Improving weld quality with optimized bobbin tools: an innovative approach to friction stir welding of aluminium

Friction stir welding (FSW) has gained significant attention as a viable method for joining aluminum alloys due to its ability to produce high-quality welds. In recent years, bobbin tools have emerged as an innovative tool geometry for FSW of aluminum. Because of their unique tool design and weld setup, there is no backing plate needed and weak points such as root defects cannot form. The creation of strong and high-quality joints in similar aluminum structures is a challenging task for welding processes. In this regard, the current study aims at investigating the effect of shape-optimized bobbin tools on the welding quality of the joints. For this purpose, a simulation of the critical run-in process was performed in an initial step. Thus, the contact conditions between the tool and the work-piece could be analyzed, and a qualitative impression was gained of the welding behavior of this welding set-up. Subsequently, the tool was shape-optimized by imposing ideal contact conditions. The optimized and non-optimized tools were then used to perform FSW on similar aluminum joints made of AA5754. The resulting joints were analyzed for their mechanical and microstructural properties, and it was found that the optimized tool led to a different microstructure and tensile strength than the non-optimized tool. Therefore, this study provides a new and effective approach to improve the weld quality of similar aluminum joints by optimizing the geometry of bobbin tools through simulation

Prozesscharakterisierung des Kompaktierungsverhaltens metall-ultraschallgeschweißter Verbindungen aus Cu-ETP und Aluminium-Fahrzeugleitungen

Das wärmearme Fügeverfahren des Metall-Ultraschallschweißens (USMW) gewinnt zunehmend Bedeutung in der Aerospace- und Automobilindustrie für die Erzeugung elektrisch leitfähiger Verbindungen. Trotz seines wachsenden Einsatzes besteht sowohl aus industrieller als auch aus wissenschaftlicher Sicht ein erhebliches Defizit im Verständnis dieses Prozesses, insbesondere beim Fügen von Fahrzeugleitungen und Terminals. Diese Arbeit zielt darauf ab, das Prozessverständnis zu vertiefen und neue Methoden zur Prozessüberwachung zu entwickeln. Im Fokus der experimentellen Analysen standen die thermischen, mechanischen, metallurgischen und vibrometrischen Eigenschaften des Schweißprozesses. Thermografische Messungen verdeutlichten, dass die Wärmeentwicklung primär im Kontakt zwischen Fahrzeugleitung und Sonotrode auftritt. Vibrometrische Untersuchungen offenbarten ein charakteristisches Schwingungsverhalten des Ambosses, das Ansätze für eine fortgeschrittene Prozessüberwachung bietet. Ein innovatives, auf dem thermoelektrischen Effekt basierendes Verfahren zur Bestimmung der Fügezonentemperatur ermöglichte eine präzise und kostengünstige Überwachung des Fügeprozesses. Zudem erwies sich die Rekonditionierung von kontaminierten Litzenleitungen durch Kaltgasplasma als effektiv, wodurch die Schweißbarkeit von stearinsäurekontaminierten Verbindungen nahezu vollständig wiederhergestellt wurde. Diese Ergebnisse verbessern das Prozessverständnis und erhöhen die Prozesssicherheit des USMW-Verfahrens, was dessen industrielle Anwendung erheblich unterstützt.The low heat joining process of ultrasonic metal welding (USMW) is increasingly important in the aerospace and automotive industries for creating electrically conductive connections. Despite its growing use, there is a significant lack of understanding of this process from both an industrial and scientific point of view, especially in the joining of vehicle wires and terminals. This work aims to deepen process understanding and to develop new methods for process monitoring. The focus of the experimental analyses was on the thermal, mechanical, metallurgical, and vibrometric characteristics of the welding process. Thermographic measurements clarified that heat development primarily occurs in contact between the vehicle wiring and the horn. Vibrometric studies revealed a characteristic vibration behavior of the anvil, offering approaches for advanced process monitoring. An innovative method based on the thermoelectric effect for determining the joining zone temperature enabled precise and cost-effective monitoring of the welding process. Additionally, the reconditioning of contaminated wires through cold gas plasma proved effective, almost completely restoring the weldability of stearic acid-contaminated connections. These results improve the process understanding and increase the process safety of the USMW process, significantly supporting its industrial application

Analysis of the Oscillation Behavior of Hybrid Aluminum/Steel Joints Realized by Ultrasound Enhanced Friction Stir Welding

Friction stir welding (FSW) is an innovative solid-state joining process, which is suitable for joining dissimilar materials with strongly differing physical and chemical properties such as aluminum and steel. Where other joining methods such as fusion welding struggle to achieve appropriate joint strengths due to the excessive formation of brittle aluminum-rich intermetallic phases (IMP), FSW joints of aluminum and steel only show small layers of IMP, thus, sufficient tensile strengths in proximity to the maximum tensile strength of the weaker aluminum base material can be reached. With the aim to optimize the mechanical and microstructural properties of such dissimilar joints for widening the field for possible industrial applications, several hybrid friction stir welding methods have been developed which include an additional energy input, whereas the ultrasound enhancement (USE-FSW) is one of the most promising. The current work was carried out on AA6061/DC04 joints which were successfully friction stir welded with and without ultrasound support, in respect to the influence of varying the ultrasound transmission side. The functionality of the USE-FSW setup could be verified by multi point laser vibrometer measurements. Additionally, a higher proportion of transversal oscillation for the transmission of power ultrasound into aluminum could be detected using a scanning vibrometer. In comparison to the conventionally friction stir welded joints the ultrasound enhancement led to an avoidance of weld defects and an increase of the steel particle volume in the stir zone. The joint produced with power ultrasound transmission via aluminum resulted in a more uniform interface

Arc Brazing of Aluminium, Aluminium Matrix Composites and Stainless Steel in Dissimilar Joints

The publication describes the approaches and results of the investigation of arc brazing processes to produce dissimilar joints of particle reinforced aluminium matrix composites (AMC) to aluminium alloys and steels. Arc brazing allows for low thermal energy input to the joint parts, and is hence suitable to be applied to AMC. In addition, a braze filler B-Al40Ag40Cu20 alloyed with Si with a liquidus temperature of below 500 °C is selected to further reduce the thermal energy input during joining. The microstructures of the joining zones were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and X-ray diffraction analysis (XRD), as well as their hardness profile characterised and discussed. Joint strengths were measured by tensile shear tests, and resulting areas of fracture were discussed in accordance to the joints’ microstructures and gained bond strength values

Mechanical and Microstructural Characterization of Ultrasonic Welded NiTiCu Shape Memory Alloy Wires to Silver-Coated Copper Ferrules

The aim of this study was to investigate the mechanical behavior, and the microstructure of NiTiCu shape memory alloy wires joined with silver-coated copper ferrules via ultrasonic spot welding. Therefore, the electrical resistance was measured during tensile testing, and the joints were analyzed by scanning electron microscopy. Energy-dispersive X-ray spectroscopy has determined the compounds of the developed welding zones. Furthermore, the influence of the ultrasonic welding on the transition temperatures of the NiTiCu wires was examined via differential scanning calorimetry. Tensile tests have shown that the ultimate tensile strengths of the joints reached almost 100% of that of the base material. An additional heat treatment rebuilt the typical shape memory alloy behavior after the ultrasonic welding process detwinned the martensitic wires. In addition, the B19′ structure of the welding zone and the ultrasonic spot-welding process did not affect the transition temperatures of the shape memory alloy

Verfahren zum Herstellen einer stoffschlüssigen Verbindung von Werkstücken mittels Rührreibschweiße

In the method for producing a material bond between workpieces by means of friction stir welding, during the rotation and performance of the feed movement, vibrations are introduced by at least one device (2) into the workpieces (8), into the joining zone of the workpieces (8), via the holder of the pin-like tool (1, 11), the holder of a shoulder (10, 16d) not connected to the pin-like tool, and/or a counterholder (9) arranged on the side of the workpieces (8) opposite from the holder of the pin-like tool (1, 11), at a frequency that corresponds to a natural resonant frequency of the device used for introducing the vibration. A device that is designed for carrying out a thermal pulse method can be used on its own or in addition for introducing vibrations at a frequency that corresponds to the natural resonant frequency of the holder of the pin-like tool (1, 11) with the pin-like tool (1, 11) into the workpieces (8), the holder of the pin-like tool, a shoulder (10) of the pin-like tool and/or the counterholder (9)

Hybrid joints of die-casted aluminum/magnesium by ultrasound enhanced friction stir welding (USE-FSW)

As consistent lightweight construction nowadays becomes more and more important in smart production processes, the demand for joints of dissimilar materials increases steadily due to their variety of advantages in engineering. Friction stir welding (FSW) is an innovative pressure welding technique, which offers the ability to realize such dissimilar joints while achieving high tensile strengths. Furthermore, it has been proved that ultrasound enhanced friction stir welding (USE-FSW) has an additional positive effect on the joint strength of these compounds due to the additional introduction of mechanical energy into the joining zone through influencing the formation of brittle intermetallic phase (IMP) and particle allocation in the weld nugget. In this paper, the influence of power ultrasound introduction via USE-FSW on hybrid joints of industrially die-cast aluminum alloy EN AC-48000 (AlSi12CuNiMg) and magnesium alloy AZ91 (MgAl9Zn1) has been investigated. Besides mechanical testing, light microscopic and scanning electron microscopic investigations (SEM) as well as differential scanning calorimetry have been conducted. Furthermore, corrosion behavior of the base material and X-ray radiographic images of FSW and USE-FSW joints have been examined. Additionally, the influence of different ultrasound powers and changes in the introduction side on the tensile strength and microstructure of the joints has been investigated