Schweißen mit dem Laserstrahl im Vakuum

Welding with the Laser Beam in Vacuum In the vehicle industry, beam welding methods are successfully applied for the joining of high‐quality parts. Here, the focus is mainly put on drive section components. Especially in component manufacturing of couplings, toothed wheel – shaft joints and drive shafts, electron beam welding using small vacuum cycle chambers is applied. The application of powerful solid‐state lasers results, however, often in negative consequences, such as soiling by process emissions or increased tendency to spatter. The application of laser beam welding in vacuum allows for the reduction of these side effects and, at the same time, for the increase of penetration depth and weld quality. This article introduces first results gained from tests made with workpieces from the vehicle industry.     

Schweißen im Behälter- und Apparatebau

Welding in Tank and Plant Construction Since a relatively limited number of plastics types are used, the welding tasks involved in chemical apparatus engineering can be accomplished with just a few welding techniques are well-known and welding can be carried out efficiently, reliably and economically by this means. In this respect, however, a number of important principles have to be observed. The DVS guidelines provide vital information on questions relating to calculation, design, personnel, equipment, material and testing. Extrusion welding enjoys prime importance as regards quality and economic aspects.     

Der Einfluß von Temperatur und Zeit beim Schweißen von Baustählen mit Strahlen hoher Intensität

Temperature and Time Dependent Fusion Welding with Beams of High Intensity By a special set-up very high local and time-dependent temperature gradients were measured in the weld zone of beam affected areas. Under certain weld conditions a leading preheat wave does not exist. As to the resulting microstructure in the beam, the characteristic steep temperature curves do not allow any prediction. Zones of enlarged hardness were reduced by different heat-treatments.     

Untersuchungen zum Schweißen der aushärtbaren Aluminiumlegierungen AlMgSi 1 und AlCuMg 1 mit einem gepulsten Festkörperlaser

Investigations on the Welding of the Age Hardenable Aluminium Alloys AlMgSi 1 and AlCuMg 1 Using a Pulsed Solid State Laser The age hardenable aluminium alloys AlMgSi 1 and AlCuMg 1 were laser welded using a pulsed 1.2 kW Nd: YAG-laser. Butt welds of 1mm thick plates were produced. With a gap width of 50 μm good welds good be produced even without filler. The small beam diameter (approximately 0.2mm in the focal point) leads to small welds and heat affected zones. The grain size within the weld is small and the amount of grain boundary liquation in the mushy zone is low due to the high temperature gradient in the melt pool. In samples which were welded in the age hardened condition the hardness in the weld drops down to the level of the homogenized condition. However, no significant evaporation or oxidation of alloying elements happens and the maximum hardness can be regained by a complete age hardening treatment. The tensile strength is higher than that of conventional welded sheets but the fatigue strength is reduced significantly.     

Einfluß von Schweißen und Kaltumformung auf das Kurzzeitschwingfestigkeitsverhalten von austenitischem Stahl

Influence of Welding and Cold Forming on the Low-Cycle-Fatigue Behaviour of Austenitic Steel The low-cycle-fatigue behaviour of the austenitic steel X 10 CrNiTi 189, as received and welded, was investigated after cold forming up to 10 per cent by strain controlled tests. The fatigue life to crack initiation of the unwelded material is 10 times higher than the fatigue life of the butt-welded and unfinished material. The grinding of the butt-welds however leads to an increase of the fatigue life by a factor of 4 in comparison to the unfinished state. In comparison to these results obtained under 1 Hz the reduction of the frequency to 0.1 Hz causes a significant cyclic hardening and decrease of the fatigue life. The cold forming remains in all cases without influence. This hardening is a result of the diffusionless transformation of the austenitic microstructure into ferromagnetic α′-martensite under the lower frequency. The increase of the hardness caused also by the cold forming makes the stainless material more sensitive to corrosion.     

Untersuchung von Schmelz‐ und Rekristallisationsprozessen sowie Riss‐, Oxid‐ und Porenbildung beim Schweißen

Investigation of melting and re‐crystallization processes and of crack, oxide and pore formation during welding In the paper some known investigation methods of the primary re‐crystallization and of the structure of the crystallization front are discussed. All these methods have disadvantages, in some cases they cause a limited validity or are expensive. The presented new method is based on the micrographic recording of the melting and solidifying metal surfaces. The method overcomes the above‐mentioned disadvantages. It is able to investigate in the welding seams not only the primary re‐crystallization processes but also the secondary ones including the formation of cracks and pores and the appearance of non‐metallic inclusions like oxides. The facilities of the method are demonstrated on some examples of use.     

Neue Entwicklungen auf dem Gebiet der Schweißtechnik

Recent Development in the Field of Welding Technique. Because of important advantages as soundness of gap, no overlapping and possibility of mechanization the welding procedure takes a considerable plave in the wide field of joint techniques. Often the mechanical properties of the weld metal exceed the values of the base metal. The following report describes recent welding techniques: welding with cored-wire electrodes, the narrow-gap-welding and electron-beam welding at atmosphere. This procedures are often used for the welding of new grades of materials.     

Erfahrungen beim Schweißen gasempfindlicher hochreiner Werkstoffe

Experiences in Welding Highly Pure, Gas-Sensitive Materials Highly pure steels and non-ferrous react during processing, particularly welding, with atmospheric gases and change their service properties. Hence special measures are often necessary in forming and inert gas welding. Taking the specific example of a high pure chromium steel (superferritic), welding properties, processing data and selection of suitable inert gas torches are described. The possibility of applying this information to other materials such as titanium is discussed.     

Schwingfestigkeit schubbeanspruchter Schweißverbindungen nach dem örtlichen Konzept

Fatique strength of shear loaded welded joints according to the local concept In the present work local stress values for fatigue loaded welded joints under shear stresses are derived according to the concept of local elastic stresses by means of test data of the relevant literature re‐analysed in a uniform matter and of numerically obtained notch stress concentration factors. Together with the derived statistically based scatter band of the particular S‐N‐curves and of the local characteristic stress values the obtained results form a reliable basis for codes designing shear stress fatigue loaded welded joints. Further fatigue tests may be desirable howewer under observing usual standards in arranging, carrying out and evaluating fatigue investigations.     

Spannungsberechnungen in Schweißnahtmodellen mit Hilfe neuer Werkstoffgesetze

Stress Calculation in a Weld Model with the Help of New Material Laws Based on the incremental formulations of the material theory from Mises for two dimensional problems a subroutine has been developed for using new material laws in finite element programs. Using this subroutine a phenomenological material law has been used to consider the influence of the strain in finite element calculation of inhomogeneous weldments.     

Schweißverhalten von Aluminium und seinen Legierungen

Weldability of Aluminium and Al Alloys Aluminium is behind steel the most used metal. Advantages of Al-materials are the low weight, the favourable strength and deformation properties, the good corrosion resistance and the good electrical and thermal conductivity. Welding of aluminium encounters difficulties due to high melting oxide layer at the surface, the strong heat dissipation from the welding region, the tendency to form craters or pores and the high heat extension. This contribution describes the basic facts and special features of arc welding and weld properties of aluminium and Al-alloys during welding.     

Elektrodenauswahl für das WIG‐Unterwasser‐Schweißen

Selection of electrode for GTA‐Underwater Welding Reproducible good weld quality and economical benefit of underwater‐welding require a complete automation. For this purpose Gas Tungsten Arc‐welding (GTA or TIG) offers numerous advantages, especially for the root and the following hot pass run. Disadvantages of GTA‐welding are the low weld deposit rate and the limited lifetime of the tungsten electrode. Already small wear damages cause wide alterations of the arc under high surrounding pressure, so that a suited choice of the electrode enables to increase the productivity considerably. Therefore the influence of the electrode features on welding process, arc stability, arc ignition, weld geometry and electrode wear has been investigated. For quick and elementary selection of electrode an assessment catalogue was elaborated.     

Lebensdauer von Schweißverbindungen unter mehrachsigen Belastungen mit variablen Amplituden – Schadensakkumulation und Hypothese der wirksamen Vergleichsspannung

Fatigue Life of Welded Joints under Multiaxial Variable Amplitude Loading – Damage Accumulation and the Effective Equivalent Stress Hypothesis Flange‐tube joints from fine grained steel FeE 460 with different notch factors were investigated under biaxial constant and Gaussian variable amplitude loading (bending and torsion) in the range of 10⁴ to 5 · 10⁶ cycles to crack initiation and break‐through, respectively. In order not to interfere with residual stresses they were stress relieved by a heat treatment. Damage accumulation under a Gaussian spectrum can be assessed for in‐ and out of phase combined bending and torsion using an allowable damage sum of 0.35 for weldments in the as‐welded state and 0.16 for joints with machined weldments with a lower notch factor of the critical area. For the evaluation of multiaxial in‐ and out‐of‐phase stresses the introduced hypothesis of the effective equivalent stress leads to good results. For this, the knowledge of local strains or stresses is necessary. This hypothesis considers the fatigue‐life reducing influence of out‐of‐phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from the weld geometry and loading mode were included.     

Charakterisierung des Ermüdungszustandes in zyklisch beanspruchten Schweißverbindungen durch röntgenographische und mikromagnetische Kenngrößen

Characterization of the Fatigue of Cyclically Loaded Welded Joints by X-Ray Diffraction and Micromagnetic Testing The fatigue behaviour of welded Joints is influenced by the state of the material, its microstructure and residual stresses. By means of the micromagnetic Barkhausen-noise testing method in connection with x-ray diffraction the behaviour of cyclically loaded welded joints of the steel S355 is investigated. Proved by the results of the present investigations, the macro-and micro-residual stresses, micromagnetic and strain characteristic values are strongly connected with each other. Plastic deformations in the HAZ and base material during cyclic loading were identifies by a significant relaxation of the micro-residual stresses and a characteristic change in the micro-residual stresses determined by X-ray profile analysis. Analogous to the growing plastic strain amplitude an advancing damage process in the material is accompained by a significant change in the micromagnetic parameters. As a conclusion the micromagnetic testing method can be suited for the identification of fatigue processes in the material before a final damager of the specimen.     

Schweißen von Hohlstrukturen und offenporösen Metallschäumen für den Einsatz in Kombi‐Kraftwerken

Welding of Hollow Structures and Open‐Porous Metal Foams for Application in Combined Cycle Power Plants For applications within the scope of novel cooling concepts joining technologies for sandwich composites and open‐porous metal foams are researched in the context of the Collaborative Research Centre 561 “Thermally highly loaded, porous and cooled multi‐layer systems for combined cycle power plants”. The research motivation and application fields of the different structures are defined. Welding processes and strategies for manufacturing these structures are specified as well as the joining technologies’ characteristics. Planned future works for enhancements of the processes and structures are listed.     

Abscheidung optisch,elektrisch und akustisch wirksamer Schichten mit dem Doppel‐Ring‐Magnetron

Numerous applications in optics, electronics and sensor technology require thin dielectric films. Conventionally they are deposited by evaporation, activated evaporation, rf‐sputtering or CVD‐techniques. This paper describes the deposition of such films using reactive Pulse Magnetron Sputtering. This technology not only enables a tenfold deposition rate compared to the conventional techniques but also offers new possibilities for influencing film growth. For example it is possible to alter film composition during deposition and hence to deposit complete optical systems without interruption of the plasma process. Furthermore the energetic bombardment of the growing film can be controlled in a wide range by the pulse mode and the pulse parameters. This can be used to either deposit very dense films by strong energetic bombardment or to deposit films at low thermal load onto temperature sensitive substrates. Examples of film deposition for laser optics, electrical insulation applications and surface acoustic wave devices show how these new technological possibilities advantageously can be used for creating innovative layer systems. Film deposition is carried out in stationary mode using a Double Ring Magnetron. This type of magnetron ensures film thickness uniformity better than ± 1 % on 8” substrates by the superposition of the thickness distributions of two concentric discharges.     

Beschichten,Reparieren und Generieren durch Präzisions‐Auftragschweißen mit Laserstrahlen

Laser beam build‐up welding belongs to the technical group of thermal coating. With a coating thickness between 0.1 and 3 mm it is positioned close to PTA and TIG cladding. The special features consist in the excellent controllability of the cladding process, high precision of the material deposition, low thermal influence on the workpiece and low base material mixing, the absence of mechanical effects on the melt pool as well as the large number of coating and substrate materials available for the manufacturing process. Currently, the most important application is the repair of complex shaped and expensive components and tools. Examples are wear damaged moulds, metal forming dies, or aircraft engine components, which original properties can be completely restored by accurate and local replacement of the lost material. In the field of surface protection, laser technology offers advanced solutions for the surface modification of light alloys. Components of Ti, Al or Mg alloys can be protected effectively against wear and corrosion by laser cladding, alloying, and hard particle dispersing. Generating of metal Prototypes by CNC controlled Direct Metal Deposition is a further application of the laser technique. Using this method, mould inserts, active parts of tools, or engine components can be generated directly from the 3D CAD data.