Dr. Alexander Kratky Profile

Dr. Alexander Kratky

at Technische Univ Wien

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Publications (3)

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Proceedings Article | 22 April 2009 Paper

Processing with kW fibre lasers: advantages and limits

A. Kratky, D. Schuöcker, G. Liedl

Proceedings Volume 7131, 71311X (2009) https://doi.org/10.1117/12.816655

KEYWORDS: Fiber lasers, Laser cutting, Head, Laser processing, Nd:YAG lasers, Carbon dioxide lasers, Solid state lasers, Metals, Laser applications, Mirrors

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Up-to-date fibre lasers produce multi-kw radiation with an excellent beam quality. Compared to CO₂-lasers, fibre lasers have relatively low operational costs and offer a very high flexibility in production due to the beam delivery with process fibres. As a consequence, fibre lasers have attracted more and more attention. On the other hand, their use in industrial applications especially in the automotive industry is still limited to a certain extent and fibre lasers haven't replaced all other laser sources till now as it could be expected. In laser cutting, the small kerf width produced by fibre lasers should be advantageous since the heated volume is smaller compared to CO₂-lasers. In fact, cutting velocities are usually much higher which is also caused by the higher absorption coefficient of most metals at the wavelength emitted by fibre lasers. Nevertheless, cutting with fibre lasers of some metals - e.g. stainless steels - is restricted to a small thicknesses of approx. 5mm. The reason for this is that the surface roughness of the edges increases dramatically with the thickness of the work piece. Applications of fibre lasers include e.g. remote welding or even remote cutting of a large variety of materials with usually excellent results. Due to the excellent beam quality the aspect ratio of the weld seam in relation to the penetration depth is quite good. In the case of thin sheet metal welding such a small beam waist is beneficial - but with thicker sheet metals it is very often disadvantageous since the preparation of samples is more complicated, costs increase and requirements on clamping devices rise. In this paper, advantages and disadvantages of fibre lasers are discussed briefly. Applications of a 1.5 kW fibre laser are presented and compared to classical laser systems.

Proceedings Article | 8 May 2007 Paper

Laser assisted forming techniques

Alexander Kratky

Proceedings Volume 6346, 634615 (2007) https://doi.org/10.1117/12.738146

KEYWORDS: Metals, Heat treatments, Profiling, Semiconductor lasers, Laser applications, Titanium, Laser therapeutics, Manufacturing, Laser sources, High power lasers

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During forming processes high deformations rates can lead to cracks and rupture very easily. Especially brittle materials like titanium or magnesium make difficulties in forming. Due to the dependence of the yield strength on temperature, forming at elevated temperatures eases processing of such materials. Since forming takes place only at localized areas of the work piece selective heating is suffcient and advantageous in most cases. Selective Laser heating offers a possibility to heat only the areas of the work piece where strongest deformations are required. For this purpose several laser sources have been tested like CO₂, Diode and Nd:YAG Lasers and their advantages and disadvantages in localized heating of the work pieces will be discussed. The work presented here summarizes research activities at the Institute for Forming and High Power Laser Technology, Vienna University of Technology, on laser assisted deep drawing, laser assisted bending, wire drawing and so on during the last decade. Recent developments like roll profiling, incremental forming processes and hydro forming are discussed briefly.

Proceedings Article | 13 September 2002 Paper

Laser-assisted shaping of metallic sheets and wires: a promising new application of high-power lasers

G. Liedl, A. Kratky, Dieter Schuoecker

Proceedings Volume 4760, (2002) https://doi.org/10.1117/12.482136

KEYWORDS: High power lasers, Laser ablation, Materials processing, Metals, Laser cutting, Cladding, Rapid manufacturing, Laser applications, Laser processing, Calibration

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High power lasers are currently employed in production technology for processes with material removal as in cutting and ablation and in processes with material joining as in welding, cladding or the generation of 3-dimensional parts, e.g. for rapid prototyping. Nevertheless, lasers are rarely used in forming technology, where bulk material, sheets and wires are shaped without changing their volume. The reason for this scenario is that for forming metals large forces are needed that cannot be generated by conversion of optical energy as delivered by lasers. Nevertheless, the permanent plastic deformation of metals can be facilitated by selective irradiation with lasers in those regions of the workpiece, where the strongest deformations take place, since then the material is softened in those regions, thus reducing the necessary mechanical forces. In addition to this benefit of reduced forces also brittle materials, that cannot be deformed at room temperature without cracks or rupture, can be processed with laser assistance without the necessity of heating the whole workpiece as in hot forming, as e.g. forging. Several processes of the latter kind have up to now been investigated and successfully operated at the authors department at Vienna University of Technology/Austria, as bending, deep drawing and also dieless calibration of wires. In the actual paper an overview over successfully finished studies and newly planned investigations on laser assisted forming is given

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