Laser cutting is still the most common industrial application of CO 2 laser systems but currently available high-power fibre lasers seem to be an attractive alternative to the established CO 2 laser sources for several cutting tasks. Practical experience has shown that fibre lasers enable significantly increased travel rates in the case of inert-gas fusion cutting. This advantage in achieving higher cutting speeds in comparison to CO 2 laser cutting is however a clear function of the sheet thickness to be cut. In the first part of this article, possible reasons for this experimental fact are derived from a thermodynamic analysis of the process with consideration of the specific beam absorption characteristics under cutting conditions. After that, in the second part, a quite new laser cutting variant, namely the gas-free remote cutting process that considerably benefits from the high beam quality of fibre laser systems, is presented.

Diffraction-limited high power lasers represent a new generation of lasers for materials processing, characteristic traits of which are: smaller, cost-effective and processing "on the fly". Of utmost importance is the high beam quality of fiber lasers which enables us to reduce the size of the focusing head incl. scanning mirrors. The excellent beam quality of the fiber laser offers a lot of new applications. In the field of remote cutting and welding the beam quality is the key parameter. By reducing the size of the focusing head including the scanning mirrors we can reach scanning frequencies up to 1.5 kHz and in special configurations up to 4 kHz. By using these frequencies very thin and deep welding seams can be generated experienced so far with electron beam welding only. The excellen t beam quality of the fiber laser offers a high potential for developing new applications from deep penetration welding to high speed cutting. Highly dynamic cutting systems with maximum speeds up to 300 m/min and accelerations up to 4 g reduce the cutting time for cutting complex 2D parts. However, due to the inertia of such systems the effective cutting speed is reduced in real applications. This is especially true if complex shapes or contours are cut. With the introduction of scanner-based remote cutting systems in the kilowatt range, the effective cutting speed on the contour can be dramatically increased. The presentation explains remote cutting of metal foils and sheets using high brightness single mode fiber lasers. The presentation will also show the effect of optical feedback dur ing cutting and welding with the fiber laser, how those feedbacks could be reduced and how they have to be used to optimize the cutting or welding process

A laser remote cutting process is analyzed, which differs significantly from established laser cutting processes. On the one hand, no cutting gas is needed and a high working distance is realized. On the other hand-in opposite to conventional laser remote cutting-sheets of metal with thicknesses above 1 mm can be cut in one step. Examinations were carried out at the martensitic boron steel 22MnB5 due to its interesting applications at automotive industry and significant advantages of the presented cutting process. Large focal spots and low cutting velocities are needed when moving the laser beam over the surface of the work-piece. Mainly, the material is melted besides a little fraction of vapor, which forms a keyhole, comparable with laser deep penetration welding. Besides typical parameters, the behavior of the ejection of melt is presented. The melt exits the kerf characteristically in beam direction at the bottom of the work-piece but changes its axial direction. Therefore, two subprocesses are defined and examined separately: Subprocess A can be observed at low cutting velocities and is characterized by a pushing melt ejection, whereas subprocess B needs significantly higher velocities and results in dragging melt ejection

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The remote cutting technique provides an enormous potential in terms of cutting speeds when working on thin sheets. Even on contour cutting speeds about 100 mmin are realizable. Working without any cutting gas, the material of the cutting kerf must be vaporized partially. It is evident that the energy input must be higher than for pure melting of the cutting kerf's material. In order to characterize laser cutting processes in terms of energetic efficiency, the severance energy can be used. This parameter depends on the necessary laser power to cut a defined sheet thickness at a certain cutting speed. Hitherto, it was used to compare different laser cutting processes using different laser beam sources when cutting straight lines. In order to characterize different processes for cutting real contours, the geometry of the part to be cut is also important. The complexity of a part can be characterized by the agility. The target of this paper is to combine the severance energy and the agility in order to compare the remote cutting and the conventional fusion cutting energetically. It will be shown where remote cutting can be applied very efficiently to produce parts in a flexible and highly productive way and what the application area of conventional fusion cutting with fast axis is