Showing papers on "Welding published in 2004"

An analytical model for the heat generation in friction stir welding

Abstract: The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.

Fusion Bonding/Welding of Thermoplastic Composites

Abstract: Joining of thermoplastic composites is an important step in the manufacturing of aerospace thermoplastic composite structures. Therefore, several joining methods for thermoplastic composite components have been under investigation and development. In general, joining of thermoplastic composites can be categorized into mechanical fastening, adhesive bonding, solvent bonding, co-consolidation, and fusion bonding or welding. Fusion bonding or welding has great potential for the joining, assembly, and repair of thermoplastic composite components and also offers many advantages over other joining techniques. The process of fusion-bonding involves heating and melting the polymer on the bond surfaces of the components and then pressing these surfaces together for polymer solidification and consolidation. The focus of this paper is to review the different fusion-bonding methods for thermoplastic composite components and present recent developments in this area. The various welding techniques and the corresponding manufacturing methodologies, the required equipment, the effects of processing parameters on weld performance and quality, the advantages/disadvantages of each technique, and the applications are described.

Nickel based superalloy welding practices for industrial gas turbine applications

Abstract: The continued drive for increased efficiency, performance and reduced costs for industrial gas turbine engines demands extended use of high strength-high temperature capability materials, such as nickel based superalloys. To satisfy the requirements of the component design and manufacturing engineers, these materials must be capable of being welded in a satisfactory manner. The present paper describes the characteristic defects found as a result of welding the more difficult, highly alloyed materials and reviews a number of welding processes used in the manufacture and repair of nickel alloy components. These include gas tungsten arc (GTA) and electron beam (EB) welding, laser powder deposition and friction welding. Many of the more dilute nickel based alloys are readily weldable using conventional GTA processes; however, high strength, precipitation hardened materials are prone to heat affected zone and strain age cracking defect formation. A number of factors are found to affect the propensity f...

Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel

Abstract: The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

Joining of Al 6061 alloy to AISI 1018 steel by combined effects of fusion and solid state welding

Abstract: The joining of a 6-mm thickness Al 6061 to AISI 1018 steel has been performed by the combined effects of fusion and solid state welding. The process is derived from friction stir welding (FSW) but with an adjustable offset of the probe location with respect to the butt line. Metallographic studies by optical microscopy, electron probe microscopy, and the utilization of the X-ray diffraction technique have been conducted. It was found that the intermetallic phases Al13Fe4 and Al5Fe2 exist in the weld zone. The tool was significantly worn during welding and is broken after traveling 100 mm at a rotational speed of 917 rpm. The wear of the tool significantly affects the structure of the weld, and the tool breakage was detected by the incorporated acoustic emission (AE) sensors. It appears that the joining of an Al 6061 alloy to AISI 1018 steel with a sound heterogeneous weld microstructure is feasible using this process, and the tool breakage can be detected by the AE sensing technique.

Phase transformation dynamics during welding of Ti–6Al–4V

Abstract: In situ time-resolved x-ray diffraction (TRXRD) experiments were used to track the evolution of the α→β→L→β→α/α′ phase transformation sequence during gas tungsten arc welding of Ti–6Al–4V. Synchrotron radiation was employed for the in situ measurements in both the fusion zone (FZ) and the heat-affected zone (HAZ) of the weld, providing information about transformation rates under rapid heating and cooling conditions. The TRXRD data were coupled with the results of computational thermodynamic predictions of phase equilibria, and numerical modeling of the weld temperatures. The results show that significant superheat is required above the β transus temperature to complete the α→β transformation during weld heating, and that the amount of superheat decreases with distance from the center of the weld where the heating rates are lower. A Johnson–Mehl–Avrami phase transformation model yielded a set of kinetic parameters for the prediction of the α→β phase transformation during weld heating. Corresponding TRXRD measurements were made during weld cooling. In the HAZ, the β→α transformation during weld cooling was shown to initiate at the β transus temperature and terminate below the Ms temperature, resulting in a microstructure containing a substantial fraction of α′ martensite. In the FZ, the β→α transformation during weld cooling was shown to initiate below the Ms temperature, and to completely transform the microstructure to α′ martensite.

Characterization of plastic flow and resulting microtextures in a friction stir weld

Abstract: In friction stir welding (FSW), a rotating threaded pin tool is inserted into a weld seam and literally stirs the edges of the seam together. The dynamically recrystallized zone (DXZ) of a polished and etched FSW cross section exhibits contrasting bands (the “onion-ring” structure), the origins of which are unclear. An orientation image mapping (OIM) study suggests that the bands may correspond, respectively, to a “straight-through” current of metal bypassing the pin tool in a single rotation or less and a “maelstrom” current rotating a number of times around the pin tool.

Pulmonary responses to welding fumes: role of metal constituents.

Abstract: It is estimated that more than 1 million workers worldwide perform some type of welding as part of their work duties. Epidemiology studies have shown that a large number of welders experience some type of respiratory illness. Respiratory effects seen in full-time welders have included bronchitis, siderosis, asthma, and a possible increase in the incidence of lung cancer. Pulmonary infections are increased in terms of severity, duration, and frequency among welders. Inhalation exposure to welding fumes may vary due to differences in the materials used and methods employed. The chemical properties of welding fumes can be quite complex. Most welding materials are alloy mixtures of metals characterized by different steels that may contain iron, manganese, chromium, and nickel. Animal studies have indicated that the presence and combination of different metal constituents is an important determinant in the potential pneumotoxic responses associated with welding fumes. Animal models have demonstrated that stainless steel (SS) welding fumes, which contain significant levels of nickel and chromium, induce more lung injury and inflammation, and are retained in the lungs longer than mild steel (MS) welding fumes, which contain mostly iron. In addition, SS fumes generated from welding processes using fluxes to protect the resulting weld contain elevated levels of soluble metals, which may affect respiratory health. Recent animal studies have indicated that the lung injury and inflammation induced by SS welding fumes that contain water-soluble metals are dependent on both the soluble and insoluble fractions of the fume. This article reviews the role that metals play in the pulmonary effects associated with welding fume exposure in workers and laboratory animals.

Hydraulic shock absorber

Abstract: PROBLEM TO BE SOLVED: To prevent rattling caused by the impact and vibration of a cap with a simple constitution in a hydraulic shock absorber wherein the gap is held between a piston rod and a joint. SOLUTION: In this hydraulic shock absorber 10 wherein the piston rod 20 is projected from one end of a damper tube 11, the joint 30 is welded on a projecting end of the piston rod 20, and the cap 40 is held between the piston rod 30 and the joint 30, an uneven part 44 is formed on a contact face at the piston rod 20 side, of the cap 40. COPYRIGHT: (C)2004,JPO&NCIPI

Microstructures and mechanical properties of friction stir welds of 60% Cu–40% Zn copper alloy

Abstract: The characteristics of the microstructures and mechanical properties of friction stir welds of 60% Cu–40% Zn alloy (60/40 brass) were investigated. The defect-free welds were obtained in a relatively wide range of welding conditions; the tool rotation speed ranged from 1000 to 1500 rpm with a welding speed from 500 to 2000 mm/min, and 500 rpm—500 mm/min. The microstructures of the welds yielded extremely fine grains with some deformed grains in the stirred zone (SZ) and elongated grains in the thermo-mechanically affected zone. The hardness values within the SZ in all welding conditions were much higher than those of the base metal, increased with a decrease in heat input. The generation of refined grains in the SZ was a main factor which caused the hardness increase associated with decreasing heat input. The strengths of the all-SZ showed relative correspondence to the variation of the hardness values in the SZ.

Principles of welding : processes, physics, chemistry, and metallurgy

Abstract: THE PROCESS AND PROCESSES OF WELDING. Introduction to the Process of Welding. Classifying Welding Processes. Fusion Welding Processes. Nonfusion Welding Processes. THE PHYSICS OF WELDING. Energy for Welding. The Flow of Heat in Welds. Thermally Induced Distortion and Residual Stresses During Welding. The Physics of Welding Energy or Power Sources. Molten Metal Transfer in Consumable Electrode Arc Welding. Weld Pool Convection, Oscillation, and Evaporation. THE CHEMISTRY OF WELDING. Molten Metal and Weld Pool Reactions. Weld Chemical Heterogeneity. THE METALLURGY OF WELDING. Weld Fusion Zone Solidification. Eutectic, Peritectic, and Postsolidification Fusion Zone Transformations. The Partially Melted Zone. The Weld Heat-Affected Zone. Weldability and Weld Testing. Closing Thoughts. Appendices. Index.

Control of Laves phase in Inconel 718 GTA welds with current pulsing

Abstract: The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.

Review of resistance spot welding of steel sheets Part 1 Modelling and control of weld nugget formation

Abstract: Resistance spot welding is the principal method of welding sheet steel products. In practice, the manufacture of welds of acceptable quality depends on the definition of optimum welding parameters and the implementation of suitable controls to ensure constant weld quality over a long production run. The ability to make a weld is best defined by a weldability lobe outlining the available manufacturing tolerances between minimum and maximum limits. Both two- and three-dimensional weldability lobes exist defined in terms of weld time, welding current and electrode force. Production variables influencing weld growth are discussed, particularly the effect of electrode diameter. The importance of welding machine characteristics relative to weld growth is highlighted. In particular, the rigidity of the machine coupled with the weight and frictional effects developed in the electrode head assembly are shown to be important factors influencing weld growth. Also important are the electrical characteristics of the machine, including transformer configuration current waveform and current ‘off’ time in the nonconducting part of the waveform. A reliable control philosophy is an essential requirement of any inprocess feedback system if high quality spot welds are to be produced in high volume. Various model simulations indicate that changes, with time, in electrode/sheet and sheet/sheet interfacial resistances control weld nugget formation and growth. The relative contributions of these resistances are discussed. Heat generation and temperature distribution in the weldare determined by the current and force distribution across these interfaces. One-, two- and three-dimensional models have been developed to describe the temperature distribution in the weld zone and weld nugget growth. These models have limited application due to inadequate input data to describe the transient conditions appertaining in the weld zone. Current waveform, inductance effects, and friction/rigidity of the electrode head assembly, are not considered. Neural networks and fuzzy logic control have shown promise in classifying weld quality into predetermined groupings. The way forward is to adopt a multidisciplinary approach, taking into account the various interactions between the thermal, electrical, mechanical and metallurgical phenomena developed during the welding process. Models describing these phenomena should be interlinked to simulate heat generation and growth in the weld zone. The resulting model could be coupled with experimentally developed trends to optimise inputs to a neural network, the output of which is used, through a fuzzy logic controller, to take appropriate corrective action to ensure the required weld quality. It is stressed that any mathematical simulation or control system must take into account changes that occur at the welding electrodes as a consequence of electrode wear. The latter are discussed in Part 2 of this review.

Joining of aluminum alloy 5052 and low-carbon steel by laser roll welding

Abstract: Low-carbon steel and aluminum Alloy 5052 sheets were diffusion welded using different conditions of time, temperature, and pressure in order to understand the kinetics of diffusion and the microstructure of the interface layer. High pressures accelerated intermetallic compound formation at the interface. The interface layer consisted of aluminum-rich brittle intermetallic compounds (FeAl 3 and Fe 2 Al 5 ), which made the joints brittle. In laser roll welding, steel and aluminum sheets in a lap-joint configuration are subjected to laser heating and immediate rolling for intimate contact. Laser heating provides high temperature in a short time for melting of the aluminum alloy and diffusion. It results in formation of a thin interface layer. When the temperature is above 1473 K (1200°C), formation of iron-rich (Fe-rich) intermetallic compounds (FeAl and Fe 3 Al) is encouraged. Travel speed and roll pressure were varied and resultant joints were characterized by optical microscopy, electron-probe microanalysis (EPMA), scanning electron microscopy (SEM), X-ray diffraction, and tensile shear testing. The laser roll welded interface layer contains brittle aluminum-rich (Al-rich) intermetallic compounds on the aluminum side and slightly ductile Fe-rich intermetallic compounds on the steel side. As the travel speed increases, thinner interface layers are formed and the percentage of Fe-rich intermetallic compounds in them increases. This increases the shear strength of the joints from 11.0 to 55.9 MPa. Interface layers with a thickness of 4 to 5 μm, containing 25 to 40% Fe-rich intermetallic compounds, gave maximum shear strength.

Residual stress in friction stir-welded Al sheets

Abstract: Friction stir welding (FSW) is a relatively new joining technique particularly for aluminum alloys that are difficult to fusion weld. A potential field of application is aircraft structures where cost and weight can be reduced by using new joining techniques instead of riveting. Efforts are currently being made to qualify FSW for this purpose. In this study, the influence of a coolant applied during welding of Al sheets on the residual stress state of the FSW joint was investigated. Liquid CO2 coolant was applied near the weld seam for rapid cooling of the weld zone. The residual stresses across the weld were measured by neutron diffraction. Three sheets were produced, one without cooling, and two with cooling, where two different distances of the coolant nozzles from the FSW tool were chosen. The results show that, by applying a coolant, the magnitude of the tensile stress in the center of the weld can be reduced significantly.

Virtual Training for Welding

Abstract: A mixed reality system has been created for simulating gas metal arc welding (GMAW) welding. This simulation system is intended for use in training human welders. The system is comprised of a real welding torch attached to a force feedback device, a head-mounted display, a 6 DOF tracking system for both the torch and the user's head, and external audio speakers. The welding simulation is based on empirical results from detailed analysis of a series of test welds. The simulation runs in real-time, using a neural network to determine the quality and shape of the created weld based on the orientation and speed of the welding torch. The welding process and resulting weld bead are displayed in a virtual environment. Weld quality and recorded process values can be displayed after welding for review.

Marangoni convection and weld shape variations in Ar-O2 and Ar-CO2 shielded GTA welding

Abstract: Increasing the oxygen or the carbon dioxide concentration in the argon-based shielding gas leads to an increase in the weld metal oxygen content when the oxygen or carbon dioxide concentration is to be lower than 0.6 vol.% in the shielding gas. However, when the O2 or CO2 concentration is higher than 0.6 vol.% in the Ar-based shielding gas, the weld metal oxygen is maintained around 200 ppm–250 ppm. An inward Marangoni convection mode in the weld pool occurs when the weld metal oxygen content is more than 100 ppm. When it is lower than 100 ppm, the Marangoni convection would change to the outward direction and the weld shape varies from a deep narrow to a shallow wide shape. The effective ranges of O2 and CO2 concentrations for deep penetration are same. A heavy layer of oxides is formed when the O2 or CO2 concentration in the shielding gas is more than 0.6 vol.%. Based on the thermodynamic calculation of the equilibrium reactions of Fe, Si, Cr and Mn with oxygen in liquid iron for the oxide products, FeO, SiO2 ,C r 2O3 and MnO and the experimental oxygen content in the weld metal, Cr2O3 and SiO2 oxides are possibly formed at the periphery area of the liquid pool surface under the arc column during the welding process. One model is proposed to illustrate the role of the oxide layer on the Marangoni convection on the pool surface at elevated temperature. The heavy oxide layer inhibited the fluid flow induced by the Marangoni convection and also became a barrier for the oxygen absorption into the molten weld pool. © 2004 Elsevier B.V. All rights reserved.

Kissing Bond Phenomena in Solid-State Welds of Aluminum Alloys

Abstract: The occurrence and nature of kissing bonds have been studied in three solid-state welding processes: friction stir welding, extrusion charge welding, and extrusion seam welding. A kissing bond is the descriptive term for two surfaces lying extremely close together, but not close enough for the majority of the original surface asperities to have deformed sufficiently in contact for atomic bonds to be created. Depending on their location and extent, they may have detrimental effects on the fatigue life and through-thickness load-bearing capacity of the component. This paper presents analogies between kissing bonds in the above-mentioned joining methods using fractographic evidence and phenomenological hypotheses. The effects of these discontinuities on the mechanical properties of these joints produced in 6xxx-Series aluminum alloys used in automotive and marine structural applications are discussed.

Joining of Materials and Structures: From Pragmatic Process to Enabling Technology

Abstract: Introduction to Joining: A Process and a Technology Mechanical Joining Mechanical Fasteners, Integral Attachments, & Other Mechanical Joining Methods Adhesive Bonding & Cementing Adhesives, Cements, Mortars, and the Bonding Process Welding as a Joining Process The Basics of Welding Metallurgy Brazing: A Subclassification of Welding Soldering: A Subset of Brazing Other Joining Processes: Variants & Hybrids Joining Metals, Alloys, and Internetallics Joining of Ceramics and Glasses Joining of Polmeric Materials Joining Composite Materials and Structures Joining Dissimilar Material Combinations Joining Structures and Living Tissue.