Gas tungsten arc welding process 1/2
2022-02-09
New foreign trade regulations
2022-02-16Gas tungsten arc welding process 2/2
Gas tungsten arc welding basic operation
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 arc initiation
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.
Gas tungsten arc welding tack weld
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.
Gas tungsten arc welding positioned welding
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 following points should be paid attention to when conducting positioning weld welding:
- The welds must be positioned according to the requirements specified in the welding procedure. The welding rod of the same grade and specification as stipulated in the formal welding process shall be used for welding with the same welding process parameters; If the process requires preheating before welding and slow cooling after welding, the positioning weld shall also be preheated before welding and slow cooling after welding. The preheating temperature is the same as during formal welding.
- The arc starting and arc closing end of the positioning weld should be smooth and not too steep, to prevent the welding joint at both ends of the welding penetration. Position weld must ensure good fusion, weld pass can not be too high.
- Position welding is discontinuous welding, the workpiece temperature is lower than normal welding, due to insufficient heat and easy to produce incomplete welding, so the welding current should be slightly higher than formal welding 10%~15%. After positioning welding, welding must be done as soon as possible to avoid stopping or storing for too long.
- The length, residual height, spacing and other dimensions of the positioning welds can generally be selected according to Table Gas tungsten arc welding-7. However, the size and quantity of the positioning welds can be appropriately increased for the parts that play an important role in ensuring the size of the welds.
- The positioning weld cannot be welded at the intersection of the weld or the place where the direction of the weld changes sharply. Usually, it should be at least 50mm away from these places to weld the positioning weld.
- In order to prevent the workpiece from cracking during welding, forced assembly should be avoided as far as possible. If the structure is assembled by force, the length of the positioning weld shall be increased according to the specific situation and the time of positioning weld shall be reduced.
Gas tungsten arc welding and joint
Base coat
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.
Weld
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.
Quality control of welded joints
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 position of arc re-ignition is behind the original arc pit, so that the weld overlaps 20~30mm, and generally no or only a small amount of welding wire is added at the overlaps.
The weld pool should be penetrated to the root of the weld joint to ensure that the joint is fused.
Gas tungsten arc welding wire filling
The basic operation of wire filling
Continuous wire filling
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.
Intermittent wire feeding (also known as drip wire feeding)
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.
The wire is fused together with the blunt edge and the groove
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.
Notes for wire filling
It is necessary to wait for both sides of the groove to melt before filling the wire, so as not to cause poor fusion.
- When filling the wire, the welding wire should be at an Angle of 15° with the workpiece surface. It should be entered from the leading edge of the molten pool and then withdrawn, and so on.
- Fill silk evenly, speed appropriate. Too fast, high welding seam; Too slow, the weld is concave and bite edge. The end of the wire should always be in an argon protected zone.
- When the gap is larger than the diameter of the welding wire, the welding wire should swing synchronously with the arc. No matter what kind of wire filling action is adopted, wire feeding speed should be adapted to welding speed.
- Fill the welding wire, should not put the welding wire directly under the arc, the welding wire is too high is not appropriate, should not let the droplet to the pool “drip crossing”. Figure Gas tungsten arc welding-11 shows the correct position of wire filler.
- In the process of operation, if the tungsten electrode and the welding wire collide accidentally, there will be a short circuit, which will produce a great splash and smoke; Will cause weld contamination and tungsten clip. At this time, should immediately stop welding, grinding wheel to remove the contaminated place, until grinding metal luster. The contaminated tungsten electrode should be re-arced elsewhere to melt the contaminated end or re-sharpened before welding can continue.
- When withdrawing the welding wire, do not let the end of the welding wire withdraw from the argon gas protection zone, so that the end of the welding wire will be oxidized and enter the molten pool in the next spot, resulting in oxide slag inclusion or porosity.
Tungsten electrode inert gas welding arc closing
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.
