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Bi G.,Singapore Institute of Manufacturing Technology | Sun C.N.,Singapore Institute of Manufacturing Technology | Gasser A.,Fraunhofer Institute for Laser Technology
Journal of Materials Processing Technology | Year: 2013

In this paper, the process monitoring and control in laser aided additive manufacturing (LAAM) were studied. Some key issues which affect the process monitoring and control were revealed and discussed in detail. The results show that the geometry of the parts affects the melt-pool temperature, especially where the heat dissipation is strongly limited. The power density distribution plays an important role for controlled LAAM process. The laser beam can only be defocused to a certain extent to avoid the insufficient power density due to the excessively enlarged beam size. This can cause defects on the clad surface and in the clad layer. Surface oxidation must be avoided during the process control, because surface oxidation can deteriorate the LAAM process, as indicated by the disturbances of the measured melt pool temperature. With the path-dependant process control, the dimensional accuracy of the deposition can be significantly improved. © 2012 Elsevier B.V.

Brandl E.,Airbus | Heckenberger U.,Airbus | Holzinger V.,Airbus | Buchbinder D.,Fraunhofer Institute for Laser Technology
Materials and Design | Year: 2012

In order to produce serial parts via additive layer manufacturing, the fatigue performance can be a critical attribute. In this paper, the microstructure, high cycle fatigue (HCF), and fracture behavior of additive manufactured AlSi10Mg samples are investigated. The samples were manufactured by a particular powder-bed process called Selective Laser Melting (SLM) and machined afterwards. 91 samples were manufactured without (30 °C) and with heating (300 °C) of the building platform and in different directions (0°, 45°, 90°). Samples were tested in the peak-hardened (T6) and as-built condition. The Wöhler curves were interpolated by a Weibull distribution. The results were analysed statistically by design of experiments, correlation analysis, and marginal means plots. The investigations show that the post heat treatment has the most considerable effect and the building direction has the least considerable effect on the fatigue resistance. The fatigue resistance of the samples, however, is high in comparison to the standard DIN EN 1706. The combination of 300 °C platform heating and peak-hardening is a valuable approach to increase the fatigue resistance and neutralize the differences in fatigue life for the 0°, 45°, and 90° directions. © 2011 Elsevier Ltd.

Weitenberg J.,RWTH Aachen | Russbuldt P.,Fraunhofer Institute for Laser Technology | Eidam T.,Friedrich - Schiller University of Jena | Pupeza I.,Max Planck Institute of Quantum Optics
Optics Express | Year: 2011

We demonstrate a high-finesse femtosecond enhancement cavity with an on-axis obstacle. By inserting a wire with a width of 5% of the fun-damental mode diameter, the finesse of F = 3400 is only slightly reduced to F = 3000. The low loss is due to the degeneracy of transverse modes, which allows for exciting a circulating field distribution avoiding the obstacle. We call this condition quasi-imaging. The concept could be used for output coupling of intracavity-generated higher-order harmonics through an on-axis opening in one of the cavity mirrors. © 2011 Optical Society of America.

Kumstel J.,Fraunhofer Institute for Laser Technology | Kirsch B.,RWTH Aachen
Physics Procedia | Year: 2013

Polishing of metals by remelting with laser radiation is a method for automated polishing of 3D surfaces. A thin surface layer is molten and the surface tension leads to a material flow from the peaks to the valleys. The achievable polishing quality depends on the material and its quality. Results for polishing of titanium- and nickel-based alloys with cw laser radiation are represented in this paper. Starting from a roughness of Ra=1μm a Ra value of 0.16 μm is achieved in 7 s/cm2 for Ti6Al4V and a Ra value of 0.11 μm is achieved in 10 s/cm2 for Inconel718. © 2013 The Authors.

Scharun M.,RWTH Aachen | Fricke-Begemann C.,Fraunhofer Institute for Laser Technology | Noll R.,Fraunhofer Institute for Laser Technology
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2013

The identification and separation of different alloys are a permanent task of crucial importance in the metal recycling industry. Laser-induced breakdown spectroscopy (LIBS) offers important advantages in comparison to the state-of-the-art techniques for this application. For LIBS measurement no additional sample preparation is necessary. The overall analysis time is much smaller than for the state-of-the-art techniques. The LIBS setup presented in this study enables mobile operation with a handheld probe for the analysis of metallic materials. Excitation source is a fibre laser with a repetition rate of 30 kHz and a pulse energy of 1.33 mJ. The compact optical setup allows measurements at almost every point of a sample within 5 ms. The generated plasma light is analysed using a Multi-CCD spectrometer. The broad spectral coverage and high resolution provide an outstanding amount of spectroscopic information thereby enabling a variety of calibration approaches. Using a set of Al-based and a set of Fe-based samples the analytical performance of uni- and multivariate calibrations is evaluated. The same sample sets are analysed with a commercial state-of-the-art spark-discharge optical emission spectrometer allowing an assessment of the achieved results. Even though the possible analytical correctness of the fibre laser based LIBS measurements is found to similar or even better than that of the conventional technique, advantages of the multivariate data evaluation have not yet been realised in the investigations. However, due to the in situ sample preparation and short measurement times, fibre-laser based LIBS offers superior features. © 2013 Elsevier B.V. All rights reserved.

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