Showing papers on "Welding published in 2005"

Welding Metallurgy and Weldability of Stainless Steels

Abstract: Preface 1 Introduction 2 Phase Diagrams 3 Alloying Elements and Constitution Diagrams 4 Martensitic Stainless Steels 5 Ferritic Stainless Steels 6 Austenitic Stainless Steels 7 Duplex Stainless Steels 8 Precipitation-Hardening Stainless Steels 9 Dissimilar Welding of Stainless Steels 10 Weldability Testing Appendix 1: Nominal Compositions of Stainless Steels Appendix 2: Etching Techniques for Stainless Steel Welds Author Index Subject Index

Computational welding mechanics

Abstract: Computer Simulation of Welding Processes.- Thermal Analysis of Welds.- Evolution of Microstructure Depending on Temperature.- Evolution of Microstructure Depending on Deformations.- Carburized and Hydrogen Diffusion Analysis.- Welded Structures and Applications of Welding in Industrial Fields.- Fracture Mechanics.- Input Data for Computational Welding Mechanics.

A local model for the thermomechanical conditions in friction stir welding

Abstract: The conditions under which the deposition process in friction stir welding is successful are not fully understood. However, it is known that only under specific thermomechanical conditions does a weld formation occur. If these conditions are not present, void formation will occur leading to a faulty weld. The objective of the present work is to analyse the primary conditions under which the cavity behind the tool is filled. For this, a fully coupled thermomechanical three-dimensional FE model has been developed in ABAQUS/Explicit using the arbitrary Lagrangian–Eulerian formulation and the Johnson–Cook material law. The model accounts for the compressibility by including the elastic response of the aluminium matrix. The contact forces are modelled by Coulomb's Law of friction, making the contact condition highly solution dependent. Furthermore, separation between the workpiece and the tool is allowed. This is often neglected in other models. Once non-recoverable separation is estimated by the model, a void develops. This is suggested as a preliminary criterion for evaluating the success of the deposition process. Of special interest is the contact condition along the tool/matrix interface, which controls the efficiency of the deposition process. In most models presented previously in the literature, the material flow at the tool interface is prescribed as boundary conditions. In all other contact models, the material is forced to keep contact with the tool. Therefore, the models are unable to predict when the suitable thermomechanical conditions and welding parameters are present. In the present work, the quasi-stationary thermomechanical state in the workpiece is established by modelling the dwell and weld periods. The different thermomechanical states in the colder, stiffer far-field matrix and the hotter, softer near-field matrix (under the tool) result in contact at the tool/matrix interface, thus, no void formation is observed. The steady-state model results are compared to the plunge force and heat generation observed in experimental welds in AA2024-T3.

Laser Processing of Engineering Materials: Principles, Procedure and Industrial Application

Abstract: Introduction Evolution of Laser Material Processing Lasers Systems for Material Processing Engineering Materials Laser Processing Diagrams Athermal Processing Structural Change Surface Hardening Deformation and Fracture Surface Melting Cladding Conduction Joining Cutting Marking Keyhole Welding Thermal Machining Opportunities Glossary Appendices

Fatigue strength of steel and aluminium welded joints based on generalised stress intensity factors and local strain energy values

Abstract: Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the present paper the weld toe region is modelled as a sharp, zero radius, V-shaped notch and the intensity of asymptotic stress distributions obeying Williams’ solution are quantified by means of the Notch Stress Intensity Factors (NSIFs). When the constancy of the angle included between weld flanks and main plates is assured and the angle is large enough to make mode II contribution non-singular, mode I NSIF can be directly used to summarise the fatigue strength of welded joints having very different geometry. By using a large amount of experimental data taken from the literature and related to a V-notch angle of 135°, two NSIF-based bands are reported for steel and aluminium welded joints under a nominal load ratio about equal to zero. A third band is reported for steel welded joints with failures originated from the weld roots, where the lack of penetration zone is treated as a crack-like notch and units for NSIFs are the same as conventional SIF used in LEFM. Afterwards, in order to overcome the problem related to the variability of the V-notch opening angle, the synthesis is made by simply using a scalar quantity, i.e. the mean value of the strain energy averaged in the structural volume surrounding the notch tips. This energy is given in closed form on the basis of the relevant NSIFs for modes I and II and the radius RC of the averaging zone is carefully identified with reference to conventional arc welding processes. RC for welded joints made of steel and aluminium considered here is 0.28 mm and 0.12 mm, respectively. Different values of RC might characterise welded joints obtained from high-power processes, in particular from automated laser beam welding. The local-energy based criterion is applied to steel welded joints under prevailing mode I (with failures both at the weld root and toe) and to aluminium welded joints under mode I and mixed load modes (with mode II contribution prevailing on that ascribable to mode I). Surprising, the mean value of ΔW related to the two groups of welded materials was found practically coincident at 2 million cycles. More than 750 fatigue data have been considered in the analyses reported herein.

Resistance welding : fundamentals and applications

Abstract: WELDING METALLURGY Solidification in Resistance Spot Welding Phase Transformations in RSW Cracking References ELECTROTHERMAL PROCESSES OF WELDING Introduction Electrical Characteristics of Resistance Welding Thermal Characteristics of Resistance Welding Heat Balance Electrode Life Lobe Diagrams References WELD DISCONTINUITIES Classification of Discontinuities Void Formation in Weld Nuggets Cracking in Welding AA6111 Alloys Cracking in Welding AA5754 Alloys References MECHANICAL TESTING Introduction Shop Floor Practices Instrumented Tests References RESISTANCE WELDING PROCESS MONITORING AND CONTROL Introduction Data Acquisition Process Monitoring References WELD QUALITY AND INSPECTION Weld Quality Attributes Destructive Evaluation Nondestructive Evaluation References EXPULSION IN RESISTANCE SPOT WELDING Influence of Expulsion on Spot Weld Quality Expulsion Process and Detection Expulsion Prediction and Prevention Examples References INFLUENCE OF MECHANICAL CHARACTERISTICS OF WELDING MACHINES Introduction Mechanical Characteristics of Typical Spot Welders Influence of Machine Stiffness Influence of Friction Influence of Moving Mass Follow-Up in a Welding Cycle Squeeze Time and Hold Time Measurement Other Factors References NUMERICAL SIMULATION IN RESISTANCE SPOT WELDING Introduction Coupled Electrical-Thermal-Mechanical Analysis Simulation of Contact Properties and Contact Area Simulation of Other Factors Modeling of Microstructure Evolution Examples of Numerical Simulation of RSW Processes References STATISTICAL DESIGN, ANALYSIS, AND INFERENCE IN RESISTANCE WELDING RESEARCH Introduction Basic Concepts and Procedures Experiments with Continuous Response Experiments with Categorical Responses Computer Simulation Experiments Summary References INDEX

Review of laser hybrid welding

Abstract: In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more efficiently in the future.In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more ...

Microstructure and mechanical properties of friction stir welded SAF 2507 super duplex stainless steel

Abstract: The microstructure and mechanical properties of friction stir (FS) welded SAF 2507 super duplex stainless steel were examined. High-quality, full-penetration welds were successfully produced in the super duplex stainless steel by friction stir welding (FSW) using polycrystalline cubic boron nitride (PCBN) tool. The base material had a microstructure consisting of the ferrite matrix with austenite islands, but FSW refined grains of the ferrite and austenite phases in the stir zone through dynamic recrystallisation. Ferrite content was held between 50 and 60% throughout the weld. The smaller grain sizes of the ferrite and austenite phases caused increase in hardness and strength within the stir zone. Welded transverse tensile specimen failed near the border between the stir zone and TMAZ at the retreating side as the weld had roughly the same strengths as the base material.

Thermal modelling of laser welding and related processes: a literature review

Abstract: The main emphasis of this review is on thermal modelling and prediction of laser welding in metals. However as similar techniques are employed to model conventional welding processes such as arc, resistance and friction, as well as related processes such as alloying, cladding and surface hardening, part of this review is given over to the modelling of these processes where appropriate. The time frame of the review is up to the year 2002.

Numerical and experimental studies of the mechanism of the wavy interface formations in explosive/impact welding

Abstract: Explosively driven impact welding is a true example of multidisciplinary research as the phenomena associated with it fall under the various branches of engineering science. A great deal of the work in, and collaboration between various specialised fields have been expended on the subject. However, a comprehensive quantitative theory capable of giving an accurate description and prediction of the parameters and of the characteristic features of explosively welded components does not exist. Most of the investigators considered the welding process as a solid state welding process, but some believed that the process is a fusion welding process. Interfacial waves are the most discussed aspect of explosive welding. The presence of jet in the collision region, and the transient fluid-like behaviour under high pressure have led many investigators to seek an explanation and a characterisation of these waves in terms of a flow mechanics of one kind or another. In this study, part of the welding process was numerically analysed. A finite difference engineering package was used to model the oblique impact of a thin flyer plate on a relatively thick base. The results were validated by data from carefully controlled experiments using a pneumatic gun. Straight and wavy interfaces and jetting phenomena were modelled, and the magnitude of the waves and the velocity of jet predicted. The numerical analysis predicted a hump ahead of the collision point. Wave formation appears to be the result of variations in the velocity distribution at the collision point and periodic disturbances of the materials. Higher values of plastic strain were predicted in wavy interfaces. Bonding was found to be a solid state welding process. Phase changes which occur may be due to high temperatures (but less than the melting temperature) at the collision point.

Characteristics of the kissing-bond in friction stir welded Al alloy 1050

Abstract: Initial oxide layer on the butt surface fragments during friction stir welding (FSW) often remaining as a faint zigzag-line pattern on the cross section. When remnants of the oxide layer often adversely affects the mechanical properties in the weld, it is called as “kissing-bond”. The present study systematically examines the effect of oxide array on the bend property in the root region of friction stir (FS) welded Al alloy 1050 by transmission electron microscopy (TEM) to clarify the identity of “kissing-bond”.

Linear friction welding of Ti-6Al-4V: Processing, microstructure, and mechanical-property inter-relationships

Abstract: The linear friction welding behavior of Ti-6Al-4V was investigated using varying processing conditions of frequency (15 to 70 Hz), amplitude (1 to 3 mm), pressure (50 to 90 MPa), and axial shortening (1 to 2 mm). Examination of linear friction welded Ti-6Al-4V using microscopic techniques indicated that the process requires certain critical conditions at the interface and its adjacent region to be reached for producing joints without structural defects along the weld centerline, such as voids or oxide inclusions. Characterization of the weldments included analysis of the microstructural features of the weld and thermomechanically affected zones (TMAZs) in relation to the parent material. It was observed that in the weld region, exposure to supertransus temperatures (>995 °C) combined with hot-deformation working and rapid cooling after joining produced recrystallization of the beta grain structure that had a Widmanstatten alpha-beta transformation microstructure. In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Through examination of the mechanical properties, using microhardness and tensile testing, the integrity of the joints was determined in order to assess the impact of the various processing parameters and to define the optimum welding conditions.

Flash welding of conducting polymer nanofibers

Abstract: The welding of certain polymeric nanofibers can be accomplished by exposure to an intense short burst of light, such as is provided by a camera flash, resulting in an instantaneous melting of the exposed fibers and a welding of the fibers where they are in contact. The preferred nanofibers are composed of conjugated, conducting polymers, and derivatives and polymer blends including such materials. Alternatively, the nanofibers can be composed of colored thermoplastic polymeric fibers or opaque polymers by proper selection of the frequency or frequency range and intensity (power) of the light source. The flash welding process can also be used to weld nanofibers which comprise a blend of polymeric materials where at least one of the materials in the blend used to form the nanofiber is a conductive, conjugated polymer or a suitable colored thermoplastic. Alternatively the material blend used to form the nanofibers may comprise a polymeric material containing a colored additive, which is not necessarily a polymer, for example carbon black, or a colored nano-particulate organic or inorganic material, dye or pigment.

Welding of Transparent Materials Using Femtosecond Laser Pulses

Abstract: We report on laser welding between transparent materials without the insertion of intermediate layers such as glue by use of near-infrared femtosecond laser pulses. When femtosecond laser pulses are focused at the interface of transparent materials, the material around the focal point is melted and resolidified because of the temperature increases due to the localized nonlinear absorption of optical pulse energy. We experimentally succeeded in laser welding between two pieces of silica glass without the insertion of an intermediate layer by femtosecond laser pulses. This technique has a possible application to the joining of semiconductors such as silicon crystals.