Schweißbarkeit und Tragfähigkeit von MAG-geschweißten Stumpfnähten als Mischverbindung von Baustählen mit unterschiedlicher Festigkeit. - In: DVS Congress 2023, (2023), S. 289-299
Kurzfassung S. 14
Effect of partial and global shielding on surface-driven phenomena in keyhole mode laser beam welding. - In: Welding in the world, ISSN 1878-6669, Bd. 0 (2023), 0, insges. 1-22 S.
Partial shielding by means of local gas supply has proven to be very effective in reducing spatter. Besides the effect of gas-induced dynamic pressure, the shielding of oxygen is also highly relevant for melt pool dynamics and spatter formation due to the growth of oxides and the influence on surface tension. Therefore, this paper addresses the effect of local supplied argon on oxide growth and seam topography during keyhole mode laser beam welding of high-alloy steel AISI 304. To determine the shielding quality, the results are compared to laser beam welding in a global argon atmosphere. The topography of the upper weld seams was analyzed by scanning electron microscopy (SEM). An X-ray microanalysis (EDX) in line scan modus was performed to determine and to locate the elements which are covering the specimen surface. The chemical state of the found elements was quantified by X-ray photoelectron spectroscopy (XPS). In a last step, high-speed synchrotron X-ray imaging was performed to separate the effect of the gas-induced pressure and the gas-induced shielding on keyhole geometry. The results show that a local supply of argon contributes to a significant difference in oxide growth, affecting melt pool convection and weld seam geometry. It was further shown that the effect of gas flows at low flow rates is primarily because of oxygen shielding, as no significant difference in keyhole geometry was found by high-speed synchrotron X-ray imaging.
https://doi.org/10.1007/s40194-023-01627-y
Einfluss zusätzlich induzierter Temperaturfelder beim Laserstrahlschweißen dünner Bleche. - Ilmenau : Universitätsverlag Ilmenau, 2023. - 1 Online-Ressource (XIII, 168 Seiten). - (Fertigungstechnik - aus den Grundlagen für die Anwendung ; Band 17)
Technische Universität Ilmenau, Dissertation 2023
Während des Laserstrahlschweißens entstehen thermisch induzierte Dehnungen und Spannungen, die zu Verschiebungen der Fügepartner im Prozess führen. Diese Verschiebungen werden durch den Einsatz von Spannsystemen in der Produktion unterbunden. Jedoch sind diese Systeme zumeist nur für eine einzelne Schweißaufgabe ausgelegt. Aufgrund der zumeist massiven Bauweise der Systeme und des anwendungsspezifischen Einsatzes dieser ergeben sich hohe Kosten. Somit ist man bestrebt, die Spannsysteme einfacher zu gestalten und damit Bewegungsfreiheiten der Fügepartner im Prozess zu akzeptieren. Um nun die auftretende Querverschiebung zu minimieren, können zusätzliche Wärmequellen oder Wärmesenken genutzt werden, um Einfluss auf das Temperaturfeld und damit auf das Dehnungsfeld zu nehmen. Im Rahmen dieser Arbeit wurde daher zunächst der Einfluss variierender Schweißparameter (Schweißgeschwindigkeit, voreingestellter Spalt) bei einer einseitig gespannten Fügekonfiguration am I-Stumpfstoß untersucht. Dazu erfolgten Untersuchungen vordergründig am hochlegierten Stahl 1.4301. Unter Verwendung eines Diodenlasers wurde der Einfluss einer zusätzlichen Wärmequelle auf die Verschiebung im Prozess und das gesamte Verzugsverhalten charakterisiert und bewertet. Der Abstand der beiden Wärmequellen zueinander, die Laserleistung und die Spotabbildung wurden dazu variiert. Die Untersuchungen wurden zunächst an einer Blechdicke von 1 mm durchgeführt und sie wurden im Anschluss an die Blechdicken 0,5 mm und 2 mm übertragen. Es ist festzuhalten, dass durch den Einsatz der zweiten Wärmequelle die Verschiebung minimiert und damit längere Schweißnahtlängen erzielt wurden. Jedoch trat ein höherer Beulverzug auf, der auf die vermehrten Längsspannungen im Bauteil zurückzuführen ist. Die Wirkungsweise der zweiten Wärmequelle wurde unter Anwendung der FE-Methoden und einer analytischen Beschreibung näher beleuchtet. Unter Anwendung einer CO2-Düse wurde die Wärmesenke abgebildet, um das sich ausbildende Temperaturfeld zu verkleinern. Ebenfalls wurde der Einfluss der Senke auf die Querverschiebung im Prozess und auf den globalen Verzug nach dem Schweißprozess charakterisiert und bewertet. Für die drei zuvor genannten Blechdicken zeigt sich dabei, dass die Verschiebung im Prozess minimiert und damit eine vollständige Durchschweißung erzielt wurde. Auch nimmt der Gesamtverzug der Bauteile ab. Darüber hinaus fanden vergleichende Untersuchungen an der Aluminiumlegierung EN AW 5754 statt. Es wurde festgestellt, dass die hier im Vergleich zum Stahl höhere Verschiebungen auftraten. Durch den Einsatz der Wärmequelle wurde keine Reduzierung der Verschiebung erzielt. Jedoch wurde unter Anwendung der Wärmesenke eine Minimierung der Verschiebung erreicht und damit längere Schweißnahtlängen realisiert.
https://doi.org/10.22032/dbt.57468
Transient arc characteristic of a commutation switch utilizing high velocity contact separation. - In: Plasma physics and technology, ISSN 2336-2634, Bd. 10 (2023), 2, S. 81-84
Commutation circuits are commonly used for low on state resistance and high current interruption capability if this can not be achieved by a single device or single current switching path. In case of fault detection, a very fast commutation of the current from the low-impedance main current path into the parallel high-current interrupting path is necessary. For single usage applications a low-cost approach is the utilization of a pyrotechnical switch in the low-impedance path. Compared to other electromechanical switches, those switches provide very high velocity of contact separation and thus a fast arc voltage rise with short commutation times. Here, measurements of the contact movement of a pyrotechnical switch were carried out using optical high speed imaging and an arc elongation up to 100ms−1 was calculated. From this, transient arc characteristics were measured in a simplified commutation network during the period until current zero in the low-impedance main current path.
https://doi.org/10.14311/ppt.2023.2.81
Monitoring of joint gap formation in laser beam butt welding using neural network-based acoustic emission analysis. - In: Crystals, ISSN 2073-4352, Bd. 13 (2023), 10, 1451, S. 1-14
This study aimed to explore the feasibility of using airborne acoustic emission in laser beam butt welding for the development of an automated classification system based on neural networks. The focus was on monitoring the formation of joint gaps during the welding process. To simulate various sizes of butt joint gaps, controlled welding experiments were conducted, and the emitted acoustic signals were captured using audible-to-ultrasonic microphones. To implement an automated monitoring system, a method based on short-time Fourier transformation was developed to extract audio features, and a convolutional neural network architecture with data augmentation was utilized. The results demonstrated that this non-destructive and non-invasive approach was highly effective in detecting joint gap formations, achieving an accuracy of 98%. Furthermore, the system exhibited promising potential for the low-latency monitoring of the welding process. The classification accuracy for various gap sizes reached up to 90%, providing valuable insights for characterizing and categorizing joint gaps accurately. Additionally, increasing the quantity of training data with quality annotations could potentially improve the classifier model’s performance further. This suggests that there is room for future enhancements in the study.
https://doi.org/10.3390/cryst13101451
Influence of tool-base metal interference on the performance of an aluminium-magnesium alloy joined via bobbin tool friction stir welding. - In: Metals, ISSN 2075-4701, Bd. 13 (2023), 7, 1215, S. 1-16
Bobbin tool friction stir welding (BTFSW) is a variant of the FSW process which uses the special two-shoulder tool that forms the top and bottom of a weld surface. As such, a significant simplification of the welding setup is achieved. One of the dominant parameters of the BTFSW process is the interference between the tool shoulder pinch gap and the weld metal thickness. In this research, the influence of interference of the square pin tool with convex shoulders on process temperature, microstructure, tensile, impact, and bend performance were studied, and appropriate correlations were devised. The base metal was an aluminum-magnesium alloy in which the interference varied in the range of 0.1 to 0.5 mm. Wormhole defects and irregularities were found in all specimens except in the specimen welded with 0.4 mm interference. An optimal interference of 0.4 mm resulted in the best mechanical properties, which, in terms of tensile strength and reduction of area, were similar to the base metal. Furthermore, the impact strength was significantly higher, which was attributed to the grain refinement effect in the nugget zone.
https://doi.org/10.3390/met13071215
Mechanical properties of MAG butt welded dissimilar structural steel joints with varying strength from grade S355 up to S960. - In: Welding in the world, ISSN 1878-6669, Bd. 67 (2023), 12, S. 2791-2802
Mixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.
https://doi.org/10.1007/s40194-023-01600-9
Similarity analysis of engineer-to-order parts based on a knowledge graph. - In: 16th CIRP Conference on Intelligent Computation in Manufacturing Engineering, (2023), S. 44-49
By estimating manufacturing costs and times at an early design stage, design of a part and production planning can be improved to significantly reduce product costs. Therefore, a concept for automated estimation of costs and times based on similarity analysis is introduced. This concept is based on a semantic and machine-interpretable representation of part geometries, manufacturing processes and machine capabilities stored in a knowledge graph and uses a semantic distance combined with a numerical distance to compare a new part design with already produced parts. With combined similarity measures and information on manufacturing process steps stored in the knowledge graph, it is possible to estimate the expected manufacturing costs and times.
https://doi.org/10.1016/j.procir.2023.06.009
Geometric feature extraction in manufacturing based on a knowledge graph. - In: Heliyon, ISSN 2405-8440, Bd. 9 (2023), 9, e19694, S. 1-15
In times of global crises, the resilience of production chains is becoming increasingly important. If a supply chain is interrupted, a cost-effective solution must be established quickly. In the context of Industry 4.0, the concept of smart manufacturing offers a solution for fast and automated decision-making in production planning. The core idea of smart manufacturing is the digitalization of the product life cycle and the linking of individual phases of this cycle. Computer Aided Process Planning (CAPP) plays an important role as the connecting element between design and manufacturing. An important prerequisite for CAPP is the automated analysis of 3D models of components. The aim of this work is the development of an automatic feature recognition (AFR) -method to recognize geometric manufacturing features and their properties from 3D-models and then store them in a knowledge base. In that way, the result of the design can be automatically analysed and compared with manufacturing information afterwards in order to achieve an automated process planning. Geometric and topological information of a 3D model (STEP-AP242 format) generated by CAD systems is extracted by a Python-script developed and stored in an ontology-based knowledge base. The extracted product data is analysed using a Python-script to identify manufacturing features. To provide a comprehensive extensibility of the model, geometric features are defined according to a layered and hierarchical structure.
https://doi.org/10.1016/j.heliyon.2023.e19694
Temporal resolution of acoustic process emissions for monitoring joint gap formation in laser beam butt welding. - In: Applied Sciences, ISSN 2076-3417, Bd. 13 (2023), 18, 10548, S. 1-17
With the increasing power and speed of laser welding, in-process monitoring has become even more crucial to ensure process stability and weld quality. Due to its low cost and installation flexibility, acoustic process monitoring is a promising method and has demonstrated its effectiveness. Although its feasibility has been the focus of existing studies, the temporal resolution of acoustic emissions (AE) has not yet been addressed despite its utmost importance for realizing real-time systems. Aiming to provide a benchmark for further development, this study investigates the relationship between duration and informativeness of AE signals during high-power (3.5 kW) and high-speed (12 m/min) laser beam butt welding. Specifically, the informativeness of AE signals is evaluated based on the accuracy of detecting and quantifying joint gaps for various time windows of signals, yielding numerical comparison. The obtained results show that signals can be shortened up to a certain point without sacrificing their informativeness, encouraging the optimization of the signal duration. Our results also suggest that large gaps (>0.3 mm) induce unique signal characteristics in AE, which are clearly identifiable from 1 ms signal segments, equivalent to 0.2 mm weld seam.
https://doi.org/10.3390/app131810548