United States

Additive manufacturing of copper using laser powder bed fusion (PBF-LB/M) enables the production of highly complex components. However, the processing of copper by means of near-infrared laser radiation is challenging due to its absorptivity of only 5 to 20 %. Using a keyhole welding process with a Gaussian intensity distribution increases the absorptivity to up to 53 % due to multi-reflection. This enables the production of components with a density larger than 99.5 % and electrical conductivity larger than 90 %IACS, but this type of welding leads to keyhole porosity due to keyhole instabilities. One way of counteracting is the use of a heat conduction welding process. However, due to the Gaussian intensity distribution, it is not possible to supply sufficient energy to eliminate lack-of-fusion porosity and concurrently avoid the formation of a keyhole. Ring-shaped beam profiles have proven their advantages in stabilizing the PBF-LB/M process with a tendency towards higher laser power, but pure copper has not yet been processed in this way. Therefore, this study investigates the potential of three ring-shaped beam profiles to produce specimens with a density of more than 99.5 % and their respective electrical conductivity using a laser power of up to 1,300 W. In order to understand the underlying welding process, the weld geometry of single-tracks is analyzed. Specimens with a density of up to 99.77 % and an electrical conductivity of up to 101.62 %IACS are produced, whereby the material properties and welding regime depend on the selected ring-shaped beam profile.

ICALEO 2024

Laser Powder Bed Fusion of Pure Copper using Ring-shaped Beam Profiles

near-infrared laser radiation

pure copper

beam shaping

laser powder bed fusion

additive manufacturing

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

technical paper

The present battery production process reaches only a low yield rate in the range of 75 to 90 percent. The complete manufacturing process includes 250 single process steps. Many of these process steps are based on the application of laser beams. The application specialist look as of today just on the point of interaction of the laser beam and assume a constant perfect quality of the workpiece. Online monitoring systems usually just monitor the weld area and don't take variations in the process steps before into account. This paper takes the variation of all process steps into account. The quality reached of many production steps, can get analized by photonic based sensors. In order to increase the yield in battery production, the use of photonic based sensors and the use of these results in a closed loop system to react immediately is one of the possibility to avoid scrap in production. Due to the high number of process steps and interaction of each of these steps, the help of artificial intelligence algorithm are required to achieve a positive impact. The paper describes 3 process steps with a closed loop control system including a solution to rework the results of the process.

On the Way to Battery Production with Zero-Defects With the Use of AI and Photonics

Due to its exceptional dimensional stability in harsh thermal conditions and excellent mechanical and optical properties, Corning ultra-low expansion (ULE®) glass is the material of choice in many high-demanding fields such as aerospace, astronomy, and advanced optics. This material has recently attracted renewed attention with the advent of femtosecond laser technology, with a particular focus on the interaction of ultrafast pulses and the material itself. Phenomena like the formation of self-assembled nanogratings and their thermal stability as well as the darkening of laser-affected zones have then been characterized. This paper presents how to exploit femtosecond selective laser etching (SLE) techniques to manufacture truly three-dimensional (3D) components. To demonstrate the micron-scale accuracy and repeatability of this process from the mm- to the cm-size range, various devices are designed and fabricated: fiber hole arrays with different hole densities, sizes, orientations, and shapes; and fiber V-groove arrays. Additionally, a mechanical flexural fiber mount is presented as an example of how multiple functionalities can be monolithically integrated into a single piece of glass through SLE technology. An example of a passive alignment substrate for optical components is also shown. SLE technique represents a new advancement in the field of microscale manufacturing, enabling the scalable production of custom-designed ULE® glass structures with unprecedented precision and complexity, paving the way for the miniaturized integration of highly stable components.

High Precision Microscale 3D Manufacturing of Ultra Low Expansion Glass by Femtosecond Selective Laser Etching

The increasing demand for miniaturization in electronics has driven the need for advanced fabrication techniques capable of producing through-glass vias (TGVs) with high precision, minimal spacing, and low defect rates. Ultrafast laser-based methods, particularly laser drilling and selective laser etching (SLE), have emerged as critical technologies in the fabrication of TGVs for 3D microchip stacking. Glass offers superior electrical properties, such as reduced signal loss, improved thermal stability and mechanical strength compared to traditional materials like silicon. This study presents advancements in ultrafast laser drilling techniques for TGV fabrication. We demonstrate the feasibility of taper-free fabrication of high-aspect-ratio holes, addressing a common challenge in traditional ablation-based drilling methods. By controlling laser parameters and employing optimized processing strategies, we achieve uniform hole diameters below 100 um, reaching an aspect ratio of 1:20 without chemical etching. Our research focuses on process speed optimization to enhance fabrication efficiency. Moreover, we demonstrate a high aspect ratio and high-speed percussion drilling of through holes for the glass substrates thicker than 0.5 mm. The results were obtained using <200 uJ ultrashort pulses at 1030 nm wavelength (Jasper X0, Fluence, Poland). Our findings highlight the remarkable capabilities of ultrafast laser drilling for TGV fabrication for new microchip generation.

Advancements in Femtosecond Laser Drilling Techniques for Through-Glass Vias

Femtosecond laser processing is used in a wide range of  modern technology manufacturing. Its significance is particularly evident in sectors that demand high accuracy and minimal heat effects, like microelectronics, biomedical devices, and photonics. The field has recently seen ultraviolet (UV) wavelengths become a standard in laser processing as optical coatings have become resistant to prolonged exposure to UV radiation. These features have opened up exciting new avenues in both manufacturing and scientific research.

In this study, we explore the application of novel femtosecond laser that produces a flat-top intensity distribution, at a wavelength of 254 nm (4th harmonic of fundamental 1030 nm radiation). The 4th harmonic offers unique advantages in material processing due to its position in the direct absorption regime for multiple glass and polymer materials. Our experiments demonstrate the effective ablation of soda-lime glass using this specific wavelength.

A key feature of our methodology is the employment of a flat-top intensity distribution in the laser beam. Comparing to the conventional case of the Gaussian intensity distribution, a notable advantage is the consistent size of the damage patterns (craters) in both transverse directions, irrespective of variations in pulse energy or number of pulses impinged. This consistency is not achievable with traditional Gaussian distributions, making this approach more precise and predictable. In addition, the flat-top DUV laser source may be used for the removal of coatings on transparent substrates.

Processing of Transparent Glass Using a Femtosecond Duv Flat-Top Laser Source

The parameter space of beam shaping methods for laser driven processes is getting broader looking at spatial light modulators or coherent beam combining. While systems technology is improving, the knowledge on using beam shaping is mostly empirical driven and not - yet - based on a comprehensive understanding of causalities in the process physics. This presentation will, based on a comprehensive literature study, show some fundamental thoughts on how to connect beam shaping to process physics. To do so, laser deep welding is used as an example process, ready to be improved. In the presentation systems technology will be touched and compared. A process driven view on beam shaping will be developed and then connected to systems technology. Own research results will be used to underline the hypotheses given.

Beam Shaping vs. Feature Synchronous Energy Coupling

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.

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

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.

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On the Way to Battery Production with Zero-Defects With the Use of AI and Photonics

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