Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
Dokumenttyp
Sprache
- Englisch (101)
- Deutsch (25)
- Russisch (2)
- Italienisch (1)
- Mehrsprachig (1)
Schlagworte
- Laser beam welding (35)
- Solidification cracking (19)
- Laser metal deposition (11)
- Hybrid laser arc welding (10)
- Additive manufacturing (9)
- Laser welding (8)
- Hybrid laser-arc welding (7)
- Microstructure (7)
- Thick-walled steel (7)
- Critical strain (6)
- Laserstrahlschweißen (6)
- Numerical simulation (6)
- Additive Manufacturing (5)
- Hot cracking test (5)
- Laser Metal Deposition (5)
- Mechanical properties (5)
- Thermography (5)
- Additive Fertigung (4)
- Electromagnetic weld pool support (4)
- Elektromagnetische Schmelzbadunterstützung (4)
- Inconel 718 (4)
- Laser-Pulver-Auftragschweißen (4)
- Laserhybridschweißen (4)
- Stainless Steel (4)
- 316L (3)
- 9%Ni steel (3)
- High power laser beam welding (3)
- Hot cracking (3)
- Hybrid Laser Arc Welding (3)
- Laser hybrid welding (3)
- Mechanical mismatching (3)
- Partial penetration (3)
- Ti-6Al-4V (3)
- Weld pool shape (3)
- Aluminium (2)
- Austenitic stainless steels (2)
- Bulging effect (2)
- CTW-Test (2)
- Charpy impact toughness (2)
- Circumferential weld (2)
- Cryogenic steel (2)
- Defokussierung (2)
- Duplex AISI 2205 (2)
- Duplex stainless steel (2)
- Duplex steels (2)
- Edge effects (2)
- Electromagnetic weld pool control (2)
- End crater (2)
- Endkrater (2)
- Ferromagnetischer Stahl (2)
- Full penetration (2)
- Gap bridgeability (2)
- Hardness (2)
- Heißrissresistenz (2)
- Hot crack (2)
- Hybrid welding (2)
- In situ strain (2)
- LMD (2)
- Laser beam Welding (2)
- Laser-Hybridschweißen (2)
- Local critical strain (2)
- Matching ferritic welding electrode (2)
- Material transport (2)
- Melt pool dinamics (2)
- Nickel (2)
- Optical flow (2)
- Optical measurement (2)
- Optical measurment technique (2)
- Pipe manufacturing (2)
- Pipeline (2)
- Preheating (2)
- Process monitoring (2)
- Rundnaht (2)
- SMAW (2)
- Ship building (2)
- Single pass welding (2)
- Strain rate (2)
- Temperature behavior (2)
- Thermal cycles (2)
- Thermografie (2)
- Weld defects (2)
- Weld pool (2)
- Weldability (2)
- laser welding (2)
- Überlappbereich (2)
- 3D Druck (1)
- 3D printing (1)
- 3DDruck (1)
- 9%Ni steel, (1)
- AC magnetic field (1)
- Additiv (1)
- Analytical model (1)
- Artificial Intelligence (1)
- As-shielded arc welding (1)
- Aufbaustrategie (1)
- Austenitic welding electrode (1)
- Austenitische Stähle (1)
- Bending test (1)
- Build - up Strategy (1)
- Build-up strategy (1)
- Bulge effect (1)
- Bulging (1)
- CFD model (1)
- CFD-model (1)
- CO2 lasers (1)
- CTW test (1)
- Clad steels (1)
- Combined laser manufacturing (1)
- Contact element (1)
- Conventional Ni-based austenitic welding electrode (1)
- Convolutional neural network (1)
- Corrosion (1)
- Crater (1)
- Critical strain rate (1)
- Cryogenic Steel (1)
- DIC technique (1)
- Deposition rate (1)
- Dickblech (1)
- Different welding position (1)
- Digitale Bildkorrelationstechnik (1)
- Direct Energy Deposition (1)
- Direct Laser Metal Deposition (1)
- Direct energy deposition (1)
- Duplex (1)
- Duplex stainless steels (1)
- Edge quality (1)
- Electromagnetic Force (1)
- Electromagnetic Weld Pool Support (1)
- Electromagnetic backing (1)
- Electromagnetic stirring (1)
- Electromagnetic support (1)
- Electromagnetic weld pool support system (1)
- Elektromagnetische Badstütze (1)
- Elektromagnetische Schmelzbadsicherung (1)
- Elektromagnetische Schmelzbadstütze (1)
- Element transport (1)
- Equivalent heat source (1)
- Externally loaded test (1)
- FE-model (1)
- FEA (1)
- FEM (1)
- Ferritic welding electrode (1)
- Ferromagnetic steel (1)
- Ferromagnetic steels (1)
- Festigkeit (1)
- Fiber laser (1)
- Filler material distribution (1)
- Filler wire mixing (1)
- Fine-grained Steel (1)
- Finite element analysis (1)
- Finite element method (FEM) (1)
- Flow pattern (1)
- Fresnel reflection (1)
- Full Penetration (1)
- Full penetration welding (1)
- Fusion zone size (1)
- GTAW (1)
- Gas shielded arc welding (1)
- Hartmann effect (1)
- Heat flow (1)
- Heat source models (1)
- Heißriss (1)
- Heißrissanfälligkeit (1)
- High brightness (1)
- High power (1)
- High power laser keyhole welding (1)
- High strength steel (1)
- High-Power Welding (1)
- High-power Laserbeam Welding (1)
- High-power fibre laser (1)
- High-power laser beam (1)
- High-power laser beam welding (1)
- High-strength low-alloy steel (1)
- Hochfester Stahl (1)
- Hochleistungsschweißen (1)
- Hybrid Laser-Arc Welding (1)
- Hybrid-laser-arc welding (1)
- Hydrostatic and arc pressure exceed the Laplace pressure (1)
- IR-Spektroskopie (1)
- IR-spectroscopy (1)
- Imaging (1)
- Impact absorbed energy (1)
- Kaltzähe Stähle (1)
- Keyhole mode laser beam welding (1)
- Keyhole mode welding (1)
- Keyhole stability (1)
- Lamé curves approximation (1)
- Laser Beam Welding (1)
- Laser Metal Deposition (LMD) (1)
- Laser Metal Deposition; Laser Beam Welding; Duplex; Stainless Steel (1)
- Laser Powder Bed Fusion (1)
- Laser Pulver Auftragsschweißen (1)
- Laser beam weliding (1)
- Laser cutting (1)
- Laser keyhole welding (1)
- Laser metal deposition (LMD) (1)
- Laser metal fusion (1)
- Laser surfacing (1)
- Laser-Pulver-Auftragschweißen (LPA) (1)
- Laser-Pulver-Auftragschweißen; Laserstrahlschweißen, Duplex, Pufferschichten (1)
- Laser-beam welding, (1)
- Laser-hybrid welding (1)
- Laserpulverauftragschweißen (1)
- Laserstrahl-(Hybrid)schweißen (1)
- Laserstrahl-MSG-Hybridschweißen (1)
- Liquid Metal Embrittlement (1)
- Lokale Effekte (1)
- Longitudinal weld (1)
- Lorentz force (1)
- Low Temperature Toughness (1)
- Lötrissigkeit (1)
- MSG-Schweißen (1)
- MWIR (1)
- Macro Processing (Joining, Welding) (1)
- Magnetic bath support (1)
- Magnetic field (1)
- Magnetohydrodynamics (1)
- Magnettechnik (1)
- Maintenance (1)
- Manganese (1)
- Marangoni flow (1)
- Matching ferritic filler metal (1)
- Mechanical Properties (1)
- Mechanical-technological properties (1)
- Melt pool dynamics (1)
- Metal (1)
- Metal mixing (1)
- Microstructure Tensile strength (1)
- Misalignment of edges (1)
- Modellierung (1)
- Modified spray arc (1)
- Multi - physical modeling (1)
- Multi-physical modelling (1)
- Multispectral thermography (1)
- NIR (1)
- Natural convection (1)
- Ni-based austenitic filler metal (1)
- Ni-based austenitic welding electrode (1)
- Nickel-based superalloy (1)
- Novel metrology (1)
- Novel optical measurement (1)
- Novel optical metrology (1)
- Numerical modeling (1)
- Numerical modelling (1)
- Numerical process simulation (1)
- Numerical simulations (1)
- Optical measurement technique (1)
- Optische Emissionsspektroskopie (OES) (1)
- Oscillating magnetic field (1)
- Partial penetration welding (1)
- Pendelstrategie (1)
- Penetration depth (1)
- Pipe Welding (1)
- Pipeline steel X120 (1)
- Pipeline steel of grade X120 (1)
- Plasma cutting (1)
- Plasma-cut samples (1)
- Plume heating (1)
- Post-weld heat treatment (1)
- ProMoAM (1)
- Process chain (1)
- Process simulation (1)
- Pufferschichten (1)
- Repair and overhaul (1)
- Rissanfälligkeit (1)
- Rissbildung (1)
- SEP-1220-3 (1)
- SWIR (1)
- Schallemissionsanalyse (SEA) (1)
- Schweißeignung (1)
- Schweißen von kaltzähen Stählen (1)
- Schweißunregelmäßigkeiten (1)
- Secondary heat source (1)
- Selective Laser Melting (1)
- Self-restraint test (1)
- Shielding gases (1)
- Shipbuilding steel (1)
- Simulation (1)
- Single-pass welding (1)
- Software (1)
- Solidification (1)
- Solidification behaviour (1)
- Solidification craking (1)
- Spiralstrategie (1)
- Stainless steel (1)
- Stainless steels (1)
- Strain fields prediction (1)
- Strain measurement (1)
- Submerged arc welding (1)
- Superelliptic Lamé curves (1)
- TES (1)
- Temperature distribution (1)
- Temperature emissivity separation (1)
- Temperaturentwicklung (1)
- Tensile strength (1)
- Thermal analysis (1)
- Thermo-fluid flow (1)
- Thermographie (1)
- Thick Materials (1)
- Thick materials (1)
- Thick plate welding (1)
- Thick plates (1)
- Thick-Walled Steel (1)
- Thick-plate welding (1)
- Thick-walled Structures (1)
- Ti - 6Al - 4V (1)
- Toughness (1)
- Turbine blade (1)
- Turbine industry (1)
- Two-run welding technique (1)
- Untersuchung laserstrahlgeschweißter Verbindungen (1)
- V-notch impact toughness (1)
- Vacuum (1)
- Vakuum (1)
- Vapor recondensation (1)
- Weld imperfections (1)
- Weld pool geometry (1)
- Weld pool shape approximation (1)
- Weld pool support (1)
- Weld root (1)
- Welding simulation (1)
- Welding thermal cycle (1)
- Werkstofffragen (1)
- Werkstoffranking (1)
- Widerstandspressschweißen (1)
- Widerstandspunktschweißen (1)
- Windkraftanlagen (1)
- X8Ni9 (1)
- YAG lasers (1)
- cryogenic steel (1)
- hardness (1)
- hochfeste Stähle (1)
- laser hybrid welding (1)
- local effects (1)
- microstructure (1)
- tensile strength (1)
- thermal cycles (1)
- thick plate welding (1)
- vacuum (1)
- Ökonomische und ökologische Vorteile (1)
Organisationseinheit der BAM
- 9 Komponentensicherheit (93)
- 9.3 Schweißtechnische Fertigungsverfahren (91)
- 8 Zerstörungsfreie Prüfung (6)
- 8.0 Abteilungsleitung und andere (6)
- 1 Analytische Chemie; Referenzmaterialien (2)
- 1.9 Chemische und optische Sensorik (2)
- 9.0 Abteilungsleitung und andere (2)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (1)
Eingeladener Vortrag
- nein (11)
Impiego di un dispositivo per il vuoto locale di tipo mobile nell'applicazione del processo laser.
(2016)
Lo sviluppo del pennacchio di vapore durante la saldatura laser
di metalli con direzioni di propagazione lungo l'asse del
fascio laser comporta una riduzione della potenza del laser
assorbita nel keyhole. Questi effetti negativi possono essere
notevolmente attenuati mediante l'applicazione di una ridotta
pressione ambientale, diminuendo così l'interazione
tra il fascio laser ed i prodotti dell'evaporazione, condizione
che favorisce la stabilità del processo di saldatura e si traduce
in una maggiore profondità di penetrazione. Una tecnica
convenzionale utilizza il principio della camera a vuoto, simile
a quello utilizzato per la saldatura a fascio elettronico.
L'applicazione di questa tecnica è limitata dalle dimensioni
della camera e riduce quindi i vantaggi di questo approccio,
particolarmente per componenti di grandi dimensioni. Abbiamo
dimostrato la possibilità di applicazione del vuoto in
forma localizzata con apparecchiature mobili, che consentono
di generare una pressione ridotta solo in una piccola zona
attorno al keyhole. Utilizzando un dispositivo di chiusura
appositamente progettato per la pressione, di tipo mobile,
che può essere spostato lungo l'asse del giunto è possibile ottenere
una pressione assoluta di circa 200 mbar. Questo è
sufficiente per aumentare la profondità di penetrazione di
circa il 50%. I campioni di acciaio grado S355 sono stati
saldati con una potenza laser incrementale da 5 kW a 12
kW a pressione atmosferica e confrontati con quelli saldati
a pressione ambiente di 200 mbar. La valutazione della sezione
longitudinale ha rivelato un aumento della profondità
di penetrazione dei giunti di circa il 35%. Inoltre, sono stati
eseguiti test di saldatura in configurazione di giunti testa a
testa con lamiere di 15 mm di spessore con diverse potenze
associate al fascio laser eseguiti a pressione atmosferica ed
a pressione ambiente ridotta di circa 200 mbar. L'aumento
nella profondità di penetrazione fino al 40% è relativo alla
pressione ridotta. In particolare, basse velocità di saldatura
con pressione ridotta si sono rivelate particolarmente vantaggiose
in termini di aumento della penetrazione.
Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solide-liquid phase transition was taken into account and the solidification was modelled by the Carman-Kozeny equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.
Entwicklung eines Verfahrens zur Untersuchung der Heißrissresistenz lasergeschweißter Verbindungen
(2016)
In den letzten Jahrzehnten hat sich die Strahlschweißtechnik signifikant weiterentwickelt und als effizientes und wirtschaftliches Werkzeug in der Industrie etabliert. Für die Untersuchung der Heißrissresistenz verschiedener Werkstoffe existieren zahlreiche eigen- und fremdbeanspruchende Tests. Diese wurden aber speziell für andere Schweißverfahren, insbesondere das Lichtbogenschweißen, konzipiert.
Daher besteht die Notwendigkeit eines geeigneten Heißrisstests, bei dem Werkstoffe realen Strahlschweißbedingungen ausgesetzt werden können. Die Entwicklung sowie die Standardisierung einer aussagekräftigen experimentellen Methode stellen einen wichtigen Schritt auf dem Weg zur Vermeidung von Heißrissen und damit für die Gewährleistung der Sicherheit von gefügten Bauteilen dar. Ziel der Forschungsarbeiten ist es, einen geeigneten Test zur effektiven Untersuchung der Heißrissanfälligkeit von lasergeschweißten Verbindungen zu konzipieren und zu entwickeln.
The paper describes an experimental investigation of high power laser beam welding with an electromagnetic weld pool support for up to 20 mm thick plates made of duplex steel (AISI 2205) and mild steel (S235JR). The results of the welding tests show a successful application of this technology at ferromagnetic metals. Irregular sagging was suppressed successfully. An ac-power of less than 2 kW at oscillation frequencies between 800 Hz and 1.7 kHz is necessary for a full compasation of the hydrostatic pressure. Thus, it was demonstrated that the electromagnetic weld pool support is not only limited to non-ferromagnetic metals like austenitic steels. For future studies with duplex steel, the use of filler material has to take into account with regard to the balance of the mixed austenitic and ferritic phases.
The aim of the present work was to investigate the possibilities of hybrid laser arc welding regarding reliable production of longitudinal welds of high strength pipe steels X80 and X120 and to evaluate achievable mechanical properties of laser hybrid welds. The study focused on weld toughness examination in low temperature range up to -60 °C. SЮТЭКЛХО ПТХХОЫ ЦКЭОЫТКХЬ were identified in the context of this task. It could be shown that metal cored electrodes guaranteed sufficient Charpy impact toughness at low temperature for both investigated materials. Modern arc welding technologies such as modified pulsed spray arc were used to promote deeper Penetration of the filler material into the narrow laser welding gap. Edge preparation with a 14 mm deep root face was considered as optimum, because no penetration of the filler material could be detected beyond this depth limit and therefore any metallurgical influences on the weld metal properties through the welding wire could be excluded.
Die Reduktion des Fahrzeuggewichts ist ein wesentlicher Ansatz zur Ver-ringerung des Energie- und Ressourcenverbrauchs und damit zur Senkung der CO2-Emissionen im Automobilbau. In der Karosserieentwicklung kann der vermehrte Einsatz von Aluminiumwerkstoffen einen bedeutenden Beitrag dazu leisten. Im preissensitiven Umfeld des Karosseriebaus etabliert sich das bei Stahlanwendungen genutzte Widerstandspunktschweißen zunehmend auch für Aluminiumverbindungen. Verfahrensbedingte Herausforderungen, wie verkürzte Elektrodenstandzeiten und mangelnde Kenntnis über den Einfluss von Imperfektionen auf die Festigkeit, begrenzen dennoch die Weiterverbreitung des Verfahrens und stellen die Prozessrobustheit insgesamt in Frage. Im Rahmen des hier vorgestellten Forschungsvorhabens wurden das Auftreten verschiedener Brucharten experimentell untersucht und Prognosefunktionen zur Abschätzung der Tragfähigkeit von Widerstandspunktschweißverbindungen unter verschiedenen Belastungsfällen erstellt. Anschließend wurde der Einfluss von Oberflächenrissen und Rissen in der Schweißlinse auf die Scherzugfestigkeit sowohl experimentell als auch simulativ analysiert.
Die Weiterentwicklung des Laser-Pulver-Auftragschweißens im Bereich der additiven Fertigung stellt dieses Verfahren vor neue Herausforderungen.
Bauteile können schnell und endformnah hergestellt werden, was diese Technik für den Prototypenbau sowie Kleinserienfertigung interessant macht.
Die Vielzahl an Varianten, um ein Volumen aus einzelnen Schichten aufzubauen, erhöhen die Möglichkeiten die Eigenschaften des entstehenden Bauteils zu beeinflussen. Hierfür müssen Strategien entwickelt werden, welche einen gleiclunäßigen Materialauftrag bei gleichzeitig optimalen Materialeigenschaften gewährleisten.
Die durchgeführten Untersuchungen behandeln den Einfluss von Pendelstrategien sowie Spiralstrategien auf die Temperaturentwicklung und stellen diese vergleichend gegenüber. Um den unterschiedlichen Bedingungen bei der Bauteilfertigung Rechnung zu tragen, wurden Versuche in Randbereichen sowie im zentralen Bereich des Testobjekts untersucht. Die Ergebnisse verdeutlichen die Notwendigkeit angepasste Baustrategien zu entwickeln, um durch einen stabilen Fertigungsprozess Qualität und Eigenschaften eines Bauteils gewährleisten zu können.
Using the novel optical measurement technique together with the optical flow algorithm, a twodimensional deformation analysis during welding has been conducted. This technique provides for the first time a measurement of the strain field locally in the immediate vicinity of the assumed solidification front. The described procedure of the opticalmeasurement allows to determine the real martial-dependent values of critical strain and strain rate characterising transition to the hot cracking during laser welding processes. The local critical strain that obtained in the assumed solidification showed that the local critical strain decreases as the strain rate increases. Moreover, this phenomenon has also been shown with results from the CTW-test, since the global strain decreases with an increase in the external strain rate.
Laser Metal Deposition offers the chance to build near net shape parts. The temperature evolution within the process has an influence on track and layer geometries. There are special travel path strategies required to produce near net shape components and reduce shape deviation resulting of error propagation.
This paper deals with the temperature progression of individual layers and the maximum heating of deeper substrate regions. Spiral and zig-zag strategies are examined. The investigations are carried out using S235JR as substrate and 316L as powder material. The influence of different strategies on temperature evolution is discussed.
The results from the experiments show that various production strategies are associated with different temperature fields. Furthermore, the extent of the temperature variations of layer strategies and layer position are strongly dependent on the production direction. These results demonstrate the importance of developing suitable build-up strategies for parts of complex shape to ensure a stable process with constant temperature as well as even layers.
Laser metal deposition is described with its applications for additive manufacturing. The necessary process chain is discussed, with regard to weld bead dimensions and 3D build-up strategy. Metallurgical cross sections, x-ray and tensile tests are conducted. As demonstrative components, a gas turbine burner and a turbine blade are shown.
Hybrid laser arc welding of thick-walled ferromagnetic steels with electromagnetic weld pool support
(2017)
Electromagnetic weld pool support system is illustrated successfully for hybrid laser arc welding of 20 mm ferromagnetic steels. Welding of thick-walled steels in flat position and reduced welding velocities is possible. Skin depth must be smaller than the plate thickness for protect the electric arc against external oscillating magnetic field. Residual magnetic field has a low influence, the deflection of the arc can be neglected. At high AC frequency more AC power is needed for ideal compensation (Hysteresis losses).
Untersuchungen der Heißrissanfälligkeit laserstrahlgeschweißter Verbindungen austenitischer Stähle
(2017)
Die lokalen Dehnungen bzw. Dehngeschwindigkeiten im heißrisskritischen Temperaturintervall sind Funktionen des Temperaturfeldes im Nahbereich des Schmelzbades (Schweißverfahren, Werkstoff), der thermo-mechanischen Kennwerte des Versuchswerkstoffes sowie von außen aufgebrachten Verfor-mungen. Da die lokal vorherrschenden Dehnungen im Nahbereich des Schmelzbades nicht bzw. nur mit sehr aufwendigen Methoden ermittelt werden können, dienen bespielweise die im CTW-Test (Controlled Tensile Weldability) von außen aufgebrachten Dehnungen oder Dehnraten als Kriterium für die Heißriss-empfindlichkeit. In dieser Studie wurde CTW-Test zur Untersuchung der Heißrissresistenz verschiedenen austenitischen Stählen eingesetzt.
This technique is the first to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front. Dependency between the external strain rate and the critical local strain has been observed. The local critical strain in vicinity of the solidification front has observed between 3.6 and 4.2%.
Over the past decade, laser beam welding has significantly evolved and established itself as an efficient tool in the industry. Solidification cracking and the weldability of materials have been highly contentious issues for many years. Today, there are many self and externally loaded tests to investigate the hot cracking resistance of steels. The purpose of this paper is to compare the susceptibility of three stainless steel grades to hot cracking by using an externally loaded hot cracking test (CTW) and a self-restraint test in accordance with SEP-220-3. The repeatability and effectiveness of the results are discussed. The experimental results are widely dispersed, implying a low predictive value for the self-restraint test. On the other hand, the results from the externally loaded test exhibit excellent repeatability and provide a quantitative characterization of the susceptibility of steels to hot cracking.
Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking as well as the weldability of materials is still since many years a highly contentious issue, particularly regarding the causes of the hot crack formation. Many of studies have been conducted to determine the critical conditions of occurrence of the solidification cracking. In this study a 2D in-situ observation technique in conjunction with laser diodes as the illuminating source has been employed to measure the arising strain field during the laser beam welding process. For the first time the employed technique enabled the in-situ measurement of the transient strain field at the surface of the workpiece directed to the laser beam in the critical range, where the solidification cracking normally occurs. Thus the critical threshold strain values at high temperatures characterizing transition from crack free to crack concomitant welding process could be deduced.
Die experimentellen Untersuchungen innerhalb dieses Berichtes zeigen die erfolgreiche Anwendung einer elektromagnetischen Schmelzbadstütze beim Laser-strahl(hybrid)schweißen von ferromagnetischen Stäh-len mit einer Werkstückdicke von bis zu 20 mm. Bis-lang wurde dieses System zur Kompensation des hydrostatischen Druckes von Aluminiumlegierungen und austenitischen Stählen eingesetzt. Zunächst wur-den die Versuche an Duplexstählen vorgenommen, die jeweils zur Hälfte aus Austenit und Ferrit bestehen. Im Anschluss daran wurden die Versuche auf bis zu 20 mm dicke Werkstücke aus Baustahl erweitert. In-nerhalb der Versuchsreihen wurden die AC-Leistung sowie die Oszillationsfrequenz variiert. Für Werk-stückdicken von 15 mm war eine AC-Leistung von ca. 1 kW notwendig, um die Wurzelüberhöhung in die Bewertungsgruppe B der für laserstrahlgeschweißten Stähle gültigen DIN EN ISO 13919-1:1996-09 einord-nen zu können. Mit zunehmender AC-Leistung wird die Wurzelüberhöhung sukzessive reduziert. Nach erfolg-reicher Erweiterung auf ferromagnetische Werkstoffe wurde die Anwendung der Technologie für das Laser-strahlhybridschweißen demonstriert, indem praxisrele-vante Y-Nähte an 20 mm dicken Baustählen ohne Wurzelüberhöhung einlagig in Wannenlage geschweißt wurden. Trotz der Beeinflussung des Lichtbogens durch das oszillierende Magnetfeld sowie des zusätz-lich zum hydrostatischen Druck zu berücksichtigenden Lichtbogendruckes wurde eine ideale Kompensation auf der Wurzelseite erzielt.
Die Erweiterung des Anwendungsspektrums der elekt-romagnetischen Schmelzbadstütze auf ferromagneti-sche Werkstoffe sowie auf das Laserstrahlhybrid-schweißen eröffnet für zukünftige industrielle Anwen-dungen ein großes Potenzial. Das einlagige Schwei-ßen dickwandiger Bauteile mittels Hochleistungslasern wird in Kombination mit der elektromagnetischen Schmelzbadstütze attraktiver. In nachfolgenden Un-tersuchungen wird der Einsatz der elektromagneti-schen Schmelzbadstütze beim Laserstrahlhybrid-schweißen von Pipelinestählen angestrebt, v. a. im Hinblick auf die Spaltüberbrückbarkeit und der me-chanisch-technologischen Eigenschaften der Schweißverbindungen. Zudem ist beim Schweißen von Duplexstählen der Einsatz von Zusatzwerkstoffen zu berücksichtigen, um das Gleichgewicht zwischen austenitischer und ferritischer Phasen zu stabilisieren.
Partial penetration welding with fiber laser on 20mm thick plates was carried out in horizontal position to study the role of secondary heating in modeling of high power fiber laser welding. Experiments were carried out using 18.8kW laser with 1.5 m/min welding speed at Ar assist gas flow rates of 0, 17, 29, and 40 l/min, all four cases show similar bead shape with bright emission of vapor plume. Numerical simulations were performed using volume of fluid method by considering three different models as models A–C. Model A considers only Fresnel reflection inside the keyhole using real time tracking of free surface. Model B considers vapor recondensation flux inside keyhole along with model A. Finally, model C is used, which considers vapor plume heating at 4100K temperature along with models A B. Secondary heating by recondensation and vapor plume is vital in modeling of high power fiber laser welding; especially, the upper part of the bead is more influenced due to secondary heating. Tungsten particles are also used to visualize the flow pattern of melt pool.
Elektromagnetische Schmelzbadkontrolle wurde erfolgreich für Laser-MSG-Hybridprozess an einem (ferromagnetischen) 20 mm Baustahl und einem Pipelinestahl eingesetzt.
Einlagiges Laserstrahlschweißen von dickwandigen(>20 mm) in PA-Position bei geringeren Schweißgeschwindigkeiten prinzipiell möglich.
Reduzierung der Schweißgeschwindigkeit beim Laserstrahlschweißen hat eine Verringerung der notwendigen Laserleistung und eine Verbesserung der mechanisch-technologischen Eigenschaften von Schweißverbindungen zur Folge.
Recently developed fibre lasers provide multi-kilowatt beam power with high quality at impressive energy efficiency. Combined with gas metal arc welding (GMAW) equipment these lasers can be used in a hybrid process to weld thick-walled constructions single-pass, that are currently welded using multi-pass techniques. The main benefits are a reduction of heat induced distortions, due to the low heat input, as well as savings in filler material and process time. Probable applications can be found in power generation, ship building and pipeline constructions. An orbital (girth) laser-hybrid process using a 20 kW fibre laser and a GMAW torch is currently examined at the BAM, Berlin. The aim of this research is to obtain a stable and crack free girth welding process and to demonstrate its application in pipeline construction. The experiments are carried out on 16 mm thick plates as well pipe rings with 36" (914 mm) pipe diameter of X65. Particular welding parameters, such as welding speed, GMAW power, arc length are varied and their influence on the appearance of the weld in the different welding positions is analyzed. Even though issues remain that demand further research it could already be shown that the rings can be welded using a girth hybrid process that is divided into two half girth processes in downward direction.
One of the main factors affecting the use of lasers in the industry for welding thick structures is the process accompanying solidification cracks. These cracks mostly occurring along the welding direction in the welding center, and strongly affect the safety of the welded components. In the present study, to obtain a better understanding of the relation between the weld pool geometry, the stress distribution and the solidification cracking, a three-dimensional computational fluid dynamic (CFD) model was combined with a thermo-mechanical model. The CFD model was employed to analyze the flow of the molten metal in the weld pool during the laser beam welding process. The weld pool geometry estimated from the CFD model was used as a heat source in the thermal model to calculate the temperature field and the stress development and distributions. The CFD results showed a bulging region in the middle depth of the weld and two narrowing areas separating the bulging region from the top and bottom surface. The thermo-mechanical simulations showed a concentration of tension stresses, transversally and vertically, directly after the solidification during cooling in the region of the solidification cracking.