The principle of argon arc welding

Argon arc welding is a welding method that uses inert gas argon as the shielding gas.

Characteristics of argon arc welding

The quality of the weld seam is high. As argon is an inert gas that does not react chemically with metals, alloy elements will not be burned, and argon does not melt in the metal.

The welding process is basically a process of metal melting and crystallization. Therefore, the protection is better, and a relatively pure and high-quality weld seam can be obtained.

The welding deformation stress is small. Because the arc is compressed and cooled by the argon gas flow, the arc heat is concentrated, and the temperature of the argon arc is very

high, so the Heat-affected zone is small, so the welding stress and deformation are small, especially for thin piece welding and pipe backing welding.

The welding range is wide, and almost all metal materials can be welded, especially suitable for welding metals and alloys with active chemical composition.

Classification of argon arc welding

Argon arc welding can be divided into tungsten electrode argon arc welding (non consumable electrode) and consumable electrode argon arc welding according to different electrode materials.

According to its operating methods, it can be divided into manual, semi-automatic, and automatic argon arc welding.

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 materials, equipment, tools, and related process parameters required for welding the workpiece, including selecting the correct welding machine

(such as AC welding machine for aluminum alloy welding), selecting the correct tungsten electrode and gas flow rate.

▶ Firstly, it is necessary to obtain the welding current and other process parameters from the welding process card. Then choose tungsten electrode (generally speaking, 2.4mm diameter is more

commonly used, and its current adaptation range is 150-250A, except for aluminum). ▶ Based on the diameter of the tungsten electrode, choose a nozzle with a diameter of 2.5 to 3.5 times the inner

diameter of the nozzle.

▶ Finally, the gas flow rate is selected 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 should

not exceed the inner diameter of its nozzle, otherwise it is easy to produce pores.

(2) Check if the welding machine, gas supply system, water supply system, and grounding are intact.

(3) Check if the workpiece is qualified:

▶ Is there any oil, rust or other dirt (the weld seam must be clean and dry within 20mm) ▶ Is the groove angle, gap, and blunt edge suitable. If the groove angle and gap are large, there will be a large amount

of welding, which is prone to weld overlap. Small groove angles, small gaps, and thick blunt edges are prone to incomplete fusion and incomplete welding. Generally speaking, the groove angle is 30 °~32 °,

the gap is 0-4mm, and the blunt edge is 0-1mm.

▶ The misalignment should not be too large, usually within 1mm.

▶ Whether the length and number of points of positioning welding meet the requirements, and whether the positioning welding itself has no defects.

Operation techniques of argon arc welding

Argon arc welding is an operation where both hands move simultaneously, which is the same as drawing a circle with the left hand and a square with the right hand in our daily lives. Therefore, it is recommended

that personnel who are just starting to learn argon arc welding undergo similar training, which is helpful for learning argon arc welding.

(1) Wire feeding: divided into inner filling and outer filling.

▶ External filling wire can be used for backing and filling, using a large current. The welding wire head is on the front of the groove, and the left hand pinches the welding wire, continuously sending it into the molten

pool for welding. The groove gap requires small or no gap. Its advantages include high production efficiency and easy mastery of operating skills due to its high current and small gap. Its disadvantage is that when

used for bottoming, the operator cannot see the melting of the blunt edge and the reinforcement of the reverse side, which can easily lead to incomplete fusion and unsatisfactory reverse formation.

▶ The inner filler wire can only be used for backing welding. It is used with the left thumb, index finger, or middle finger to cooperate with the wire feeding action. The little finger and ring finger clamp the welding wire

to control the direction, and the welding wire is tightly pressed against the blunt edge on the inner side of the groove and melted together with the blunt edge for welding. The gap between the groove is required to be

greater than the diameter of the welding wire. If it is a plate, the welding wire can be bent into an arc. Its advantage is that the welding wire is on the opposite side of the groove, which can clearly see the blunt edge

and the melting situation of the welding wire. The residual light of the eyes can also see the situation of the reverse reinforcement, so the welding seam fusion is good, and the reverse reinforcement and incomplete

fusion can be well controlled. The disadvantage is that the operation is difficult, requiring welders to have more proficient operating skills. Due to the large gap, the welding amount increases correspondingly, and the

gap is large, resulting in low current and slower work efficiency compared to external wire filling.

(2) The welding handle is divided into a crank and a mop. ▶ The handle is used to slightly press the welding nozzle onto the weld seam, and the arm is greatly shaken for welding. Its advantages are that the welding

nozzle is pressed onto the weld seam, and the welding handle is very stable during operation. Therefore, the weld seam is well protected, with good quality, beautiful appearance, and high product qualification rate.

Especially for overhead welding, it is very convenient. When welding stainless steel, it can obtain a very beautiful appearance color. Its disadvantage is that it is difficult to learn, as the arm swings greatly, making it

impossible to weld in areas with obstacles.

▶ A mop is a welding nozzle that gently leans or does not lean against the weld seam, and the right little or ring finger also leans or does not lean against the workpiece. The arm swings slightly, dragging the welding

torch for welding. Its advantages are easy to learn and good adaptability, but its disadvantages are that the shape and quality are not good, especially when welding overhead without a handle, which is convenient

for welding. It is difficult to obtain the ideal color and shape when welding stainless steel.

(3) Arc striking is generally carried out using an arc striking device (high-frequency oscillator or high-frequency pulse generator). The tungsten electrode does not contact the welding element to ignite the arc. When

there is no arc striking device, contact arc striking is used (mostly used for construction site installation, especially high-altitude installation). Red copper or graphite can be placed on the groove of the welding element

to ignite the arc. However, this method is more cumbersome and less commonly used. Generally, a slight stroke of welding wire is used to directly short circuit and quickly disconnect the welding element and tungsten

electrode, igniting the arc.

(4) After the welding arc is ignited, it should be preheated for 3-5 seconds at the beginning of the welding piece to form a molten pool and start wire feeding. When welding, the angle of the welding gun should be appropriate

and the welding wire should be fed evenly. The welding gun should move forward smoothly, swing left and right slightly slower on both sides, and slightly faster in the middle. Pay close attention to the changes in the molten

pool. When the molten pool becomes larger, the weld seam becomes wider, or there is a depression, it is necessary to accelerate the welding speed or adjust the welding current again. When the fusion of the molten pool is

poor and there is a feeling that the wire feeding cannot move, the welding speed should be reduced or the welding current should be increased. If it is a backing weld, the attention of the eye should be focused on the blunt

edges on both sides of the groove, and the residual light from the corner of the eye should be on the opposite side of the seam. Pay attention to other changes in height.

(5) If the arc is stopped directly, it is easy to produce shrinkage holes. If there is a welding gun with an arc starter, the arc should be stopped intermittently or adjusted to the appropriate arc stopping current to slowly stop the arc.

If there is no arc starter welding machine, the arc should be slowly led to the side of the groove without producing shrinkage holes. If shrinkage holes are generated, they should be polished and dried before welding can be carried out.

If the arc is to be terminated at the joint, it should be polished into an inclined groove first. After the joint is fully melted, it should be welded forward by 10-20mm and then slowly terminated to prevent shrinkage. In production,

it is often seen that joints are not polished into inclined edges, and the welding time at the joints is directly extended. This is a very bad habit, as it is easy to produce concave joints, incomplete fusion of joints, and reverse detachment

at the joints, which affects the appearance of the forming process. High alloy materials can also easily produce cracks. After welding, the appearance inspection is qualified, and the power and air must be turned off when leaving.