Fraunhofer ILT Research Articles

Tracking greenhouse gases with a laser

AbstractFaced with advancing climate change, we drastically need to monitor and understand the various sources and sinks of greenhouse gases worldwide in real time. One approach to accomplishing this is to regulate and monitor man‐made methane emissions. Laser systems as developed by researchers at Fraunhofer ILT offer ways to do exactly that. At the heart of lidar instruments, they can precisely determine greenhouse gases in the atmosphere with high spatial and temporal resolution, even from great distances, and do so worldwide.

Tracking greenhouse gases with a laser

AbstractFaced with advancing climate change, we drastically need to monitor and understand the various sources and sinks of greenhouse gases worldwide in real time. One approach to accomplishing this is to regulate and monitor man‐made methane emissions. Laser systems as developed by researchers at Fraunhofer ILT offer ways to do exactly that. At the heart of lidar instruments, they can precisely determine greenhouse gases in the atmosphere with high spatial and temporal resolution, even from great distances, and do so worldwide.

Enabling metal substrates for garnet-based composite cathodes by laser sintering

In this study, a laser irradiation method developed by Fraunhofer ILT was used to sinter screen-printed cathode layers of LiCoO2 (LCO) and Li7La3Zr2O12 (LLZO) directly on a stainless steel current collector. The laser sintering method was proved to be a promising method to sinter the composite cathode onto steel with greatly reduced side reactions and material degradation. In comparison, conventional sintering and another light-absorption-based sintering method, namely rapid thermal processing (RTP) in a lamp furnace, led to almost complete decomposition of the LLZO phase accompanying with the detrimental formation of LaCoO3 and CoO. Phase and morphology analysis of the laser-sintered cathodes using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy confirmed sintering of LCO and LLZO through the layer with small amounts of secondary phases (LaCoO3, Li0.5La2Co0.5O4 and CoO). The resulting porous matrix of the laser-sintered cathode was infiltrated with a polyethylene oxide (PEO) electrolyte to connect the cathode to an LLZO separator and a Li metal anode without an additional sintering step. This model cell was used to evaluate the electrochemical activity of the laser-sintered composite cathodes, which exhibited a specific discharge capacity of 102 mAh g−1 at 4.0 V in the first electrochemical cycle.

Deposition strategies for generating cuboid volumes using extreme high-speed directed energy deposition

Extreme high-speed directed energy deposition (EHLA) is a variant of directed energy deposition (DED-LB) developed at Fraunhofer ILT in cooperation with RWTH Aachen University. Because of a powder gas jet setup that is aimed at melting particles in the laser beam before they enter the melting pool, high process speeds of up to several hundred meters per minute and a layer thickness as thin as 25 μm can be achieved. EHLA is generally applied for rotationally symmetric coating applications. In previous experiments on a prototype machine of ponticon GmbH, EHLA was used for building up dense volumes, thus qualifying its use for additive manufacturing, now termed EHLA 3D. In this work, using iron-base alloy 1.4404 and a process speed of 40 m/min, cubic volumes are produced with EHLA 3D. Different deposition strategies commonly used in DED-LB are tested for their transferability to EHLA 3D. The results of different deposition strategies achieving the best near net shape geometry are shown in comparison to DED-LB. Furthermore, the influence of the deposition strategy and used technology on thermal management and microstructure are investigated. The best near net shape is achieved in this comparison using a contour-hatch strategy with 1.5 contours per layer and a 90° rotation of the hatch, both for EHLA and DED-LB. The microstructure of EHLA 3D built cubes is more similar to a typical laser powder bed fusion microstructure than to a typical DED-LB microstructure with respect to grain size and structure.

Controlling 100 lasers automatically via the cloud

AbstractIn the Cluster of Excellence “Internet of Production” (IoP), two hundred scientists at RWTH Aachen University in cooperation with Fraunhofer ILT have set up a data center for controlling and monitoring industrial processes. The concept for this is based on a project for controlling laser systems developed at the Fraunhofer Institute for Laser Technology ILT and uses the open source software Kubernetes. A corresponding system has been running successfully at the institute for two years, and with it the institute can automatically and remotely install the software for new lasers in just a few minutes.

Development of a high-speed laser material deposition process for additive manufacturing

Extreme high-speed laser material deposition (EHLA) is a variant of laser material deposition (LMD) with a modified powder gas jet focus. EHLA allows deposition at high process speeds in the range of several hundred meters per minute and the deposition of layers as thin as 25 μm. Feed rates can be in the range of 50 g/min or above. The processing of material combinations with poor weldability or different melting points is possible, with simultaneously smaller heat-affected zone and dilution zone compared to conventional LMD. Until now, EHLA has mainly been used for applying wear-resistant and corrosion-resistant coatings to rotationally symmetric parts, where high process speeds are achieved by rotation of the substrate. Developing EHLA for additive manufacturing (AM) aims at manufacturing highly individualized parts with high volume buildup rates and finer structural resolution compared to conventional LMD. The main steps toward harnessing EHLA for AM, termed EHLA 3D, are (a) process parameter development for volume buildup through deposition of multiple layers on top of each other and (b) the development of system technology that allows relative spatial movement between the powder nozzle and the substrate at high speeds and high accuracy in three dimensions. With a fast back-and-forth motion, high acceleration rates are necessary to ensure high volume buildup rates and high powder deposition efficiency. In this work, a specially designed tripod machine concept that has been developed in cooperation at Fraunhofer ILT is introduced. Theoretical considerations concerning achievable powder deposition efficiency as a function of process speed and acceleration of the handling system are presented. Furthermore, the results of process parameter development for up to 40 m/min with the iron-base alloy 1.4404 are shown. Virtually pore-free deposition of cuboid volumes is demonstrated. The mechanical values of the additively manufactured volumes are compared to the values for solution-annealed material, conventional LMD-manufactured samples, and samples produced by laser powder bed fusion (LPBF). Finally, an outlook on future research activities required for further development of EHLA 3D is given, covering system technology, buildup strategies, software integration, and possible applications of the new technology in repair, coating, and (hybrid-)additive contexts.

Polygon scanning system for high-power, high-speed microstructuring

A key requirement in automotive industry is reducing weight through innovative lightweight construction concepts. For multi-material construction the manufacture of plastic-metal hybrids poses a particular challenge due to the chemical and physical dissimilarity. At Fraunhofer ILT, a process chain has been developed for connecting thermoplastics with metals. First, the metal surface is microstructured with laser radiation to create undercut structures for the interlocking of polymer and metal, which are connected afterwards via a thermal joining process. Although laser-microstructuring is already a fast process, for automotive cycle times higher processing speeds are required. In this contribution a new polygon-based scanning system is combined with a 2 kW single mode fiber laser for a continuous high-speed microstructuring process of metals as pretreatment for local UD-tape-reinforcements. The scanner setup and first microstructuring results on different metals are presented.

Hot or Cold Ablation – That's the Question

AbstractA new generation of ultrafast lasers with high average powers and high repetition rates is coming to the market. Those systems in principle bring together high precision processing and high throughput. But with high average power thermal effects show up the demand for a careful process planning. A new simulation tool from Fraunhofer ILT incorporates such effects and allows for precise process optimization even at high average laser power.

Novel process for butt-joined plastic-metal hybrid compounds

Particularly in the automotive industry, there is a persistent problem arising from the need to reliably and permanently bond dissimilar materials such as plastics and metals. To solve this problem, experts at the Fraunhofer ILT in Aachen have come up with a solution that is suitable for industrial applications. Unlike adhesive bonding, the process works without additives or additional intervals for hardening or surface cleaning. Starting from the state-of-the-art process used today, the chain can be optimized for butt connections to a novel process using the thermal energy applied by the microstructuring process of the metal component. A new joining device is introduced, which allows the microstructuring of the metal component with an angle of incidence. After heating the component by the microstructuring process, it is pressed into the plastic component in the same joining device. The liquid plastic flows inside the inclined microstructures, which have a big undercut groove and a barb-like effect in the tensile shear load direction. After curing, the connection is based on a mechanical interlocking between the two components. At first suitable microstructuring parameters are evaluated to achieve a homogeneous melt flow of the plastic inside the cavities, which enables a high structure filling-rate and a good mechanical performance of the joint in tensile shear tests. Furthermore, the resulting temperature distribution is evaluated by thermocouples. Different influencing factors on the strength are evaluated like various penetration depths, different structure distances, or different clamping offsets of the plastic component.

Fully Integrated Process Control

AbstractLaser beam brazing and welding are well established joining techniques in the automotive industry; in particular for the body in white production. These processes are mainly used to join two‐piece trunk lids as well as to connect the roof and sidewall with a visible seam or to weld doors in steel or aluminum. Hence, the requirements upon the optical appearance of the brazed seams are very high and quality monitoring is essential. In cooperation of Scansonic MI GmbH and Fraunhofer ILT, a first prototype of a fully integrated on‐line process control system has been developed — SCeye.

High Power Femtosecond Lasers

AbstractThe InnoSlab concept was developed at Fraunhofer ILT more than 15 years ago using Nd‐based laser crystals. InnoSlab is a highly efficient amplification setup that allows for an extremely broad range of laser parameters due to its inherently simple setup. Today InnoSlab using Yb‐based laser crystals is the leading amplifier technology for achieving highest output power in the ultrashort pulse regime.

Tracking the contour

AbstractIn recent years the use of modern solid‐state lasers has brought about a distinct increase in operational speed in laser materials processing. Whether with scanners or fixed optics, high speeds – as far as possible in various axes at the same time – have almost become the norm. But although the movement of the optic is precisely calculated, the position of the processing point can deviate from the planned contour. Help is at hand, thanks to a process monitoring system developed by Fraunhofer ILT which precisely tracks the relative movement of work piece and optic. It enables acceleration related deviations from the set contour and speed to be measured exactly and the numerical control system to be adjusted accordingly. The kinematics measurement can be adapted to most laser processes (e.g. welding, brazing, cutting, selective laser melting, etc.) as an optional metrology method.

High-speed scanning laser-induced breakdown spectroscopy at 1000 Hz with single pulse evaluation for the detection of inclusions in steel

Spatially resolved information about the distribution and chemical composition of inclusions in steel are gained by scanning methods, such as scanning electron microscopy with energy dispersive X-ray spectroscopy, electron probe microanalysis or capillary-X-ray flourescence. Scanning laser-induced breakdown spectroscopy (LIBS) offers distinct advantages in contrast to these conventional methods. Sample polishing or high vacuum conditions are not necessary, a simple grinding of the sample is sufficient for the preparation. Analysing times can be reduced significantly. At Fraunhofer ILT a measuring system was developed enabling for the first time high-speed scanning LIBS with measuring frequencies of up to 1000 Hz. Sample surfaces with dimensions up to 110×45 mm2 can be analyzed. Light elements such as C, N, O, P, and S are detected, which is demonstrated by the identification of nonmetallic inclusions in steel. Principle, features and results of high-speed scanning LIBS with a spatial resolution<20 μm are presented.