This paper presents an extension to a general-purpose hydrodynamic simulation model for laser-based processes, enabling the simulation of ultrashort pulse laser ablation of dielectric materials. The model incorporates free electron generation through multi-photon and tunneling ionization, avalanche ionization, charge carrier recombination, as well as their diffusion and advection. These processes are fully coupled with compressible multi-phase hydrodynamic equations, allowing for the investigation of phenomena typically unobservable experimentally.\\

A comprehensive validation against experimental data assesses the model's accuracy across various laser parameters. The study also includes a detailed parameter analysis, providing insights into optimal processing conditions. Additionally, the effects of novel beam shapes on ablation dynamics and material removal efficiency are explored, such as the employment of Laguerre-Gaussian beams with orbital angular momentum, so called vortex beams. This extended model offers a powerful tool for understanding and optimizing ultrashort pulse laser ablation of dielectric materials.

Ultra-short pulsed (USP) laser ablation of metals is a key process in precision manufacturing, enabling applications such as micro-drilling. Advancing both its fundamental understanding and industrial applicability requires a detailed investigation of the underlying ablation mechanisms.

This work presents results of a fully three-dimensional multiphysical simulation framework based on continuum mechanics, incorporating a two-temperature model, Drude absorption, compressible Navier-Stokes equations, and pressure- and temperature-based phase change models. To enhance predictive power, a pseudo van der Waals equation of state for the gas phase and a novel material model for the liquid phase have been implemented, specifically designed to address near-critical and supercritical regimes.

The study elucidates ablation mechanisms, from spallation to phase explosion, across a wide range of fluences governed by variations in pulse energy, diameter, and duration. The findings provide new insights into USP laser-metal interactions, contributing to both improved process understanding and optimized laser processing strategies.

This study investigates the application of Optical Coherence Tomography (OCT) for real-time monitoring of the 3D-EHLA (3D-Extreme High Speed Laser Metal Deposition) process. The OCT enables precise measurement of layer thickness and immediate detection of process deviations. The results confirm the capability of OCT to consistently monitor the layer heights at deposition speeds up to 200 m/min. While this project focuses on monitoring, the findings suggest that OCT can also be reliably used for feedback control in future implementations. This integration enhances the reliability of the 3D-EHLA process and supports its implementation in industrial environments. The use of OCT provides a robust solution for addressing the challenges of high-speed additive manufacturing, ensuring product integrity and process efficiency.

In laser-based directed energy deposition (DED), a well-aligned powder stream relative to the laser beam is essential for maximizing process efficiency and minimizing material loss. A detailed understanding of powder stream propagation is therefore critical. In this study, high-speed imaging was used to investigate particle behavior within the powder stream. Using a multi-step evaluation method, the mean velocity, velocity variations, and flight direction of individual particles were determined. Powder channels with varying surface roughness—ranging from Ra = 2.16 µm to 0.27 µm—were tested to assess their influence on stream characteristics. The results reveal that lower channel roughness leads to increased mean particle velocity and significantly narrower flight angles. Specifically, the divergence angle decreased by approximately 61%, which suggests the potential for a more focused powder stream and reduced material loss. These findings offer valuable insights into optimizing powder delivery systems for enhanced efficiency and precision in laser-based DED processes.

EN AW-7075 (AlZn5,5MgCu) is a high strength aluminum alloy for aerospace applications suffering from poor weldability due to solidification cracking susceptibility. In this study, crack free Laser Metal Deposition (LMD) of EN AW-7075 is enabled by adding up to 1 %vol of TiC-nanoparticles (35-55 nm) to the powder feedstock. It was found that nanoparticles are successfully incorporated into the melt pool where they provide for a grain refinement due to inoculation, and thereby eliminate hot cracking.

Moreover, the addition of nanoparticles enhances the absorption of the laser wavelength in the powder (as measured with an Ulbricht sphere) and was found that the incoupling efficiency of the processing laser beam was increased which affects the melt pool dimensions and further helps to prevent lack of fusion defects in processes with the same parameters.

Optical coherence tomography (OCT) can be used to determine the depth of the keyhole during laser deep penetration welding. However, due to the nature of the OCT data a statistical evaluation approach is necessary, reducing the possible temporal resolution. At the same time, keyhole welding is a strongly dynamic process and the penetration depth of welds can fluctuate even under constant process parameters. In this study the time scales on which weld penetration depth deviations can be detected are investigated by examining longitudinal cross sections of weld seams and comparing to the corresponding OCT measurements. Differences between the Materials Steel (S235JRC), Aluminum (EN AW-5083) and Copper (Cu-ETP) are examined. Results show that OCT measurement frequencies are high enough for spontaneous weld depth deviations to be recognized with sufficient precision. Thus, controlling the laser power to achieve a more uniform weld depth driven by real-time OCT measurements is a plausible approach.

Additive manufacturing (AM) of steel is gaining traction in the construction industry, offering the ability to fabricate complex geometries and optimize resource use. Among the AM techniques, Laser-Based Powder Directed Energy Deposition (DED-LB) is notable as it provides a compromise of relatively high productivity with respect to powder bed fusion and fine resolution with respect to arc based DED processes. However, the common steel grades often encounter challenges in meeting construction requirements, including limited compatibility with conventional structural steels concerning bolted and welded assemblies. This study tackles these challenges by developing the DED-LB process with a novel high-strength steel powder feedstock. Through an extensive experimental campaign, the research evaluates the processability of the material, focusing on achieving dense and crack-free steel components. The results highlight optimized deposition strategies providing high mechanical strength, opening new possibilities for its adoption in the construction sector for medium to large sized products.

During laser deep penetration welding, involuntary disturbances of the nominal process can lead to seam imperfections. Due to their possible impairing characteristics on the mechanical properties of the seam, it is of high interest to reliably detect these defects. This can be done by means of sensor based inline process monitoring. While the sensor data can be used to identify the defect location and perform post process repair work, it can also build the foundation to reweld the detected seam segments inline. This study demonstrates an approach to detect process anomalies during laser deep penetration welding of hidden T-joints inline and use a LabVIEW based control algorithm to utilize the scanning capabilities of the welding optic to reweld the defected seam area inline to enhance the seam quality and possibly eliminate necessary post process work.

In order to optimize the behaviour of keyhole and melt pool during laser welding, recent beam shaping technologies allow for manipulating the intensity distribution. Dynamic beam shaping by means of coherent beam combining offers almost unlimited flexibility in changing the intensity distribution on the workpiece surface. The intensity distribution can be dynamically modulated at MHz frequencies. The effects of this fast modulation of the beam shape at previously unachievable frequency ranges has not yet been thoroughly investigated. Within the framework of this study we analyzed the frequency-dependent behaviour of the keyhole and melt pool geometry when changing beam shape periodically at different frequencies. The geometric dimensions were determined by means of Highspeed imaging and polarization goniometer. The results specify the frequency related requirements and limits in dynamic beam shaping during laser welding processes, which are of highest significance to design optimization strategies in laser welding processes.

The identification of optimal process parameters is crucial for the development of high-quality laser welding processes. A challenge in laser welding lies in the occurrence of defects such as spatter, undercuts and hot cracks, which result from instabilities in the keyhole and melt pool during the welding process. A recent study demonstrated that dynamic beam shaping using a laser based on Coherent Beam Combining can effectively stabilize the welding process, as shown for copper welding, which can contribute to an improved weld seam quality. However, determining suitable process parameters typically requires extensive and time-consuming experimental investigations, combined with process-specific expertise. In this study, Bayesian optimisation was applied to efficiently identify parameters for welding using dynamic beam shaping, achieving weld seams with defined depths and minimal defects while significantly reducing the number of required experiments, even at high welding speeds. The experiments were conducted on AW5754.

Using high-speed laser melt injection (HSLMI), it is possible to generate wear-resistant metal matrix composite (MMC) surfaces on tools with excellent productivity. Since high laser intensities are required for the process, strong interactions can occur between hard particles and the laser beam. For reducing the interaction time and gaining a better understanding of the role of particle transport and incorporation in the HSLMI process, the trajectories of spherical fused tungsten carbide (SFTC) particles were analyzed using high-speed imaging. The trajectories were divided into a transport path and an incorporation path. The identified interaction mechanisms were particle deformation, formation of agglomerates and particle disintegration. The volume flow rate of the feeding gas was found to have a decisive influence on both the transport time and the incorporation time of the particles. Consequently, an increased volume flow rate led to a significant reduction in interactions between SFTC particles and the laser beam.

In laser deep penetration welding a constant weld depth is an essential quality measure that is usually obtained by on-line process monitoring techniques such as optical coherence tomography (OCT). However, due to the lack of referential information about the keyhole shape, the extraction of meaningful information about the keyhole from the OCT signal is limited to the keyhole depth which is acquired by means of statistical analyses. In this research on-line X-ray-recordings alongside OCT measurements were conducted during the welding of pure aluminium (EN AW-1050A) in the Rosenthal regime to enable a more profound interpretation of the OCT signal. The comparison between both measurements enabled a correlation between geometric keyhole features and characteristics of the OCT frequency analysis, resulting in an improved time-resolution for the extraction of the keyhole depths. Furthermore, metallographic longitudinal cross-sections were used to investigate how close the keyhole depth is linked to the actual welding depth.

A method for determining material hardness of metals is based on laser-induced shockwaves generated with a pulsed TEA-CO2 nanosecond laser. The laser creates a plasma, which interacts further with the laser beam and subsequently generates a shockwave. The shockwave is ignited above a spherical indenter, made of Al2O3, which is pushed thereby into the metal surface. The indentation geometry can be analyzed to draw conclusions about material properties. The process duration depends mainly on two factors: Generating and analyzing the indentations. To speed up the indentation process an approach with a constant movement of the specimen during indentation was tested. The results indicate that velocities up to 1.8 m/min do not have a significant influence on indentation diameter and depth. Therefore, positioning times with acceleration and deceleration can be avoided and thus up to 30 indentations per second with a distance of 1 mm between each indentation could be realized.

The growth of e-mobility has driven a rising demand for copper welding, a process made difficult by copper’s high reflectivity and thermal conductivity, which often lead to defects like porosity and spattering. Beam shaping enhances weld quality by optimizing energy distribution. Multi-Plane Light Conversion technology offers exceptional flexibility in beam shaping, making it essential to determine the most effective beam configurations.

This study explores multi-physics simulations of various beam shapes, including asymmetric designs, and their impact on key weld seam characteristics such as capillary stability and surface finish. We will outline the process for identifying an optimal beam shape, examine how to adapt it into a manufacturable design, and discuss criteria for evaluating its performance against other configurations, including symmetric shapes and unshaped beams.