The new remote-controlled Coherent HIGHmotion 2D welding head and Coherent HighLight FL-ARM laser enable in-depth laser welding of copper over large work areas.

Introducing two new products from Coherent that enable laser welding of copper >3 mm thick on a large work area (100 mm x 140 mm). Coherent's innovations enable high-speed processing of large parts - such as busbars - because the system can complete multiple welding jobs at widely separated locations without having to physically relocate the process head or the part being welded.

Coherent HIGHmotion 2D welding head

The first of these new products is an extension of our existing Coherent HIGHmotion 2D remote-controlled 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, highly focused laser spot over a larger scan area with minimal focal shift. Precise focusing of the laser beam 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 scanner retains all the capabilities of this industry-proven laser welding scanner, including positioning accuracy, high performance stability and compatibility with both Coherent HIGHvision and SmartSense+ systems.

HighLight FL-ARM laser source

The second product introduced is a lower numerical aperture (NA) version of our HighLight FL-ARM fiber laser. This delivers exactly the required low NA input beam for optimal performance of low magnification HIGHmotion 2D devices. In addition, it adds the ability for the ARM laser to independently control and modulate the power in the center and ring beam. This capability has proven successful in eliminating spatter when welding copper. The HighLight FL-ARM also offers superior bounce-back resistance, which increases operational reliability.

The HighLight FL-ARM laser has already seen great success in copper welding. When manufacturers look to extend this success to produce the deep welds required for e-mobility tasks, such as laser busbar welding, they run into a "speed limit". One reason for this speed limit is the limited size of the F-theta lens scanning field.

What prevents the scanning field from being enlarged? The problem is that increasing the size of the scanning field of the Ftheta lens means increasing its focal length, which increases the size of the focus point (assuming everything else remains the same). However, a small point with a large concentration of energy is necessary to achieve the large penetration through the material that is required for deep welds. Thus, at some point the working point of the laser beam is too large to achieve the required energy concentration. This is shown in the animation.

The size of the spot can be reduced again by increasing the focal length of the input collimator; this is a lens array 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.

The problem is that increasing the focal length of the collimator means zooming out the laser source. And at some point, the diverging diameter of the laser beam becomes too large to pass through the collimator and scanning optics without being partially clipped. This is undesirable, because the clipped portion of the beam means a loss of power, which brings us back to the original problem.

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 the use of a longer focal collimator without losing the beam, which in turn allows the use of a longer focal length (wider field of view) of the F-theta imaging lens. This combination provides a small focus point (high brightness) over a large scanning field. The problem is seemingly solved.

However, substantially reducing the NA of a fiber laser - without reducing its power or otherwise degrading its performance - is not so easy. Coherent was the first and currently the only company to achieve this. And that's why the new lower magnification HIGHmotion 2D process head, especially in conjunction with the new low NA HighLight FL-ARM laser, enables faster deep welding of copper.

Read more about the Coherent HIGHmotion 2D laser process head and the Coherent HighLight FL-ARM laser.

Learn more about laser copper welding.