Author
Ludger Overmeyer
Other affiliations: Baker Hughes
Bio: Ludger Overmeyer is an academic researcher from Leibniz University of Hanover. The author has contributed to research in topics: Welding & Laser. The author has an hindex of 19, co-authored 334 publications receiving 2128 citations. Previous affiliations of Ludger Overmeyer include Baker Hughes.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this paper, an overview over laser-based additive manufacturing with comments on the main steps necessary to build parts to introduce the complexity of the whole process chain is presented. But despite good sales of AM machines, there are still several challenges hindering a broad economic use of AM.
415 citations
TL;DR: Time-resolved images of femtosecond-laser-induced melt dynamics in 60 nm gold films on glass substrates show that the formation process can be compared to jetting behavior induced by cavitation bubbles near a free liquid surface.
Abstract: This work presents time-resolved images of femtosecond-laser-induced melt dynamics in 60 nm gold films on glass substrates. Melt dynamics induced by laser radiation with focus diameters of 6 μm and 8 μm (FWHM) at constant laser fluence is investigated with a temporal resolution of 10 ns. In both cases, the formation of the microbumps and gold jets takes at least 250 ns. It is shown that the formation process can be compared to jetting behavior induced by cavitation bubbles near a free liquid surface. This is confirmed by SEM illustrating a re-entrant spike through a hole in the microbump.
110 citations
TL;DR: An all-fiber component with a signal feedthrough capable of combining up to 6 fiber-coupled multi-mode pump sources to a maximum pump power of 400 W at efficiencies in the range of 89 to 95%, providing the possibility of transmitting a high power signal in forward and in reverse direction.
Abstract: We developed an all-fiber component with a signal feedthrough capable of combining up to 6 fiber-coupled multi-mode pump sources to a maximum pump power of 400 W at efficiencies in the range of 89 to 95%, providing the possibility of transmitting a high power signal in forward and in reverse direction. Hence, the fiber combiner can be implemented in almost any fiber laser or amplifier architecture. The complete optical design of the combiner was developed based on ray tracing simulations and confirmed by experimental results.
101 citations
TL;DR: In this article, a reproducible laser material deposition (LMD) and laser remelting (LR) process was used to construct a monocrystalline microstructure for turbine blade tip repair.
Abstract: High pressure single-crystal turbine blades made from nickel-based superalloys can withstand temperatures of up to 1100 °C due to their superior creep and fatigue properties compared to polycrystalline material. However, these parts undergo erosion and cracking due to the extreme conditions they are subject to in the engines of commercial airplanes. Since there is no effective method of repairing these expensive parts, while maintaining the necessary microstructure, the need to develop and establish a reproducible process is of high importance. The process of Laser Material Deposition (LMD) has shown promising results in the building-up of single-crystal or directionally solidified structures, while laser remelting has been shown to extend this monocrystalline height. By combining the two processes, this study aimed to deposit and remelt single-crystal structures on substrates of the nickel-based superalloys CMSX-4 and turbine blade tips of PWA 1426. Experiments were carried out to establish laser parameters that resulted in a monocrystalline microstructure. This study showed that the combination of cladding and remelting can be used to deposit single-crystal structures and was able to establish a reproducible laser process to this effect. The results obtained indicate that the process is a promising candidate for the repair of turbine blade tips and warrants further research into the microstructure and thermomechanical properties of the repaired areas.
82 citations
TL;DR: Laser cladding has become an established technology for parts repair and surface modification for cost-intensive components due to ongoing improvements of laser sources, process technology and strategy, the range of applications for laser deposition processes is continuously increasing as discussed by the authors.
80 citations
Cited by
More filters
[...]
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
33,785 citations
Journal Article•
TL;DR: The first direct detection of gravitational waves and the first observation of a binary black hole merger were reported in this paper, with a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ.
Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.
4,375 citations
31 Oct 2001
TL;DR: The American Society for Testing and Materials (ASTM) as mentioned in this paper is an independent organization devoted to the development of standards for testing and materials, and is a member of IEEE 802.11.
Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.
3,792 citations
01 Jan 2016
TL;DR: In this paper, the authors present the principles of optics electromagnetic theory of propagation interference and diffraction of light, which can be used to find a good book with a cup of coffee in the afternoon, instead of facing with some infectious bugs inside their computer.
Abstract: Thank you for reading principles of optics electromagnetic theory of propagation interference and diffraction of light. As you may know, people have search hundreds times for their favorite novels like this principles of optics electromagnetic theory of propagation interference and diffraction of light, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some infectious bugs inside their computer.
2,213 citations
TL;DR: Polymers are by far the most utilized class of materials for AM and their design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed.
Abstract: Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....
2,136 citations