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Gourishetti, Saichand; Schmidt, Leander; Römer, Florian; Schricker, Klaus; Kodera, Sayako; Böttger, David; Krüger, Tanja; Kátai, András; Bös, Joachim; Straß, Benjamin; Wolter, Bernd; Bergmann, Jean Pierre
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
Balos, Sebastian; Labus Zlatanovic, Danka; Kulundzic, Nenad; Janjatovic, Petar; Dramicanin, Miroslav; Lanc, Zorana; Hadzistevic, Miodrag; Radisic, Slobodan; Rajnovic, Dragan; Pecanac, Milan
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
Brätz, Oliver; Arnim, Mareike; Eichler, Stefan; Gericke, Andreas; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth-Michael
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
Duden, Anna J.; Köhler, Tobias; Peters, Diana; Redeker, Julian; Girkes, Florian; Bergmann, Jean Pierre; Vietor, Thomas
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
Köhler, Tobias; Song, Buchao; Bergmann, Jean Pierre; Peters, Diana
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
Kodera, Sayako; Schmidt, Leander; Römer, Florian; Schricker, Klaus; Gourishetti, Saichand; Böttger, David; Krüger, Tanja; Kátai, András; Straß, Benjamin; Wolter, Bernd; Bergmann, Jean Pierre
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
Diegel, Christian; Mattulat, Thorsten; Schricker, Klaus; Schmidt, Leander; Seefeld, Thomas; Bergmann, Jean Pierre; Woizeschke, Peer
Interaction between local shielding gas supply and laser spot size on spatter formation in laser beam welding of AISI 304. - In: Applied Sciences, ISSN 2076-3417, Bd. 13 (2023), 18, 10507, S. 1-25

Background. Spatter formation at melt pool swellings at the keyhole rear wall is a major issue for laser deep penetration welding at speeds beyond 8 m/min. A gas nozzle directed towards the keyhole, that supplies shielding gas locally, is advantageous in reducing spatter formation due to its simple utilization. However, the relationship between local gas flow, laser spot size, and the resulting effects on spatter formation at high welding speeds up to 16 m/min are not yet fully understood. Methods. The high-alloy steel AISI 304 (1.4301/X5CrNi18-10) was welded with laser spot sizes of 300 μm and 600 μm while using a specially designed gas nozzle directed to the keyhole. Constant welding depth was ensured by Optical Coherence Tomography (OCT). Spatter formation was evaluated by precision weighing of samples. Subsequent processing of high-speed images was used to evaluate spatter quantity, size, and velocity. The keyhole oscillation was determined by Fast Fourier Transform (FFT) analysis. Tracking the formation of melt pool swellings at the keyhole rear wall provided information on the upward melt flow velocity. Results. The local gas flow enabled a significant reduction in the number of spatters and loss of mass for both laser spot sizes and indicated an effect on surface tension by shielding the processing zone from the ambient atmosphere. The laser spot size affected the upward melt flow velocity and spatter velocity.



https://doi.org/10.3390/app131810507
Brätz, Oliver; Arnim, Mareike; Eichler, Stefan; Gericke, Andreas; Henkel, Knuth-Michael; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike
Load-carrying capacity of MAG butt and fillet welded joints on high-strength structural steels of grade S960QL and S960MC. - In: ce/papers, ISSN 2509-7075, Bd. 6 (2023), 3/4, S. 587-594

The use of high-strength structural steels brings great advantages in constructions regarding material requirements, weight reduction and productivity. Different steel grades within the S960 range are commercially available but not yet represented in Eurocode 3. The weldability of these steels is limited to smaller process windows to ensure the high material properties. In contrast to steels with moderate strength, there is a considerable risk of softening in the heat-affected zone causing a strength reduction of the connection. By now, the current EN 1993-1-12 only extends the design rules to cover steel grades up to S700. Therefore, the potential of these high-strength steels cannot be used to its full extent in structural engineering. This study, made within a steel application research project (FOSTA P 1507), deals with the weldability and load-carrying capacity of butt and fillet welded joints of S960QL and S960MC produced by gas-shielded metal arc welding. The influence of different bevel geometry, filler metal, and plate thicknesses was investigated. To extend the design rules up to S960, a need of an amendment was found for some combinations.



https://doi.org/10.1002/cepa.2478
Arnim, Mareike; vonEichler, Stefan; Brätz, Oliver; Hildebrand, Jörg; Kuhlmann, Ulrike; Bergmann, Jean Pierre; Flügge, Wilko
Study on load-carrying capacity of MAG butt-welded mixed connections with different steel strengths. - In: ce/papers, ISSN 2509-7075, Bd. 6 (2023), 3/4, S. 1458-1463

Mixed connections of normal-strength steel and high-strength steel can enable an optimum resource-saving use of materials by adapting the material strength to the forces acting on them. But the design and calculation of butt-welded mixed connections is not clearly regulated in the currently valid standards EN 1993-1-8 and EN 1993-1-12. In the research project Effective design concepts for mixed connections in steel structures an extensive experimental program with 180 mixed connections has been conducted to investigate the load-carrying capacity and behaviour of these connections. The weld joint specimens were made with normal-strength steel S355J2+N and different high-strength steels S690QL, S700MC or S960QL. Varying parameters were also the filler metals, plate thicknesses, weld bevels and the heat input during welding. The influence of these parameters on the load-carrying capacity and the deformation behaviour of mixed connections was investigated. Moreover, high-resolution microhardness mappings (UCI) on the welded specimens were carried out to examine the formation of the soft zone in the heat-affected zone of the high-strength steels.



https://doi.org/10.1002/cepa.2262
Eichler, Stefan; Arnim, Mareike; Brätz, Oliver; Hildebrand, Jörg; Gericke, Andreas; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth-Michael
Heat management and tensile strength of 3 mm mixed and matched connections of butt joints of S355J2+N, S460MC and S700MC. - In: ce/papers, ISSN 2509-7075, Bd. 6 (2023), 3/4, S. 1476-1482

High-strength structural steels are beneficial in terms of the sustainability of constructions due to the possible reduction of weight and overall material needs. Nevertheless, high-strength steels have a smaller processing parameter range in regarding the specific heat input and resulting cooling rate. Especially the cooling time t8/5 characterizing the time span to cool down from 800 to 500 ˚C is an important indicator. Single layer butt-welded gas metal arc welding (GMAW) connections of 3 mm plates between normal strength (S355J2+N, S460MC) and high-strength steels (S700MC) as well as matched connections (S460MC, S700MC) are carried out. Hereby, the influence of the energy input, melting rate, joint preparation, filler metal (matching and undermatching) and backing methods are observed. Spatially resolved IR-thermal observation shows variations within the welds of up to 50 % in the cooling time t8/5 depending on those parameters. These fluctuations lead to significant changes of the microstructure within the melting and heat-affected zone. UCI hardness mappings show the softening and microstructural change within these zones. Those soft zones can be the region of failure for butt welded connections as shown by transverse tensile tests with spatially resolved optical strain measurements. The results obtained can be used to define more precise welding procedures of these types of connections and also are used to develop design rules for mixed connections made of normal strength and high-strength steel.



https://doi.org/10.1002/cepa.2265