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Laser Welding Process Parameters - Power, Speed, Defocus Distance, Shielding Gas

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Laser Welding Process Parameters - Power, Speed, Defocus Distance, Shielding Gas

  1. Power:

    • Definition: Laser welding power refers to the energy delivered per second by the laser beam to the workpiece surface.

    • Purpose: Power directly influences welding speed and penetration depth. Higher power accelerates the formation of the weld pool and material penetration, but excessive power may lead to overly deep or wide weld pools, affecting welding quality.

    • Adjustment: Power is adjusted based on material type, thickness, and specific welding requirements. Power adjustment is typically managed using power controllers or laser equipment control systems.

  2. Speed:

    • Definition: Welding speed is the rate at which the laser welding head moves during the welding process.

    • Purpose: Speed affects heat input and weld pool formation. Higher speeds reduce heat input, lowering weld pool temperature and size, suitable for thin materials or high-speed production applications. Lower speeds facilitate deeper material fusion, suitable for welding thick plates.

    • Adjustment: Speed is adjusted according to material thickness, desired welding speed requirements, and weld quality standards. Speed is typically controlled by the welding machine's control system or motion platform.

  3. Defocus Distance:

    • Definition: Defocus distance refers to the distance between the laser welding focal point and the workpiece surface.

    • Purpose: Adjusting defocus distance affects the size and shape of the welding focal spot, thereby influencing energy distribution and weld pool size.

    • Adjustment: Defocus distance is adjusted based on material type, welding depth requirements, and weld seam geometry. Typically adjusted using focus distance adjusters or by altering the position of the focusing lens.

  4. Shielding Gas:

    • Definition: During laser welding, shielding gas is used to protect the molten pool and weld seam from contamination by oxygen and other external gases.

    • Purpose: Shielding gas prevents oxidation and hydrogen cracking, thereby enhancing weld quality and reliability. Common shielding gases include argon, helium, and nitrogen.

    • Adjustment: Selecting the appropriate shielding gas and adjusting gas flow rate and distribution based on welding material type, process requirements, and welding environment ensures effective protection.

The laser welding system consists of a laser source, optical fiber for transmission, and collimation/focusing optics such as collimating lenses or galvanometer mirrors. The laser beam emitted from the fiber is divergent and needs to be collimated by collimating lenses to transform it into a parallel beam. It then passes through focusing lenses to achieve a focused state (using the magnifying glass effect). During the laser welding process, key parameters for adjustment include power, speed, defocus distance, and shielding gas.

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if the speed is too fast, it can result in a V-shaped characteristic like the one shown in the diagram.

Power: This refers to the laser welding power, typically set through waveform settings. Laser welding involves an energy conversion process that affects heat input and absorption. Therefore, controlling waveform and power requires substantial process experience. Different materials, thicknesses, weld seam forms, and equipment variations all necessitate attention to energy. Waveform changes can impact the variation in unit energy output. Generally, software facilitates these settings, allowing accumulation of knowledge regarding energy variations for different materials. Experience is crucial in crack control; for butt welding, the metallographic features correspond to fusion depth and width. If fusion depth and width are too small, increase energy; if too large, reduce energy.

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Different power levels directly affect penetration depth, as shown in the metallographic diagram for different energy powers.

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Energy levels that are too low often result in spot welding or lack of fusion, as shown in the diagram, where only a thin surface layer melts and the penetration depth is shallow, making it difficult to meet process requirements.

Defocus amount: Initially, the laser beam does not have uniform energy distribution at every position. The energy is most concentrated at the focal point where the spot size is smallest (the laser acts on a smaller area, concentrating energy). Therefore, all parameter adjustments need to be made after determining the focal point to be meaningful. Finding the focal point is crucial and technically demanding.

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Protective gas: There are many types of protective gases used in industrial applications. For cost control on production lines, nitrogen is commonly used, while laboratories primarily use argon, with some using helium or other inert gases for specific purposes. During laser welding, which involves high-temperature and intense reactions where metals melt and evaporate, metals become highly reactive at high temperatures. If exposed to oxygen, this can lead to vigorous reactions, resulting in spattering and a rough, uneven weld surface. Therefore, protective gas is used to create an oxygen-free environment in the vicinity of the molten pool during welding. This prevents intense oxidation reactions that can lead to poor weld quality and rough external surfaces of the weld bead.

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Excessive protective gas can blow away the molten pool, while insufficient gas fails to shield the molten pool from oxygen effectively. It's essential to adjust the protective gas according to the specific conditions on-site to achieve optimal results.


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