Showing papers on "Welding published in 1998"

Properties of friction-stir-welded 7075 T651 aluminum

Abstract: Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure, a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased, while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength. Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable potential for welding 7075 T651 aluminum.

Dynamics of keyhole and molten pool in laser welding

Abstract: In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primarily unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the porosity formation is one of the serious problems in very high-power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wave laser welding by high-speed optical and x-ray transmission methods, the cavity formation process and its suppression measures.

Marangoni effects in welding

Abstract: The problem of it variable weld penetration or casttocast variation in GTA/TIG welding is discussed. It is shown that for normal GTA/TIG welding conditions the HeipleRoper theory is valid, i.e. tha...

Intercalation vortices and related microstructural features in the friction-stir welding of dissimilar metals

Abstract: Dissimilar plates (0.6 cm thick) of copper and 6061 aluminum alloy; and 2024 aluminum alloy and 6061 aluminum alloy were friction-stir welded at various rotation speeds (400–1200 rpm) and traverse speeds of 1 to 3 mm/s, and produced variations of vortex and other swirl-like intercalations, especially near the weld-zone/work-piece interface. These vortex-like structures are composed of dynamically recrystallized, fine-grained intercalation microstructures which have been observed by optical metallography, scanning electron microscopy and transmission electron microscopy. They are similar to those characterizing mechanical alloying. Such microstructures are especially fascinating because although they resemble vortex instabilities which occur in turbulent fluids, they are formed by extreme deformation in the solid state since centerline temperatures through the weld zone are about 420°C, or ∼0.7 TM in the 6061 aluminum system.

Rapid prototyping of metal parts by three-dimensional welding

Abstract: Three-dimensional welding has the ability to produce strong, fully dense metal parts in layers. Adaptation of a weld cladding technique has enabled the production of parts wider than normal...

Optimisation of the weld bead geometry in gas tungsten arc welding by the Taguchi method

Abstract: In this paper, determination of the welding process parameters for obtaining an optimal weld bead geometry in gas tungsten arc welding is presented. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each welding process parameter on the weld bead geometry, and to predict the optimal setting for each welding process parameter. Experimental results are presented to explain the proposed approach.

Numerical analysis of GTA welding process with emphasis on post-solidification phase transformation effects on residual stresses

Abstract: The objective of this work was to analyze the residual stress state in spot welds made in an HY-100 steel disk by an autogenous gas tungsten arc (GTA) welding process An uncoupled thermal-mechanical finite element (FE) model was developed that took into account the effects of liquid-to-solid and solid-state phase transformations Effects of variations in mechanical properties due to solid-state phase transformations on residual stresses in the weld were studied Extensive experimental testing was carried out to determine the mechanical properties of HY-100 steel The residual stresses in the disk with the spot weld were measured by a neutron diffraction (ND) technique The FE results are in good agreement with the ND measurements The results show that the volumetric changes associated with the austenite to martensite phase transformation in HY-100 steel significantly affect residual stresses in the weld fusion zone and the heat affected zone

Friction stir welding process to repair voids in aluminum alloys

Abstract: The present invention provides an in-process method to repair voids in an aluminum alloy, particularly a friction stir weld in an aluminum alloy. For repairing a circular void or an in-process exit hole in a weld, the method includes the steps of fabricating filler material of the same composition or compatible with the parent material into a plug form to be fitted into the void, positioning the plug in the void, and friction stir welding over and through the plug. For repairing a longitudinal void (30), the method includes machining the void area to provide a trough (34) that subsumes the void, fabricating filler metal into a strip form (36) to be fitted into the trough, positioning the strip in the trough, and rewelding the void area by traversing a friction stir welding tool longitudinally through the strip. The method is also applicable for repairing welds made by a fusing welding process or voids in aluminum alloy workpieces themselves.

A dynamic model of drops detaching from a gas metal arc welding electrode

Abstract: A dynamic model of drop detachment in gas metal arc welding is presented for low and moderate welding currents in an argon-rich plasma. Simulations performed with this model are compared with extensive experimental measurements of constant-current welding images and with limited experimental measurements of pulsed-current welding images. The comparisons indicate that the experimental axial magnetic forces are much less potent than the calculated axial magnetic forces when welding-current transients are not present. To explain this finding the hypothesis that internal flows are able to develop under the relatively quiescent conditions that exist during drop development in constant-current welding is advanced.

Fused loop of filamentous material and apparatus for making same

Abstract: This invention is a fused loop (10) of an elongated material such as a surgical suture, and apparatus for making the loop. Portions of one or more segments (12) to be joined together are fused in a welding process to form a welded joint (14). The shear area of the fused portion (20) of the joint (14) determines the strength of the joint (14), and is thus preferably relatively large. Various configurations for the welding apparatus facilitate the creation of relatively large fused portions (20) of the joint (14) by maximizing contact between at least one of the welding members of the apparatus, and at least one of the segments (12) to be joined.

Friction stir welding with roller stops for controlling weld depth

Abstract: Stir friction welding is accomplished by applying force to plunge a nonconsumable, rotating welding post into the region to be welded. The rotation creates friction which at least partially melts the material to be welded, as the welding post penetrates. The force is continued, causing the post to continue to penetrate. A set of rollers associated with the welding head eventually reaches the surface of the workpiece when the welding post reaches the proper depth, and prevents further penetration of the welding post. In one embodiment of the invention, the rollers have crowned surfaces, and the force is applied by a hydraulic cylinder.

Contact backup roller approach to FSW process

Abstract: A welding apparatus (28) for forming a circumferential weld (56) includes a base (30) and a spindle (32) extending perpendicularly from the base. Along the spindle, at its proximal and distal portions, first and second workpiece supporters (38, 40) are provided, respectively, to position workpieces (42) to be welded together therebetween. Between the first and second workpiece supporters, a first arm (44) and a second arm (48) are provided, both extending perpendicularly from the spindle. To a distal end of the first arm, an internal backup roller (46) is rotatably attached, and to a distal end of the second arm, an internal drive roller (50) is rotatably attached. One or more external rollers (52a, 52b), each rotatably attached to an external support (66), are further provided. The internal and external rollers are driven by variable-speed programmable motors (not shown). In operation, the workpieces are mounted onto the apparatus, being sandwiched between the internal rollers and the external rollers. A friction stir welding tool (58) is positioned externally with its probe opposing the internal backup roller. As the programmable motors drive the rollers to continuously draw the workpieces between the friction stir welding tool and the internal backup roller, the friction stir welding tool forms a circumferential weld to join the workpieces together.

Optimisation of pulse frequency in pulsed current gas tungsten arc welding of aluminium–lithium alloy sheets

Abstract: Effects of current pulsation frequency on weld bead microstructure, hardness, and tensile properties in AA8090 type aluminium-lithium alloy sheets were studied. It was observed that the structure in the as solidified weld was predominantly columnar in the case of the conventional (i.e. continuous current) gas tungsten arc welding process. The grain structure became finer and more equiaxed with the introduction of current pulsation. Moreover, there was an optimum frequency range over which the grain refinement was a maximum. The same optimum frequency range corresponded with maxima in hardness, ultimate tensile strength, and percentage elongation. Tensile strength increased, in general, after solution treatment and aging (STA). The best combination of tensile properties was achieved for welds deposited under a 6 Hz pulse frequency in the STA condition.

Friction-stir welding: microstructural characterization

Abstract: The microstructures of friction-stir welded aluminum alloys (1100 and 6061) are dominated by dynamic recrystallization. Friction-stir welding of 6061 aluminum to copper produced a complex, intercalated microstructure which was also dominated by dynamic recrystallization. The friction-stir welding process is characterized by extreme plastic deformation in the solid state; there is no associated melting.

Arc welding monitoring device

Abstract: An arc welding monitoring device which can easily recognize the correspondence between the operating path of a robot, namely, the weld line information of a work to be welded and detected data such as welding voltages and currents. The monitoring device is provided with means (4 and 5) which detect at least either welding currents or welding voltages, a means (14) which retains the detected data of the means (4 and 5), a means (14) which stores the operating path of the robot, and a means (12) which displays at least either the welding currents or welding voltages detected by means of the detecting means (4 and 5) and the operating path of the robot stored by means of the storing means (14) on a display, sets an extent on the operating path displayed on the display, and makes arc welding monitoring displays within the set extent.

Apparatus for friction stir welding

Abstract: The invention concerns an apparatus for friction stir welding, comprising a welding unit including a welding head, a worktable including a backing unit to support the workpieces to be welded together along their joint line, and clamping means to clamp the workpieces to the worktable in a direction towards one another during the welding operation. The backing unit consists of at least two backing parts or of at least one backing part and one additional welding head, said backing parts being freely exchangeable, one for the other, before each welding operation as is also each backing part freely exchangeable for the additional welding head, and vice versa.

Smithells light metals handbook

Abstract: General physical and chemical constants Metallography Equilibrium diagrams General physical properties Mechanical testing Mechanical properties of metals and alloys Sintered materials Casting alloys and foundry data Heat treatment Guide to corrosion control Electroplating and metal finishing Welding Index.

Mechanical properties of laser-welded cast titanium joints under different conditions

Abstract: Statement of the problem. Data on optimal conditions for laser welding commercial pure cast titanium used in dental restorations are sparse and not well established. Purpose. The mechanical properties of laser-welded cast commercially pure titanium under different laser welding conditions were evaluated to find the optimal parameters in terms of duration and voltage (energy level). Material and methods. Fifty-seven cast pure titanium specimens according to ISO specification 6871 were divided into nine experimental groups and one control group. The sectioned titanium bars were laser-welded under different duration (8, 10, and 12 ms) and energy (290, 300, and 310 V) levels and evaluated for ranges of ultimate tensile strength (374 to 562 MPa), 0.2% yield strength (206 to 338 MPa), and percentage elongation (2.49% to 10.58%). Results. Under a suitable laser-welding setting parameter the ultimate tensile strength and 0.2% yield strength of experimental groups were weaker than the unsectioned control specimens (control group ultimate tensile strength 540 ± 11 MPa, 0.2% yield strength 258 ± 49 MPa) or too brittle (control group percentage elongation 12.41% ± 1.83%). Two-way ANOVA, nonparametric tests showed that voltage was the only significant factor for all parameters studied ( p Conclusion. Optimal duration and voltage (energy level) used in laser welding for cast CP grade I titanium bar was superior to or comparable with and produced properties that were superior to or comparable with the unsectioned control specimens. (J Prosthet Dent 1998;79:477-83.)

Chromium, nickel and manganese in shipyard welding fumes

Abstract: Tests were conducted to determine the effects of base metal and welding electrode composition on welding fume. Materials included HY-100 and HSLA-100 high-strength, low-alloy steels. Shielded metal arc welding (SMAW) was performed with E1 1018-M electrodes and gas metal arc welding (GMAW) with MIL-100S-1 electrode wire. These tests included measurement of fume composition, fume generation rates and worker breathing zone fume. Sampling of welding fume also was conducted in a shipyard. This study concludes that some shipyard welding and cutting operations, materials and processes will be impacted by the recent and anticipated reductions in exposure limits. Additional controls will be required to comply with these reductions. Results indicate: . Exposure to hexavalent chromium can be expected when welding or cutting materials that contain chromium or chromates. These materials include stainless steels, high-chromium nickel alloys and some low-alloy steels. . The highest nickel levels occurred during SMAW and GMAW of stainless steels and nickel alloys. However, only the samples in enclosed spaces exceeded the proposed limit for nickel. . SMAW, GMAW and flux cored arc welding (FCAW) of stainless steels, carbon steels and low-alloy steels produced the highest manganese levels. . Eight-hour TWA levels of hexavalent chromium of up to 1-2 μg/m 3 were found during shipyard and laboratory sampling of SMAW of HY-100 using E11018-M and E12018-M electrodes. Similar levels also may be possible when welding with these electrodes on other materials.

Characteristics of resistance welding of lap shear coupons. Part I: Heat transfer

Abstract: A transient three-dimensional finite element model for resistance welding of thermoplastic matrix composite lap shear specimens was established. The basic model assumes orthotropic heat conduction in the composite parts and accounts for heat losses by radiation as well as natural convection, involving latent heat effects. The rough contact surface between the heating ply and composite adherends was simulated by means of a thermal gap-conductance concept. Heat generation through the bundles of fibres in the heating ply was modelled. Different welding configurations of lap shear specimens were evaluated, namely APC-2 laminate/PEEK film, APC-2 laminate/PEI film and CF-PEI laminate/PEI film. `Time to melt' and `time to cause thermal degradation' were predicted and compared with experimental data available in the literature, and close agreement was obtained. Localised thermal degradation at the bonding interface was identified for high input power levels, and heat flow to the bulk laminate for long processing times was exhibited.

An analysis of the formation of metal droplets in arc welding

Abstract: A dynamic two-dimensional arc model has been used to investigate the effects of the various forces acting on the droplet in gas metal arc welding (GMAW). The model is based on the equations of conservation of mass, energy, momentum and current, Ohm's law and a Maxwell equation. The model treats the welding wire, the plasma and the workpiece. For molten metal droplets at the tip of the welding wire, we account for effects of inertia, gravity, surface tension, magnetic force, viscous drag force and arc pressure. Calculations are presented for a 1.6 mm diameter wire of mild steel for arcs in argon to determine the separate effects of these forces on droplet formation. It is found that, for arcs in pure argon at currents around the transition from the globular transfer mode to the spray transfer mode, viscous drag and arc pressure effects are approximately self-cancelling. It is also found that forces have a much larger effect than do forces on the transition from globular to spray modes of metal transfer.