The angle between the welding torch and the weldment is too small, which will reduce the protective effect of argon; The included angle is too large, which makes it difficult to operate and add welding wire. When manual TIG welding is used to weld girth seam, the angle between welding gun, welding wire and weldment is shown in the left figure below, and the angle of fillet weld is shown in the right figure below.
Arc initiation: Manual TIG welding has three arc initiation methods: contact short circuit arc initiation, high frequency high voltage arc initiation and high voltage pulse arc initiation.
The contact short-circuit method is to lift the arc immediately after the tungsten electrode contacts the surface of the weldment approximately vertically (70 ~ 85). This method will produce a large short-circuit current when short-circuiting, which will lead to the burn and shape deterioration of the tungsten electrode tip, make the arc disperse or even drift during the welding process, affect the stability of the welding process, and even cause tungsten inclusions.
High-frequency and high-voltage pulse arc initiation is to install a high-frequency or high-voltage pulse device in welding equipment, and automatically cut off the high-frequency or high-voltage pulse after arc initiation. The method is simple to operate, can ensure the geometric shape of the tungsten tip and is easy to ensure the welding quality.
Arc extinguishing: if the arc is not extinguished properly, it will produce arc pits, resulting in cracks, burning through, blowholes and other defects. During operation, the following methods can be used to extinguish the arc:
Adjust the attenuation current value on the welding machine, loosen the switch on the welding gun when extinguishing the arc, so as to attenuate the welding current, gradually speed up the welding speed and wire filling speed, and then extinguish the arc.
Reduce the included angle between the welding torch and the weldment, lengthen the arc so that the arc heat is mainly concentrated on the welding wire, speed up the welding and increase the wire filling amount, and extinguish the arc after filling the arc pit.
When the girth weld is extinguished, the arc should be slightly lengthened first, and the arc should be extinguished after lap welding for 20~30mm without adding or adding a small amount of welding wire.
Operation form of welding torch: Generally, the welding torch for manual TIG welding only moves in a straight line, and the moving speed of the welding torch should not be too fast, otherwise the protective effect of argon gas will be affected.
Linear motion: There are three ways of linear motion: linear uniform motion, linear intermittent motion and linear reciprocating motion.
Linear uniform motion refers to the linear, stable and uniform motion of the welding gun along the weld seam, which is suitable for welding thin plates such as stainless steel and heat-resistant steel. Its characteristics are stable welding process and good protection effect. This can ensure the stability of welding quality.
Linear intermittent motion means that the welding gun needs to stay for a certain time in the welding process to ensure penetration, that is, the linear motion along the weld is an intermittent process. It is mainly used for welding medium and heavy plates.
Linear reciprocating motion refers to the reciprocating linear motion of the welding gun along the weld, which is characterized by controlling the heat, making the weld well formed and preventing burning through. Mainly used for welding aluminum and its alloy sheet.
Transverse swing: it is a small swing to meet the special requirements of welds and different joint forms. There are three common forms: arc zigzag swing, arc zigzag swing and R-shaped swing.
When the arc is zigzag, the welding gun draws a semicircle horizontally and moves forward in a zigzag manner similar to the arc, as shown in the following figure A. This method is suitable for large T-joint, thick plate lap joint and thick plate butt joint with groove. During operation, the welding torch stays on both sides of the weld for a little longer, and the moving speed can be appropriately accelerated when passing through the center of the weld, so as to obtain a high-quality weld.
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Arc zigzag lateral swing means that the welding gun not only draws an arc in the welding process, but also moves forward in an oblique shape, as shown in Figure B. This method is suitable for uneven fillet weld. During operation, the welding torch is biased towards the protruding part, and the welding torch moves sideways in zigzag arc, so that the arc stays on the protruding part for a long time, thus melting the protruding part without adding or adding less filler wire.
R-shaped swing means that the lateral swing of the welding gun is similar to R-shaped motion, as shown in Figure C, and this method is suitable for butt joint of thick plates with different thicknesses. When working, the welding gun not only moves in an R-shape, but also slightly leans towards the thick plate during welding, so that the arc stays on one side of the thick plate for a little longer to control the melting speed on both sides and prevent the thin plate from burning through when the thick plate is not fully welded.
Wire feeding mode: the addition of filler wire has great influence on weld quality. Wire feeding is too fast, the weld is easy to accumulate, and the oxide film is difficult to remove; If the wire feeding is too slow, the weld is easy to bite or bite. Therefore, you should be skilled in feeding silk. There are two commonly used wire feeding methods: finger continuation method and manual method.
Finger continuation method: the welding wire is sandwiched between thumb, index finger and middle finger, and the middle finger and ring finger are supported. When the thumb moves the welding wire forward, the forefinger moves backward, then the thumb quickly moves the welding wire back to the forefinger, and then the thumb moves the welding wire forward, thus repeatedly feeding the welding wire into the molten pool. This method is suitable for long welded joints.
Manual method: the welding wire is clamped between the thumb, forefinger and middle finger, and the finger is not moved. Through the back and forth movement of the hand or arm along the weld and the repeated up and down movement of the wrist, the welding wire is sent into the molten pool. This method is widely used. According to the mode of welding wire feeding into the molten pool, it can be divided into four types: pressure feeding method, continuous method, inching method and dripping method.
The press-in method is shown in Figure A below. Gently press down the welding wire by hand, so that the end of the welding wire is close to the edge of the molten pool. This method is simple to operate, but because of the long welding wire, the end of the welding wire is unstable, easy to swing and difficult to feed.
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As shown in Figure B, the continuous feeding method is to put the end of the welding wire into the molten pool and move the hand forward, so that the welding wire is continuously added into the molten pool. This method is suitable for thin welding wires or joints with large gaps, but it is not easy to ensure the welding quality and is rarely used.
As shown in Figure C, the inching method moves the wrist up and down repeatedly, slowly moves the hand backward, and gradually adds the welding wire to the molten pool. When this method is adopted, due to the repeated up-and-down movement of the welding wire, the oxide film on the surface of the molten pool can be fully removed under the action of electric arc when the welding wire is lifted, thus preventing slag inclusion, and at the same time, because the welding wire is added at the front of the molten pool, it is beneficial to reduce blowholes. Therefore, it is widely used.
Dropping method, as shown in Figure D, moves the welding wire up and down repeatedly by hand, and drops the molten drops after the welding wire melts into a molten pool. This method has the same advantages as the point shift method, so it is often used.
Left welding method and right welding method: As shown in the following figure, manual TIG welding is divided into left welding method and right welding method according to the moving direction and wire feeding position of the welding gun.
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Left welding method: When welding, the welding heat source (welding gun) moves from the right end to the left end of the joint and points to the part to be welded, which is called left welding method. The left welding wire is located in front of the arc. This method is convenient for observing the molten pool. Welding wire is often added by point shift method and drop addition method, and the weld is well formed and easy to master. So the application is more common.
Right welding method: in the welding process, the welding heat source (welding gun) moves from the left end to the right end of the joint and points to the welded part, which is called right welding method. The right welding wire is located behind the arc. It is difficult to observe the molten pool and control the temperature of the molten pool during operation, but the penetration depth is deeper than that of the left welding method and the weld seam is wider, which is suitable for thick plate welding, but it is difficult to master.
Characteristics of welding in different positions
Flat welding: When flat welding, it is required that the arc conveying and welding wire feeding are coordinated and uniform, which is suitable for welding with various thicknesses and materials. According to the thickness of the weldment, the corresponding groove is opened, and the welding gun can make zigzag arc motion or linear motion. When welding weldments with different thicknesses, the arc is slightly biased to one side of the thick plate, and the welding gun can make linear or R-shaped motion. If the root gap is large, the included angle between the welding torch and the weldment can be reduced, and the welding speed and wire feeding speed can be accelerated.
Vertical welding: During vertical welding, in order to prevent molten pool metal and droplets from dripping downwards, the temperature of molten pool should be controlled, and smaller welding current and thinner filler wire should be selected. The arc should not be drawn too long, and the downward inclination angle of the welding torch should not be too small, otherwise it will cause various welding defects.
Transverse welding: transverse welding is easy to master, but the horizontal angle of welding torch and the feeding angle of welding wire must be paid attention to when operating.
Overhead welding: Overhead welding is difficult. In order to prevent the metal and droplets in the molten pool from flowing downward under the action of gravity, the welding current should be small, the welding speed should be fast, and the gap between the groove and the root should be appropriately small.
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Extended data:
Advantages of argon arc welding:
1, argon protection can isolate the adverse effects of oxygen, nitrogen and hydrogen in the air on the arc and molten pool, reduce the burning loss of alloy elements, and obtain dense, splash-free and high-quality welded joints;
2. Argon arc welding has the advantages of stable arc combustion, concentrated heat, high arc column temperature, high welding production efficiency, narrow heat affected zone, and low stress, deformation and crack tendency of welded parts;
3, argon arc welding is open arc welding, which is convenient for operation and observation;
4, the electrode loss is small, the arc length is easy to maintain, there is no flux and coating during welding, and it is easy to realize mechanization and automation;
5. Argon arc welding can weld almost all metals, especially some refractory metals and oxidizable metals, such as magnesium, titanium, molybdenum, zirconium, aluminum and their alloys;
6, not limited by the position of weldment, all-position welding can be carried out.