Arc welding is a welding method that uses the high temperature generated by an arc to melt the welding rod and workpiece, thereby achieving a metal connection. Arc welding has the advantages of simple operation, low equipment cost, and wide application range, and is widely used in mechanical manufacturing, construction, repair, and maintenance fields. The quality and efficiency of arc welding depend on the operator's techniques and methods, so it is essential to master the basic principles and standardized operations of arc welding.
I. Basic Principles of Arc Welding
The basic principle of arc welding is to use current to produce ionization between the welding rod and the workpiece in the air gap, forming a stable arc. The arc is a high-temperature plasma, with temperatures reaching thousands or even tens of thousands of degrees Celsius, capable of melting the metals of the welding rod and workpiece. The outer layer of the welding rod is coated with flux, which decomposes and melts under the action of the arc, generating shielding gas and slag to prevent oxygen and nitrogen from entering the molten pool, causing oxidation and nitriding. The core of the welding rod is a metal wire, which also melts under the action of the arc, entering the molten pool as filler metal for the weld. As the arc moves, the molten pool moves accordingly, with slag covering the surface of the molten pool to protect the metal from oxidation. When the molten pool cools, the metal solidifies, forming the weld joint, and achieving metallurgical bonding between the welding rod and the workpiece.
II. Basic Techniques of Arc Welding
The basic techniques of arc welding include arc starting, electrode manipulation, and arc extinguishing, each with its own skills and requirements that welders need to master and flexibly apply.
1）Arc Starting
Arc starting refers to the process of establishing an arc between the welding rod and the workpiece, marking the beginning of arc welding. The purpose of arc starting is to pass current through the welding rod and workpiece, generating ionization to form a stable arc. There are two methods of arc starting: scratch start and striking start.
The scratch start method involves aligning the front end of the welding rod with the workpiece, then twisting the wrist to lightly scratch the surface of the workpiece with the welding rod, lifting the rod 2-4mm to generate an arc in the air. The arc length should be maintained within the range allowed by the diameter of the welding rod. The advantage of scratch start is its ease of mastery and suitability for welding in various positions, but it can scratch the surface of the workpiece, affecting the appearance of the weld.
The striking start method involves bending the wrist downward, lightly tapping the welding rod against the workpiece, then quickly lifting it 2-4mm to form an arc. The advantage of a striking start is that it avoids scratching the surface of the workpiece and is suitable for welding with aesthetic requirements, but it is difficult to master and can lead to sticking or extinguishing of the arc.
Skills and requirements for arc starting are as follows:
Before starting the arc, check the connection of the welding equipment and power source, ensure good contact between the welding rod and clamp, and verify the dryness of the welding rod, cleanliness of the workpiece surface, suitability of the welding position, and correctness of welding parameters to ensure smooth arc starting.
Maintain an angle of 60-80 degrees between the welding rod and the workpiece during arc starting to facilitate arc stability and rod melting. The direction of rod tilt should align with the welding direction to facilitate weld formation and slag removal.
Control the lifting speed and height of the welding rod during arc starting to avoid too fast or too slow, too high or too low, which can cause arc extinguishing or short-circuiting. Generally, the lifting speed should be between 0.5-1 second, and the lifting height should be between 2-4mm, making the arc length equal to or slightly larger than the diameter of the welding rod.
After starting the arc, quickly move it to the starting point of welding to begin the process. If the arc is too long or too short, adjust the height of the welding rod promptly to maintain the arc length within the appropriate range. If the arc is unstable or extinguished, promptly re-start it to avoid arc craters or porosity in the weld.
2）Electrode manipulation
Electrode manipulation refers to the process of moving the welding rod along the welding direction and laterally under the action of the arc to melt the metal of the welding rod and workpiece, filling the weld seam. It is the main step in arc welding. The purpose of welding is to evenly melt the metal of the weld seam, forming a good weld joint. There are various techniques for welding, with commonly used ones including straight-line, circular, triangular, and Z-shaped.
The straight-line welding method involves maintaining a certain arc length during welding and moving forward without swinging. This method provides a stable arc and allows for greater penetration, suitable for welding thicker workpieces or joints requiring full penetration, but it results in narrower weld seams, prone to porosity and cracking.
The circular welding method involves continuous circular motion of the welding rod end while moving forward. This method ensures the sufficient temperature of the molten metal, facilitates the release of gases such as oxygen and nitrogen from the melt pool, and helps the slag float, suitable for flat weld seams on thicker workpieces, but it leads to wider weld seams, prone to weld beads and excessive weld height. The circular motion welding method is divided into two types: regular circular and slanted circular. The regular circular motion refers to the circular movement of the welding rod parallel to the welding direction, while the slanted circular motion refers to the circular movement of the welding rod at a certain angle to the welding direction.
The triangular welding method involves moving the welding rod end in a triangular motion while advancing. This method ensures uniform temperature distribution of the molten pool, and facilitates the release of gases and slag, suitable for flat and fillet weld seams on thinner workpieces, but it results in narrower weld seams, prone to welding defects. The triangular motion welding method is divided into two types: regular triangular and inverted triangular. The regular triangular motion refers to the triangular movement of the welding rod parallel to the welding direction, while the inverted triangular motion refers to the triangular movement of the welding rod perpendicular to the welding direction.
The Z-shaped welding method involves moving the welding rod end in a Z-shaped motion while advancing. This method widens the molten pool, facilitates weld formation and slag coverage, suitable for vertical and overhead weld seams on thinner workpieces, but it leads to wider weld seams, prone to excessive weld height and weld beads. The Z-shaped welding method is divided into two types: forward Z-shaped and reverse Z-shaped. The forward Z-shaped welding method refers to the Z-shaped motion of the welding rod parallel to the welding direction, while the reverse Z-shaped welding method refers to the Z-shaped motion of the welding rod perpendicular to the welding direction.
Skills and requirements for welding are as follows:
Maintain a certain arc length, generally 1-1.5 times the diameter of the welding rod, to ensure arc stability and rod melting. Excessive arc length leads to unstable arcs, metal oxidation in the weld seam, and poor weld formation, while insufficient arc length leads to arc extinguishing, rod sticking, metal nitriding in the weld seam, and reduced weld quality.
Control the welding rod's speed and amplitude to ensure uniform melting of the weld seam, avoiding excessively wide or narrow, high or low weld seams, which can cause welding defects. The welding rod's speed should generally match its melting rate, and its amplitude should match the width of the weld seam.
Observe the shape and size of the molten pool during electrode manipulation, and adjust the position and angle of the welding rod promptly according to changes in the molten pool to maintain its proper state. Typically, the length of the molten pool should be 2-3 times the diameter of the welding rod, its width should be 1-1.5 times the diameter of the welding rod, and its depth should be 0.5-1 times the diameter of the welding rod.
Observe the distribution and flow of slag during electrode manipulation, and adjust the welding rod's movement accordingly to ensure that the slag covers the surface of the molten pool, protecting the metal in the pool. Typically, the thickness of the slag should be 0.5-1 times the diameter of the welding rod, its width should be slightly larger than the width of the weld seam, and its flow should be consistent with the welding direction.
3）Arc Extinguishing
Arc extinguishing refers to the process of disconnecting the arc at the end of welding, marking the end of arc welding. The purpose of arc extinguishing is to allow the metal of the weld seam to cool smoothly, avoiding the formation of arc craters and porosity and other welding defects. There are two methods of arc extinguishing: increasing and retracting.
The increasing method involves gradually raising the welding rod at the end of welding to increase the arc length and reduce the current until the arc extinguishes. This method is simple to operate and suitable for welding thicker workpieces or joints requiring full penetration, but it can lead to arc craters and porosity at the end of the weld seam.
The retracting method involves slightly retracting the welding rod at the end of welding to re-melt the metal at the end of the weld seam, then quickly raising the rod to extinguish the arc. This method avoids arc craters and porosity and is suitable for welding thinner workpieces or weld seams requiring good appearance, but it is more difficult to operate and can result in excessively wide or high weld seams.
Skills and requirements for arc extinguishing are as follows:
Before extinguishing the arc, check whether the length of the weld seam meets requirements, whether the weld seam is well-formed, and whether its quality is acceptable, to ensure smooth arc extinguishing.
During arc extinguishing, maintain the angle between the welding rod and the workpiece, and avoid swinging the rod, which can cause arc instability. The direction of rod tilt should align with the welding direction to facilitate weld formation and slag removal.
Control the lifting speed and height of the welding rod during arc extinguishing to avoid too fast or too slow, too high or too low, which can cause arc instability or extinguishing. Generally, the lifting speed should be between 0.5-1 second, and the lifting height should be between 4-6mm, making the arc length slightly larger than the diameter of the welding rod.
After arc extinguishing, promptly remove the slag from the surface of the weld seam with a hammer or scraper, inspect the appearance and quality of the weld seam, and repair or re-weld if defects are found.
This article introduces the basic principles and standardized operations of arc welding, including arc starting, welding, and arc extinguishing, as well as the characteristics and application ranges of various welding techniques. The aim is to help you understand and master the skills and requirements of arc welding, improving your arc welding quality and efficiency. The article also reminds you to pay attention to safety and standards during welding, avoiding welding defects and accidents. I hope this article inspires and helps you.
