I. Core Welding Principle: Energy Conversion and Material Melting
Heat conduction stage: At low power or short exposure, heat transfers through the material by conduction, causing surface softening.
Melting stage: Sufficient energy creates a molten pool through local material melting.
Vaporization stage (in keyhole welding): High power density vaporizes the material, forming a "keyhole" that allows the laser to penetrate deeply, creating a weld with a high depth-to-width ratio.
II. Key Components and Their Functions
Laser Generator: Produces high-energy laser beams, determining power (e.g., 100 W–10 kW) and wavelength (e.g., 1064 nm for fiber lasers, 10.6 μm for CO₂ lasers).
Optical System: Includes lenses, mirrors, and galvo scanners to focus the beam and control spot position/shape, impacting welding accuracy and efficiency.
Motion System: Comprises servo motors and guides to move the workpiece or laser head, enabling trajectory control (linear, curvilinear, 3D welding).
Cooling System: Water or air cooling prevents overheating of the laser generator and optical components, ensuring stable operation.
Control System: Integrated software (e.g., PLC, specialized welding software) sets parameters (power, speed, pulse frequency) and monitors the process.
Shielding Gas System: Delivers inert gases (argon, nitrogen) or reactive gases (CO₂) to protect the molten pool from oxidation and improve weld quality.
III. Main Welding Modes and Characteristics
Low power density (<10⁵ W/cm²) allows heat to transfer through conduction, forming a shallow, wide molten pool. Ideal for thin materials (<1 mm), it yields smooth welds with minimal deformation, suitable for electronics and precision parts.
High power density (>10⁵ W/cm²) vaporizes material to create a "keyhole," letting the laser penetrate deeply. The keyhole moves with the laser, and the molten pool solidifies into a deep-narrow weld. This suits thick materials (1–20 mm), such as automotive bodies and aerospace components, with fast speed and a depth-to-width ratio up to 10:1.
IV. Critical Welding Parameters
Laser Power: Determines energy input. Higher power enables deeper penetration for thick materials, while insufficient power causes incomplete welds.
Welding Speed: Must match power. Excessive speed leads to incomplete fusion, and too slow a speed expands the heat-affected zone and causes deformation.
Spot Diameter: Affects energy density. Smaller spots concentrate energy for fine welding.
Pulse Frequency and Width (for pulsed lasers): Control heat input to minimize thermal deformation in thin or heat-sensitive materials.
Defocus Distance: The distance between the laser focus and workpiece surface. Positive defocus (focus above the surface) suits surface welding, while negative defocus (focus inside the material) is for deep penetration.
V. Material Adaptability and Applications
Suitable Materials:
Metals: Stainless steel, carbon steel, aluminum alloy, copper, titanium alloy, nickel alloy, and dissimilar materials (e.g., copper-aluminum).
Non-metals: Certain plastics and ceramics (with specialized equipment).
Typical Applications:
Manufacturing: Automotive parts (body, battery cases), electronics (circuit boards, connectors), aerospace (engine components).
Medical: Precision welding of catheters and implantable devices.
New energy: Welding of lithium battery tabs and photovoltaic modules.
VI. Advantages and Limitations of Laser Welding
Advantages:
Concentrated energy enables high-speed welding and minimal heat-affected zones, reducing deformation.
Non-contact processing avoids mechanical damage to workpieces, suitable for hard-to-reach areas.
High precision and consistent weld quality, ideal for mass production.
Wide material adaptability, including dissimilar materials.
Limitations:
High initial equipment cost, making it less suitable for small-batch production.
Strict requirements for workpiece fit-up and surface cleanliness.
Complex maintenance for optical systems and laser generators.
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Ryder