Welding is a process of joining two or more metals together through the application of heat. Welding typically involves heating a material to its melting point so that the base metal melts to fill the gaps between the joints, forming a strong connection. Laser welding is a connection method that uses laser as a heat source.
Take the square case power battery as an example: the battery core is connected by laser through multiple parts. During the entire laser welding process, material connection strength, production efficiency, and defective rate are three issues that the industry is more concerned about. The material connection strength can be reflected by the metallographic penetration depth and width (closely related to the laser light source); the production efficiency is mainly related to the processing capability of the laser light source; the defect rate is mainly related to the selection of the laser light source; therefore, this article discusses the common ones on the market. A simple comparison of several laser light sources is conducted, hoping to help fellow process developers.
Because laser welding is essentially a light-to-heat conversion process, several key parameters involved are as follows: beam quality (BBP, M2, divergence angle), energy density, core diameter, energy distribution form, adaptive welding head, processing Process windows and processable materials are mainly used to analyze and compare laser light sources from these directions.
Singlemode-Multimode Laser Comparison
Single-mode multi-mode definition:
Single mode refers to a single distribution pattern of laser energy on a two-dimensional plane, while multi-mode refers to the spatial energy distribution pattern formed by the superposition of multiple distribution patterns. Generally, the size of the beam quality M2 factor can be used to judge whether the fiber laser output is single-mode or multi-mode: M2 less than 1.3 is a pure single-mode laser, M2 between 1.3 and 2.0 is a quasi-single-mode laser (few-mode), and M2 is greater than 2.0. For multimode lasers.
Because laser welding is essentially a light-to-heat conversion process, several key parameters involved are as follows: beam quality (BBP, M2, divergence angle), energy density, core diameter, energy distribution form, adaptive welding head, processing Process windows and processable materials are mainly used to analyze and compare laser light sources from these directions.
Singlemode-Multimode Laser Comparison
Single-mode multi-mode definition:
Single mode refers to a single distribution pattern of laser energy on a two-dimensional plane, while multi-mode refers to the spatial energy distribution pattern formed by the superposition of multiple distribution patterns. Generally, the size of the beam quality M2 factor can be used to judge whether the fiber laser output is single-mode or multi-mode: M2 less than 1.3 is a pure single-mode laser, M2 between 1.3 and 2.0 is a quasi-single-mode laser (few-mode), and M2 is greater than 2.0. For multimode lasers.
As shown in the figure: Figure b shows the energy distribution of a single fundamental mode, and the energy distribution in any direction passing through the center of the circle is in the form of a Gaussian curve. Picture a shows the multi-mode energy distribution, which is the spatial energy distribution formed by the superposition of multiple single laser modes. The result of multi-mode superposition is a flat-top curve.
Common single-mode lasers: IPG YLR-2000-SM, SM is the abbreviation of Single Mode. The calculations use collimated focus 150-250 to calculate the focus spot size, the energy density is 2000W, and the focus energy density is used for comparison.
Comparison of single-mode and multi-mode laser welding effects
Single-mode laser: small core diameter, high energy density, strong penetration ability, small heat-affected zone, similar to a sharp knife, especially suitable for welding thin plates and high-speed welding, and can be used with galvanometers to process tiny parts and highly reflective parts (extremely reflective parts) ears, connecting pieces, etc.), as shown in the figure above, single-mode has a smaller keyhole and a limited volume of internal high-pressure metal vapor, so it generally does not have defects such as internal pores. At low speeds, the appearance is rough without blowing protective air. At high speeds, protection is added. The gas processing quality is good, the efficiency is high, the welds are smooth and flat, and the yield rate is high. It is suitable for stack welding and penetration welding.
Multi-mode laser: Large core diameter, slightly lower energy density than single-mode laser, blunt knife, larger keyhole, thicker metal structure, smaller depth-to-width ratio, and at the same power, the penetration depth is 30% lower than that of single-mode laser, so it is suitable for use Suitable for butt weld processing and thick plate processing with large assembly gaps.
Composite-Ring Laser Contrast
Hybrid welding: The semiconductor laser beam with a wavelength of 915nm and the fiber laser beam with a wavelength of 1070nm are combined in the same welding head. The two laser beams are coaxially distributed and the focal planes of the two laser beams can be flexibly adjusted, so that the product has both semiconductor laser welding capabilities after welding. The effect is bright and has the depth of fiber laser welding.
Semiconductors often use a large light spot of more than 400um, which is mainly responsible for preheating the material, melting the surface of the material, and increasing the material’s absorption rate of fiber laser (the material’s absorption rate of laser increases as the temperature increases)
Ring laser: Two fiber laser modules emit laser light, which is transmitted to the material surface through a composite optical fiber (ring optical fiber within cylindrical optical fiber).
Two laser beams with annular spot: the outer ring is responsible for expanding the keyhole opening and melting the material, and the inner ring laser is responsible for the penetration depth, enabling ultra-low spatter welding. The inner and outer ring laser power core diameters can be freely matched, and the core diameter can be freely matched. The process window is more flexible than that of a single laser beam.
Comparison of composite-circular welding effects
Since hybrid welding is a combination of semiconductor thermal conductivity welding and fiber optic deep penetration welding, the outer ring penetration is shallower, the metallographic structure is sharper and slender; at the same time, the appearance is thermal conductivity, the molten pool has small fluctuations, a large range, and the molten pool is more stable, reflecting to a smoother appearance.
Since the ring laser is a combination of deep penetration welding and deep penetration welding, the outer ring can also produce penetration depth, which can effectively expand the keyhole opening. The same power has greater penetration depth and thicker metallography, but at the same time, the stability of the molten pool is slightly less than The fluctuation of optical fiber semiconductor is slightly larger than that of composite welding, and the roughness is relatively large.
Post time: Oct-20-2023
