Introduction to the characteristics, advantages and disadvantages of arc welding

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1. What is arc welding?

Arc welding is a welding technique that melts and joins metals by creating a high-temperature arc between an electrode and a metal workpiece. The high temperatures generated by arc melt the metal and form a strong welded joint. To protect the welding area from oxygen and other contaminants in the air, a flux or shielding gas is often used. Arc is widely used, including electrode arc, tungsten inert gas welding (TIG), metal inert gas welding (MIG), etc., and is suitable for welding various metals, such as steel, aluminum, copper, etc. It is widely used in sectors such as manufacturing, construction and the automotive industry, providing a strong, long-lasting connection.

2. Principle of arc welding

The welding arc is powered by a welding power source. Under a certain voltage, a strong and lasting discharge occurs between the electrode (or the end of the welding wire or welding rod) and the workpiece. The essence of the welding arc is gas conduction, that is, the neutral gas in the space where the arc is located decomposes into positively charged positive ions and negatively charged electrons under a certain voltage, which is called ionization. These two charged particles move toward the two poles respectively. Directional movement causes the local gas to conduct electricity and form an arc. The arc converts electrical energy into thermal energy, heating and melting metal to form a welded joint.

Because after the arc is induced and “ignited”, the discharge process itself can produce charged particles required to maintain the discharge, which is a self-sustaining discharge phenomenon. Moreover, the arc discharge process has low voltage, high current, high temperature and strong luminescence. With the help of this process, electrical energy is converted into thermal energy, mechanical energy and light energy. Welding mainly uses its thermal energy and mechanical energy to achieve the purpose of joining metals.

During welding, the arc burns between the welding rod and the workpiece to be welded, causing the workpiece to be welded and the core of the welding rod to melt to form a molten pool. At the same time, the electrode coating is also melted and reacts chemically to form slag and gas, which protects the end of the electrode, the molten droplets, the molten pool and the high-temperature weld metal.

3. Arc welding category

Common arc methods mainly include electrode arc welding (SMAW)submerged arc welding (SAW), gas tungsten arc welding (GTAW or TIG welding), plasma arc welding (PAW) and gas metal arc welding (GMAW or MIG). welding, MAG welding), etc.

(1) Electrode arc welding

Welding rod arc uses the welding rod and the workpiece as two electrodes. During welding, the heat and blowing force of the arc are used to locally melt the workpiece. At the same time, under the action of arc heat, the end of the welding rod melts to form droplets, and the workpiece is partially melted to form an oval-shaped pit filled with liquid metal. The melted liquid metal of the workpiece and the droplets form a molten pool. During the welding process, the coating and non-metallic materials The inclusions melt with each other and undergo chemical changes to form a non-metallic substance called slag covering the surface of the weld. As the arc moves, the molten pool cools and solidifies to form a weld.

(2) Submerged arc welding

Submerged arc is a method of welding where the arc burns under a layer of flux. The metal electrode used in submerged arc is a bare welding wire that is automatically fed without interruption. During the welding process, a welding trolley or other mechanical and electrical devices are generally used to realize automatic movement of the arc. The arc of submerged arc is buried under the granular flux and burns. The arc heat causes the part of the workpiece where the arc directly acts, the end of the welding wire and the flux to melt and evaporate. The gases evaporated by the metal and flux form a closed cavity around the arc. Burns in this cavity. The cavity is surrounded by a slag film composed of slag produced by melting the flux. This slag film not only well isolates the air from contact with the arc and molten pool, but also prevents arc light from radiating out. The welding wire heated and melted by the arc falls in the form of droplets and mixes with the molten workpiece metal to form a molten pool. The less dense slag floats on the molten pool. In addition to mechanical isolation and protection of the molten pool metal, the slag also undergoes a metallurgical reaction with the molten pool metal during the welding process, thus affecting the chemical composition of the weld metal. As the arc moves forward, the molten pool metal gradually cools and crystallizes to form a weld. After the molten slag floating on the upper part of the molten pool cools, a slag shell is formed to continue to protect the weld at high temperatures and prevent it from being oxidized.

(3) Tungsten arc welding

Tungsten argon arc refers to an arc method that uses tungsten or tungsten alloy (thorium tungsten, cerium tungsten, etc.) as the electrode and argon gas as the protective gas. It is referred to as TIG welding or GTAW welding. During welding, filler metal may or may not be added depending on the groove form of the weld and the performance of the weld metal. Filler metal is usually added from the front of the arc. Due to the special characteristics of aluminum, magnesium and its alloy materials, AC tungsten arc is required for welding, while DC tungsten arc is used for other metal materials. In order to control the heat input, pulsed tungsten arc is increasingly used.

(4) Plasma arc welding

Plasma arc is a special form of arc. This arc also uses tungsten or tungsten alloy (thorium tungsten, cerium tungsten, etc.) as the electrode of the arc, and uses argon as the protective gas. However, the tungsten electrode does not extend out of the nozzle, but retracts in. Inside the nozzle, the nozzle is water-cooled, also called a water-cooled nozzle. The inert gas is divided into two parts. One part is the gas ejected between the tungsten electrode and the water-cooling nozzle, which is called ion gas; the other part is the gas ejected between the water-cooling nozzle and the protective gas cover, which is called the ion gas. Shielding gas, using plasma arc as a heat source, can be used for welding, cutting, spraying and surfacing, etc.

(5) Gas metal arc welding

Gas metal arc means that the welding wire replaces the tungsten electrode. The welding wire itself is one pole of the arc, which plays the role of conduction and arc burning. At the same time, it serves as a filling material, which is continuously melted and filled into the weld under the action of the arc. The commonly used protective gas around the arc can be the inert gas Ar, the active gas CO2, or the Ar+CO2 mixed gas, etc. Gas metal arc using Ar as the shielding gas is called MIG welding; gas metal arc using CO2 as the shielding gas is called CO2 welding.

4. Advantages of arc welding

Arc welding is a welding method widely used in industry and manufacturing and offers numerous advantages. Here is a more detailed description of these advantages:

(1) Versatility:

Arc welding works on a variety of metals and alloys, including steel, stainless steel, aluminum, copper, and more. This means it can be used in a variety of applications, from construction to automotive manufacturing to marine and aviation.

(2) High efficiency:

The high temperatures generated by arc can quickly melt metal and significantly shorten welding time. This high efficiency is particularly suitable for industries that require rapid production and large-scale manufacturing.

(3) Welding strength:

The arc temperature produced by arc can be as high as several thousand degrees Celsius, which is enough to penetrate deep into the metal and form a strong weld. The welded connection is usually stronger than the base material itself, ensuring the stability and safety of the structure.

(4) Diversity:

There are many different methods of arc, including stick arc (SMAW), metal inert gas welding (MIG), tungsten inert gas welding (TIG), submerged arc (SAW), etc. These methods allow the welder to choose the best welding method based on specific needs.

(5) Economical and affordable:

The cost of equipment and consumables for arc is relatively low. Rod arc, in particular, can be widely used in small-scale businesses or personal projects due to its simple equipment and wide range of consumables.

(6) Portability:

Some arc equipment is small, lightweight and easy to carry. This portability makes arc particularly useful on construction sites, maintenance sites or mobile construction.

(7) Various welding positions:

Arc can be performed in a variety of positions, including flat, vertical, horizontal and overhead welding. This flexibility makes arc very practical on complex structures and construction projects.

(8) Stable welding quality:

Using appropriate welding techniques and equipment, arc can achieve high-quality welds that meet the requirements of multiple industry standards and specifications.

(9) Various welding applications:

In addition to traditional manufacturing and construction applications, arc is also used in pipe welding, shipbuilding, pressure vessels and the aerospace industry, among others.

5. Disadvantages of arc welding

Arc welding defects refer to shortcomings or imperfections that may occur during the welding process or in the welding result, and these defects may affect the quality and performance of the welded joint. The following are common defects in arc:

(1) Weld cracks:

Cracks may appear in welds due to stress concentrations in the weld area, thermal shock, or material defects. Cracks can weaken the welded joint, leading to potential structural failure.

(2) Slag inclusion:

During the welding process, residues of flux or welding rod may be trapped in the weld, forming slag inclusions. This defect can cause weld discontinuities and weaken the strength of the welded joint.

(3) Not fused:

When the arc temperature is insufficient or the welding speed is too fast during the welding process, lack of fusion may occur. This means that the weld is not completely fused to the base material, resulting in an unstable welded joint.

(4) Stomata:

During arc, air or other gases can become trapped in the molten metal, forming pores. These pores can weaken the integrity of the weld and increase the risk of stress concentrations.

(5) Irregular shape of weld:

Welds may have irregular shapes, such as excessive bulges or depressions, due to welding technique or equipment problems. This irregularity affects the appearance and performance of the welded joint.

(6) Welding spatter:

During the arc process, metal spatter may cause the surface of the welding area to be rough and affect the quality of the weld. This may also require additional cleaning and sanding.

(7) Welding flash:

When there is too much welding material during the welding process, welding spatter may form. Weld flash results in irregularly shaped welds that may require additional grinding and treatment.

(8) Welding heat affected zone defects:

The high temperatures of arc can cause microstructural changes in the base material near the weld area, resulting in increased hardness or stress concentrations. This may affect the performance and fatigue resistance of the welded joint.

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