United States

The laser energy absorption on the keyhole wall is decisive for the thermodynamic behavior and the resultant weld properties in the high-power laser beam welding process. Consequently, a realistic implementation of the effect of the laser radiation on the weld metal is crucial to obtain reliable and accurate simulation results. However, its highly transient nature on a microsecond scale makes the quantitative analysis challenging. In this paper, the influence of the relevant welding parameters, e.g. laser power, welding speed and focus position, on the laser energy absorption is studied statistically, namely in a time-averaged manner, by utilizing multi-physical modeling, in which the three-dimensional transient keyhole dynamics and thermo-fluid flow are calculated. The free surface is tracked by the volume-of-fluid algorithm. An advanced ray-tracing method based on a localized Level-Set strategy is employed to consider the underlying laser-material interactions, i.e. the multiple reflections and Fresnel absorption. The results show that the focus position has a remarkable effect on the time-averaged laser absorption, to which more attention should be paid. In contrast, the laser energy distribution regime is only slightly influenced by the welding speed in the studied parameter range between 1.5 m/min and 3 m/min. The comparison between the calculated results and the experimental measurements ensures the validity of the proposed model.

ICALEO 2024

A Parametric Study of the Laser Energy Absorption in High-power Laser Beam Welding

parametric study

numerical modeling

laser energy absorption

laser beam welding

technical paper

  #### Welcome to the 43rd annual ICALEO!

Attention laser enthusiasts, innovators, and industry leaders! Get ready to immerse yourself in the exciting world of lasers at the 43rd annual ICALEO conference. This year, we gathered in the iconic city of Hollywood, California, for cutting-edge technology, groundbreaking presentations, and unparalleled networking opportunities.
Whether you're a seasoned professional or new to the field of photonics, the 43rd annual ICALEO had something for everyone. 

#### General Chair Welcome Message

It is with immense joy and anticipation that I extend a warm welcome to each and every one of you as the General Chair of this year's ICALEO conference.

This year, we find ourselves in the iconic setting of Hollywood, serving as a fitting backdrop for the extraordinary developments in laser technology and applications unfolding in our community.

Our main sessions cover a diverse range of topics, from the intricacies of micro and nano processing to the transformative power of laser additive manufacturing. We will explore the frontiers of battery technology, delve into the intricate world of artificial intelligence, and witness the seamless integration of lasers into these realms.

For those joining us for the first time, we extend an especially heartfelt welcome. ICALEO is not just a conference; it's a convergence of minds, ideas, and innovations. Beyond the formal sessions, I encourage you to engage in informal exchanges. The spirit of discovery and camaraderie is as much a part of the ICALEO experience as the scheduled sessions.

Thank you for being a part of ICALEO 2024. Whether you are a returning participant or a first-time attendee, your presence adds immeasurable value to our vibrant community. May this conference be, this year again, a catalyst for inspiration, collaboration, and breakthroughs that will resonate in our community and beyond.

Eric Mottay<br>
Congress General Chair, ICALEO 2024


#### About LIA

The Laser Institute of America (LIA) is the professional society for laser applications and safety. Our mission is to foster lasers, laser applications, and laser safety worldwide. Serving the industrial, medical, research and government communities for over 50 years, LIA offers technical information, training and networking opportunities to laser users
from around the globe.

#### About LIA Conferences

The conferences of the Laser Institute of America are the town square of the laser community. A large and diverse group, laser professionals often find themselves disconnected from each other. LIA conferences, however, bring the university researcher, the business executive and the production floor user together under one roof for a unique and
rewarding networking opportunity.

#### Program Tracks
Below is the list of all tracks that were on ICALEO 2024 Conference.

##### Laser Additive Manufacturing
* The Laser Additive Manufacturing (LAM) track is a forum to explore the latest innovations and research in laser-based additive manufacturing (LAM). The Laser Additive Manufacturing track focuses on diverse topics, including laser-based powder bed fusion (PBF-LB), directed energy deposition (DED), and other emerging techniques revolutionizing modern manufacturing processes. From materials science to process optimization, from design innovation to industrial implementation, this track connects researchers, engineers, and industry leaders to exchange insights and share breakthroughs in laser additive manufacturing.

##### Laser Materials Macroprocessing
* The Macroprocessing track comprises some of the most productive laser processing applications. Although these applications have been broadly adopted, researchers and industry are persistently innovating to provide new techniques and novel technologies to advance macro materials processing. The attendees will share and discuss those exciting achievements of their research with peers in these macroscopic specialized sessions.

##### Laser Materials Microprocessing
* The Microprocessing track will consist of papers and talks featuring a wide spectrum of applications and innovative equipment for materials processing in microscales with a strong focus on processes with Short and Ultrashort Pulsed Lasers. The presentations will introduce the latest and greatest advancements in their respective fields, presented by world-leading companies and research organizations. This year we will have talks around the headlines of “Beam shaping”, “Glass”, “Surface processing” and “Drilling” between other topics.

##### Frontiers in Laser Applications
* The Frontier in Laser Applications (FLA) track explores recent, cutting-edge applications of lasers, highlighting innovation at the transition of research and industry. The track has included presentations from a variety of fields: Novel 3-D Printing, Advanced Manufacturing, Laser Manufactured Devices, and Frontiers in Laser Processing. The sessions under the Frontier in Laser Application track promise to bring diverse and unique perspectives from real-world applications across laser manufacturing.

##### Laser in Battery Manufacturing
* Electrification is crucial to address global environmental challenges. The laser plays a key role in most manufacturing steps in battery production with all possible laser applications from ablation, structuring, welding, cutting, and marking. Further improvements in the batteries’ power densities, fast charging properties, and yield in battery production are related to photonics and, thus, lasers. We will hear and discuss the latest developments in research, development, and industrial applications. Join us for this year’s Battery Track.

##### Artifical Intelligence in Laser Processing
* The track ‘Artificial Intelligence in Laser Processing’ at ICALEO 2024 explores the fusion of AI and laser manufacturing. Discover cutting-edge research on optimizing laser processes and enhancing manufacturing efficiency. Explore AI’s diverse applications in parameter optimization, quality prediction, real-time process monitoring, and control. Join us to unlock the potential of AI-driven solutions revolutionizing laser materials processing, delivering unprecedented precision, productivity, and innovation.
<br><br>


To access the site please register [**here**](https://icaleo.org/attend). 

Are you an LIA Member? Find a special discount code in your LIA account at https://www.lia.org/user to apply to your registration for additional savings!

Please register for the ICALEO 2024 Conference to join the event.

Attention laser enthusiasts, innovators, and industry leaders! Get ready to immerse yourself in the exciting world of lasers at the 43rd annual ICALEO conference. 

Recent research has investigated in-situ process characterization for laser welding and Laser-based Powder Bed Fusion of Metals (PBF-LB/M) via a reflection measurement in the laser wavelength. These studies successfully identified the prevailing process regime and the formation of a vapor depression based on in-situ integrating sphere data. This approach has great potential to accelerate the process development by reducing the required ex-situ specimen testing. Unfortunately, the measurement with an integrating sphere does not allow its application as an in-line monitoring system without significantly restricting the process design because the integrating sphere is placed within the gas flow and limits the working area with its small aperture close to the process zone. Therefore, this work investigates directional reflection-based process monitoring in the laser wavelength for laser welding and PBF-LB/M of AISI 316L under insignificant restrictions to the system. For this, the changes in direction and intensity of the reflected laser radiation are monitored for bare plate experiments at various laser powers with photodiodes, which are fiber-coupled to parabolic dish collectors surrounding the working area. These experiments are conducted in a wide working area. It was found that a characteristic change in the reflection direction coincides with the threshold for vapor depression formation, which was previously identified with the integrating sphere. These results show great potential for in-line process monitoring because this novel measuring approach adds directional information to reflection monitoring while decreasing its impact on the process design.

In-Line Process Monitoring in Laser Welding and Powder Bed Fusion of Metals Using Directional Reflection Measurements

Directed energy deposition (DED) for additive manufacturing applications is commonly realized by the usage of industrial robots. The DED processing end effectors are usually mounted on industrial robot systems and can therefore be moved and oriented in up to many degrees of freedom. However, the design of the powder nozzle and the programming of the robot can limit the movement options. For this reason, translational movements, as with conventional 3D printers, are still common today. The end effector is usually guided vertically over the component surface. Although welding in forced position (PA) is preferred.

It may be necessary to tilt the end effector in order to gain advantages during processing due to the constrained position. This is particularly advantageous for overhang structures and is often realized with the help of a turn-tilt positioning table in combination with an industrial robot. However, this approach is in some cases not possible due to geometrical constrains. To extend applications in this direction, advanced methods for slicing the components and programming the robot movements are necessary. The main aspect of this work is the development, testing and evaluation of a multidimensional DED manufacturing approach. This is tested on a thin-walled component with defined overhang areas and compared with conventional approaches. Different strategies are assessed in terms of the geometrical match of the target geometry. Influences of strategies on the results are evaluated. It can be shown that multidimensional path planning approaches lead to a better match of the target geometry.

Influence of Robot-Guide Strategies on the Geometry of Directed Energy Deposition Components

To design future laser manufacturing processes for welding of copper materials, more and more high-end analysis methods are required. A fundamental process understanding by analyzing cause-and-effect relations of process dynamics using inline in situ diagnostics allows for an improved description of laser material interaction. Strategies for a reliable and robust welding process are derived from the findings. In this study, a four-step advanced methodical approach is presented and discussed. In the first step, a fundamental process description of the geometry of the vapor capillary and the formation of weld defects is developed. Therefore, welds on electrolytic tough pitch copper (Cu-ETP) and CuSn6 are carried out to analyze the temporal and spatial vapor capillary dynamics depending on laser power, welding speed, and focal diameter. This fundamental process understanding is transferred to the welding of copper pins in the form of I-pins. For this purpose, impurities and imperfections were applied to the pin surface to investigate the effects on the process result. As a third step, strategies by means of laser intensity distributions were adapted to compensate for imperfections in the welding process. Finally, a sensor vision system is adapted for ideal welding results. Investigations are based on in situ synchrotron analysis at Petra III, DESY in Hamburg. For the experiments, a TRUMPF TruDisk laser (100/400 μm fiber diameter), a TRUMPF TruFiber 6000P (50/100 μm fiber diameter), and a single-mode fiber laser (14 μm fiber diameter) were used. The focal diameter was adjusted with the optical system depending on the investigation.

A Development Workflow Based on In Situ Synchrotron Investigations to Optimize Laser-Processing of Copper Pins

In the realm of laser powder bed fusion, an emerging field with significant growth potential, we still find ourselves at a pioneering stage characterized by the intricate interplay between laser beam properties and their interaction with powdered material.  It is commonly assumed that a high-quality laser having a low M2 value would maintain a consistent M2 value uniformly across the build plate.  However, contrary to this assumption, variations do occur across the build plate, not due to fluctuations in the laser's M2 value, but rather due to alterations in the beam's geometry.  Even in scenarios where the F-theta lens or the 3-D galvo system operate at diffraction-limited conditions, the reality persists that a Gaussian beam with a low M2 value positioned at the nominal zero-zero point of the galvo system will inevitably lose its circular profile at positions beyond the zero-zero point.  At non-zero angles, the beam undergoes distortion, presenting itself to the powdered material as a conic section of the single-mode Gaussian beam.  Employing an innovative M2 measurement apparatus, we have quantified the M2 variation inherent in a fiber laser galvo scanning system across a scan field measuring 175mm x 175mm.  This understanding of the M2 variant holds significant promise in facilitating the stabilization of an optimal spot size.  Through dynamic focusing adjustments based on the powder bed's positional information, we can effectively compensate for the observed variance, thereby enhancing the overall performance and reliability of the laser powder bed fusion process.

M2 Projection Variant in Laser Powder Bed Fusion Systems

Smart-Alloying enables local modification of the chemical composition of metallic components within additive manufacturing processes. This new method represents an innovative process for localized grading of metallic materials in laser-based additive manufacturing. Smart-Alloying involves applying nanoparticulate alloying elements onto the surfaces of additive manufactured components in precise doses using suspensions. The method is shown here using a laser powder bed fusion (PBF-LB/M) as an example. By coating the base material powder and exposing it to the laser source, localized modifications in chemical composition and altered properties can be achieved. Using a chromium-rich ferritic stainless steel as an example, significant alterations in the fundamental microstructure are attained through localized re-alloying of carbon. Investigation utilizing FIB-SEM elucidate the evolution of increasing carbon content within the re-alloyed area. Next to the formation of chromium-rich carbides and ultrafine regions of needle-like martensite, retained austenite could be made visible. The completely renewed microstructure is then further modified using secondary exposures of the laser source. Under the influence of the subsequent melting process, there is an increasing distribution of the re-alloyed carbon, resulting in a completely new structure of a line-shaped duplex microstructure. The integration of secondary exposure introduces a completely novel aspect, offering the potential to merge localized grading via Smart-Alloying with targeted application of laser parameters.

Smart-Alloying for Tailored Microstructures in Laser-Based Metal Additive Manufacturing

The trajectory of metal additive manufacturing is transitioning from rapid prototyping towards on-demand and serial production. Consequently, the paramount objective remains the enhancement of additive manufacturing processes like laser-based powder bed fusion of metals (PBF-LB/M) to meet modern manufacturing needs and reduce environmental impact. Shielding gas flow significantly influences mechanical properties in PBF-LB/M by protecting metal from oxidation and removing process by-products from the powder melting zone. Accordingly, improper shielding gas flow distribution can result in poor part quality, excessive inert gas consumption, and contamination of the building chamber. Presently, a lack of consensus remains regarding which configuration of shielding gas supply is most appropriate in terms of process efficiency. This is the comprehensive investigation of a localized and vertically directed shielding gas flow and its effects on the properties of parts, also taking into account the reduction of inert gas consumption. In contrast to previous investigations, it is shown that enhanced surface roughness and relative density of the parts, as well as minimized contamination of the optics inside the building chamber is achieved through more efficient removal of metal plume particles from the processing zone by localized gas flow. Moreover, the developed computational fluid dynamics (CFD) simulation model enabled the efficient determination of particularly promising gas flow configurations. Furthemore, the validation of the simulation model is demonstrated in an experimental environment. Finally, by localizing shielding gas flow, energy consumption can be reduced by almost half.

Enhancing the Efficiency of Laser-based Powder Bed Fusion of Metals through the Use of Localized and Vertically Directed Shielding Gas Flow

Laser cladding with wire feeding is an advanced surface modification technology that has experienced significant growth in recent decades due to its high deposition rate,

efficient material utilization, strong metallurgical bonding, low dilution ratio, and minimal heat-affected zone. Despite these advantages, the thermo-physical and metallurgical mechanisms underlying the laser wire cladding process are complex, making it challenging to identify the interrelationships among materials, design, process parameters, and performance using traditional expertise or conventional expert systems. This study presents a comprehensive overview of process development, parameter optimization, numerical simulations, and real-time sensing in laser hot-wire cladding using a high-power direct diode laser. A mathematical model was developed to correlate geometric characteristics and dilution ratios with laser processing parameters, establishing the desired process window to enhance deposition rates and achieve high-quality clad layers. To address the effects of residual stresses on mechanical integrity and fatigue life, a three-dimensional uncoupled thermo-mechanical finite element model was developed to predict temperature evolution and thermally induced residual stress distribution in cladding process. Furthermore, a multi-sensor monitoring system, integrating a high-speed camera, spectrometer, and infrared camera, was employed to detect real-time variations in cladding conditions. This study also introduces the concept of a digital twin for the laser wire cladding system, aimed at providing interactive feedback among materials, design, process parameters, and performance to enhance the overall process control and quality.

Laser Cladding with Wire Feeding Using a High Power Direct Diode Laser: Process Fundamentals, Numerical Simulation, and Real-time Monitoring

Electrochemical reduction of CO2 and H2O to synthesize gas (H2 and CO mixture) is of significant interest due to established industrial pathways to tune the H2 to CO composition to generate an array of valuable products including methanol, synthetic fuel, synthetic natural gas, and hydrogen. However, controlled H2:CO ratios are challenging on CO-active electrocatalysts like silver. We demonstrate that applying laser engineering to adjust the surface wetting state of a silver electrocatalyst with water contact angles θw ranging from 47° and 135°, H2:CO ratios can be tuned from 1 to 4 at modest potentials (-0.7 V vs. RHE, RHE - reversible hydrogen electrode) with almost total unity Faradaic efficiency. Both hydrophilic (θw = 47°) and more hydrophobic (θw = 135°) samples showed an increasing H2:CO trend with rising potentials (0.7 V - 1.2 V vs. RHE) due to mass transport. Conversely, a silver electrocatalyst with θw = 110° exhibited a constant H2:CO ratio of 4. This indicates catalyst wettability potentially affects *H and *HOCO intermediates' adsorption, impacting H2:CO ratios. Our results show the feasibility of syngas composition control on silver catalysts via surface wettability, providing a simpler alternative to complex multicomponent electrocatalytic systems. These findings open new avenues for the design of electrocatalysts with tailored syngas production capabilities, which could have significant implications for the sustainable production of chemicals and fuels.

Fine-Tuning Syngas Composition using Laser Surface Modified Silver Electrode for CO2 Electroreduction

With high-speed laser melt injection (HSLMI), it is possible to generate wear-resistant metal matrix composite (MMC) surfaces on tools with great productivity. Since high laser intensities are required for reaching high process speeds, strong interactions between powder particles and the laser beam can occur. In order to reduce the interaction time and to receive a better understanding of the role of particle transport in the HSLMI process, trajectories of spherical fused tungsten carbide (SFTC) particles were analyzed by high-speed imaging. The trajectories were divided into the path from the powder nozzle to the weld pool surface and the incorporation path. First, it was investigated how the travel time is affected by the volume flow rate of the feeding gas and by the powder feed rate. Second, the incorporation of the SFTC particles was analyzed and the incorporation time was measured. It was found that the volume flow rate has a decisive influence on both the travel time and the incorporation time of the particles. Consequently, an increased volume flow rate lead to a significant reduction of the interactions between SFTC particles and the laser beam. Furthermore, a decrease in incorporation time was determined towards the center of the weld pool. Whereas the majority of the SFTC particles was incorporated immediately, some particles dwelled on the surface of the weld pool before being incorporated.

Influencing the Powder Particle Transport in High-Speed Laser Melt Injection

We discuss the direct fabrication of embedded, graphitized features within high-purity, synthetic single-crystal diamond through ultrafast laser micromachining, for the purpose of creating narrow conductive plates in diamond. As an incorporating substrate, carbon in the form of highly pure synthetic diamond offers numerous advantageous physico-chemical properties, including hardness, durability, optical transparency, and extremely high electrical resistance. On the other hand, graphitic carbon can exhibit exceptionally low electrical resistance. For example, sandwich structures consisting of a thin sheet of diamond between two sheets of graphite with areal dimensions of 5 × 1 mm2 and 1 µm gaps between plates may be formed and evaluated. To realize these forms of regionally converted diamond, we employ ultrafast laser micromachining with high numerical aperture focusing and precise positioning control to disrupt the crystalline matrix of a well-confined volume within single-crystal synthetic diamond, forming embedded graphitic features. Graphitized plate regions 1 µm thick with 1 µm separations can be fabricated in this manner, and empirical I-V measurements indicate resistances as low as ~kΩ. We compare plates formed through both Gaussian and Bessel-beam focusing techniques, and we also address challenges involved with fabricating closely parallel, embedded graphitic plates in thick diamond substrates, including aberration, machining time, and cracking.

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A Parametric Study of the Laser Energy Absorption in High-power Laser Beam Welding

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In-Line Process Monitoring in Laser Welding and Powder Bed Fusion of Metals Using Directional Reflection Measurements

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