We present an intra-cavity frequency doubled Q-switched diode-pumped alexandrite ring-laser directly emitting in the UV at 386 nm. Using LBO as nonlinear crystal, the laser yields a pulse energy up to 3 mJ at 500 Hz with an excellent beam quality of M 2 = 1.1. The pulse length is about 920 ns, allowing for very narrow bandwidth in single longitudinal mode operation. The optical-to-optical efficiency for the UV laser is > 9% and almost unchanged compared to the fundamental laser. First injection-seeding experiments show single longitudinal mode operation. The parameters of the laser are suitable for the use as an emitter in a multi-purpose atmospheric Doppler lidar system.

A simplified model based on data from literature is presented, to determine the x-ray emission spectrum as function of laser pulse energy, wavelength and peak intensity, to assess applications and radiation safety requirements.

Simultaneous machining and coating (SMaC) is a novel hybrid technology developed by the Fraunhofer Institute for Laser Technology ILT that combines additive manufacturing through extreme high-speed laser material deposition (EHLA) with a simultaneously engaged turning process. In the present work, the parallelization of the two subprocesses is successfully demonstrated. For the first time, systematic investigations into the influence of residual heat from the deposition process on the machining process and the properties of the resulting coating, respectively, are conducted. The study specifically examines geometric deviations, surface roughness, and tool wear. One of the main parameters affecting the residual heat introduced into the turning process is the distance between the tool center points of the EHLA deposition head and the turning tool Delta z. This parameter is identified as a primary factor influencing the dimensional accuracy of the coating geometry. The results show that SMaC not only offers potential for increasing the productivity of the process chain but also has a positive effect on the service life of the cutting tools involved, potentially improving the workability of hard coating materials. Improvements in terms of the attainable surface roughness are also observed. These investigations provide a basis for research into further aspects of the SMaC process, such as adaptive tool path control methods to enhance dimensional accuracy and the influence of induced compressive stresses in processing highly brittle coating materials.

Laser Powder Bed Fusion (LPBF) offers possibilities towards a sustainable manufacturing due to high powder material recycling rates or manufacturing of lightweight and topology optimized (TO) components. In order to evaluate sustainability respectively resource consumption, Life Cycle Assessment (LCA) is employed, and a virtual model of the physical LPBF process is developed. For conclusive modeling, however, primary data of resource flows and energy consumption must be known. Especially the influence of topology optimization on the resource consumption in LPBF and on the resulting footprint of manufactured geometries is barely investigated. In the present work, TO approaches on an aerospace component are used to reduce the components volume. Two iterations of the component are built on a commercial LPBF system and primary energy data is measured. A LCA model has been developed to compare the ecological impacts of these iterations. Results indicate that by applying TO, the footprint can be reduced. (c) 2024 The Authors. Published by Elsevier B.V.

In the additive manufacturing of components using powder-based laser metal deposition (LMD), the heating of the volume during buildup is a decisive factor for process stability and contour accuracy. If the process parameters remain constant, this intrinsic heating leads to deviations in the deposited layer thickness during the process because of changes in the melt pool volume. This leads to contour deviations and potentially causes the process to fail if the process parameters are no longer within the suitable range. Particularly in the case of complex geometries, this previously required time-consuming process development for adapted process parameters and buildup strategies. This paper examines the potential of data-driven approaches to enhance the stability and precision of LMD processes. To this end, a machine learning (ML) model is employed to optimize laser power settings. The objective of the study is to reduce the thermally induced geometric deviations that often occur during the LMD process by utilizing experimental data. The methodology employs the use of the alloy Inconel 718, renowned for its high strength and temperature resistance, in conjunction with the utilization of computer numerical control machines equipped with laser and imaging systems. The ML model is trained to predict the optimal laser power required to obtain consistent melt pool properties. The results demonstrate that the ML approach is an effective means of reducing geometric deviations.

Laser material deposition (LMD) is a widely used coating process in industry. However, to increase its economic appeal, higher process speeds are required. The solution to this challenge is an innovative modification known as extreme high-speed laser material deposition (EHLA). EHLA allows for an impressive increase in process speed from 2 m/min for conventional LMD to 500 m/min. With the ability to adjust process parameters, EHLA can generate tailor-made surface properties, expanding its potential application beyond current industrial uses. In this novel study, we explore the effects of relative positioning between tools (laser beam and powder–gas jet) and substrate on the surface properties of EHLA coatings. By laterally and axially offsetting the tools, the proportional energy coupling of the laser radiation into the powder–gas jet and substrate can be modified. Altering the position of the powder–gas jet can also affect the weld pool flow or number of particle attachments, thereby affecting surface properties. This approach allows for the adjustment of surface roughness over a wide range—from smooth, quasi-laser-polished surfaces to rough surfaces covered with particle adhesions.

Within laser additive manufacturing (directed energy deposition with laser beam), processes are further distinguished by the form of the filler material. In terms of availability, storage, safety, and cost, wire is commonly the preferred filler material in comparison to powder. Despite these advantages, due to the different material transfer modes, a greater process control is required. Within this work, an experimental setup for electrical-resistance-measurement within the laser material deposition process with a coaxial wire feed and its possible use for an automated process control is investigated. The measurement is performed between a wire, a substrate, and over the melt pool. One main influencing factor on process stability is derived from the timing of the trigger sequence of the laser power, process feed, and wire feed at the start and end points of every track. Consequently, inaccurate settings of the trigger sequence can, e.g., lead to deviations in track length and part geometry. Additionally, a smooth transfer of the wire into the melt pool is imperative during part build-up to ensure a stable deposition process. Variation in laser power, wire feed, process feed, or wire transfer mode can lead to process instabilities. This can result in imperfections, bonding defects, or pores in the tracks and layers that will add up in built components and must be avoided for defectfree three-dimensional geometries. Within the experiments, it is investigated whether the resistance-measurement provides consistent results under varying conditions and potentially can be utilized to automate the trigger sequence of deposition. Furthermore, it is investigated whether different wire transfer modes can be linked to the measured resistance values during welding of single tracks.

Pursuit of an academic career is often co associated with a PhD which also is a qualification for all types of jobs in industry. However, in Germany most PhD programs focus on university-based, basic, and applied research and aim to demonstrate concepts while the transfer to industry and real products is subordinate. This is where Fraunhofer comes in: our natural science and engineering PhD students participate in solving real-world problems for our industrial customers with innovative and scientific approaches while they simultaneously pursue basic research questions with an application relevance for their PhD thesis. As an example, in this paper we present a multiphysics laser diode simulation software (SEMSIS) which was developed within two industrially funded PhD projects at the Fraunhofer Institute for Laser technology ILT. In the fusion research, a vast number of high-power laser diodes are used as pump sources for the high-energy pulsed lasers in inertial confinement fusion. Improving their electro-optical efficiency and making them more robust against external optical feedback represents a crucial step towards their use in economically competitive fusion power plants. In the presented simulation software tool SEMSIS, the complex interaction of electrical, optical, thermal as well as mechanical properties and their impact on efficiency, filamentation and reliability of high-power diode lasers can be analyzed to address the previously mentioned requirements in fusion research.

The manufacturing of high-speed steel (HSS) components using the laser powder bed fusion (LPBF) process could create an unprecedented combination of the materials’ mechanical properties and the design freedom enabled by the process to unlock new applications, such as milling heads with functionally optimized cooling channels. However, the processing of HSS with the LPBF process shows high susceptibility to cracking. This contribution aims to reduce hot cracking for the processing of HS2-2‑2 by investigating the influences of preheating temperature, laser power, and scan speed on the formation of hot cracks. The density and melt pool geometry of the produced parts are measured to further examine the relationship between the processing conditions and the resulting properties. The influence of various process parameters on the formation of hot cracks can be demonstrated. Further investigation shows a relation between hot cracking and the melt pool geometry. With a narrow and shallow melt pool, influenced by laser power and scan speed, the number of hot cracks can be reduced.

Laser material deposition (LMD) is a laser-based additive manufacturing process that is widely used for fabrication, diversification, and repair of parts in various industries. LMD processes can be distinguished by the form of the filler material. In terms of availability, storage, safe handling, and price, filler material in wire form often has advantages over powdered materials. In this work, the influence of tool path planning on the deposition accuracy and the process stability of LMD with coaxial wire feed is studied. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annular shaped laser beam without any shadowing. While the process is completely directionally independent, the stability is linked to the wire feed rate, laser power, and process feed rate. Additionally, the ratio between the wire and the laser beam diameter affects the stability. Movement of the wire inside the annular beam may result in shadowing and process abort. Changes in the working distance (defocusing) lead to changes in the beam diameter, which affects the process stability. This can result in imperfections, i.e., bonding defects, or pores in the tracks and layers that will add up in the built components and must be avoided for imperfection-free three-dimensional geometries. On even surfaces, the geometry of the deposited tracks is controlled by changing the laser power, the wire feed speed, and the process speed. When building three-dimensional parts, critical points of the tool path planning are acute angled corners and crossing points. In the experiments, boundaries for the process stability in critical points are established and track geometries are compared to previous results. Furthermore, different strategies for the avoidance of material accumulation at the start, end, and crossing points are investigated. The different approaches are discussed, and finally an outlook for further use and possible applications is given.

Aluminum-magnesium-scandium-zirconium (AlMgScZr) alloys need to be rapidly cooled from the liquid state to obtain a high degree of solute supersaturation that helps to exploit the precipitation hardening potential of the material. While AlMgScZr alloys have been successfully used in laser powder bed fusion (LPBF) processes, there has been little research in the field of laser directed energy deposition (DED) of the material. The limited previous studies have shown that the performance of AlMgScZr parts fabricated with DED only reached about 60% of that of the parts fabricated with LPBF. In view of breaking through the limitation associated with the process conditions of conventional DED, this work demonstrates the DED of AlMgScZr alloys in high-speed process regimes and elucidates the mechanism of enhancing the hardness and tensile strength of AlMgScZr alloys by increasing the cooling rate by one to two orders of magnitudes, as well as reducing the track overlapping and the porosity of the specimens during the process. A maximum average hardness of nearly 150 HV0.1 and a max. tensile strength of 407 MPa are obtained by using an energy per unit length of 5400 J/m and a powder feed rate per unit length of 0.25 g/m.

In the Laser Powder Bed Fusion (LPBF) process, parts are built out of metal powder material by exposure of a laser beam. During handling operations of the powder material, several influencing factors can affect the properties of the powder material and therefore directly influence the processability during manufacturing. Contamination by moisture due to handling operations is one of the most critical aspects of powder quality. In order to investigate the influences of powder humidity on LPBF processing, four materials (AlSi10Mg, Ti6Al4V, 316L and IN718) are chosen for this study. The powder material is artificially humidified, subsequently characterized, manufactured into cubic samples in a miniaturized process chamber and analyzed for their relative density. The results indicate that the processability and reproducibility of parts made of AlSi10Mg and Ti6Al4V are susceptible to humidity, while IN718 and 316L are barely influenced.

In this paper, a processing strategy is investigated to increase the geometric accuracy of parts fabricated by laser powder bed fusion (LPBF). Pulsed wave emission (pw) is used for contour exposure in combination with a continuous wave (cw) emission for bulk volume exposure. With the goal of discrete solidification of adjacent melt pools, process parameters of laser power PL, scanning speed vs, and relative pulse overlap ∆xo are developed for contour exposure. Samples with variable contour angles are fabricated to investigate the effect of the pw contour exposure on excessive melting in critical areas of the part prone to overheating. Geometric accuracy and surface roughness are evaluated using SEM images of surface topography and optical surface roughness measurements, respectively. It is observed that excessive melting can be suppressed by using pw contour exposure and usage of modified process parameters. Due to the discretized energy input in pw emission mode, smaller melt pools with lower melt pool fluctuation and powder erosion are produced. The maximum applicable scanning speed is limited by the solidification time of the melt pool and is significantly lower compared to conventional cw contour exposure parameters. Therefore, a combination of cw volume exposure with high process productivity and pw contour exposure for high geometric accuracy is beneficial to limit productivity losses and increase accuracy in part building.

Porosity is a limiting factor in the processing of aluminum-alloys with Directed Energy Deposition (DED) and other Additive Manufacturing technologies, such as Laser Powder Bed Fusion. Especially the mechanical properties of additively manufactured samples are strongly dependent from the porosity, and thus, the understanding of the parameters influencing the porosity is crucial. In this work, a detailed study of factors, which usually are not considered but can affect the porosity of AlMgScZr-alloy DED samples, is presented. To this end, the influence of powder drying, remelting of deposited layers, shielding gas conditions (argon), addition of ceramic nanoparticles, powder morphology and substrate surface conditions are studied and the emerging of shell-like pores is discussed. Experiments were carried out with two DED process variants, namely conventional DED and EHLA (a German acronym for extreme high-speed directed energy deposition), working in significantly different process regimes. DED samples ranging from high porosity (with cross-sectional porosities of more than 10%) to almost fully dense (with cross-sectional porosities of 0.01-0.5%) were manufactured. The findings of this study are considered to be applicable to other aluminum alloys.

Ti-6Al-4V is the most prominent titanium alloy widely used e.g. for aerospace applications. Conventionally, many Ti-6Al-4V aerospace components are produced by a multi-stage hot forging process followed by subsequent machining which often generates a high amount of scrap. Additive manufacturing (AM), such as powder-based laser material deposition (p-LMD), enables parts to be made with geometric freedom and near-net-shape, but so far lacks high deposition rates. The present study proposes high-deposition-rate laser material deposition manufacturing using a large laser beam diameter and increased scanning speed to achieve deposition rates up to 5 kg/h. As Ti-6Al-4V is prone to oxygen pick-up, the process was performed in an inert atmosphere. We determined suitable process windows for tracks without fusion defects and low porosity and investigated microstructure and hardness.

In the present study, we propose a hybrid manufacturing route to produce high-quality Ti6Al4V parts, combining additive powder laser directed energy deposition (L-DED) for manufacturing of preforms, with subsequent hot forging as a thermomechanical processing (TMP) step. After L-DED, the material was hot formed at two different temperatures (930 °C and 1070 °C) and subsequently heat-treated for stress relief annealing. Tensile tests were performed on small sub-samples, taking into account different sample orientations with respect to the L-DED build direction and resulting in very good tensile strengths and ductility properties, similar or superior to the forged material. The resulting microstructure consists of very fine grained, partially globularized alpha grains, with a mean diameter ~0.8–2.3 µm, within a beta phase matrix, constituting between 2 and 9% of the sample. After forging in the sub-beta transus temperature range, the typical L-DED microstructure was no longer discernible and the anisotropy in tensile properties, common in additive manufacturing (AM), was significantly reduced. However, forging in the super-beta transus temperature range resulted in remaining anisotropies in the mechanical properties as well as an inferior tensile strength and ductility of the material. It was shown, that by combining L-DED with thermomechanical processing in the sub-beta transus temperature range of Ti6Al4V, a suitable microstructure and desirable mechanical properties for many applications can be obtained, with the advantage of reducing the material waste.

Spontaneous parametric down-conversion can produce pairs of entangled photons with very different wavelengths. Using SPDC, the scheme of Imaging with Undetected Photons promises to be a versatile tool to facilitate imaging in various spectral ranges and various interferometer designs and geometries. Here, we tackle the task of Imaging with Undetected Photons with a Mach-Zehnder-type Interferometer in MIR. With imaging achieved in a preliminary setup, we investigate the limitations set by nonlinear conversion efficiencies, optical resolution, laser power, and fluorescence of optics on our way to Imaging with Undetected Photons in MIR.

Extreme high-speed laser material deposition, known by its German acronym EHLA, is a new variant of laser material deposition (LMD) with powdered additives. This variant’s process control is unlike that of LMD, where the powder melts as it contacts the melt pool. In the EHLA process, the laser beam melts the powder above the surface of the substrate to deliver a liquid to the melt pool. At a given intensity distribution in a laser beam, the heating of powder particles in the beam path depends largely on the three-dimensional powder particle density distribution (PDD) and the relative position within the laser beam caustic. As a key element of a comprehensive numerical process model for EHLA, this paper presents a statistical/numerical model of the powder-gas jet, as previously published in Experimentelle und modelltheoretische Untersuchungen zum Extremen Hochgeschwindigkeits-Laserauftragschweißen. The powder-gas jet is characterized experimentally and described with a mathematical model. This serves to map the PDD of the powder-gas flow—and particularly the particle trajectories for different grain fractions—as well as the powder mass flows and carrier and inert gas settings, to a theoretical model. The result is a numerical description of the particle trajectories that takes into account the measured particle size distribution with calculations made on the assumption of a constant particle velocity and linear trajectories of the particles.