Welding principle of Shielded Metal Arc Welding (SMAW)

SMAW, also be well known as electrode arc welding, is a fusion welding method in which the arc is induced by the electrode and the welding parts are melted by the arc heat. It is the most widely used and common welding method at present.

Worker making sparks while welding steel

Arc is an air conduction phenomenon. The welding arc is a strong and persistent discharge phenomenon generated in the gas medium between the electrode and the workpiece. During the welding process, the electrode and the weldment are respectively connected to the two electrodes of the welding power source. When the welding core of the electrode contacts the surface of the weldment, the circuit is turned on, and a large short-circuit current is generated at the same time. Since there is a certain resistance at the contact, according to Q=I2Rt, a large amount of heat will be generated there, and the heat will rapidly heat up and melt the contact. When the electrode is lifted by 2~4mm, the gas medium between the electrode and the weldment is ionized, producing conductive electrons and positive ions. Under the action of the electric field, the electrons move to the anode, and the positive ions move to the cathode. They collide and recombine continuously, converting kinetic energy into heat energy, thereby generating strong light and high heat, and forming an arc between the end of the electrode and the weldment.

Principles of MAW01-Tianqiao

​​The arc melts the end of the electrode and the corresponding weldment at the same time. The weld metal melts to form a molten pool, and the electrode metal melts to form a droplet. The molten droplets enter the molten pool under the action of gravity and arc blowing force, fuse with the metal of the weldment, and form a weld after solidification. During the welding process, the coating melts to form slag and a large amount of gas is generated, which protects and metallurgically treats the molten pool metal.

The welding arc consists of three parts: the cathode area, the anode area and the arc column area. The cathode area emits electrons, and the temperature is low, about 2400K; the anode area accepts electrons, and the temperature is high, about 2600K; the center temperature of the arc column area is the highest, about 6000~8000K.

Principles of MAW04-Tianqiao

When using DC arc welding power source (such as arc welding rectifier) ​​for welding, there are two connection methods: positive connection and reverse connection. Positive connection is the connection method in which the electrode is connected to the negative electrode and the workpiece is connected to the positive electrode. Since the positive electrode accepts electrons and generates more heat, the weldment is easy to penetrate, so this connection method is often used for welding thicker workpieces. Reverse connection is the connection method in which the electrode is connected to the positive electrode and the workpiece is connected to the negative electrode. Since the heat generated by the electrons emitted by the negative electrode is less, the weldment is not easy to burn through, so this connection method is often used for welding thin workpieces.

Principles of MAW02-Tianqiao

The heat generated by the welding arc is proportional to the product of the arc voltage and the welding current (ie, Q=IUt). Usually, the voltage between the weldment and the electrode when the arc is stably burned is called the arc voltage, and the arc voltage is usually in the range of 20~35V. Because the arc voltage changes little, the arc heat is mainly adjusted by adjusting the welding current in production.

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Post time: Dec-30-2022

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