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  1. Laser metal cutting with tailored beam patterns

    Fleming Ove Olsen Has potential to outperform fiber and CO 2 lasers High brightness, high power solid state laser sources such as fiber lasers show potential in the next generation of laser metal cutting. At IPU, (formerly the Institute for Product Development), the development of a new concept for laser cutting with single-mode fiber lasers has been initiated within two projects: DOEFLAC and ROBOCUT, in co-operation with a number of project partners.1 FIGURE 1. Classical laser cutting, state-of-the-art keyhole laser cutting, and cutting with a tailored laser beam pattern. Initial experimental tests have demonstrated that this new approach has the potential to outperform state-of-the-art fiber and CO 2 laser cutting,2 producing faster, better and cheaper cutting than both of these laser cutting technologies. It is projected that after the completion of the two projects, this cutting technology will be matured to a level where it can be manufactured and marketed on normal commercial terms. Tailored beam patterns The projects rely on a principle where the cutting process is performed with a complex laser beam pattern as opposed to traditional laser cutting using a single round laser beam. By using dedicated beam patterns created by utilizing the unique focusing properties of high-power single-mode fiber lasers, it becomes possible to assign a part of the total laser power to create a keyhole, such as that used in laser welding or in laser cutting. The remaining power will be distributed on the melt behind the main beam to create a suitable high vapor pressure distribution over the molten material surface. This makes it possible to establish a local pressure distribution on the melt flowing out of the cut kerf, which far exceeds the pressures that can be obtained by classical coaxial gas jets in laser cutting. As a result, very narrow cut kerfs can be produced. The new process has the potential of producing burr free cutting in a wide cutting rate range, high-speed cutting capability and quality cut kerfs in narrow contour cutting (FIGURES 1 and 2). Further, by tailoring the laser beam pattern correctly (adding a "lid" beam pattern), the melt flow can be directed out of the kerf opposite to the incoming laser beam even without applying a cutting gas. Thus a one-pass remote cutting technology can be developed that has a clear potential in removing the molten material from the cut kerf much more efficiently than state-of-the-art remote laser cutting, making remote laser cutting interesting industrial technology. Beam shaping The core of this laser cutting technology is the beam shaping, which can be established in different ways, for example: Designing a system with a number of single-mode fiber lasers. Transmit these beams to the cutting head via a beam combiner structure instead of putting all the single-mode beams into one large transmission fiber, as used in high power multimode fiber laser configurations. FIGURE 2. Principle of a tailored laser beam intensity Applying one single-mode fiber laser source. Apply an advanced optical system with a specially designed artificial hologram, also known as a diffractive optical element (DOE), to transform the input laser beam to a radiation pattern that is optimal for a given laser cutting production (FIGURE 3). As the beam pattern (FIGURE 2) is asymmetric, the DOE must be turned according to the actual cutting direction as sketched in FIGURE 3. FIGURE 3. Principle of remote laser cutting system with a tailored laser beam pattern. The mechanism of creating vapor pressure by intense laser light has been known for several decades from laser drilling and keyhole laser welding, where the local vapor pressure is the driving mechanism of penetration in drilling and for creating and maintaining the keyhole in welding. Keyhole laser cutting has also been known for ~20 years since a group of scientists at Fraunhofer ILT3 developed sheet metal cutting at high speed with CO 2 lasers. Keyhole laser cutting with CO 2 lasers was, however, limited to very thin sheets due to the strong plasma formation in the keyhole (as is also known in high power CO 2 laser welding). The combination of the focusability of the high brightness fiber lasers and their wavelength makes it possible to perform keyhole cutting in thicker sections because the fiber laser can cut very fast compared with the CO 2 laser.4 Keyhole cutting can be more efficient than the classical laser cutting, where the molten material is flowing down in front of the laser beam, because the melt can much more efficiently be removed from the center line in the cut front. This makes the melt film thickness smaller and thereby ensures efficient heat conduction from the melt surface, where the laser light is absorbed in the melt front, where the energy is required for melting more material.5 However, the melt flow around the laser beam in keyhole cutting causes quality problems. The molten material is running down at the cut sides, deteriorating the cut quality because the fiber lasers can cut fast, but not with high cut qualities when the material's thickness is increased. FIGUR E 4. Potential of cutting with tailored laser beam pattern with assist gas. As in classical laser cutting and state-of-the-art keyhole cutting, the coaxial gas assist is the only driving force for melt removal; the kerfs must be enlarged, compared to the optical limitations of a single-mode fiber laser, to reduce the pressure down through the cut kerf.4 Here the pressure obtainable by laser radiation is larger, and large pressures can be maintained through the entire cut kerf. Therefore, the new approach with tailored laser beams can be designed from entirely optical limitations, which have the potential of cutting with narrower kerfs than in state-of-the-art laser cutting. FIGURE 5. Cutting potential of remote cutting with tailored laser beam pattern. Experiments so far The experiments conducted so far with this new approach show a clear-cut quality improvement over a wide range of cutting rates and have demonstrated that almost burr-free cuts can be obtained. The potential of the two projects is obvious (FIGURES 4 and 5). Furthermore, results from one pass remote laser melt cutting from TRUMPF6 have demonstrated that the principle of melt removal works only with laser radiation. The TRUMPF solution, however, is based upon a round laser beam, which must be defocused to realize the mechanism. This is not an optimal solution because the melt here must run out of the kerf in front of the laser beam, which their published results show clearly. Another remote cutting technique is demonstrated by Fraunhofer Institute IWS,7 where a highly focused round single-mode laser beam is scanned over the surface multiple times, performing deep engraving. This technique is only suitable for thin sheet cutting, and the advantage of the scanning is more or less lost because of the need for multiple scans. The key work in the project is currently focusing on the computation and manufacturing of the DOEs for the test phases and establishing experimental facilities at Aalborg University, including a 3 kW single-mode fiber laser. ✺ References DOEFLAC is a EUROSTARS project with 4 partners: IPU (DK); Laser Optical Engineering (UK); CyLaser (IT); and Optoskand (SE). ROBOCUT is funded by the Danish High Technology Foundation. The project has as partners: IPU (DK); IAI A/S (DK); Grundfos A/S (DK); Micronix ApS (DK); Aalborg University (DK); Volvo Car Production (SE); and KUKA Nordic (SE). Olsen, F. O., Hansen, K.S. & Nielsen, J.S., "Development of multibeam fiber laser cutting," Journal of Laser Applications, Vol. 21, Issue 3, pp. 133-138. Preissig, K.-U.; Petring, D. and Herziger, G., "High speed laser cutting of thin metal sheets," SPIE, Vol. 2207, ISBN 0-8194-1508-1, pp. 96-110 (1994). Wandera, C.; Salminen, A.; Olsen, F.O. and Kujanpää, V., "Cutting of stainless steel with fiber and disc laser," Paper 404, Congress Proceedings, 25th International Congress on Application of Lasers and Electro-Optics: ICALEO 2006, Orlando, FL: Laser Institute of America. Olsen, F.O., "An evaluation of the cutting potential of different types of high power lasers," Paper 401, Congress Proceedings, 25th International Congress on Application of Lasers and Electro-Optics: ICALEO 2006, Orlando, FL: Laser Institute of America. Olschowsky P., "Vapor-pressure fusion cutting, a new remote cutting technology," Presentation at 4th Primes Workshop, Seeheim (DE), 08.09.2010.  http://www.iws.fraunhofer.de/projekte/remocut/remocut.pdf. Fleming Ove Olsen (foo@ipu.dk ) is a senior engineer at IPU, Lyngby, Denmark.    

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    Thu, 1 Sep 2011

  2. The globalization of industrial laser processes

    This month's features offshore from the US are examples of ILS ' global outreach to bring readers the latest in industrial laser material processing.

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    Wed, 14 Sep 2016

  3. Laser microfabrication in Lithuania

    The Lithuanian laser industry has just celebrated its 30th birthday, and laser technologies started to be used in the country around the same time 30 years ago.

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    Wed, 14 Sep 2016

  4. Fiber laser machine ensures lowest price for sheet metal cutter

    After extensive research into fiber laser cutting machines on the market, McAuley Engineering conducted cutting trials at three potential suppliers.

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    Wed, 14 Sep 2016

  1. Metal cutter American Special Metals opens new distribution center

    Online Articles

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    Tue, 1 Mar 2016

  2. Lasers shine when the stars are aligned

    This issue could easily have been dubbed "the marking special" since we present three perspectives on laser marking difficult materials by a variety of processing options.

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    Fri, 15 Jul 2016

  3. New 4kW laser enters fiber laser market

    Milpitas, Calif. – JDSU has announced that it has collaborated with Amada, a manufacturer of machine tools for metal fabrication, to develop a new high-power 4 kW fiber laser. The fiber laser has been integrated into a new sheet metal cutting system that Amada plans to start selling to the Japanese ...

    Online Articles

    Online Articles

    Tue, 27 Jul 2010

  4. LIA presents the latest in laser cutting advancements at LME

    Advances in laser metal cutting , a staple of modern manufacturing, will be the subject of a keynote address by Mitchell Van Zuiden of Bystronic at the Laser Institute of America's annual Lasers for Manufacturing Event (LME) on Sept. 23, 2014, in Schaumburg, IL.

    Online Articles

    Online Articles

    Mon, 4 Aug 2014

  5. UK companies shift to fiber laser cutting

    Ashford, Kent, and Burges Hill, W. Sussex, U.K.– Two progressive U.K. companies, Kent Metal Developments Ltd. (KMD) and Cirrus Laser Ltd., have added fiber laser metal cutting to their customer capabilities.

    Online Articles

    Online Articles

    Mon, 16 May 2011

  6. Laser allows single-step marking on automotive glass

    Lasers have touched many segments of the auto industry, including laser marking of car windshields.

    Magazine Articles

    Magazine Articles

    Fri, 13 May 2016

  7. Trumpf automated fiber laser cutting

    Burke Doar, Trumpf VP of sales and marketing, describes the company's TruLaser 5030 and 3030 laser cutting machines, which both now offer BrightLine fiber functionality.

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    Video

    Video

    Tue, 1 Dec 2015

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  8. 2012 Annual Economic Review and Forecast

    The dynamic world of industrial laser materials processing lived up to its reputation in 2012 as the world's economies fluctuated wildly with random news of ...

    Magazine Articles

    Magazine Articles

    Tue, 1 Jan 2013

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