A Breakthrough for Cutting with Fiber Lasers

Most compact 5 kW fiber laser in the laser industry can be equipped with the new Corona technology from nLight. Different beam profiles, diameters, and power distributions are possible thanks to the “all in fiber”-design and can be changed at full power on the fly to a specific process. (Source: nLight / Optoprim)

The sheet metal cutting market is dominated by fiber lasers because of their unmatched combination of productivity, precision, and cost-effectiveness. Fiber lasers in the 2 – 4 kW range have become the workhorses for many fabrication shops, offering faster and more precise cutting of thin metal than legacy cutting technologies, such as CO2 lasers and plasma torches. Many fiber laser systems are, however, designed for cutting a limited range of metal thicknesses. Specifically, a small, tightly focused ­laser beam provides the fastest cutting speeds for thin gauges, but for thicker plates this small beam has significant limitations in edge quality and maximum thickness. Alternatively, a larger beam can improve the edge quality for thick plate because of the wider kerf, but with a substantial speed penalty for cutting thin sheet.

Large fabrication shops may purchase multiple fiber laser tools, where each tool is dedicated to cutting a particular thickness range: a small-beam system for light gauges and a larger-beam system for thicker plates. Smaller fabrication shops that rely on one tool to cut the full range of metals will have lower productivity if they are limited to one spot size, especially if they have a diverse job mix. These shops typically change the focusing lens in the cutting head to better optimize the laser spot size for a given job. Each change of the lens causes productivity losses when the laser is not cutting, and it risks contamination of the lens and the cutting head, which can result in catastrophic failure and significant repair costs and downtime.

Oxygen-assisted cutting results of 25.4 mm mild steel with a standard 4 kW fiber laser (on top) and a 4 kW Corona fiber laser (below). The dramatically better edge quality provided by Corona is evident.
Specifically, with the Corona, the roughness is 3× lower, the edge is significantly straighter, and the perpendicularity is greatly improved. The Corona provides consistent drop performance, whereas the conventional fiber laser does not because of slag on the bottom edge of the part and a concave edge shape. (Source: nLight / Optoprim)

The ability to automatically tune the laser spot size would greatly extend the applicability, productivity, and process window of fiber lasers. Most existing approaches entail motorized free-space optics. Examples include zoom cutting heads, fiber-to-fiber or free-space-to-fiber couplers that vary the launch conditions into the fiber, or fiber-to-­fiber switches with two to four outputs coupled to independent process fibers. Such free-space optical approaches entail significant cost and complexity and can degrade tool performance and reliability. They are sensitive to misalignment, contamination, and environmental conditions (temperature, vibration), introduce power dependence (thermal lensing) and optical loss, and / or have slow switching speed. Zoom cutting heads, which incorporate a motorized lens within the head, are larger and heavier than standard cutting heads, resulting in reduced acceleration and imposing additional design requirements on the gantry and motors. Tool designers resorting to these approaches are required to pass along the cost, performance, and reliability burden to their customers (the end users).

nLight has developed a novel, all-­fiber technology, “Corona”, that enables rapid tuning of the fiber laser spot size directly from the feeding fiber over a range of more than 3× without any of the drawbacks of free-space approaches. In addition, Corona fiber lasers provide beam shapes that have shown improved cutting quality for various metals, including flat-top and annular (“donut”) beams. Corona fiber lasers at the 4 kW power level have delivered greatly improved performance over conventional fiber lasers for sheet metal cutting of mild steel, stainless steel, aluminum, and copper, for mild steel thicknesses up to 25 mm, enabling the development of “universal” tools for optimized cutting of a wide range of metal thicknesses.

The Corona fiber laser output beam is continuously tunable between ~100 and ~300 μm. The critical and unprecedented feature of Corona is that this tuning of the beam shape is accomplished all within fiber and with no free-space optics, thereby maintaining all of the performance, stability, efficiency, and reliability advantages of fiber lasers. The full laser power is available at each Index setting.

An additional advantage of Corona is that beam tuning is very rapid, with a transition time from the smallest to the largest diameter of less than 30 ms. The fiber laser continues to operate at full power during an Index change, with no need to turn off (or “blank”) the laser while changing the beam shape.

Read more details in the article by Dahv Kliner and Brian Victor, and meet the experts from nLight and its German distributor, Optoprim, at EuroBlech, Hall 11, Booth J141. (Source: Optoprim)

Reference: D. A. V. Kliner & B. Victor (nLIGHT): A Breakthrough for Fiber Lasers – Tunable beam quality enables optimized cutting of thin and thick metal, online 18 September 2018, DOI: 10.1002/latj.201800029

Links: nLIGHT Inc., Vancouver, Wash., USAOptoprim Germany GmbH, Unterschleißheim,
Germany

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