Showing papers on "Welding published in 2002"

Three-dimensional modeling of the friction stir-welding process

Abstract: This paper presents an attempt to model the stir-welding process using three-dimensional visco-plastic modeling. The scope of the project is focused on butt joints for aluminum thick plates. Parametric studies have been conducted to determine the effect of tool speeds on plate temperatures and to validate the model predictions with available measurements. In addition, forces acting on the tool have been computed for various welding and rotational speeds. It is found that pin forces increase with increasing welding speeds, but the opposite effect is observed for increasing rotational speeds. Numerical models such as the one presented here will be useful in designing welding tools which will yield desired thermal gradients and avoid tool breakage.

Parameters controlling microstructure and hardness during friction-stir welding of precipitation-hardenable aluminum alloy 6063

Abstract: The aluminum (Al) alloys 6063-T5 and T4 were friction-stir welded at different tool rotation speeds (R), and then distributions of the microstructure and hardness were examined in these welds. The maximum temperature of the welding thermal cycle rose with increasing R values. The recrystallized grain size of the weld increased exponentially with increasing maximum temperature. The relationship between the grain size and the maximum temperature satisfied the static grain-growth equation. In the as-welded condition, 6063-T5 Al was softened around the weld center, whereas 6063-T4 Al showed homogeneous hardness profiles. Different R values did not result in significant differences in the hardness profile in these welds, except for the width of the softened region in the weld of 6063-T5 Al. Postweld aging raised the hardness in most parts of the welds, but the increase in hardness was small in the stir zone produced at the lower R values. Transmission electron microscope (TEM) observations detected a similar distribution of the strengthening precipitates in the grain interiors and the presence of a precipitation-free zone (PFZ) adjacent to the grain boundaries in all the welds. Microstructural analyses suggested that the small increase in hardness in the stir zone produced at the lower R values was caused by an increase in the volume fraction of PFZs.

Microstructural studies of friction stir welds in 2024-T3 aluminum

Abstract: Friction stir welds in 7 mm thick, 2024-T351 aluminum rolled sheet material have been completed. Metallurgical, hardness and quantitative energy dispersive X-ray measurements have been performed which demonstrate that a segregated, banded, microstructure consisting of alternating hard particle rich and hard particle poor regions is developed. Mixed-mode I/II monotonic fracture experiments confirm that the observed banded microstructure affects the macroscopic fracture process. Since the band spacing is directly correlated with the welding tool advance per revolution, our results indicated that the opportunity exists to manipulate the friction stir weld process parameters in order to modify the weld microstructure and improve a range of material properties, including fracture resistance.

The welding of aluminium and its alloys

Abstract: Introduction to the Welding of Aluminium. Welding metallurgy. Material Standards, Designations and Alloys. Preparation for Welding. Welding Design. TIG Welding. MIG Welding. Other Welding Processes. Resistance Welding Processes. Welding procedure and welder approval. Weld Defects and Quality Control. Appendices.

Modeling of laser keyhole welding: Part I. mathematical modeling, numerical methodology, role of recoil pressure, multiple reflections, and free surface evolution

Abstract: A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification will be provided in the companion article (Part II).

Material flow and microstructure in the friction stir butt welds of the same and dissimilar aluminum alloys

Abstract: The material flow and microstructural evolution in the friction stir welds of a 6061-Al alloy to itself and of a 6061-Al alloy to 2024-Al alloy plates of 12.7 mm in thickness were studied under different welding conditions. The results showed that plastic deformation, flow, and mechanical mixing of the material exhibit distinct asymmetry characteristics at both sides of the same and dissimilar welds. The microstructure in dissimilar 6061-Al/2024-Al welds is significantly different from that in the welds of a 6061-Al alloy to itself. Vortex-like structures featured by the concentric flow lines for a weld of 6061-Al alloy to itself, and alternative lamellae with different alloy constituents for a weld of 6061-Al to 2024-Al alloy, are attributed to the stirring action of the threaded tool, in situ extrusion, and traverse motion along the welding direction. The mutual mixing in the dissimilar metal welds is intimate and far from complete. However, the bonding between the two Al-alloys is clearly complete. Three different regions in the nugget zone of dissimilar 6061-Al/2024-Al welds are classified by the mechanically mixed region (MMR) characterized by the relatively dispersed particles of different alloy constituents, the stirring-induced plastic flow region (SPFR) consisting of alternative vortex-like lamellae of the two Al-alloys, and the unmixed region (UMR) consisting of fine equiaxed grains of the 6061-Al alloy. Within all of these three regions, the material is able to withstand a very high degree of plastic deformation due to the presence of dynamic recovery or recrystallization of the microstructure. The degree of material mixing, the thickness of the deformed Al-alloy lamellae, and the material flow patterns depend on the related positions in the nugget zone and the processing parameters. Distinct fluctuations of hardness are found to correspond to the microstructural changes throughout the nugget zone of dissimilar welds.

Automatic identification of different types of welding defects in radiographic images

Abstract: Radiographic testing is a well-established non-destructive testing method to detect subsurface welding defects. In this paper, an automatic computer-aided identification system was implemented to recognize different types of welding defects in radiographic images. Image-processing techniques such as background subtraction and histogram thresholding were implemented to separate defects from the background. Twelve numeric features were extracted to represent each defect instance. The extracted feature values are subsequently used to classify welding flaws into different types by using two well-known classifiers: fuzzy k-nearest neighbor and multi-layer perceptron neural networks classifiers. Their performances are tested and compared using the bootstrap method.

Characterization of a friction-stir-welded aluminum alloy 6013

Abstract: The aluminum alloy 6013 was friction-stir welded in the T4 and the T6 temper, and the microstructure and mechanical properties were studied after welding and after applying a postweld heat treatment (PWHT) to the T4 condition Optical microscopy (OM), transmission electron microscopy (TEM), and texture measurements revealed that the elongated pancake microstructure of the base material (BM) was transformed into a dynamically recrystallized microstructure of considerably smaller grain size in the weld nugget Strengthening precipitates, present before welding in the T6 state, were dissolved during welding in the nugget, while an overaged state with much larger precipitate size was established in the heat-affected zone (HAZ) Microhardness measurements and tensile tests showed that the HAZ is the weakest region of the weld The welded sheet exhibited reduced strength and ductility as compared to the BM A PWHT restored some of the strength to the as-welded condition

System and method providing distributed welding architecture

Abstract: A system and method provides a distributed welding architecture in accordance with the present invention. The system includes a welder (124, 126, 128) operatively coupled to a server and a network interface to enable a network architecture, the network architecture serving a network that communicates with at least one remote system (30, 140, 310, 806). The remote system (30, 140, 310, 806) includes at least one remote interface (70) to communicate with the network architecture, wherein the remote system (30, 140, 310, 806) accesses at least one HTTP socket to establish web communications with the welder (124, 126, 128) and loads at least one application from the welder (124, 126, 128). The remote system (30, 140, 310, 806) accesses at least one Welding Application socket via the at least one application to exchange information between the welder (124, 126, 128) and the remote system (30, 140, 310, 806), wherein the at least one application includes at least one of a weld configuration component (74), a weld monitoring component (78), and a weld control component (82) to interact with the distributed welding system.

Mechanical response of friction stir welded AA2024: experiment and modeling

Abstract: The mechanical response of heterogeneous structures, such as weldments, is largely governed by the response of the local constituents. In the present paper, the global and local mechanical response of friction stir welded AA2024 is examined experimentally and numerically. Full field strain measurements are obtained on transversely loaded tensile specimens via the digital image correlation technique. Assuming an iso-stress configuration, local constitutive data were determined for the various weld regions and used as input for a 2-D finite element model. The simulation results were compared with the experimental results to assess the viability of the modeling approach and the validity of the iso-stress assumption

Hydrogen trapping in ferritic steel weld metal

Abstract: A brief overview is given of the role of hydrogen trapping in hydrogen management of steel welding. The concept of hydrogen trapping is introduced in conjunction with efforts in reducing hydrogen cracking in steel welding. Appropriate selection of hydrogen traps offers the potential to control the content and distribution of hydrogen in steel weldments. The effectiveness of hydrogen traps through selective alloying in reducing the concentration of diffusible hydrogen during welding thermal cycles is evaluated, particularly in its use as a substitute for costly weld heat treatment practices. The relationship of weld metal microstructure and hydrogen contents to the effective use of hydrogen trapping elements is discussed. The fundamental aspects which control hydrogen content as well as hydrogen distribution in steel are discussed, such as the statistical thermodynamics and the transport of hydrogen in steel containing traps. As tools for investigating potential hydrogen traps, several experimental...

A unified numerical modeling of stationary tungsten-inert-gas welding process

Abstract: In order to clarify the formative mechanism of weld penetration in an arc welding process, the development of a numerical model of the process is quite useful for understanding quantitative values of the balances of mass, energy, and force in the welding phenomena because there is still lack of experimentally understanding of the quantitative values of them because of the existence of complicated interactive phenomena between the arc plasma and the weld pool The present article is focused on a stationary tungsten-inert-gas (TIG) welding process for simplification, but the whole region of TIG arc welding, namely, tungsten cathode, arc plasma, workpiece, and weld pool is treated in a unified numerical model, taking into account the close interaction between the arc plasma and the weld pool Calculations in a steady state are made for stationary TIG welding in an argon atmosphere at a current of 150 A The anode is assumed to be a stainless steel, SUS304, with its negative temperature coefficient of surface tension The two-dimensional distributions of temperature and velocity in the whole region of TIG welding process are predicted The weld-penetration geometry is also predicted Furthermore, quantitative values of the energy balance for the various plasma and electrode regions are given The predicted temperatures of the arc plasma and the tungsten-cathode surface are in good agreement with the experiments There is also approximate agreement of the weld shape with experiment, although there is a difference between the calculated and experimental volumes of the weld The calculated convective flow in the weld pool is mainly dominated by the drag force of the cathode jet and the Marangoni force as compared with the other two driving forces, namely, the buoyancy force and the electromagnetic force

Dilution and microsegregation in dissimilar metal welds between super austenitic stainless steel and nickel base alloys

Abstract: Super austenitic stainless steels are often welded using high Mo, Ni base filler metals to maintain the corrosion resistance of the weld. An important aspect of this processing is the weld metal dilution level, which will control the composition and resultant corrosion resistance of the weld. In addition, the distribution of alloying elements within the weld will also significantly affect the corrosion resistance. Dissimilar metal welds between a super austenitic stainless steel (AL-6XN) and two Ni base alloys (IN625 and IN622) were characterised with respect to their dilution levels and microsegregation patterns. Single pass welds were produced over the entire dilution range using the gas tungsten arc welding process. Microstructural characterisation of the welds was conducted using light optical microscopy, scanning electron microscopy, and quantitative image analysis. Bulk and local chemical compositions were obtained through electron probe microanalysis. The quantitative chemical information w...

Method and apparatus for welding

Abstract: A method and apparatus for welding include initiating a pulse welding process includes initiating a welding arc by providing CC type welding power, maintaining the arc by providing CV type power. Then, pulse type welding power is provided. The method and system can be used to start short circuit, or other welding processes by providing short circuit power, or welding power of a given mode, instead of providing pulse power. Also, in one alternative, a method and system of initiating a pulse, short circuit, or given welding process includes initiating a welding arc by providing CC type welding power at least until a pseudo-equilibrium for the arc is established. Then, providing welding power in a pulse, short circuit, or the given mode.

Modeling of laser keyhole welding: Part II. Simulation of keyhole evolution, velocity, temperature profile, and experimental verification

Abstract: This article presents the simulation results of a three-dimensional mathematical model using the level set method for laser-keyhole welding. The details of the model are presented in Part I.[4] The effects of keyhole formation on the liquid melt pool and, in turn, on the weld bead are investigated in detail. The influence of process parameters, such as laser power and scanning speed is analyzed. This simulation shows very interesting features in the weld pool, such as intrinsic instability of keyholes, role of recoil pressure, and effect of beam scanning.

Modelling and optimization of a GMA welding process by genetic algorithm and response surface methodology

Abstract: The welding process, due to its complexity, has relied on empirical and experimental data to determine its welding conditions. However, trial-and-error methods to determine optimal conditions incur considerable time and cost. In order to overcome these problems, a genetic algorithm and response surface methodology have been suggested for determining optimal welding conditions. First, in a relatively broad region, near-optimal conditions were determined through a genetic algorithm. Then, the optimal conditions for welding were determined over a relatively small region around these near-optimal conditions by using response surface methodology. In order to give different objective function values according to the positive or negative response from the set target value in the optimization problem, a desirability function approach was used. Application of the method proposed in this paper revealed a good result for finding the optimal welding conditions in the gas metal arc (GMA) welding process.

Non-destructive control of industrial materials by means of lock-in thermography

Abstract: Lock-in thermography is employed for non-destructive control to evaluate several aspects of industrial interest: inclusions of spurious materials in both carbon-epoxy and glass-epoxy, impact damage and delaminations occurring around holes during drilling in carbon-epoxy, bonding improvements in Certran® after plasma treatments and steel modifications after welding. Phase images are analysed to find quantitative information for industrial characterization.