Showing papers on "Welding published in 2001"

Mechanical engineering design

Abstract: Part I Basics1 Introduction2 Statistical Considerations3 Materials4 Load and Stress Analysis5 Deflection and StiffnessPart II Failure Prevention6 Failures Resulting from Static Loading7 Fatigue Failure Resulting from Variable LoadingPart III Design of Mechanical Elements8 Screws, Fasteners, and the Design of Nonpermanent Joints9 Welding, Brazing, Bonding, and the Design of Permanent Joints10 Mechanical Springs11 Rolling-Contact Bearings12 Lubrication and Journal Bearings13 Gears - General14 Spur and Helical Gears15 Bevel and Worm Gears16 Clutches, Brakes, Couplings and Flywheels17 Flexible Mechanical Elements18 Shafts and AxlesA Appendix A Useful TablesB Appendix B Solutions to Selected ProblemsIndex

A process model for friction stir welding of age hardening aluminum alloys

Abstract: In the present investigation, a numerical three-dimensional (3-D) heat flow model for friction stir welding (FSW) has been developed, based on the method of finite differences. The algorithm, which is implemented in MATLAB 5.2, is provided with a separate module for calculation of the microstructure evolution and the resulting hardness distribution. The process model is validated by comparison with in-situ thermocouple measurements and experimental hardness profiles measured at specific time intervals after welding to unravel the strength recovery during natural aging. Furthermore, the grain structure within the plastically deformed region of the as-welded materials has been characterized by means of the electron backscattered diffraction (EBSD) technique in the scanning electron microscope (SEM). Some practical applications of the process model are described toward the end of the article.

Visualization of the material flow in AA2195 friction-stir welds using a marker insert technique

Abstract: The material flow in solid-state, friction-stir, butt-welded AA2195-T8 was investigated using a marker insert technique (MIT). Markers made of AA5454-H32 were embedded in the path of the rotating friction stir welding (FSW) tool and their final position after welding was detected by metallographic means. Changes in material flow due to welding parameter and tool geometry variations were examined. The method provides a semiquantitative, three-dimensional view of the material transport in the welded zone. Because of the placement of markers at different positions at the weld centerline, the material transport in the longitudinal, transverse, and the vertical directions could be studied. Markers embedded in the path of the tool remain continuous after welding. The material transport, which is not symmetrical about the weld centerline, was such that the bulk of the material was transported to a position behind its original position. Superimposed on the primary motion of material in the horizontal plane of the weld is a circulation about the longitudinal axis of the weld. This circulation is found to increase with increasing weld energy.

Friction stir welding method

Abstract: There is provided a method capable of decreasing a friction force in friction stir welding, in which a welding tool is used. In a method of friction stir welding workpieces together by rotating and pressingly plugging a welding tool, formed from a harder material than the workpieces, into a weld zone of the workpieces and moving the welding tool relatively in a welding direction, a power supply device allows a current to flow between the welding tool 1 and the workpieces to cause resistance heating of the welding tool. Combined use of resistance heating makes it possible to decrease a friction force. Preferably, a conductive ceramic is coated on surfaces of the welding tool to cause resistance heating.

Finite element modeling and simulation of welding part 1: increased complexity

Abstract: Simulation of welding has advanced from the analysis of laboratory setups to real engineering applications during the last three decades. This development is outlined and the directions for future research are summarized in this review, which consists of three parts. This part shows that the increased complexity of the models gives a better description of the engineering applications. The important development of material modeling and computational efficiency are outlined in Parts 2 and 3, respectively.

Modeling Variation Propagation of Multi-Station Assembly Systems With Compliant Parts

Abstract: Products made of compliant sheet metals are widely used in automotive, aerospace, appliance and electronics industries. One of the most important challenges for the assembly process with compliant parts is dimensional quality, which affects product functionality and performance. This paper develops a methodology to evaluate the dimensional variation propagation in a multi-station compliant assembly system based on linear mechanics and a state space representation. Three sources of variation: part variation, fixture variation and welding gun variation are analyzed. The proposed method is illustrated through a case study on an automotive body assembly process.

Finite element modeling and simulation of welding. part 2: improved material modeling

Abstract: Simulation of welding has advanced from the analysis of laboratory setups to real engineering applications during the last three decades. This development is outlined and the directions for future research are summarized in this review, which consists of three parts. The material modeling is maybe the most crucial and difficult aspect of modeling welding processes. The material behavior may be very complex for the large temperature range considered.

Observations on chip formation and acoustic emission in machining Ti–6Al–4V alloy

Abstract: Orthogonal cutting tests were undertaken to investigate the mechanisms of chip formation for a Ti–6Al–4V alloy and to assess the influences of such on acoustic emission (AE). Within the range of conditions employed (cutting speed, v c =0.25–3.0 m/s , feed, f=20–100 μm ), saw-tooth chips were produced. A transition from aperiodic to periodic saw-tooth chip formation occurring with increases in cutting speed and/or feed. Examination of chips formed shortly after the instant of tool engagement, where the undeformed chip thickness is slightly greater than the minimum undeformed chip thickness, revealed a continuous chip characterised by the presence of fine lamellae on its free surface. In agreement with the consensus that shear localisation in machining Ti and its alloys is due to the occurrence of a thermo-plastic instability, the underside of saw-tooth segments formed at relatively high cutting speeds, exhibiting evidence of ductile fracture. Chips formed at lower cutting speeds suggest that cleavage is the mechanism of catastrophic failure, at least within the upper region of the primary shear zone. An additional characteristic of machining Ti–6Al–4V alloy at high cutting speeds is the occurrence of welding between the chip and the tool. Fracture of such welds appears to be the dominant source of AE. The results are discussed with reference to the machining of hardened steels, another class of materials from which saw-tooth chips are produced.

Microtexture in the friction-stir weld of an aluminum alloy

Abstract: In order to characterize plastic flow during friction-stir welding, the microtextures in a friction-stir weld of the precipitation-hardened aluminum alloy 6063 have been analyzed by orientation imaging microscopy (OIM). The base-material plate has a Goss orientation. The weld center region, except for the upper surface, takes a typical shear texture component with two types of orientations. The orientations have a pair of common {111} and 〈110〉 parallel to the cylindrical pin surface and transverse direction of the plate, respectively. The typical texture component is also observed around the weld center on the midsection, although it rotates about the plate normal direction. A microtexture analysis after postweld heat treatment has suggested that dynamic recrystallization during friction-stir welding generates the recrystallized grains at the weld center.

Heterogeneity of crystallographic texture in friction stir welds of aluminum

Abstract: Over the past decade, friction stir welding (FSW) has rapidly become an important industrial joining process, particularly in the aluminum industry Included among the advantages of FSW are such important attributes as improved weld strength and the elimination of cracking and porosity During the friction stir process, the metal undergoes a tortuous deformation path that is not yet fully understood The crystallographic texture that evolves during FSW contains sharp spatial gradients that undoubtedly influence the integrity of the weld and surrounding region in subsequent performance The locally measured textures are discussed in the context of the material flow required to produce such textures, ultimately resulting in an estimate of the flow field present during FSW

Melting and Welding Semiconductor Nanowires in Nanotubes

Abstract: and deformations are obtained after removal of the silica matrix using aqueous HF. Our study indicates that mesoporous silicas such as C16MCM-41, C22MCM-41, and SBA-15 can act as good templates for the synthesis of Pd nanowires. Moreover, a significantly depressed melting point of the Pd nanowires is observed around 300 C. To the best of our knowledge, this is the first report on the synthesis and thermal behavior of Pd nanowires of less than 10 nm diameter. Along with our matrix-assisted process, in particular, our low-temperature CVI approach is attractive because it can be carried out under conditions mild enough to avoid any disruption of both the desired material and the template structure. The combined matrix-assisted and CVI process can be extended not only to other sizes of nanowires but also to multidimensional structures using appropriate host architectures.

Thermal plasmas in gas mixtures

Abstract: The calculation and measurement of the properties of thermal plasmas in mixtures of different gases are reviewed. The calculation of composition, thermodynamic properties and transport coefficients is described. Particular attention is given to the calculation of diffusion coefficients, which is a significant problem in mixed-gas plasmas. The combined diffusion coefficient formulation is shown to be a useful method for the treatment of diffusion. Computational fluid dynamic modelling of thermal plasmas in gas mixtures is considered, using the examples of demixing in welding arcs, the turbulent mixing of atmospheric air into a plasma jet and a plasma waste destruction process. Diagnostic techniques for mixed-gas plasmas, in particular emission spectroscopy, laser scattering and laser-induced fluorescence, are discussed.

Weld metal composition change during conduction mode laser welding of aluminum alloy 5182

Abstract: Selective vaporization of volatile elements during laser welding of automotive aluminum alloys affects weld metal composition and properties. An experimental and theoretical study was carried out to seek a quantitative understanding of the influences of various welding variables on vaporization and composition change during conduction mode laser welding of aluminum alloy 5182. A comprehensive model for the calculation of vaporization rate and weld metal composition change was developed based on the principles of transport phenomena, kinetics, and thermodynamics. The calculations showed that the vaporization was concentrated in a small high-temperature region under the laser beam where the local vapor pressure exceeded the ambient pressure. The convective vapor flux driven by the pressure gradient was much higher than the diffusive vapor flux driven by the concentration gradient. The computed weld pool geometry, vaporization rates, and composition changes for different welding conditions agreed well with the corresponding experimental data. The good agreement demonstrates that the comprehensive model can serve as a basis for the quantitative understanding of the influences of various welding variables on the heat transfer, fluid flow, and vaporization occurring during conduction mode laser welding of automotive aluminum alloys.

Mechanical properties and microstructure of gas tungsten arc welded magnesium AZ91D plates

Abstract: Gas tungsten arc (GTA) welds were performed on 4-mm thick plates, machined from as-cast magnesium AZ91D ingots. The microstructure and defect formation was investigated by optical and scanning electron microscopy. Mechanical properties were determined by standard tensile tests on small-scale specimens. A wide heat affected zone (HAZ) (>3 mm) was created adjacent to the fusion line that consisted of two regions: (1) a partially melted zone (PMZ), created near the fusion line; and (2) a wide region, which was heat affected without melting. It was found that, after resolidification, a continuous Al12Mg17 phase existed along the PMZ grain boundaries that markedly reduced the joint strength to below that of fully annealed Mg-AZ91D alloys. In contrast, specimens machined from welded metal exhibited improved strength and ductility that resulted from the microstructural refinement caused by the rapid cooling during resolidification of the fusion zone. When the creation of a large PMZ was prevented, as in electron beam welding, the joint strength was comparable to that of the base metal.

Finite element modeling and simulation of welding. part 3: efficiency and integration

Abstract: Welding simulation has advanced from the analysis of laboratory setups to real engineering applications during the last three decades. This development is outlined and the directions for future research are summarized in this review, which consists of three parts. This parts focuses on computational strategies and how they are integrated with other methods to facilitate the use of simulations in engineering. These developments have lead to the increased application of welding simulations in industry.

Comparison of keyhole and conventional gas tungsten arc welds in commercially pure titanium

Abstract: Keyhole gas tungsten arc welding (GTAW), a novel process recently developed at CSIRO Manufacturing Science and Technology, Australia, has been used to join commercially pure (CP) titanium. The process enables single pass, out of chamber welding of 12.7 mm thick CP titanium without expensive filler metal addition or joint preparation. The microstructure and mechanical properties of the resultant weld joint have been compared with those of a multipass conventional GTAW joint in CP titanium prepared from plates of the same thickness with a double-V edge preparation and the addition of a matching filler metal. It was shown that the differences in the net heat input and weld thermal cycles associated with the two processes led to similar microstructures, albeit of different degrees of refinement. As a result, the tensile and hardness properties of the two welded joints were similar to each other and comparable to those of the base material. The acicular nature of the fusion zone microstructure in both welds led to a significant increase in their notch toughness over that of the base material. It is concluded that the keyhole GTAW, with its significantly higher productivity combined with the simplicity of proven technology and low capital investment requirements, can be successfully applied in the welding of heavy section CP titanium, without sacrificing the metallurgical quality associated with the GTAW process.

Flux-cored wire for gas shielded arc welding

Abstract: Provided is a flux-cored wire which is excellent in welding activity in all position welding, and excellent in the strength and low-temperature toughness of weld metal as welded (AW) and after PWHT. The flux-cored wire contains the proper amount of C, Si, Mn, Ni, B, Mg, V, Ti oxide, metal Ti, Al oxide, metal Al, Si oxide, metal fluoride, P and Nb.

Factors affecting the properties of friction stir welded aluminum lap joints

Abstract: Friction stir welding (FSW) is a solid-state joining process invented at The Welding Institute (TWI) in 1991. The ability to produce high-quality welds in high-strength aluminum alloys sets FSW apart from typical fusion welding techniques. The process has mainly been used for making butt joints in aluminum alloys. Development of FSW for use in lap joint production would expand the number of applications that could benefit from the technique. In this study, an extensive investigation was carried out on FSW lap joints, including interface morphology and mechanical properties. Two materials, Alclad 2024-T3 and AI7075-T6, sheet materials commonly used in the aerospace industry, were joined. Welding variables included welding speed, rotational speed and, of particular importance, tool dimensions. Examination of metallographic cross sections and failure locations showed a critical sheet interface present in all welds. Consequently, a second weld pass was added to eliminate the critical sheet interface. Results indicated FSW lap joints may, on the basis of strength, potentially replace other joining processes like resistance spot welding and riveting.

Effect of vacuum on penetration and defects in laser welding

Abstract: The effect of vacuum on weld penetration and porosity formation was investigated in high-power cw CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation, and liquid flow in the molten pool during high-power YAG laser welding under various conditions through the microfocused x-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of the molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, although the middl...

Monitor for electric arc welder

Abstract: A monitor for an electric arc welder as the welder performs a selected arc welding process by creating actual welding parameters, such as arc current and arc voltage, between an advancing welding wire and a workpiece, where the process involves an arc and is defined by a series of rapidly repeating wave shapes constituting a weld cycle with a cycle time, the wave shapes are each segmented into time states having command signals corresponding to the actual parameters and a time duration. The monitor selects a specific wave shape state, reads one of the actual parameters, compares the actual read parameter with a function of the command signal corresponding to the actual parameter, and uses the comparison to generate a characteristic of the welding process during the selected state.

Device for metal welding

Abstract: The invention relates to a device for metal welding, comprising a shielding element ( 1 ) which allows visual monitoring of the working process but protects the eyes from light radiation. The device comprises a video camera ( 5 ) which is directable towards the welding zone for recording the welding process in the form of video signals transmitted, via an image processing unit, to a video display unit ( 7 ), which the user is able to view and which is placed in or on the inside of the shielding element ( 1 ). The image processing unit reads process data from the video signals and presents the same via the video display unit.

Spot welding system and method for sensing welding conditions in real time

Abstract: Methods and apparatus are provided for monitoring resistance spot welding process conditions in real time by using welding data in an energy balance model in integral form to estimate the mean weld temperature and to predict process conditions such as occurrence of splash, and weld diameter. Using predicted welding process conditions, welding parameters are modified in real time to prevent splash and produce sound welds.