Comparison of single fiber, annular light, blue light, green light, red and blue composite welded copper alloy
Continued from the previous book: several points why copper alloys are difficult to weld have been introduced: high thermal conductivity (fast heat dissipation), high reflection (low laser absorption), and large fluctuations in absorption rateThese characteristics can lead to defects such as false welding, spatter, porosity, and poor appearance forming
As shown in the figure, you can clearly see the spatter and porosity caused by the instability of the copper welding process, these two defects are most common in the laser welding process of copper
Splash formation mechanism: spatter droplet force analysis: in the process of deep penetration welding of copper alloy, the spatter droplet is mainly affected by the surface tension of the liquid, its own gravity, and the upward shear force given by the high-pressure metal vapor in the keyholeThe shear force is dominant. Generally, the splash is mainly generated from the edge of the keyhole opening, and the flying out is mainly the droplet at the edge of the keyhole, with the fluctuation of the molten pool, once it emerges from the keyhole, it will directly face the metal vapor that erupts violently upward, and is subjected to shear force in the vertical direction, overcoming the surface tension and its own gravity to fly out of the molten pool to form a splash.
Porosity formation mechanism: keyhole type porosity is mainly caused by the instability of the keyhole in the laser welding process, because the keyhole is hollow, once the keyhole collapses as shown in Figure E, the liquid molten pool will close the keyhole, and the metal steam will be rolled into the molten pool, when the metal steam can not escape from the surface of the copper molten pool in time and solidify in the molten pool, it will form a porous hole with a larger diameter in the weld.
In order to solve these defects that often occur in copper alloys, there are several technical solutions on the market, namely fiber laser swing welding (single-mode 14um, multi-mode within 50um), annular spot 100), blue light, green light, red and blue composite, next, briefly introduce the advantages and limitations of various processes, and then have the opportunity to detail the defect suppression mechanism and application scenarios of each technical route in a single article.
Fiber laser swing welding.
Material**: Effects of sidewall grain growth on pore formation in narrow gap oscillating laser welding
Laser oscillation relieves stomata.
Advantages of fiber laser swing welding:
Fiber swing is the most cost-effective solution at present, that is, the process window needs to be groped and explored, the main core diameter of the commonly used laser is in the range of 14-50um, 2kw-6kw, mainly for the connection with an effective penetration depth of less than 1mm, which is the best single-mode laser effect, and the single-mode laser in the general lithium battery industry has more single-mode applications, and the conventional one is 1kw, 2kw, the maximum power can reach 3kw, the small core diameter can provide a high enough laser energy density, can instantly melt the copper alloy, and avoid the initial virtual welding;
At the same time, the small core diameter can also be matched with the swing welding head and galvanometer welding head to realize the welding of various swing trajectories, which can expand the weld pool, stabilize the keyhole, help the gas overflow, make the welding process more stable, and reduce spatter and porosity
Deficiencies: The power of single-mode market-oriented products is limited, and the non-oscillating pores cannot be avoided, in order to achieve high line energy heat input and achieve large penetration, low-speed welding is extremely unstable (the keyhole is too small and easy to collapse), the oscillating comprehensive travel speed, and the penetration depth is limited, generally at 0Within 5mm;Commonly used for 0Overlapping welding and butting within 5mm, the speed can reach about 40mm s;
Ring spot welding:
Material**: IPG
Ring spot, because it was the earliest coherent launch of related technology products, adjustable ring mode laser (ARM), each manufacturer has its own naming method, the market of point ring laser, ring mode laser, The ring spot has one meaning, the principle is universal: it is mainly composed of two fiber laser composites, different from fiber semiconductor composites, the outer ring laser also belongs to the fiber laser with high power density, which is responsible for heating the base metal while expanding the keyhole opening, and the high power density of the inner ring laser is used to penetrate the metal to achieve deep penetration welding(Optical fiber semiconductor composite is less used in copper welding because semiconductors are both red light and have a much lower power density, so they basically do not play a role in heating copper substrates.) ）
Ring-spot welding stabilizes the enlarged keyhole opening.
As shown in the figure, this is a real-time diagram of the keyhole of the molten pool taken directly above the annular spot welding, which can be seen that the annular spot can effectively expand the keyhole opening, improve the stability of the welding process, and at the same time expand the area of the molten pool, reduce the solidification speed of the molten pool, which is conducive to the escape of the pores and reduce the porosity of the weld.
Annular spot swing welding.
At the same time, the adjustable ring die laser can also add swing, the swing welding process is more stable as shown in the figure, basically no spatter, can effectively reduce the incidence of spatter in the copper alloy welding process, and provide a variety of core diameter and power combinations, the current single mode ring (14 100) and 50 150 core diameter combination (IPG AMB 5000-5000) can achieve stable and efficient processing of copper alloy within 5mm;The processing speed is about 50mm s (stable penetration depth 4.).About 5mm), annular multi-power matching has become the mainstream technology of copper laser welding.
The infrared laser is mainly in the above two directions, and the next is a brief introduction to the new technical route of short-wave laser
The use of red light for welding still cannot avoid the instability of heat input caused by the drastic change of thermal conductivity and absorption rate of copper alloy due to solid-liquid transformation, so some companies have begun to try short-wave and multi-wave solutions.
Advantages of short-wave welding: Assuming a 6 kW infrared laser is used as the heat source and pure copper is heated at room temperature, then an absorption rate of 5% means a heating effect of 300W. If you use 450nm blue light to heat, the absorption rate is 65%, and to get the same heating effect, only 300W 65% 461W is required. However, when the material reaches the "solid-liquid" melting point, the increase in absorption rate and the decrease in thermal conductivity will increase the heating effect by about 20% (heat dissipation decrease, absorption rate increase). This extra 20% heating effect means an extra 1200W of heating power for a 6kW infrared laser, which will cause the processing state to become extremely unstable, and the accumulated heat will instantly reach the boiling point of the next stage of vaporization, producing copper metal vapor, causing boiling and splashing. (This paragraph is referenced from industry boss Gu Zheng (Blu-ray application article published by Shanghai Hanyu Optical Fiber Communication Technology *** in 2019, you can contact the author in the background if you need documents).
Blue laser welding
The absorption rate of copper to blue laser is more than 47%, taking the blue light faucet laserline as an example, the current maximum power of blue light can be 4kw, the core diameter is about 600um, and the lowest core diameter can reach 400um, laserline should represent one of the highest levels of blue light at present
Material**: Laserline official website.
Blue light thermal conductivity (material**: laserline).
Blu-ray welding hairpin motor (material**: laserline).
Advantages: As shown in the figure above, the high absorption rate and large spot of blue light can achieve large gap compatibility with hairpin flat wire motors, and at the same time, the high absorption rate, the welding process is very stable, there is basically no heat input fluctuation, and it can basically achieve zero spatter and high-speed welding, and it is generally not easy to have faults in foil welding, and it is also very potential in low spatter and high-speed welding. At the same time, copper also has advantages in the welding of dissimilar materials, which can weld dissimilar materials with fewer defects.
Disadvantages: blue laser absorption rate is high, but it belongs to direct semiconductor laser, the beam quality is relatively poor, the minimum core diameter can be 400um, compared with green light can be about 50um, red light can be done 14um, so blue light is mainly used for thermal conduction welding, suitable for copper alloy splicing within 1mm, can not achieve overlap welding penetration welding;
At the same time, due to the large core diameter, blue light is generally difficult to use galvanometer for matching and welding, mainly with the collimation welding jointThe blue light heat-affected zone is large (large spot) and may involve the deformation of the material to consider.
Green laser welding technology:
Green light should be one of the newer technologies, only developed in recent years, the current market there are two main companies to provide green laser products, the highest power of green light is 3kw, has been realized in the processing application of high reflective materials;
Advantages: The absorption rate of copper alloy for green light laser is about 40%, which is nearly 10 times higher than the absorption rate of copper alloy for red light of 3-5%.Compared with blue light, the core diameter of green fiber can be smaller than that of blue light, which can reach about 50um, so that the laser energy can be concentrated on the surface of the material, and can be matched with galvanometers for long-distance flight weldingThe green laser is suitable for thermal conductivity and deep penetration welding of copper alloys within 2mm.
Disadvantages: The main reason is the cost, because the new product has just come out and there are few applications, and there are many places where it is necessary to verify the reliability and stability, including the performance of the laser in all aspects.
Green light applications. It can be clearly seen that the green light welded copper alloy has obvious keyholes, indicating that the green light can achieve deep penetration welding of copper alloys, and at the same time, the green light swing can achieve more stable processing in the welding process and achieve low spatter and low defect welds.
Red and blue composite laser welding
Material**: Laserline official website.
Advantages: In view of the fact that blue light cannot achieve deep penetration welding, and the light spot is large, it is thought of using blue light and red light for compounding, red light can achieve small core diameter and high power to play the penetration depth, and blue light uses the high absorption rate of copper to quickly melt to provide the absorption rate of red light, and at the same time, the large spot of blue light can also expand the molten pool, delay the solidification of the molten pool, and achieve low spatter, low porosity and high-quality welding to a certain degree.
As shown in the figure: the upper part is pure blue light thermal conduction welding, and the lower part is red and blue composite, and the keyhole in the middle of the molten pool can be clearly seen, indicating that the red and blue composite can quickly and stably form a keyhole, transition from thermal conductivity to deep penetration welding, and achieve a larger weld depth-to-width ratio, that is, greater penetration depth and connection strength.
Source: laserline
As shown in the figure above, relying on the super penetration power of infrared laser, it can achieve stable processing of copper alloy within 3mm, and the red and blue composite energy is comparable to that of the ring spot.
At the same time, the red and blue composite of this composite heat source has many advantages and heat source composite form also comes from the function of the welding joint, this piece is very gratifying, the country is in a leading position, Jiaqiang can provide the red and blue composite head, swing composite head, is also developing the galvanometer composite head: plus the swing makes the red and blue heat source with a larger window and play space, for dissimilar material welding, unequal thickness material welding, Heat-sensitive materials can flexibly allocate energy to the heat source, and there are many advantages, which will be introduced in a special article in the future.
Material**: Hall laser (blue light is more professional).
Hall laser is applied to the welding of some dissimilar materials, and the effect is good, and it can be seen that there is no obvious segregation of the weld metallographic, because the absorption rate of blue light by dissimilar materials and the action of low-power blue light are more difficult to generate intermetallic compounds, which makes the weld quality higher.
For a more detailed analysis, there will be time to update it slowly in the future, and I hope that my colleagues will give me more advice if there is something wrong.
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2. The material part of this article is on the Internet, if there is any infringement, please contact to delete;
3. With the development of lithium battery, photovoltaic and laser, more and more engineers have begun to contact lasers, considering that laser technology is an extremely practical technology, the current lack of relevant Xi information on the market, this is aimed at disseminating the relevant basic knowledge of laser process application and promoting the development of the industry.