The principle of welding (용접의 원리)

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https://youtu.be/DJ5Z6cWWJaE?si=YLF_Eqz9SKDbyptD

The principle of welding is the process of joining two or more materials—usually metals or thermoplastics—by causing coalescence, typically through high heat, intense pressure, or a combination of both.

​Unlike soldering or brazing, which use a lower-melting-point filler metal without melting the base materials, welding melts the base metals themselves at the joint.

​Core Mechanics of Welding

​Melting and Fusion: Intense energy (electric arc, gas flame, laser, or friction) raises the temperature at the contact surface of the base materials beyond their melting point. The molten liquid pools merge into a single continuous mass.

​Coalescence upon Cooling: As the heat source moves away, the molten pool cools and solidifies, forming a atomic-level crystal structure that bonds the pieces into a unified part.

​Filler Material: A rod or wire is often introduced into the molten pool to supply extra volume and strengthen the joint, though some techniques (autogenous welding) rely solely on the base metal.

​Key Requirements for a Successful Weld

​Concentrated Heat Source: Provides enough energy to overcome the material's melting point without overheating the entire component.

​Shielding/Protection: At high temperatures, molten metal reacts rapidly with atmospheric gases like oxygen, nitrogen, and hydrogen, causing rust, porosity, and structural weakness. Shielding gas (e.g., argon, CO₂) or solid flux shields the weld pool from atmospheric contamination.

​Oxide Film Removal: Metals naturally form oxide layers on their surface. The heat, flux, or electrical polarity helps break down this layer so pure metal-to-metal fusion can occur.

​Main Energy Sources Used in Welding

​Electric Arc (e.g., TIG, MIG, Stick): Creates an electrical discharge between an electrode and the workpiece, generating temperatures exceeding 3,000°C–6,000°C.

​Gas Flame (Oxy-Fuel): Combines oxygen and fuel gas (like acetylene) to generate a high-temperature flame.

​Mechanical/Friction: Uses physical friction or ultrasonic vibrations to generate heat locally without fully melting the entire bulk structure.
​High-Energy Beams (Laser/Electron Beam): Focuses concentrated light or particle beams for ultra-precise, deep-penetration welds.


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