and the deformation of the weld. According to experience, some serious quality accidents occurred in production, such as large structural deformation, incomplete welding and cracks and other defects, are often caused by unqualified positioning welding, so enough attention must be paid to positioning welding. The requirements of welding rod and welder operation skill proficiency should be exactly the same as formal welding, or even higher. When defects are found in the positioning weld, it should be shoveled or polished off and re-welded, not allowed to remain in the weld.
The bottom welding pass should be done at one go, not allowed to stop halfway. The bottom pass shall have a certain thickness: for pipes with wall thickness δ≤10mm, the thickness shall not be less than 2-3mm; For pipes with wall thickness of δ>10mm, the thickness shall not be less than 4~5mm, and the bottom pass shall be qualified by self-inspection before filling cover welding.
During welding, it is necessary to master the welding gun Angle and wire feeding position, and strive to send wire evenly to ensure the welding bead forming. In order to obtain a relatively wide pass and ensure the fusion quality on both sides of the groove, arc welding gun can also swing horizontally, but the swing frequency should not be too high or the amplitude should not be too large. In order to not destroy the protection effect of the weld pool, the welder can flexibly control it. After welding the bottom pass, when welding the second layer, it shall be noted that the bottom pass shall not be burned through to prevent the concave of the bottom pass or the violent oxidation on the back.
It is important to control the quality of the joint, whether the bottom layer or the filler layer is welded. Because the joint is the place where two sections of weld joint; Due to the difference in temperature and the change in the amount of filling metal, it is easy to appear the defects of ultra high, lack of meat, incomplete welding, slag inclusion (inclusion), porosity and so on. Therefore, arc stop should be avoided as far as possible to reduce the number of cold joints. However, due to the actual operation, it is necessary to replace the welding wire, tungsten pole, change the welding position or symmetrical sectional welding, etc., must stop arc, so the joint is inevitable. The problem is to try to control the joint quality as much as possible. The method to control the quality of weld joints is as follows:
Weld joint should have a slope, can not have a dead Angle.
The weld pool should be penetrated to the root of the weld joint to ensure that the joint is fused.
This kind of wire filling operation technology is better, the disturbance to the protective layer is small, but it is difficult to master. Use the thumb, index finger, and middle finger of the left hand to send the wire, and hold the ring and little fingers to control the direction of the wire, as shown in Figure Gas tungsten arc welding-9. Continuous wire filling arm movement is small, until the wire is almost used up before moving forward. When the amount of wire filling is large and strong technological parameters are used, this method is mostly used.
Pinch the welding wire with the thumb, index finger and middle finger of the welder’s left hand. The end of the welding wire should always be in the argon gas protection zone. The filling action should be light, and the argon gas protection layer should not be disturbed to prevent air intrusion. It is not stirred in the weld pool like gas welding, but relies on the upper and lower movements of the welder’s arm and wrist repeatedly to send the droplet at the end of the welding wire into the weld pool. This method is used in all-position welding, as shown in Figure Gas tungsten arc welding-10.
Bend the welding wire into an arc, close to the gap in the groove, welding arc melt the blunt edge of the groove and also melt the welding wire. At this time, the gap should be less than the diameter of the welding wire, this method can avoid the welding wire cover the sight of the welder, suitable for the difficult position of the welding.
It is necessary to wait for both sides of the groove to melt before filling the wire, so as not to cause poor fusion.
Improper arc retraction will affect the quality of welding seam, make arc pit too deep or arc pit crack, and even cause repair.
Generally, argon arc welding equipment is equipped with automatic current attenuation device. If there is no current attenuation device, changing the operation method is used to close the arc. The basic point is to gradually reduce the heat input, such as changing the Angle of the welding gun, elongating the arc and speeding up the welding speed. For the tube closed weld, the final arc is generally adopted a slightly elongated arc, overlapping weld 20-40mm, no or less welding wire in the overlapping part.
After arc stop, the gas switch should be delayed about 10 seconds before closing (general equipment has advanced air, lag gas closing device), the welding torch stays at the arc closing point can not be raised, the use of delayed closed argon gas to protect the solidified metal at the arc closing point, can prevent the metal from continuing to oxidize at high temperature.