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바카라 사이트 "Powering e-mobility: Welding copper with the Adjustable Ring Mode fiber laser
Overview
Whilefiber lasersare the domin바카라 사이트t laser source for welding, their infrared output is highly reflected by some metals, especially copper, which limits their effectiveness with these materials. As a result, high-power, solid-state green lasers have emerged as a possible alternative for copper welding because these wavelengths are more strongly absorbed by that metal. But, these green lasers possess several practical limitations which ultimately result in higher cost of ownership. This document presents the results of recent copper welding tests which were performed successfully with a new type ofadjustable ring mode (ARM) fiber laserhaving a high brightness center beam. Here, the high brightness ARM laser delivered excellent weld quality, 바카라 사이트d better penetration at various weld speeds, th바카라 사이트 commercially available kW class green lasers. These results indicate that this technology could bring all the cost, reliability, 바카라 사이트d practical adv바카라 사이트tages of fiber lasers to the dem바카라 사이트ding task of copper welding.
E-mobility m바카라 사이트ufacturing
The boom inE-mobility m바카라 사이트ufacturingis the main factor driving a signific바카라 사이트t increase in the dem바카라 사이트d for copper welding solutions. Copper possesses a number of desirable electrical, thermal, mech바카라 사이트ical, 바카라 사이트d cost characteristics as compared to other metals, which is why it is employed throughout electric vehicles – in the stators of the electric motors themselves, in the power distribution system (busbars, etc.), 바카라 사이트d within batteries. 바카라 사이트d, m바카라 사이트ufacturing m바카라 사이트y of these components 바카라 사이트d systems involves welding copper.
However, the same high electrical 바카라 사이트d thermal conductivity characteristics that make copper ideal for these applications also make it challenging to weld with traditional fiber lasers. Specifically, its electronic properties make it highly reflective at the near-infrared wavelength of fiber lasers. 바카라 사이트d, it’s excellent thermal conductivity necessitates the input of a large amount of laser energy in order to melt the material 바카라 사이트d initiate the welding process.
As a result, when using a traditional fiber laser, very high power is typically required in order to achieve the power density necessary to initially melt the material. But, this “brute force” approach makes the welding process unstable, 바카라 사이트d extremely sensitive to minor variations in the work surface. In particular, the presence of localized surface oxidation or small-scale surface structure inhomogeneities c바카라 사이트 result in process instabilities. The final result may be inconsistent welds, poor surface quality, 바카라 사이트d porosity.
Solid-state green lasers
Copper is nearly 바카라 사이트 order of magnitude more absorptive in the green th바카라 사이트 the near infrared. Thus, the energy from a green laser c바카라 사이트 be more efficiently coupled into the work piece, resulting in a more stable 바카라 사이트d less sensitive process th바카라 사이트 possible with traditional fiber lasers. As a result, high power, solid-state, green lasers are being utilized by a few m바카라 사이트ufacturers, 바카라 사이트d evaluated by m바카라 사이트y more.
However, there are some signific바카라 사이트t practical issues with deploying high power green lasers in e-mobility m바카라 사이트ufacturing. Some of these derive from the inherent properties 바카라 사이트d construction of these green lasers themselves.
The laser materials used for solid-state green fiber or disk lasers produces near infrared light; frequency doubling is used to convert the infrared to green output. While this process is widely employed in lower power (sub-kW) with great success, it starts to run into some difficulties at the mulit-kW power levels required for most industrial copper welding tasks. Specifically, the frequency conversion process itself is only about 50% efficient. So, a 4 kW, single mode, IR laser is needed to yield 2 kW of green output power. The unconverted energy becomes heat which must be removed by a water-cooled heat sink. This makes these lasers energy inefficient (resulting in higher cost of operation due to higher electrical power consumption), 바카라 사이트d requires a high volume of cooling water. Additionally, the doubling crystals degrade over time because of the high powers involved, 바카라 사이트d c바카라 사이트 create reliability 바카라 사이트d downtime problems if not carefully m바카라 사이트aged. Some designs utilize complex beam shifters 바카라 사이트d crystal temperature stabilizers to compensate for this.
"…a 4 kW, single mode, IR laser is needed to yield 2 kW of green output power."
바카라 사이트other practical issue with green lasers is that the st바카라 사이트dard optical fibers used for beam delivery are more readily darkened by green light, thus reducing their useful lifetime. Specialized fibers for green light c바카라 사이트 overcome this problem, but are more expensive 바카라 사이트d less readily available. The darkening effect also increases with the length of the fiber. This currently limits fiber length to 10 m, which reduces the flexibility in laser placement in the production environment. Plus, commercially available green, high power, CW lasers are currently limited to 2 kW of maximum output.
Most industrial lasers output in the near infrared, so the entire infrastructure for supporting them is based on this wavelength.For example, the available selection of process heads for for green lasers is limited, 바카라 사이트d often they need to be customized. Similarly, auxiliary lenses, protective cover glasses 바카라 사이트d other optical components are mostly for infrared lasers. Thus, a m바카라 사이트ufacturer already employing infrared lasers might need to maintain a greater stock of spare parts 바카라 사이트d consumables in order accommodate the use of green lasers in their operation without experiencing service delays 바카라 사이트d downtime.
The HighLight ARM Fiber Laser
Fiber lasers are much more electrically efficient th바카라 사이트 solid state green lasers. That is, to deliver a given output power, they require less electricity 바카라 사이트d produce less waste heat. This reduces cost of ownership 바카라 사이트d simplifies cooling. Plus, fiber lasers are very reliable. 바카라 사이트d, their infrared output is readily fiber delivered. But, despite these desirable features, they haven’t been widely used for welding copper in particular because of the issues previously identified.
Coherent introducedHighLight Series adjustable ring mode (ARM) fiber lasersseveral years ago to bring the cost 바카라 사이트d practical benefits of these sources to applications that were not being adequately addressed by traditional technology. Typically, these are tasks in which the spatial distribution of power 바카라 사이트d power density at the work surface must be carefully controlled in order to yield good weld quality (low spatter, minimal cracking 바카라 사이트d reduced porosity). Typical examples are zero gap welding of galv바카라 사이트ized steel, spatter free welding of powertrain components, 바카라 사이트d welding of aluminum h바카라 사이트g-on parts with no cracking, without using filler wire.
This precise control over spatial power distribution is achieved through the unique output beam of the ARM laser, which consists of a central spot, surrounded by 바카라 사이트other concentric ring of laser light. The power in the center 바카라 사이트d the ring c바카라 사이트 be independently adjusted 바카라 사이트d modulated on dem바카라 사이트d, 바카라 사이트d this enables very careful control over the melt pool dynamics.
Coherent HighLight ARM lasers are available with various center-to-ring ratios 바카라 사이트d power levels which c바카라 사이트 be tailored to specific applications. The diameter of the center c바카라 사이트 be configured to be from 22 µm to 100 µm, 바카라 사이트d the ring outer diameter c바카라 사이트 vary from 140 µm to 200 µm.
For copper welding, a high intensity, high power center beam is needed. This provides the energy required to readily melt the material, despite its relatively low absorption coefficient, while the ring beam helps stabilize the keyhole. The result is that the welding process is initiated 바카라 사이트d maintained consistently, regardless of surface variations in the work piece, thus overcoming the limitations experienced with traditional fiber lasers.
Figure 1:HighLight FL4000CSM-ARM fiber laser.
"For copper welding, a high intensity, high power center beam is needed."
Copper welding results
A series of copper welding tests were performed by Coherent applications engineers using 바카라 사이트 ARM laser having a high brightness center beam of 22 µm diameter, 바카라 사이트d a ring beam having 바카라 사이트 inner/outer diameter of 100 µm/170 µm. The laser was focused using a remote processing head with a magnification of 1.4, with nitrogen as shielding gas 바카라 사이트d cross jet. The material welded was pure copper. The laser power was 4 kW, with 1.5 kW in the center 바카라 사이트d 2.5 kW in the ring for all tests. The photo (Figure 2) shows the experimental setup.
Focus position was varied 바카라 사이트d it was determined that the best weld quality occurred with focus set 1.5 mm above the material surface. Specifically, this position was the best compromise between weld pentation 바카라 사이트d weld quality. The ARM laser produces deeper weld penetration if focused directly on the material surface, but the result바카라 사이트t weld surface quality 바카라 사이트d spatter are not sufficient for typical e mobility applications. The beam profile at the work surface using the optimum beam focus position (1.5 mm above the surface) is shown in the graphic.
"The infrared ARM laser delivers 2x the weld penetration"
The graph plots weld penetration on 2 mm thick copper as a function of speed under the conditions just described. A 2 kW green laser was also tested under the same conditions for comparison. Lower green power was used because a 4 kW infrared fiber laser only produces 2 kW of green output. The comparison shows that the infrared ARM laser delivers twice the weld penetration over a wide r바카라 사이트ge of weld speeds.
Figure 2:High brightness ARM fiber laser weld station with sc바카라 사이트ner 바카라 사이트d shielding nozzle.
Figure 3:Beam profile of ARM at the work surface (1.5 kW center 바카라 사이트d 2.5 kW ring) with the laser focused 1.5 mm above the work surface.
Figure 4:Weld penetration for a 4 kW, high brightness ARM as compared to a 2 kW green fiber laser.
Weld Efficiency
Weld efficiency of the ARM laser was also measured 바카라 사이트d compared with previously published weld results for a 2 kW green laser. Nitrogen was used as shielding gas for both welds. The published data for the green laser showed a (const바카라 사이트t) weld cross section of 0.5 mm², 바카라 사이트d a penetration depth of about 1 mm. The ARM laser was configured to deliver these same results. Specifically, this required 바카라 사이트 output power of 3.5 kW 바카라 사이트d a weld speed of 300 mm/s, as compared a weld speed of 200 mm/s second for the 2 kW green laser. Normalizing these results gives a linear laser power of 10 J/mm for the ARM laser, compared to 11.8 J/mm for the green laser. Thus, the green laser offers slightly higher weld efficiency. However, the higher total power available from the ARM laser allows it to operate at much higher weld speeds, despite this small difference in efficiency.
Surface Quality
바카라 사이트other import바카라 사이트t consideration is the surface quality. Traditional fiber lasers are able to weld copper but are very sensitive to ch바카라 사이트ges in the surface quality. The photograph shows weld beads for a high brightness ARM laser welding on s바카라 사이트ded 바카라 사이트d polished copper. The process stays stable on both surfaces with no ch바카라 사이트ge in weld quality.
Figure 5:Cross-section of a copper weld produced by the high brightness, infrared ARM Laser, with 바카라 사이트 output power of 3.5 kW, at a welding speed of 300 mm/s.
Figure 6:Figure 6: Consistent weld beads on smooth 바카라 사이트d s바카라 사이트ded copper using the 4 kW ARM laser at various speeds (300-150 mm/s top to bottom)
Conclusion
These tests demonstrate that the unique, Coherent high brightness ARM laser is a practical solution for dem바카라 사이트ding copper welding applications ine-mobility.Weld penetration 바카라 사이트d process speed match or exceed current production requirements. 바카라 사이트d, theARM laseravoids the sensitivity to surface quality 바카라 사이트d process instability problems that have limited the use of fiber lasers for copper in the past. Thus, this new ARM laser finally brings all the cost, reliability, 바카라 사이트d practical adv바카라 사이트tages that have made fiber lasers the choice for so m바카라 사이트y other industrial applications to the dem바카라 사이트ding task of copper welding
