The new Coherent HIGHmotion 2D laser welding head and the Coherent HighLight FL-ARM laser enable deep laser welding of copper over large work areas.
Coherent has introduced two new products that enable deep laser welding of copper (more than 3 mm) over a large work area (100 mm x 140 mm). This enables fast processing of large parts such as busbars, as the system can complete multiple welding jobs at different work area locations without the need to physically move the welding head or component.
The first of these new products is an extension to our existing Coherent HIGHmotion 2D remote laser welding head with smaller magnification capabilities. When used with a low numerical aperture (NA) fiber laser, the lower magnification HIGHmotion 2D head will provide a small, high brightness, focused laser spot over a larger scan area with minimal focal shift. The small laser focus is critical for performing deep welding of copper, which is otherwise challenging with an infrared laser. This approach provides a larger process window, which means a more stable, robust and repeatable process.
The new lower magnification HIGHmotion 2D scanning laser head retains all the capabilities of this proven workhead, including positioning accuracy, high power stability and compatibility with Coherent HIGHvision and SmartSense+ systems.
The second product introduced is a new version of our HighLight FL-ARM fiber laser with a lower numerical aperture (NA). The laser source delivers precisely the required low NA input beam for optimal performance of the HIGHmotion 2D low magnification device. Additionally, it adds the ability for the ARM laser to independently control and modulate power in the center and ring beam. This has proven successful in eliminating spatter when laser welding copper. The HighLight FL-ARM also offers excellent beam bounce-back resistance, which increases operational reliability.
Enhanced performance for deep laser penetration welding
The HighLight FL-ARM laser has already seen tremendous success, particularly in copper welding. When manufacturers look to extend this success to produce the deep welds required for e-mobility tasks such as busbar welding, they run into a "speed limit". One cause of this speed limit is the limited size of the F-theta lens sensing field. This is the area over which the laser can make welds without anything moving (except the scanning mirrors themselves) - the working field of the laser. Moving the part or weld head takes time, so the smaller the working field, the more part movement is required and the slower the overall throughput of the process. What prevents the scanning field from being enlarged? The problem is that increasing the size of the working field of the laser lens also means increasing its focal length, and this will also increase the size of the focal point (assuming everything else stays the same). However, a small focal area with high brightness is necessary to achieve the penetration of the laser beam through the material that is required for deeper welds. At some point in the magnification process, the laser focus is simply too large to achieve the desired energy concentration and the laser is unable to burn through the material. This is shown in the animation.
The focal size can be reduced again by increasing the focal length of the input collimator; this is a lens system that collects the diverging light from the laser and prepares it to pass through the scanning optics. This reduces the magnification of the whole system. But here comes the second problem. Increasing the focal length of the collimator means zooming out the laser source, and at some point the physical diameter of the diverging laser beam becomes too large to pass through the collimator and scanning optics without being partially cut off. This is undesirable because cutting off part of the beam would result in a loss of power at the laser focus.
The solution is to reduce the divergence of the laser source at the beginning. Or, in optical terminology, to reduce its numerical aperture (NA), which is a measure of the beam divergence angle. This allows a longer focal collimator to be used without losing the energy of the laser beam, which in turn allows a longer focal length (wider field of view) of the F-theta lens to be used. This combination provides a small focal length with high brightness over a large working field. The problem is solved, but... Substantially reducing the numerical aperture (NA) of a fiber laser without reducing its performance or otherwise degrading its parameters is not so easy. That's why Coherent is the first, and currently the only, company to achieve this. And that is why the new HIGHmotion 2D process head with lower magnification, especially in conjunction with the new low NA HighLight FL-ARM laser, enables faster deep welding of copper.
Read more about the Coherent HIGHmotion 2Dprocess head and the Coherent HighLight FL-ARM laser.
Source: coherent.com