Welding Processes and Principles
1.1 Definition of Welding
Welding is the process of joining two or more materials, either similar or different, by creating atomic or molecular bonds through heating, applying pressure, or a combination of both. The methods used to facilitate these bonds include heating, pressing, or both simultaneously.
1.2 Classification of Metal Welding
Metal welding can be categorized based on the characteristics of the process into three main types: fusion welding, pressure welding, and brazing.
Fusion Welding
In fusion welding, the workpieces to be joined are heated until they melt and form a molten pool. Once the molten pool cools and solidifies, the materials are joined. This process is suitable for various metals and alloys and does not require the application of pressure. Sometimes, filler material is added to aid the welding process.
Pressure Welding
Pressure welding involves applying pressure to the workpieces to join them. This method is used for various metal materials and some non-metal materials. The application of pressure is essential for the welding process.
Brazing
Brazing uses a filler metal with a lower melting point than the base materials. The liquid filler metal wets the base materials, fills the joint gap, and diffuses into the base materials to create a bond. This method is suitable for welding different metals or dissimilar materials.In industrial production, fusion welding is the most widely used method. Typically, the welding process involves heating, melting, metallurgical reactions, solidification, crystallization, and forming joints.
1.3 What is Laser Welding?
Laser welding is a method that uses a focused laser beam as an energy source to generate heat and weld materials. Due to the optical properties of lasers, such as refraction and focusing, laser welding is particularly suitable for welding small parts and areas with poor accessibility. It also features low heat input, minimal welding deformation, and is unaffected by electromagnetic fields. Laser welding is an important application of laser material processing technology. Initially used in the 1970s for welding thin-walled materials and low-speed welding, the process involves heat conduction, where the laser radiation heats the workpiece surface, and the surface heat diffuses inward. By controlling parameters such as laser pulse width, energy, peak power, and repetition frequency, the workpiece melts to form a specific molten pool. Laser welding has been successfully applied to precision welding of micro and small parts due to its unique advantages.
1.4 Classification of Laser Welding
Laser welding can be classified based on various criteria:
1.4.1 By Control Method
- Manual Laser Welding Machine
- Automatic Laser Welding Machine
- Galvo Laser Welding Machine
1.4.2 By Laser Type
- YAG Laser Welding Machine
- Semiconductor Laser Welding Machine
- Fiber Laser Welding Machine
1.4.3 By Laser Power Output
- Low Power (≤1KW)
- Medium Power (1.5~10KW)
- High Power (>10KW)
1.4.4 By Laser Operation Mode
- Pulsed Laser Welding: Forms circular weld spots that overlap to create a seam.
- Continuous Laser Welding: Forms a continuous weld seam during the welding process.
1.4.5 By Welding Mode
- Heat Conduction Welding: Uses lower laser power density, where the laser heats the surface of the workpiece, causing it to melt and form a shallow molten pool.
- Deep Penetration Welding: Uses higher laser power density, where the laser melts and vaporizes the material, forming a keyhole that extends deep into the workpiece, creating a deep and narrow weld.
1.5 Modern Laser Welding Technology
1.5.1 Laser Fill Welding
Laser fill welding is an advanced technique that involves adding filler material during the welding process. It offers several advantages over traditional laser welding:
- Reduces the need for precise workpiece alignment.
- Controls the composition and properties of the weld area.
- Minimizes heat input, reducing thermal distortion.
- Allows welding of thicker materials with lower laser power.
1.5.2 Laser-Arc Hybrid Welding
Combining laser and arc welding, this technique leverages the high energy density and precision of laser welding with the efficiency and cost-effectiveness of arc welding. It results in high-quality welds with deep penetration and improved tolerance to joint fit-up.
1.5.3 Dual Beam Laser Welding
This method uses two laser beams, either from the same or different types of lasers, to improve welding stability and quality. It is particularly useful for welding thin sheets and aluminum alloys.
1.5.4 Laser Brazing
Laser brazing uses a laser beam to melt a filler material with a lower melting point than the base materials. It is a non-contact process that does not require pressure and is suitable for precise welding of small components.
1.5.5 Laser Spot Welding
Laser spot welding involves using a laser to create localized welds. It is highly precise and suitable for applications requiring minimal thermal distortion and high weld quality. By understanding these various welding processes and principles, one can appreciate the advancements and applications of modern welding technologies in different industries.
