Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2018 (230) (entfernen)
Dokumenttyp
- Vortrag (99)
- Zeitschriftenartikel (76)
- Beitrag zu einem Tagungsband (38)
- Posterpräsentation (13)
- Buchkapitel (1)
- Dissertation (1)
- Handbuch (1)
- Forschungsbericht (1)
Schlagworte
- Hydrogen (19)
- Niobium carbide (18)
- Friction (17)
- Wear (17)
- Welding (17)
- Additive manufacturing (16)
- Residual stress (12)
- NbC (11)
- Eigenspannungen (10)
- MAG-Schweißen (10)
- High-strength steels (9)
- Laser metal deposition (9)
- Microstructure (9)
- Laser beam welding (8)
- Additive Fertigung (7)
- Hardness (7)
- Solidification cracking (7)
- Additive Manufacturing (6)
- Cermet (6)
- Machining (6)
- ToF-SIMS (6)
- Cryogenic temperature (5)
- Hochfester Feinkornbaustahl (5)
- Laser welding (5)
- Mechanical properties (5)
- Neutron diffraction (5)
- Process parameters (5)
- Residual stresses (5)
- Sintering (5)
- Temperature (5)
- Tribology (5)
- Wasserstoff (5)
- Bauteilprüfung (4)
- Creep-resistant steel (4)
- Cutting tools (4)
- Diffusion (4)
- Digitalisierung (4)
- Fatigue strength (4)
- Hochfeste Feinkornbaustähle (4)
- Kaltriss (4)
- Nickel (4)
- PEEK (4)
- ProMoAM (4)
- Restraint (4)
- Schweißen (4)
- Weldments (4)
- Wärmeführung (4)
- Zerspanung (4)
- Alumina (3)
- Austenitic stainless steel (3)
- Cobalt (3)
- Data-fusion (3)
- Fe3Al (3)
- Fracture mechanics (3)
- Heat treatment (3)
- High power laser beam welding (3)
- Hot steam (3)
- Hydrogen assisted cracking (3)
- IN718 (3)
- LTT (3)
- Large-scale test (3)
- Laserstrahlschweißen (3)
- Lubricated sliding (3)
- Numerical modelling (3)
- Numerical simulation (3)
- Polymer composites (3)
- Polymers (3)
- Reibung (3)
- Residual Stresses (3)
- Schwingfestigkeit (3)
- Selective Laser Melting (3)
- Selective laser melting (3)
- Thick-walled steel (3)
- Turning (3)
- Verschleiß (3)
- AISI 304L (2)
- Adaptives Schweißen (2)
- Auftragschweißen (2)
- Bulging (2)
- CFD-model (2)
- CNG (2)
- Carbonitride (2)
- Carrier gas hot extraction (2)
- Chemical composition (2)
- Condition monitoring (2)
- Crack closure (2)
- Creep resistant steel (2)
- Critical strain (2)
- Cutting tool (2)
- DED (2)
- Deuterium (2)
- Dimensional accuracy (2)
- Dissimilar metal weld overlays (2)
- Duplex stainless steel (2)
- EBSD (2)
- Electromagnetic weld pool support (2)
- Embedded electronics (2)
- FE-model (2)
- Fatigue crack growth (2)
- Fatigue crack propagation (2)
- Fatigue crack propagation threshold (2)
- Ferromagnetischer Stahl (2)
- Fuel economy (2)
- GMA Welding (2)
- GMA welding (2)
- Generative Fertigung (2)
- Grain size (2)
- HEA (2)
- HSLA steel (2)
- Hardmetal (2)
- Hartstoffphasen (2)
- Heat control (2)
- High-strength steel (2)
- Hochfester Stahl (2)
- Hochtemperaturwerkstoffe (2)
- Hybrid laser arc welding (2)
- Hybrid laser-arc welding (2)
- Höherfester Stahl (2)
- In situ strain (2)
- LDX (2)
- LIBS (2)
- LNG (2)
- LTT Weld Filler Materials (2)
- Laser-metal-deposition (2)
- Laserimplantation (2)
- Lichtbogensensorik (2)
- MSG-Engspaltschweißen (2)
- Measurement (2)
- Metallsulfide (2)
- Multiple reflections (2)
- Nachwärmung (2)
- Neutron (2)
- Niobium carbide (NbC) (2)
- Numerical process simulation (2)
- Numerische Simulation (2)
- Offshore wind (2)
- Optical measurement (2)
- Oxidation (2)
- Process chain (2)
- Process simulation (2)
- Properties (2)
- Prozessmonitoring (2)
- Pulsed laser beam welding (2)
- Ressidual stress (2)
- Rissarrest (2)
- SLM (2)
- Selektive-laser-melting (2)
- Semi-finishing (2)
- Short cracks (2)
- Single pass welding (2)
- Solid lubricants (2)
- Steel (2)
- Strain rate (2)
- Stress corrosion cracking (2)
- Structural Integrity (2)
- TPU (2)
- Thermography (2)
- Titanium (2)
- Toughness (2)
- Transient heat transfer (2)
- Tribofilm (2)
- Tribologie (2)
- Ultraschallunterstütztes Fräsen (2)
- Vaporization (2)
- Verschleißbeständigkeit (2)
- Weld pool dynamics (2)
- Weld pool geometry (2)
- Weld pool shape (2)
- Welding simulation (2)
- X-ray diffraction (2)
- 13CrMoV9-10 (1)
- 316L (1)
- 3D-finite element modeling (1)
- 9%Ni steel (1)
- 9%Ni steel, (1)
- ADXRD (1)
- AM (1)
- Abrasion (1)
- Accelerator magnets (1)
- Acoustic emission (1)
- Adaptive MSG-Lichtbogenprozesse (1)
- Adaptive MSG-Lichtbogenschweißprozesse (1)
- Adaptive control (1)
- Adaptive welding beam oscillation (1)
- Adative arc welding processes (1)
- Adhesion (1)
- Alloys (1)
- Alternative Kraftstoffe (1)
- Alternative fuels (1)
- Aluminium oxide (1)
- Aluminium-Druckgusslegierung (1)
- Aluminum (1)
- Anlagen (1)
- Arc sensor (1)
- Artefact (1)
- Austenit (1)
- Austenitic (1)
- Austenitic stainless steels (1)
- Austenitic steel (1)
- Automated manufacturing (1)
- Automation (1)
- Automatisierte Fertigung (1)
- Automotive application (1)
- Beam oscillation (1)
- Beam oscillations (1)
- Behavior (1)
- Binder (1)
- Boundary element method (1)
- Bragg-edge (1)
- Bremsbelag (1)
- Bremsbeläge (1)
- Build-up strategy (1)
- Bulging effect (1)
- CCT diagrams (1)
- CFD model (1)
- Carbon (1)
- Carbon steel (1)
- Carrier gas hot extraction (CGHE) (1)
- Cemented carbide (1)
- Ceramic (1)
- Chemische Zusammensetzungen (1)
- Cimensional Accuracy (1)
- Clad steels (1)
- Co (1)
- Coarse grained heat affected zone (1)
- Coarse-grained heat-affected zone (1)
- Coating (1)
- Cold-welding (1)
- Complex loading (1)
- Composite (1)
- Computational fluid dynamics (1)
- Constraint (1)
- Control (1)
- Conventional Ni-based austenitic welding electrode (1)
- Coolant-free (1)
- Cooling rate (1)
- Coordinate measurement machine (1)
- Crack closure mechanisms (1)
- Cracking mechanism (1)
- Crater wear (1)
- Creep-resisting materials (1)
- Cryogenic steel (1)
- Current density (1)
- Cyclic J-integral (1)
- Cyclic R-curve (1)
- Cyclic R-curve analysis (1)
- Cyclic stress-strain curve (1)
- Cylindrical turning (1)
- DEM (1)
- DIC (1)
- DLC (1)
- DSS (1)
- Data fusion (1)
- Datenmanagement (1)
- Defekte (1)
- Deformation (1)
- Deformed geometry (1)
- Density measurement (1)
- Deposition rate (1)
- Design of experiments (1)
- Diaspore (1)
- Die-cast aluminum (1)
- Digital Image Correlation (1)
- Digital image correlation (1)
- Digitalisation (1)
- Digitization (1)
- Dilatometry (1)
- Directed Energy Deposition (1)
- Dritter Körper (1)
- Duplex (1)
- Duplex stainless steels (1)
- Dünnschichten (1)
- Edge effects (1)
- Einschlüsse (1)
- Einspanngrad (1)
- Elastic follow-up (1)
- Elastic-plastic fracture mechanics (1)
- Electrical connectors (1)
- Electro-plated nickel coatings (1)
- Electroless Ni-P (1)
- Electromagnetic influence (1)
- Electromagnetic support (1)
- Electromagnetic weld pool support system (1)
- Elektromagnetische Schmelzbadbeeinflussung (1)
- Elektromagnetische Schmelzbadunterstützung (1)
- Embrittlement (1)
- Endurance limit (1)
- Energieerzeugung (1)
- Equivalent heat source (1)
- Equivalent stress concentration factors (1)
- Equivalent volumetric heat source (1)
- Ermüdungsfestigkeit (1)
- Ermüdungsrissfortschritt (1)
- Experimental design (1)
- FEM (1)
- Fatigue fracture (1)
- Femtosecond (1)
- Femtosecond laser (1)
- Ferrit (1)
- Ferritic steels (1)
- Ferritic welding electrode (1)
- Ferromagnetic steels (1)
- Fertigungstechnologie (1)
- Fiber laser (1)
- Finite element method (FEM) (1)
- Flank (1)
- Formgedächtnislegierungen (1)
- Fracture (1)
- Fracture resistance (1)
- Fracture toughness (1)
- Fresnel reflection (1)
- Full penetration (1)
- Fusion Zone (1)
- Fusion zone size (1)
- Fusion zone, nickel alloys (1)
- Fügetechnik (1)
- Füllgradregelung (1)
- GMAW (1)
- GMAwelding (1)
- GMR (1)
- GMR sensors (1)
- GTAW (1)
- Gap bridgeability (1)
- Gap bridging (1)
- Gleeble testing (1)
- Grade S960QL steel (1)
- Grain growth (1)
- HSLA (1)
- Hard metal (1)
- Hard metals (1)
- Hard tungsten (1)
- Hard turning (1)
- Hard-turning (1)
- Heat affected zone (1)
- Heat flow (1)
- Heat recovery (1)
- Heat-affected zone (1)
- Heissrisse (1)
- Heißriss (1)
- Heißrisse (1)
- High brightness (1)
- High power (1)
- High strength steel (1)
- High-power fibre laser (1)
- High-power laser beam (1)
- High-strength steel sheets (1)
- Hochfeste Stähle (1)
- Hohlprofilknoten (1)
- Hot Cracks (1)
- Hot cracking test (1)
- Humidity (1)
- Hybrid-laser-arc welding (1)
- Hydrogen Assisted Cracking (HAC) (1)
- Hydrogen concentration (1)
- Hydrogen embrittlement (1)
- Hydrostatic and arc pressure exceed the Laplace pressure (1)
- Höherfeste Feinkornbaustähle (1)
- I-Träger (1)
- ISO 3690 (1)
- Impact absorbed energy (1)
- Implant failures (1)
- Implant-Test (1)
- In situ (1)
- In situ LIBS (1)
- In situ measurement (1)
- In718 (1)
- Inclusions (1)
- Inserts (1)
- Interrupted milling (1)
- Iron-based alloys (1)
- Karosseriebau (1)
- Keramikfeder (1)
- Kerbspannungskonzept (1)
- Keyhole welding (1)
- Kitagawa-Takahashi diagram (1)
- Komponenten (1)
- Kryogene Temperatur (1)
- Kurzrissbruchmechanik (1)
- Künstliche Intelligenz (1)
- LIBS TIG welding (1)
- LME (1)
- LTT-Legierung (1)
- Laboratory X-ray diffraction (1)
- Large scale test (1)
- Laser Metal Deposition (1)
- Laser beam melting (1)
- Laser keyhole welding (1)
- Laser surfacing (1)
- Laser- und Lichtbogenenergie (1)
- Laser-Pulver-Auftragschweißen (1)
- Laser-beam welding, (1)
- Laser-hybrid welding (1)
- Laser-induced periodic surface structures, LIPSS (1)
- Laser-metal-depositon (1)
- Laser-plasma hybrid (1)
- Laserpulverauftragschweißen (1)
- Laserstrahl-Hybridschweißen (1)
- Laserstrahlschmelzen (1)
- Life Cycle Assessment (1)
- Life Cycle Assessment (LCA) Fusion welding (1)
- Life Cycle Assessment (LCA) Impact categories (1)
- Life Cycle Assessment (LCA) Schweißprozesse (1)
- Life Cycle Assessment (LCA) Umweltwirkungen (1)
- Life prediction (1)
- Liquid metal embrittlement (1)
- Liquid phase sintering (1)
- Local critical strain (1)
- Low carbon steel (1)
- Low heat input GMA welding (1)
- Low heat input Gma welding (1)
- Low transformation temperature filler materials (1)
- Lubricants (1)
- MAG Prozesssteuerung (1)
- MAG welding (1)
- Machinability (1)
- Magnetic stray field (1)
- Magnettechnik (1)
- Material defects (1)
- Material modeling (1)
- Materialmodellierung (1)
- Melt pool dynamics (1)
- Metal (1)
- Metal Magnetic Memory (1)
- Metal matrix composite (1)
- Metallic components (1)
- Metallurgie (1)
- Methane (1)
- Micro-shrinkages (1)
- Microalloyed steels (1)
- Microstructure Tensile strength (1)
- Microstructure and texture (1)
- Misalignment of edges (1)
- Mobility (1)
- Modifizierter Sprühlichtbogen (1)
- Molybdenum disulphide (1)
- Monotonic and cyclic crack driving force (1)
- Monte-Carlo simulation (1)
- Moving mesh (1)
- Multi-pass welding (1)
- Multiple crack initiation (1)
- Multiple cracking (1)
- Nachschlagewerk (1)
- Narrow gap welding (1)
- Narrow-gap welding (1)
- Natural silver wires (1)
- NbC cermets (1)
- Neural networks (1)
- Neutron imaging (1)
- New technologies (1)
- NiTi-Legierungen (1)
- Nickel alloys (1)
- Niobcarbid (NbC) (1)
- Normen (1)
- Notch stress approach (1)
- Novel metrology (1)
- Novel optical metrology (1)
- Numerical Simulation (1)
- Numerical welding simulation (1)
- Oberflächenmessung (1)
- Oberflächenschädigung (1)
- Oberflächenstrukturierung (1)
- Oszillierendes Magnetfeld (1)
- PAEKs (1)
- PCA (1)
- PTFE composite (1)
- PTFE composites (1)
- Partial penetration (1)
- Particle erosion (1)
- Phase transformation (1)
- Photooxidation (1)
- Physical vapor deposition (PVD) (1)
- Pipeline (1)
- Pitting (1)
- Plasma-transferred-arc (1)
- Plastic deformation (1)
- Plume heating (1)
- Polymere (1)
- Polymerkomposite (1)
- Poren (1)
- Porenreduktion (1)
- Porosity (1)
- Porosity reduction (1)
- Post Weld Heat Treatment (PWHT) (1)
- Post weld heat treatment (1)
- Principal Component Analysis (1)
- Profilvermessung (1)
- Prozesskette (1)
- Prozessregelung (1)
- Prüfverfahren (1)
- R-curve analysis (1)
- Radiography (1)
- Rauheit (1)
- Reciprocating sliding (1)
- Resistance spot welding (1)
- Rissausbreitungsstadien (1)
- Rissbildung (1)
- Rissschließphenomen (1)
- SIMS (1)
- SLM printed plasma torch (1)
- SMAW (1)
- SPS (1)
- Schmelzbadstütze (1)
- Schmierstoffe (1)
- Schmierung (1)
- Schutzgasschweißen (1)
- Schweißdatenmanagement (1)
- Schweißeigenspannungen (1)
- Schweißnahtgeometrie (1)
- Schweißprozessparameter (1)
- Schweißverbindungen (1)
- Secondary heat source (1)
- Secondary stresses (1)
- Sensor (1)
- Sensorik (1)
- Short crack Propagation (1)
- Short crack propagation (1)
- Silicon nitride (1)
- Sliding friction (1)
- Solubility (1)
- Spannung (1)
- Spannungs-Dehnungs-Verhalten (1)
- Stahllegierungen (1)
- Stainless Steel (1)
- Stainless steel (1)
- Stainless steels (1)
- Statistische Versuchsplanung (1)
- Stift-Scheibe-Anordnung (1)
- Strain rates (1)
- Strain-rate (1)
- Strength mismatch (1)
- Stress Relief Cracking (SRC) (1)
- Stress relief cracking (1)
- Stress-strain behavior (1)
- Superconducting magnets (1)
- Supermartensitic Stainless Steel (SMSS) (1)
- Support configurations (1)
- Surface cracks (1)
- Synchrotron X-ray diffraction (1)
- Synchrotron diffraction (1)
- T24 / 7CrMoVTiB10-10 (1)
- TIG (1)
- TIG-welding (1)
- Temperature behavior (1)
- Temperature distribution (1)
- Temperatureinfluss (1)
- Tensile strength (1)
- Texture (1)
- Thermal cycles (1)
- Thermal desorption analysis (1)
- Thermal-desorption spectroscopy (1)
- Thermografie (1)
- Thermomechanische Eigenschaften (1)
- Thick plates (1)
- Ti-6Al-4V (1)
- Time-of-Flight secondary ion mass spectrometry (1)
- Titandiborid (1)
- Titanium alloy (1)
- Tomography (1)
- Tool (1)
- Tool wear (1)
- Traglastverhalten (1)
- Transformable steels (1)
- Tribometer (1)
- Tribooxidation (1)
- Trockenreibung (1)
- Tubular joints (1)
- Tungsten carbide (1)
- Tungsten carbide (WC) (1)
- Turbine components (1)
- UV radiation (1)
- Umweltwirkungen (1)
- Vacuum (1)
- Vakuum (1)
- Vapor recondensation (1)
- Vernetzte Produktion (1)
- Viscoplasticity (1)
- WC (1)
- WIG Schweißen (1)
- Wasserstoffgradient (1)
- Wasserstoffkonzentration (1)
- Wasserstoffunterstützte Kaltrissbildung (1)
- Wear mechanisms (1)
- Weld geometry (1)
- Weld metal (1)
- Weld pool (1)
- Weld seam geometry (1)
- Welded joints (1)
- Welding Simulation (1)
- Welding residual stresses (1)
- Werkzeug (1)
- Werstoff- und geometrische Imperfektion (1)
- Windenergie (1)
- X153CrMoV12 (1)
- Zinc (1)
- Zyklische Belastung (1)
- Zyklische R-Kurve (1)
- a-C:H (1)
- carrier gas hot extraction (1)
- contour method (1)
- neutron diffraction (1)
- residual stress analysis (1)
- µCT-analysis (1)
- Äquivalente Spannungskonzentrationsfaktoren (1)
- Ökobilanzierung (1)
Organisationseinheit der BAM
- 9 Komponentensicherheit (230) (entfernen)
Eingeladener Vortrag
- nein (99)
Additive manufacturing (AM) offers a range of novel applications. However, the manufacturing process is complex and the production of defect-free parts with a high reliability is still a challenge. Thermography is a valuable tool for process surveillance, especially in metal AM processes. The high process temperatures allow one to use cameras usually operating in the visible spectral range. Here, we compare the results of first measurements during the manufacturing process of a commercial laser metal deposition (LMD) setup using a MWIR camera with those from a VIS high-speed camera with band pass filter in the NIR range.
Aktuell werden Prozessmonitoringsysteme in der additiven Fertigung (AM) zur Überwachung der Energiequelle, des Bauraums, des Schmelzbades und der Bauteilgeometrie zumindest im metallbasierten AM schon kommerziell angeboten. Weitere Verfahren aus den Bereichen der Optik, Spektroskopie und zerstörungsfreien Prüfung werden in der Literatur als geeignet für die in-situ Anwendung bezeichnet, es finden sich aber nur wenige Berichte über konkrete Umsetzungen in die Praxis.
Die Bundesanstalt für Materialforschung und -prüfung hat ein neues Projekt gestartet, dessen Ziel die Entwicklung von Verfahren des Prozessmonitorings zur in-situ Bewertung der Qualität additiv gefertigter Bauteile in AM-Prozessen mit Laser- bzw. Lichtbogenquellen ist. Verschiedene Verfahren der zerstörungsfreien Prüfung, wie Thermografie, optische Tomografie, optische Emissionsspektroskopie, Wirbelstromprüfung und Laminografie werden in verschiedenen AM-Prozessen zum Einsatz gebracht und die Ergebnisse fusioniert. Die evaluierten Ergebnisse werden mit Referenzverfahren wie Computertomografie und Ultraschall-Tauchtechnik verglichen. Ziel ist eine deutliche Reduzierung aufwändiger und zeitintensiver, zerstörender oder zerstörungsfreier Prüfungen nach der Fertigung des Bauteiles und zugleich eine Verringerung von Ausschussproduktion.
Hier wird das Projekt als Ganzes vorgestellt und der Fokus auf verschiedene Methoden der Temperaturmessung mit Hilfe der Thermografie gelegt. Anforderungen an die Messtechnik für verschiedene AM-Systeme werden diskutiert und erste experimentelle Ergebnisse werden präsentiert.
Additive manufacturing (AM) opens the route to a range of novel applications.However, the complexity of the manufacturing process poses a challenge for the production of defect-free parts with a high reliability. Since process dynamics and resulting microstructures of AM parts are strongly influenced by the involved temperature fields, thermography is a valuable tool for process surveillance. The high process temperatures in metal AM processes allow one to use cameras usually operating in the visible spectral range to detect the thermally emitted radiation from the process. In our work, we compare the results of first measurements during the manufacturing processes of a commercial laser metal deposition (LMD) setup and a laser beam melting (LBM) setup using a MWIR camera with those from a VIS high-speed camera with band pass filter in the NIR range.
A transient simulation including the impact of the laser energy, the melting of the metal and the development of the weld pool was conducted to observe the evolution of the vapor capillary and the solidification of the melt in pulsed laser beam welding of AISI 304 steel. The phase field method was implemented to investigate the evolution and behavior of the liquid-gas interface during welding and to describe the condensed and vapor phases. The effects of phase transition, recoil pressure, thermo-capillary and natural convection, vaporization and temperature dependent material properties were taken into account. A Gaussian-like heat source under consideration of the Fresnel absorption model was used to model the energy input of the laser beam. The heat source model was extended by a newly developed empirical approach of describing multiple beam reflections in the keyhole. To validate this new model, the numerical results were compared to experimental data and good agreement regarding the size and shape of the weld pool was observed.
A simplified model for numerical simulation of laser metal deposition process with beam oscillation
(2018)
A simplified model for the numerical simulation of the laser metal deposition process with beam oscillation is proposed. The model studies circular and lateral oscillations in order to reduce the porosity of the deposited part, to increase the process efficiency and the gap bridging ability as well. The deposition rate is increased by modifying the shape and the width of the molten pool through an optimized laser beam power distribution and oscillation amplitude. The relationship between the process conditions and the shape of the fabricated part are determined. It is found that an increase of the amplitude by a lateral oscillation of the beam reduces the heat flux and hence the shape of the deposited wall. A good correlation between the numerically calculated results and the experimental measurements is obtained.
This work aims to find the thermal cycles during and after fusion welding through simulation by first calculating the resulting local temperature field in the quasi-stationary part of the process. Here complete-penetration keyhole laser beam welding with a laser power of 18 kW on a 15 mm thick slab of a low-alloyed steel at a welding speed of 2 m/min is considered. In order to physically depict the laser material interaction a multi-physics numerical model including the effects of phase transformation, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature is developed.
It uses a fixed keyhole geometry with a right truncated circular cone shape to introduce the laser beam energy to the workpiece. In a subsequent study, the resulting local temperature field is then used as an equivalent heat source in order to predict the unsteady thermal cycle during and after fusion welding. The translational movement of the laser beam through the workpiece is represented by a moving mesh approach. For the simulation, stationary heat transfer and fluid dynamics are described by a system of strongly coupled partial
differential equations. These are solved with the commercial finite element software COMSOL Multiphysics 5.0. The results of the numerical simulation are validated by experiments, where the weld bead shapes and the thermal cycles show good correlation.
The shape of the weld pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. The aim of the present work was its experimental and numerical investigation. To visualize the geometry of the melt pool in the longitudinal section a butt joint configuration of 15 mm thick structural steel and transparent quartz glass was used. The weld pool shape was recorded by means of a high-speed video camera and two thermal imaging MWIR and VIS cameras. The observations show that the dimensions of the weld pool vary depending on the depth. The regions close to the surface form a teardrop shaped weld pool. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a transient numerical simulation was performed until reaching a steady state to obtain the weld pool shape and to understand the formation mechanism of the observed bulging phenomena. A fixed keyhole with an experimentally obtained shape was used to represent the full-penetration laser beam welding process. The model considers the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. It was found that the Marangoni convection and the movement of the laser heat source are the dominant factors for the formation of the bulging-region. Good correlation between the numerically calculated and the experimentally observed weld bead shapes and the time-temperature curves on the upper and bottom surface were found.
A three-dimensional multi-physics numerical model was developed for the calculation of an appropriate equivalent volumetric heat source and the prediction of the transient thermal cycle during and after fusion welding. Thus the modelling process was separated into two studies. First, the stationary process simulation of full-penetration keyhole laser beam welding of a 15 mm low-alloyed steel thick plate in flat position at a welding speed of 2 m/min and a laser power of 18 kW was performed. A fixed keyhole with a right circular cone shape was used to consider the energy absorbed by the workpiece and to calibrate the model. In the calculation of the weld pool geometry and the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature were taken into account. The obtained local temperature field was then used in a subsequent study as an equivalent heat source for the computation of the transient thermal field during the laser welding process and the cooling stage of the part. The system of partial differential equations, describing the stationary heat transfer and the fluid dynamics, were strongly coupled and solved with the commercial finite element software COMSOL Multiphysics 5.0. The energy input in the transient heat transfer simulation was realised by prescription of the nodes temperature. The prescribed nodes reproduced the calculated local temperature field defining the equivalent volumetric heat source. Their translational motion through the part was modelled by a moving mesh approach. An additional remeshing condition and helper lines were used to avoid highly distorted elements. The positions of the elements of the polygonal mesh were calculated with the Laplace’s smoothing approach. Good correlation between the numerically calculated and the experimentally observed weld bead shapes and transient temperature distributions was found.
The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
Acoustic emission testing
(2018)
The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
In this study, a three-dimensional CFD-simulation model was developed to simulate the fluid flow in the weld pool. The CFD-model showed a bulging region in the middle of the depth, which is separated from the top surface and bottom surface by two narrowing regions. It can be concluded that the interaction of the movement of the laser source with the Marangoni vortex leads to a teardrop shape at the upper and bottom surface of the workpiece. Additionally, it shows that the bulging in the weld is a result of the backflows on the upper and lower sides due to the thermo-capillary-driven flows. The weld pool shape was used as a heat source in a two-dimensional thermomechanical model, which allows a highly accurate transformation of the weld pool dimensions obtained from the CFD model. This developed technique allows the consideration of physical aspects, which cannot be considered when using traditional heat sources. The mechanical model has shown that the chronological order of the solidification of the weld has a significant influence on the nature and distribution of the stresses in the weld. High tensile stress has been observed in the bulging region, i.e. in the susceptible region for solidification cracking, when compared to the other narrowing regions, which show compressive stress.
In this study, a three-dimensional CFD-simulation model was developed to simulate the fluid flow in the weld pool. The CFD-model showed a bulging region in the middle of the depth, which is separated from the top surface and bottom surface by two narrowing regions. It can be concluded that the interaction of the movement of the laser source with the Marangoni vortex leads to a teardrop shape at the upper and bottom surface of the workpiece. Additionally, it shows that the bulging in the weld is a result of the backflows on the upper and lower sides due to the thermo-capillary-driven flows. The weld pool shape was used as a heat source in a two-dimensional thermomechanical model, which allows a highly accurate transformation of the weld pool dimensions obtained from the CFD model. This developed technique allows the consideration of physical aspects, which cannot be considered when using traditional heat sources. The mechanical model has shown that the chronological order of the solidification of the weld has a significant influence on the nature and distribution of the stresses in the weld. High tensile stress has been observed in the bulging region, i.e. in the susceptible region for solidification cracking, when compared to the other narrowing regions, which show compressive stress.
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.
In recent years, laser beam welding has found wide applications in many industrial fields. Solidification cracks are one of the most frequently encountered welding defects that hinder obtaining a safe weld joint. Decades of research have shown that one of the main causes of such cracks are the strain and the strain rate. Obtaining meaningful measurements of these strains has always been a major challenge for scientists, because of the specific environment of the measurement range and the many obstacles, as well as the high temperature and the plasma plume. In this study, a special experimental setup with a high-speed camera was employed to measure the strain during the welding process. The hot cracking susceptibility was investigated for 1.4301 stainless steel, and the critical strain required for solidification crack formation was locally and globally determined.
This paper represents the results for proposed optical flow method based on the Lucas-Kanade (LK) algorithm applied to two different problems. The following observations can be made:
- The estimated strain and displacement for conducted tensile test are generally very close to those measured with conventional DIC-technique.
- The LK technique allows measurement of strain or displacement without special selection of a region of interest.
Using a novel optical measurement technique together with the optical flow algorithm, a twodimensional deformation analysis during welding was conducted. This technique is the first to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front. Additionally, the described procedure of the optical measurement allows the real material-dependent values of critical strain characterizing the transition to hot cracking during laser welding processes to be determined.
Due to rapid, localized heating and cooling, distortions accumulate in additive manufactured laser metal deposition (LMD) components, leading to a loss of dimensional accuracy or even cracking. Numerical welding simulations allow the prediction of these deviations and their optimization before conducting experiments. To assess the viability of the simulation tool for the use in a predictive manner, comprehensive systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to Cluster these products in new assembly oriented product families for the optimization.
Distortions in Additive Manufacturing (AM) Laser Metal Deposition (LMD) occur in the newly-built component due to rapid heating and solidification and can lead to shape deviations and cracking. This paper presents a novel approach to quantify the distortions experimentally and to use the results in numerical simulation validation. Digital Image Correlation (DIC) is applied together with optical filters to measure in-situ distortions directly on a wall geometry produced with LMD. The wall shows cyclic Expansion and shrinking with the edges bending inward and the top of the sample exhibiting a slight u-shape as residual distortions. Subsequently, a structural Finite Element Analysis (FEA) of the experiment is established, calibrated against experimental temperature profiles and used to predict the in-situ distortions of the sample. A comparison of the experimental and numerical results reveals a good agreement in length direction of the sample and quantitative deviations in height direction, which are attributed to the material model used. The suitability of the novel experimental approach for measurements on an AM sample is shown and the potential for the validated numerical model as a predictive tool to reduce trial-and-error and improve part quality is evaluated.
With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality Needs to be validated against experiments for in-situ and post-process cases. In this article, a validation is demonstrated
for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED)part: at first, the validity of the heat input is ensured and subsequently, the model’s predictive quality for in-situ
deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical Simulation model is set up in accordance with the experiment and can reproduce the measured 3-dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D-scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel Extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.