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- Laser beam welding (59)
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Organisationseinheit der BAM
- 9 Komponentensicherheit (142)
- 9.3 Schweißtechnische Fertigungsverfahren (139)
- 5 Werkstofftechnik (2)
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- 7 Bauwerkssicherheit (1)
- 7.7 Modellierung und Simulation (1)
- 9.6 Additive Fertigung metallischer Komponenten (1)
Die aktuelle Normung bezüglich mikroskopischer Untersuchungen von Schweißverbindungen und die Zulässigkeit von Mikrorissen sowie deren Definition ist nicht eindeutig. Nach der Darstellung derzeit gültiger Normen im Bereich der Bewertung von Schweißnähten, Qualifizierung von Schweißverfahren und Ausführung von Schweißverbindungen, wird auf Grundlage aktueller Schweißversuche an hochfesten vergüteten Feinkornbaustählen die Problematik von Mikrorissen diskutiert. Offene Punkte und Fragen bzw. Verbesserungsmöglichkeiten werden aufgezeigt und zur Diskussion gestellt. Schließlich wird auf die Klärung des Einflusses von Mikrorissen auf die mechanisch- technologischen Werkstoffkennwerte der Schweißverbindung unter statischer sowie zyklischer Beanspruchung hingewiesen. ---------------------------------------------------------------------------------------------------------------------------------------------------------------
Neither the latest standardisation with regard to microscopic investigations on welded joints nor the permissibility of microcracks and their definition are unambiguous. According to the representation of currently applicable standards in the fields of the assessment of welds, the qualification of welding processes and the execution of welded joints, the problems associated with microcracks are discussed on the basis of the latest welding tests on high-strength quenched-and-tempered fine-grained structural steels. Not only outstanding points and questions but also improvement possibilities are indicated and opened for discussion. Finally, attention is drawn to the clarification of the influence of microcracks on the mechanical- technological material parameters of the welded joint subjected to both static and cyclic stresses.
Schweißzugeigenspannungen in Strahlschweißnähten auf Höhe der lokalen Werkstoffstreckgrenze können die Bauteileigenschaften sowie deren Lebensdauer negativ beeinflussen. Die Nutzung der Schweißquelle für eine nachträgliche Behandlung der geschweißten Bauteile bietet eine kostengünstige und flexible Methode zur Reduzierung dieser Spannungen. Dabei wird durch einen oszillierenden defokussierten Elektronen- bzw. Laserstrahl, der Werkstoff beidseitig der Schweißnaht auf mehrere hundert Grad Celsius erwärmt, um dort zusätzliche Zugspannungsbereiche hervorzurufen. Die so erzeugten Längszugspannungszonen führen zu einer mechanischen Entlastung der Schweißnaht. Experimentelle Messungen der Längseigenspannungen an linearen Elektronen- und Laserstrahlschweißnähten im ersten Teil des Beitrags zeigten, dass die Spannungen mit diesem Verfahren um bis zu 70% reduziert werden können. In weiteren experimentellen Untersuchungen wird dieses Verfahren für kompliziertere Schweißnahtgeometrien getestet. An axialen sowie radialen Rundnähten an ferritischen Werkstoffen konnten ebenfalls hohe Spannungsreduktionen von über 50% erzielt werden. Zudem wurde dieses Verfahren mit einer für das Schweißen üblichen Laserstrahlschweißoptik ohne Scan-Funktion geprüft. Hierbei zeigte das Wärmebehandeln in zwei Arbeitsschritten noch größere Spannungsreduktionen im Vergleich zur Anwendung einer Laserstrahlscanneroptik zur quasisimultanen Wärmebehandlung auf beiden Seiten der Schweißnaht. -------------------------------------------------------------------------------------------------------------------------------------------
Residual tensile welding stresses in beam welds at the level of the local yield strength of the material may influence the properties of components as well as their service lives. The utilisation of the welding source for the subsequent treatment of the welded components offers a cost-favourable and flexible method of reducing these stresses. In this respect, an oscillating defocused electron or laser beam serves to heat the material on both sides of the weld up to several hundred degrees Celsius in order to induce additional tensile stress regions there. The longitudinal tensile stress zones produced in this way lead to the mechanical relief of the weld. Experimental measurements of the longitudinal residual stresses on linear electron and laser beam welds in the first part of the article showed that the stresses can be reduced by up to 70% with this process. In further experimental investigations, this process is tested for more complicated weld geometries. It was also possible to achieve great reductions in the stresses (over 50%) on both axial and radial circular welds on ferritic materials. Moreover, this process was tested with laser beam welding optics which are customary for welding and do not perform a scanning function. In this respect, the heat treatment in two work steps showed even greater reductions in the stresses in comparison with the application of laser beam scanner optics for quasi-simultaneous heat treatment on both sides of the weld.
IIW-2326
Austenitic and austenitic-ferritic CrMnNi-stainless steels are suitable materials in the transport and automotive industry due to their high corrosion resistance and high strength that allows weight and cost savings. This study focuses on the laser weldability of a commercial lean duplex and an austenitic high manganese stainless steel. The impact of different laser sources, i.e. a 5 kW CO2- and a 4 kW Nd:YAG-laser, and of the main process parameters on the resulting weld quality will be investigated. One important aspect will concern the appearance of weld defects such as pores and hot cracks. The factors causing such internal imperfections will be analysed in order to find effective methods for preventing them. Weld microstructure and the associated corrosion and mechanical properties will be assessed with different techniques and adequate process parameters for high quality welds will be determined. The advantages and limitations of the applied welding processes will be evaluated for future applications.
Influence of solute content and solidification parameters on grain refinement of aluminum weld metal
(2013)
Grain refinement provides an important possibility to enhance the mechanical properties (e.g., strength and ductility) and the weldability (susceptibility to solidification cracking) of aluminum weld metal. In the current study, a filler metal consisting of aluminum base metal and different amounts of commercial grain refiner Al Ti5B1 was produced. The filler metal was then deposited in the base metal and fused in a GTA welding process. Additions of titanium and boron reduced the weld metal mean grain size considerably and resulted in a transition from columnar to equiaxed grain shape (CET). In commercial pure aluminum (Alloy 1050A), the grain-refining efficiency was higher than that in the Al alloys 6082 and 5083. Different welding and solidification parameters influenced the grain size response only slightly. Furthermore, the observed grain-size reduction was analyzed by means of the undercooling parameter P and the growth restriction parameter Q, which revealed the influence of solute elements and nucleant particles on grain size.
For differentiating the applicability of various numerical welding simulation methods as well as unifying the prerequisites and the steps to be taken in simulation, normative codes are required for the user. Since any standard-like documents are currently still lacking in this field, the DIN German Institute for Standardization in partnership with the Research Association of DVS German Welding Society have set up a standards committee dealing with the preparation of respective documents.
This article focuses on the presentation of the new DIN Spec 32534-1 explaining the major simulation steps and specifying the application fields and the key terms of welding simulation. In addition, a generally valid simulation structure has been established which is intended to serve as a recommendation for customers and suppliers in formulating and handling a service order as well as for persons who start doing welding simulation for the first time. It additionally gives an overview of the other subject areas dealt with in the standards committee as well as of the international activities in this field.
In lightweight car body shell mass production, due to requirements on vehicle weight reduction and carbon dioxide emissions, joining of advanced high strength steels (AHSS) with different joining procedures and especially hybrid bonding techniques is becoming more and more important. One of these hybrid bonding techniques is the combination of resistance spot welding and adhesive bonding called weldbonding. One of the important advantages of weldbonded joints in comparison to resistance spot welded joints are the enhanced mechanical properties. To guarantee sufficiently high quality conditions regarding the strength of the weldbonded joints, the influences of the applied adhesive systems and of different base metal combinations are studied. This is carried out for both non-corrosive and corrosive environments and for the choice of different joining parameters settings. In particular, the mechanical behaviour of the weldbonded joints is investigated under quasi-static, impact and fatigue loads. Furthermore, the energy absorption of the weldbonded joints for both non-corrosive and corrosive environments is studied. It is shown that the weldbonded joints possess higher mechanical strengths in all load cases (quasi-static, impact and fatigue). Corrosive attack affects weldbonded joints, and the quasi-static strength is reduced. Resistance spot welded joints are not affected by the corrosive attack, but even after several weeks of corrosive attack, the quasi-static strength of weldbonded joints remains higher than that of resistance spot welded joints.
The results of numerical welding simulations strongly depend on its temperature field. In the present paper, the temperature field of a pulsed gas metal arc weld of structural steel S355J2+N (ASTM A572 Gr. 50) with a thickness of 5 mm is experimentally and numerically investigated. In the case of temperature field validation, volumetric Gauss and double-ellipsoid Goldak heat sources are applied. Additionally, different heat source configurations, including adaptations of thermal conductivity, are analyzed regarding their influence on the calculation of welding-induced distortion.
The investigations clarify the influence of heat source configurations on the calculated results, thus, contribute to an improved prediction of welding-induced distortion.
In-situ analysis of solid state phase transformation in TRIP-aided steels by synchrotron diffraction
(2011)
Energy dispersive synchrotron diffraction (EDXRD) analysis and 3 dimensional digital image correlations were conducted to investigate the stress and strain effected transformation behavior during tensile loading of low alloyed TRansformation Induced Plasticity (TRIP) steel. This technique allowed for phase specific stress measurement during certain tensile load steps in the elastic and also plastic regime. Additionally the simultaneous determination of the load dependent phase content was realized. The results show that the martensite transformation starts only after exceeding the overall yield point and is finished before reaching the uniform elongation, whereas a large portion of the austenite remains unchanged in the structure. Furthermore, the martensite transformation related to the stress in the γ-phase and α-phase was analyzed and quantified.