The principle of argon arc welding
Argon arc welding is a welding method that uses the inert gas argon as a shielding gas.
Characteristics of argon arc welding
1. The quality of the weld is high. Since argon is an inert gas and does not react chemically with the metal, the alloy elements will not be burned, and argon does not melt with the metal. The welding process is basically the melting and crystallization of the metal. Therefore, the protection effect is better, and a purer and high-quality weld can be obtained.
2. The welding deformation stress is small. Because the arc is compressed and cooled by the argon gas flow, the heat of the arc is concentrated, and the temperature of the argon arc is very high, so the heat affected zone is small, so the stress and deformation during welding are small, especially for thin films. Welding of parts and bottom welding of pipes.
3. It has a wide welding range and can weld almost all metal materials, especially suitable for welding metals and alloys with active chemical components.
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Classification of argon arc welding
1. According to different electrode materials, argon arc welding can be divided into tungsten arc welding (non-melting electrode) and melting electrode argon arc welding.
2. According to its operation method, it can be divided into manual, semi-automatic and automatic argon arc welding.
3. According to the power source, it can be divided into DC argon arc welding, AC argon arc welding and pulse argon arc welding.
Preparation before welding
1. Read the welding process card to understand the material of the welding workpiece, the required equipment, tools and related process parameters, including selecting the correct welding machine (such as welding aluminum alloy, you need to use an AC welding machine), and the correct selection of tungsten electrodes and gas flow.
▶First of all, we need to know the welding current and other process parameters from the welding process card. Then choose tungsten electrode (generally speaking, the diameter of 2.4mm is more commonly used, and its current adaptability range is 150~250A, with the exception of aluminum).
▶The size of the nozzle should be selected based on the diameter of the tungsten electrode. 2.5~3.5 times the diameter of the tungsten electrode is the inner diameter of the nozzle.
▶Finally, select the gas flow rate based on the inner diameter of the nozzle. 0.8-1.2 times the inner diameter of the nozzle is the gas flow rate. The extension length of the tungsten electrode must not exceed the inner diameter of the nozzle, otherwise pores will easily occur.
2. Check whether the welding machine, gas supply system, water supply system, and grounding are intact.
3. Check whether the workpiece is qualified:
▶Whether there is oil, rust and other dirt (the weld within 20mm must be clean and dry).
▶Whether the bevel angle, gap, and blunt edge are appropriate. If the groove angle and gap are large, the welding volume will be large and welding may easily occur. If the groove angle is small, the gap is small, and the blunt edge is thick, it is easy to cause incomplete fusion and incomplete welding. Generally speaking, the bevel angle is 30°~32°, the gap is 0~4mm, and the blunt edge is 0~1mm.
▶The wrong edge cannot be too large, generally within 1mm.
▶Whether the length and number of tack welding points meet the requirements, and the tack welding itself must have no defects.
How to operate argon arc welding
Argon arc is an operation in which both hands move at the same time. It is the same as the left hand drawing a circle and the right hand drawing a square in our daily life. Therefore, it is recommended that those who are just starting to learn argon arc welding should carry out similar training, which will be helpful to learn argon arc welding. .
1. Wire feeding: divided into inner filling wire and outer filling wire.
▶External filler wire can be used for bottoming and filling. It uses a larger current. The welding wire head is on the front of the groove. Hold the welding wire with your left hand and continuously feed it into the molten pool for welding. The groove gap requires a small or no gap.
Its advantage is that the current is large and the gap is small, so the production efficiency is high and the operating skills are easy to master. Its disadvantage is that if it is used for priming, the operator cannot see the melting of the blunt edge and the excess height on the reverse side, so it is easy to produce unfused and undesirable reverse forming.
▶The filler wire can only be used for bottom welding. Use the left thumb, index finger or middle finger to coordinate the wire feeding movement. The little finger and ring finger hold the wire to control the direction. The wire is close to the blunt edge inside the groove, together with the blunt edge. For melting and welding, the groove gap is required to be larger than the diameter of the welding wire. If it is a plate, the welding wire can be bent into an arc.
The advantage is that the welding wire is on the opposite side of the groove, so you can clearly see the melting of the blunt edge and the welding wire, and you can also see the reinforcement on the reverse side with your peripheral vision, so the weld is well fused, and the reinforcement and lack of fusion on the reverse side can be obtained. Very good control. The disadvantage is that the operation is difficult and requires the welder to have relatively proficient operating skills. Because the gap is large, the welding volume increases accordingly. The gap is large, so the current is low, and the work efficiency is slower than that of external filler wire.
2. The welding handle is divided into a shaking handle and a mop.
▶The rocking handle is to press the welding nozzle slightly hard on the welding seam, and shake the arm greatly to perform welding. Its advantage is that the welding nozzle is pressed on the weld seam and the welding handle is very stable during operation, so the weld seam is well protected, the quality is good, the appearance is very beautiful, and the product qualification rate is high. In particular, overhead welding is very convenient and can be used when welding stainless steel. Get a very nice looking color. The disadvantage is that it is difficult to learn. Because the arm swings greatly, it is impossible to weld in obstacles.
▶The mop means that the welding tip gently leans or not against the welding seam. The little finger or ring finger of the right hand also leans or not against the workpiece. The arm swings slowly and drags the welding handle for welding. Its advantages are that it is easy to learn and has good adaptability. Its disadvantage is that the shape and quality are not as good as the swing handle. Especially the overhead welding does not have a swing handle to facilitate welding. It is difficult to obtain the ideal color and shape when welding stainless steel.
3. Arc ignition
An arc starter (high-frequency oscillator or high-frequency pulse generator) is generally used to start the arc. The tungsten electrode and the weldment are not in contact with each other to ignite the arc. If there is no arc starter, contact arc starting is used (mostly used for construction site installation, especially high-altitude installation) , copper or graphite can be placed on the groove of the weldment to ignite the arc, but this method is more troublesome and rarely used. Generally, a welding wire is used to lightly draw the welding wire to directly short-circuit the weldment and the tungsten electrode and quickly disconnect to ignite the arc.
4.Welding
After the arc is ignited, the weldment should be preheated for 3 to 5 seconds at the beginning of the weldment. Wire feeding begins after the molten pool is formed. When welding, the angle of the welding wire gun should be appropriate and the welding wire should be fed evenly. The welding gun should move forward smoothly and swing left and right, with the two sides slightly slower and the middle slightly faster. Pay close attention to the changes in the molten pool. When the molten pool becomes larger, the weld becomes wider or concave, the welding speed should be accelerated or the welding current should be adjusted back down. When the molten pool fusion is not good and the wire feeding feels immobile, the welding speed should be reduced or the welding current should be increased. If it is bottom welding, the attention should be focused on the blunt edges on both sides of the groove and the corners of the eyes. With your peripheral vision on the other side of the seam, pay attention to the changes in other heights.
5. closing arc
If the arc is closed directly, it is easy to produce shrinkage holes. If the welding gun has an arc starter, the arc must be closed intermittently or adjusted to an appropriate arc current and the arc must be closed slowly. If the welding machine does not have an arc starter, the arc must be slowly led to the groove. Do not produce shrinkage holes on one side. If shrinkage holes occur, they must be polished clean before welding.
If the arc closing is at a joint, the joint should be ground into a bevel first. After the joint is fully melted, weld forward 10~20mm and then slowly close the arc to avoid shrinkage cavities. In production, it is often seen that the joints are not polished into bevels, but the welding time of the joints is directly lengthened. This is a very bad habit. In this way, the joints are prone to concave, unfused joints and disjointed back surfaces, which affect the appearance of the forming. For example, if it is a high alloy The material is also prone to cracks.
After welding, check that the appearance is satisfactory. Turn off the power and gas when leaving.
Post time: Dec-19-2023
