Serge André Dib, Tianqiu Xu, Daniele Colombo, Ali Gökhan Demir
The demand for precise measurements of high-speed laser welding depth is increasing due to growing e-mobility applications. Optical coherence tomography (OCT) can measure keyhole depth in real time. Newer fiber laser generations, ideal for such applications, allow single-mode core/ring configurations. However, OCT’s usability with small keyhole apertures may cause measurement inconsistencies. This work proposes a systematic analysis of signal behaviour using a contemporary fiber laser with a single-mode core and a ring with separate power control, producing focal core and ring sizes of 40 µm and 285 µm, respectively. Bead-on-plate experiments were conducted on 5 mm thick EN AW-1050 Al-alloy. Core and ring power levels were systematically analysed along with scan speeds. The OCT focal beam of 35 µm was aligned with the laser beam for different process parameters. Keyhole depth was compared to molten seam depth from metallographic cross-sections. Alignment protocols were showcased to highlight the sensitivity of OCT measurements.
Keywords: Optical coherence tomography; electric mobility; online monitoring; beam shaping
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Ecem Demir, Cemal Esen, Andreas Ostendorf
The increasing demand for lightweight, high-strength materials has led to the widespread use of aluminum alloys, in various industries. However, welding these alloys, particularly 6082, presents challenges due to their composition, which includes magnesium and silicon. The differing melting points of these elements cause inconsistent melting and solidification, leading to issues such as porosity, cracking, and reduced strength in the heat-affected zone. This study focuses on optimizing BrightLine and Rotating Bifocal Optics techniques to improve weldability and reduce defects like cracks and porosity in 6082 aluminum alloys. Both methods were successfully optimized, achieving the desired welding results.
Keywords: Rotating Bifocal Optics, BrightLine, Laser Welding, 6082 Aluminium Alloys, Disk Laser, Solid State Laser
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Apoorva Nagarkar, Patrick Sperling, Jan-Hendrik Koch, Florian Hüsing, Christian Brecher
Owing to the complex clamping requirements, accurate positioning and limited available area for processing, welding can be classified as a critical process in manufacturing of metallic bipolar plates. A shielding gas assisted welding process is used for isolating oxygen from process zone and to help reduce weld spatter. The gas flow rate can influence the dynamics of melt pool and material solidification which may aid to improve the seam quality. A system was developed for local provision of the gas during the laser welding of bipolar plates. The system can be attached to the clamping fixture to ensure even distribution of the gas in targeted locations and allows the adjustment of the gas flow rate as per requirement. Various shielding gas supply configurations were tested to verify the most effective design for optimal distribution of the gas and cross-sections of weld seams were compared.
Keywords: laser beam welding, metallic bipolar plates, welding fixture, shielding gas, integrative design
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Lucas Westermeyer, Annika Bohlen, Thomas Seefeld
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 limits of detecting weld depth fluctuations by common methods for filtering OCT-data are investigated. First the magnitudes of weld depth fluctuations are measured for the materials steel (DC-01), aluminum (EN AW-1050) and Copper (Cu-ETP) by examining longitudinal cross sections. Secondly common filtering methods are tested on simulated OCT-data in a controlled environment and evaluated in the context of the measurement frequency of the OCT-system. Results show that the weld depth fluctuations are severest in aluminum, followed by copper. The detection of the fastest fluctuations in aluminum using basic filter approaches may present difficulties mainly caused by declining filter accuracy when limited amounts of data are available. Higher OCT measurement frequencies help to solve this problem.
Keywords: keyhole welding; optical coherence tomography; process control
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Eric Pohl, Maurice Langer, Peter Rauscher, Andrés Fabián Lasagni
With new opportunities for processing, recycling and repair, thermoplastic carbon fiber-reinforced polymers (TCFRPs) offer promising approaches to address the economic and sustainability challenges of tomorrow’s aviation industry. This article describes the manufacturing process of the longitudinal butt joint of the world’s largest thermoplastic aircraft structure, created within the frame of European Union’s Clean Sky 2 project. Using a CO2 laser source, fully consolidated multidirectional reinforced TCFRP laminates with six plies are welded onto two fuselage half shells to create the longitudinal butt joint in a one-shot process. During welding, multiple parameters are adjusted constantly to achieve a joint with high homogeneity, including laser power, beam shape and feed rate. The chosen process has shown to produce joints with strengths comparable to those of reference samples produced by conventional hot press co-consolidation, without any post-processing after layup and is demonstrated on real-size component scale for the first time.
Keywords: Thermoplastic carbon fiber-reinforced polymer; Multifunctional Fuselage Demonstrator; Layup; CONTIjoin; Consolidation
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Cryogenic Hydrogen Tanks via Additive Manufacturing and Laser Beam Welding in Vacuum
Benjamin Gerhards, Frederik Diersmann, Christian Otten
The “CHASMA – Cryogenic Hydrogen Tanks via Additive Manufacturing” project aims to demonstrate an innovative liquid hydrogen tank concept for emission-free aviation. Liquid hydrogen tanks operate under a pressure of approximately 4 bar. Thermally induced pressure increases result in "boil-off" gas, Hydrogen must be vented, which reduces efficiency. To minimize this, a multilayer vacuum insulation in a sandwich structure made of additively manufactured chromium-nickel steel is being developed. The individual segments of the resulting tank must be welded together. Laser beam welding in a vacuum combines the welding process and the creation of vacuum insulation in a single step. Trials with 2 mm thick stainless steel sheets, arranged at distances of 15 – 20 mm and welded, demonstrate the process feasibility. The results show a broad parameter range for three-sheet connections, enabled by both beam oscillation and Brightline technology.
Keywords: Laser welding, Laser welding in vacuum, LaVa, hydrogen cryo tank, multi layer welding
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Benjamin Keßler, Thomas Kairet, Olivier Rigo, Pierre Billy, Petra Svarova, Axel Jahn, Dirk Dittrich
The cost aspect is becoming increasingly important in the manufacturing of complex additively manufactured components. One method of reducing costs is hybrid design, i.e. combining semi-finished products with the additively manufactured components. For this reason, the focus is on welding processes to improve overall performance of the final component. Laser welding is particularly suitable for joining components to avoid subsequent processes issues such as distortion due to the low heat input.
As part of the study, the aluminum alloys AlZn5.5MgCu (EN AW-7075) and AlSi7Mg0.6 (EN AC-42200) were used to build components using L-PBF and to weld them using laser high-frequency beam oscillation. That approach enables hot-crack free weld seams and provides high process stability towards avoidance of melt pool blow-outs. The paper shows the developed process approach and resulting properties (microstructure of the weld, tensile strength and fatigue strength) were compared with alternative welding processes (FSW, EBW and GTAW).
Keywords: laser beam welding; aluminium, additive manufacturing, laser powder bed fusion, mechanical properties
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Elucidation of the Spatter Suppression Mechanism in Keyhole Welding of Steel Using a 16kW Disk Laser
Yuji Sato, Masahiro Tsukamoto
Laser beam welding is widely utilized across various industries, including the automotive, nuclear power plant, and petrochemical sectors, due to its excellent compatibility with remote control and automation. It enables high-quality welding with a smaller heat-affected zone compared to other welding techniques. However, during high-power laser irradiation, spatter generation commonly occurs, which contributes to defects such as weld wall thinning and porosity. In our previous study, we determined that spatter generation is caused by fluctuations in the keyhole during laser irradiation in vacuum conditions. To address this issue, this study employed a multi-spot laser approach in laser beam keyhole welding to develop a spatter-free process, clarifying the effects of multi-spot lasers on spatter suppression.
Keywords: Spatter, Steel
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Lea Kroth, Andreas Schkutow, Wolfgang Burgmayr, René Geiger
Hybrid polymer-metal parts gain popularity in the industry, for example for lightweight structures or parts with combined material properties. In order to join metals and plastic laser direct joining is the process to choose, leading to strong and reliable joints. Adhesives, primers or mechanical fasteners are unnecessary in this process, allowing also for application in medical industry. Laser direct joining of metals and polymers is based on two processes. To achieve a good mechanical bond between the parts, the surface of the metal part is structured in a first step. In the second step, the polymer is heated in order to allow the melt to flow into the prepared metal structures. This becomes increasingly challenging when using the high performance polymers usually preferred in the industry with high fiber reinforcement rates. Process optimizations lead to solving challenges such as homogeneous heating, air enclosures in the structures and surface defects.
Keywords: Laser direct joining; metal-polymer connections; laser transmission weldig; high performance polymers
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Marcel Stephan, Dominic Neumayer, Lova Chechik, Dominic Bartels, Stephan Roth, Michael Schmidt
Aluminium alloys of the 7xxx series are renowned for their exceptional strength due to Mg and Zn precipitations. However, the presence of these precipitations reduces the ductility and thus the formability of these alloys, hindering their application for shaping operations e.g. in the automotive sector. One promising approach to improve the formability of this material class is by selectively evaporating these precipitation-promoting elements exploiting their lower evaporation temperature compared to the aluminium matrix. A spatially resolved evaporation can be achieved by localised laser remelting.
In this work, we present results on the selective element evaporation for AA7075. Key characteristics for describing the process are the evaporated amount of elements, the evaporation depth and gradients along z-direction. Cross-sections are analysed using EDX to determine the elemental distribution. Finally, element evaporation is correlated with melt pool size and the applied processing strategy to assess the potentials of a specific laser process
Keywords: Laser welding; Aluminium; Hybrid manufacturing
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Laser keyhole welding of dissimilar material combinations with complex intensity distribution
Manuel Marbach, Jean Pierre Bergmann, Matthias Höbel
Laser keyhole welding of dissimilar materials, such as aluminum-copper (Al-Cu) and copper-steel (Cu-1.4301), is important for joining electrical components (battery to busbar). However, the joining process remains challenging due to the narrow process window and the formation of brittle intermetallic compounds (IMCs). Beam oscillation superimposed to the weld trajectory has indicated to expand the process window by modifying heat distribution and influencing IMC formation.
This study investigates the effects of spatial and temporal beam shapes created by FlexiBeam-technology. This technology utilizes a galvo scanner for non-stationary beam shaping by means of oscillation in the kilo-Hertz regime. It generates intensity distributions, such as lines, rings, rectangles, and complex patterns. Lap-joint configurations of Al-Cu and Cu-Steel1.4301 are analyzed to study weld intermixture and IMC formation. The results show that specific beam shapes improve process stability. They also reduce IMC growth, leading to better joint quality in dissimilar material welding.
Keywords: laser keyhole welding; aluminium; AW-1050A; copper; Cu-DHP; steel; 1.4301; spatial and temporal intensity shaping; velocity power control;
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