FG Füge- und Schweißtechnik
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Laser welding was carried out using a co-axial core-ring beam, with independent control of the power to the core and the ring. The welding process was observed using high-power X-rays and high-speed imaging equipment. Adjusting the relative powers of the core and the ring beams was found to have profound effects on the shape of both the capillary created and the weld melt pool. Moderate laser power densities in the ring were found to increase the top diameter of the weld pool and reduce fluctuations in the welding process. High laser power densities in the ring led to the creation of a second capillary which largely acted independently of the capillary generated by the laser power in the core. At high power densities and welding speeds the two capillaries were almost completely separated in the direction of travel.
Laser beam welding has emerged as a powerful tool for manufacturing copper components in electrical vehicles, electronic devices or energy storage, owing to its rapid processing capabilities. Nonetheless, the material’s high thermal conductivity and low absorption of infrared light can introduce process instabilities, resulting in defects such as pores. This study employs a hybrid approach that combines in situ synchrotron X-ray imaging with compressible multiphysics process simulation to elucidate pore-forming mechanisms during laser beam welding of copper. High-speed synchrotron X-ray imaging with an acquisition rate of 20,000 images/second facilitates the identification of relevant process regimes concerning pore formation during laser beam welding of copper with a wavelength of 1070 nm. Furthermore, in situ observations with high temporal and spatial resolution present a unique database for extensive validation of a multi-physics process simulation based on welding processes using different concentric intensity distributions. These validated simulation results enable thorough comprehension of process-related pore formation based on the interaction between keyhole, melt pool and resulting flow field. The findings show that pore formation is driven by four different mechanisms: bulging, spiking, upwelling waves at the keyhole rear wall and melt pool ejections. The synergy of high- speed synchrotron X-ray imaging and multi-physics modeling provides a fundamental understanding of the chronological sequence of events leading to process-related pore formation during laser beam welding of copper.
The development of hybrid bonds between copper and aluminum is being pursued for reasons of cost, functionality, and weight, particularly in the field of electromobility, to achieve near net-zero emissions. Joining aluminum to copper is a challenge, as interfacial intermetallic compounds have a negative impact on the strength, ductility, and electrical properties of the joint. The development of brittle intermetallic compounds can be limited by targeted temperature control, making solid-phase joining processes particularly suitable. In this article, the fatigue behaviour of friction stir spot welded joints of copper CW004A and aluminum alloy AA1050A with probeless tools is studied. A melt film forms between the metals and the axial force displaces this film laterally, creating an intermediate layer of eutectic and Al2Cu in the joint area. The effect of this layer on the fatigue behaviour of the joint was investigated in this study. At high loads, failure occurs by a combination of Modes I and II with crack propagation in as well as around the bonding area, while at low loads only Mode I is observed. Typically, cracks origin at the spot outer diameter in aluminum, propagate at first in the laterally expelled melt and then through the aluminum sheet, causing unbuttoning.
Welding thin steel sheets in industrial applications is difficult because joint gaps occur during the process, which can lead to weld interruptions. Such welds are considered a reject and in order to avoid the weld to interrupt it is crucial to hinder the formation of joint gaps. Especially laser beam welding is affected by the emergence of gaps. Due to the narrow laser spot, product quality is highly dependent on the alignment and positioning of the sheets. This is typically done by clamping devices, which hold the workpieces in place. However, these clamps are suited for a specific workpiece geometry and require manual redesign every time the process changes. Adaptive clamping devices instead are designed to realize a time-dependent workpiece adjustment. Modeling the joint gap behavior to realize a controller for adaptive clamps can be difficult as the influence of heating, melting, and cooling on the joint gap formation is unknown and varies due to temperature dependent physical properties. Instead, the control parameters and actions can be derived using data-driven methods. In this paper, we present a novel data-driven approach how deep learning can be utilized to manipulate the sheet position during the weld with two actuators that apply force. A temporal convolution neural network (TCN) analyzes the change of the joint gap and predicts the required force to adapt the workpiece position. The developed method has been integrated into the welding process and improves the length of the average weld seam by 39.5% compared to welds without an active adjustment and 1.4% to welds that have been adapted with a constant force.
Laser beam welding can produce narrow, high-quality welds in various industrial joining processes. The thermal expansion and contraction of the metal during the weld results in the displacement of the sheets. That leads to the formation of joint gaps and subsequent to a process interruption. This behavior has only been analyzed to a limited extent and causes manufacturers to rely on heavy clamping systems rather than using more flexible fixtureless approaches. Due to the time-consuming and costly nature of recording and producing erroneous weld seams, such recordings and datasets are rarely available in this area. This often limits the research towards adaptable fixtureless welding setups. Because of this, we present a multi-modal dataset consisting of 100 recorded welds that tracks the metal sheets movement. The developed setup enables the determination of boundary conditions for fixtureless welding. Two types of sensors record the welding process. First, three inductive probes are applied to record the metal sheets` movement and second, a long-wave infrared (LWIR) camera records changes in the thermal radiation field. Two different welding speeds and laser powers were used to produce a variety of welds. The dataset can be used for data-driven algorithms to predict the metal movement, analyze the thermal radiation field, or develop quality control methodologies.
Spatter formation is a major issue at welding speeds above 8 m/min for full penetration laser beam welding of high-alloyed steels. In experiments using a local gas flow directed at the keyhole rear wall, a reduction in spatter formation on the specimen top side was observed for welding of AISI 304. However, the interaction between gas flow and keyhole behavior with respect to the mechanisms and locations of spatter detachment, especially on the bottom side, is not yet fully understood. High-speed synchrotron X-ray imaging enables detailed insights into the keyhole behavior and the spatter formation to obtain a deeper understanding of the underlying mechanisms.
During the reference experiments welding without shielding gas flow, the spatter detach from a melt pool swelling behind the keyhole aperture on both sides of the sheet. A gas flow with a low flow rate of 4.8 L/min reduces the spatter formation on the top side and the keyhole length due to the absence of oxygen affecting the surface tension. A swelling also forms on the keyhole front on the bottom side and small spatter detach undirected. Increasing the flow rate to 12.8 L/min elongates the keyhole, particularly on the specimen top side. The increased momentum transfer of the gas flow results in a periodic keyhole oscillation on the specimen top side. In combination with an elongated melt pool, the oscillation is directly correlated with the hump formation, caused by melt being pushed over the already solidified weld seam. In addition, spatter does not detach from the top side due to the changed melt flow and only detach from the keyhole front on the bottom side.
The paper considers the possibility of using ion-plasma spraying of coatings on low-alloy steels 4Х5MFS and 5ХNM. The choice of these grades is due to the fact that they do not contain tungsten, given the sharp increase in its deficiency, and the molybdenum content is limited, and these steels also meet the requirements for the substrate material on which the titanium nitride coating is applied. The coatings were applied by the method of condensation of the substance under ion bombardment conditions. To determine the required nitrogen pressure, titanium nitride is applied at different partial nitrogen pressures – from 310 -3 to 1 Pa. Coatings obtained under different nitrogen pressures differ in the amount and size of the droplet phase. The largest amount of the droplet phase containing α-Ti is observed in coatings obtained at nitrogen pressures of 3x10–3 Pa, 3x10–2 Pa. An increase in nitrogen pressure (4·10–1 Pa, 1 Pa) significantly reduces the level of microdistortions of crystal lattices in the coating, its plasticity increases. In this regard, the fragility of the coating decreases with its sufficiently high hardness. As laboratory tests have shown, a titanium nitride coating applied under optimal technological parameters increases the corrosion resistance of the materials on which it is applied three times, and scale resistance – two to four times.
A multifractal structural analysis of carbon alloy structures after multi-stage flow processing was carried out. The statistical dimensions of the D-300 structure varied from 4.18 to 2.47, indicating the compactness of filling the space with martensite, bainite and pearlite. Indicators of the statistical dimension of cementite in the range from 2.18 to 1.55 characterize the dimension of the D300 structure. The fractal D0, information D1, correlation D2 dimensions of martensite, bainite, pearlite also varied in the range from 2.66 to 2.13, indicating the heterogeneity of the structure. A one-to-one correspondence between the multifractal indicators of the structure and the hardness of the iron-carbon alloy was established.
This study investigates the factors affecting the mechanical performance of conventional and impulse friction stir welded (FSW and IFSW) AA2024-T351 joints under static and cyclic loading. Emphasis is placed on the influence of fracture-inducing features such as oxide inclusions, constituent particle distributions, crystallographic texture, and precipitation state. A series of IFSW welds produced at varying impulse parameters were compared to conventional FSW welds in terms of microhardness, tensile strength, fatigue life, and Taylor factor distribution. IFSW joints demonstrated a significant improvement in tensile strength and elongation, particularly at higher impulse frequencies. Enhanced material mixing due to the reciprocating tool motion in IFSW resulted in finer particle distribution, more favorable crystallographic texture, and reduced weld pitch, all contributing to increased ductility and strength. Fractographic analyses revealed that fatigue failures primarily initiated in the stir zone, typically at unplasticized metallic inclusions. However, IFSW joints displayed longer fatigue lives, particularly when impulse parameters were optimized. These findings underline the complex interplay of microstructural and textural factors in determining weld performance, highlighting IFSW as a promising technique for enhancing the durability of high-strength aluminum welds.