Showing papers on "Electric resistance welding published in 2008"

Relationship between base metal properties and friction stir welding process parameters

Abstract: Friction stir welding (FSW) is a solid state welding process for joining aluminum alloys and has been employed in aerospace, rail, automotive and marine industries for joining aluminium, magnesium, zinc and copper alloys. In FSW, the base metal properties such as yield strength, ductility and hardness control the plastic flow of the material under the action of rotating non-consumable tool. The FSW process parameters such as tool rotational speed, welding speed, axial force, etc. play a major role in deciding the weld quality. In this investigation, an attempt has been made to establish relationship between the base material properties and FSW process parameters. FSW joints have been made using five different grades of aluminium alloys (AA1050, AA6061, AA2024, AA7039 and AA7075) using different combinations of process parameters. Macrostructural analysis has been done to check the weld quality (defective or defect free). Empirical relationships have been established between base metal properties and tool rotational speed and welding speed, respectively. The developed empirical relationships can be effectively used to predict the FSW process parameters to fabricate defect free welds.

Experimental study on temperature distributions within the workpiece during friction stir welding of aluminum alloys

Abstract: This study aims to experimentally explore the thermal histories and temperature distributions in a workpiece during a friction stir welding (FSW) process involving the butt joining of aluminum 6061-T6. Different types of thermocouple layout are devised to measure the temperature histories during FSW at different locations on the workpiece in the welding direction. Successful welding processes are achieved by appropriately controlling the maximum temperatures during the welding process. Regression analyses by the least squares method are used to predict the temperatures at the joint line. A second-order polynomial curve is found to best fit the experimental temperature values in the width direction of the workpiece. The Vickers hardness test is conducted on the welds to evaluate the hardness distribution in the thermal-mechanical affected zone, the heat affected zone, and the base metal zone. Tensile tests are also carried out, and the tensile strength of the welded product is compared with that of the base metal.

Some investigations on microstructure and mechanical properties of submerged arc welded HSLA steel joints

Abstract: This paper investigates the influence of the submerged arc welding (SAW) process parameters (welding current and welding speed) on the microstructure, hardness, and toughness of HSLA steel weld joints. Attempts have also been made to analyze the results on the basis of the heat input. The SAW process was used for the welding of 16 mm thick HSLA steel plates. The weld joints were prepared using comparatively high heat input (3.0 to 6.3 KJ/mm) by varying welding current (500–700 A) and welding speed (200–300 mm/min). Results showed that the increase in heat input coarsens the grain structure both in the weld metal and heat affected zone (HAZ). The hardness has been found to vary from the weld centre line to base metal and peak hardness was found in the HAZ. The hardness of the weld metal was largely uniform. The hardness reduced with the increase in welding current and reduction in welding speed (increasing heat input) while the toughness showed mixed trend. The increase in welding current from 500 A to 600 A at a given welding speed (200 mm/min or 300 mm/min) increased toughness and further increase in welding current up to 700 A lowered the toughness. Scanning electron microscopy of the fractured surfaces of impact test specimen was carried out to study the fracture modes. Electron probe micro analysis (EPMA) was carried out to investigate the variation in wt.% of different elements in the weld metal and HAZ.

Development of an advanced A-TIG (AA-TIG) welding method by control of Marangoni convection

Abstract: A new type of tungsten inert gas (TIG) welding has been developed, in which an ultra-deep penetration is obtained. In order to control the Marangoni convection induced by the surface tension gradient on the molten pool, He gas containing a small amount of oxidizing gas was used. The effect of the concentration Of O-2 and CO2 in the shielding gas on the weld shape was studied for the bead-on-plate TIG welding of SUS304 stainless under He-O-2 and He-CO2 mixed shielding gases. Because oxygen is a surface active element for stainless steel, the addition of oxygen to the molten pool can control the Marangoni convection from the outward to inward direction on the liquid pool surface. When the oxygen content in the liquid pool is over a critical value, around 70ppm, the weld shape suddenly changes from a wide shallow shape to a deep narrow shape due to the change in the direction of the Marangoni convection. Also, for He-based shielding gas, a high welding current will strengthen both the inward Marangoni convection on the pool surface and the inward electromagnetic convection in the liquid pool. Accordingly, at a welding speed of 0.75 mm/s, the welding current of 160 A and the electrode gap of I mm under the He-0.4%O-2 shielding, the depth/width ratio reaches 1.8, which is much larger for Ar-O-2 shielding gas (0.7). The effects of the welding parameters, such as welding speed and welding current were also systematically investigated. In addition. a double shielding gas method has been developed to prevent any consumption of the tungsten electrode. (c) 2008 Elsevier B.V. All rights reserved.

Study of the Performance of Stainless Steel A-TIG Welds

Abstract: The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al2O3, Cr2O3, TiO2, SiO2 and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The experimental results indicated that the increase in the penetration is significant with the use of Cr2O3, TiO2, and SiO2. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment. It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration.

A fully coupled thermo-mechanical model of friction stir welding

Abstract: This paper presents a new developed fully coupled thermo-mechanical model of the friction stir welding process. Results indicate that the rotation of the shoulder can accelerate the material flow behavior near the top surface. The material deformation and the temperature field can have relations with the microstructural evolution. The texture of the appearance of the friction stir welds can correlate well with the equivalent plastic strain distributions on the top surface. The temperature field in the friction stir welding process is approximately symmetric to the welding line. The material flows in different thicknesses are different. The shoulder can have a significant effect on material behaviors on the top surface, but this effect is greatly weakened when the material gets closer to the bottom surface of the welding plate.

Effect of pulsed current welding on mechanical properties of high strength aluminum alloy

Abstract: High strength aluminum alloys (Al-Zn-Mg-Cu alloys) have gathered wide acceptance in the fabrication of lightweight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminum alloy are frequently the gas tungsten arc welding (GTAW) process and the gas metal arc welding (GMAW) process due to their comparatively easy applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results in inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique. Rolled plates of 6 mm thickness were used as the base material for preparing single pass welded joints. A single ‘V’ butt joint configuration was prepared for joining the plates. The filler metal used for joining the plates was AA 5356 (Al-5Mg (wt%)) grade aluminum alloy. Four different welding techniques were used to fabricate the joints: (1) continuous current GTAW (CCGTAW), (2) pulsed current GTAW (PCGTAW), (3) continuous current GMAW (CCGMAW) and (4) pulsed current GMAW (PCGMAW). Argon (99.99% pure) was used as the shielding gas. Tensile properties of the welded joints were evaluated by conducting tensile tests using a 100 kN electro-mechanical controlled universal testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in tensile strength and tensile ductility.

High-power fiber laser welding and its application to metallic glass Zr55Al10Ni5Cu30

Abstract: Fiber laser has been receiving attention due to its advantages of high-power and high-beam quality to produce narrow and deep penetration welds at high-welding speeds. Therefore, fiber laser welding is expected to apply to the joining of metallic glass which has unique properties such as high-mechanical strength or small solidification shrinkage, because extremely rapid quenching for the laser weldment or heat-affected zone (HAZ) is possible to remain amorphous. In this research, fiber laser welding was first performed with the objective of obtaining a fundamental knowledge of weld property produced in bead-on-plate welding for common marital such as Type 304 stainless steel with 6 kW fiber laser beams of several peak power densities. Deeply penetrated weld beads with narrow widths were produced with small spots of tightly focused laser beams and full-penetration welds in 8 mm thick plate could be obtained at the high-welding speed of 4.5 m/min. Subsequently, the tightly focused 2.5 kW fiber laser beam was applied to 72 m/min ultra-high-speed welding for metallic glass Zr 55 Al 10 Ni 5 Cu 30 in order to keep amorphous metals. Consequently, the weldment and HAZ remained desirably amorphous at ultra-high-welding speed with a tightly focused fiber laser beam.

Dissimilar Welding of Al and Mg Alloys by FSW

Abstract: Microstructures and mechanical properties of dissimilar welding joint between Al alloy and Mg alloy by Friction Stir Welding (FSW) were investigated in comparison with laser welding of the same combination. Dissimilar joint of Al and Mg alloy by laser welding was very brittle because of building up Mg 17 Al 12 inter metallic compounds in fusion zone. On the other hand, FSW is anticipated to welding dissimilar alloys with enough joint strength because it is a solid-state process without melting. In this paper, FSW was carried out to make dissimilar butt joints of Al alloy and AZ31 magnesium alloy with various tool rotational speed and welding speed. These joints showed higher hardness in their stir zones than that of parent AZ31 alloy because of Mg-Al inter metallic compound formation. However, the hardness of stir zone was lower than that of fusion zone of laser welding, and was changed with the welding parameters of tool rotational speed and welding speed (i.e. heat input ratio of FSW). The optimum welding conditions of Mg and Al dissimilar FSW joint and the influence of inter metallic compound distribution with mixing of materials in stir zone were discussed.

Overview of resistance spot welding control

Abstract: This paper presents an overview of resistance spot welding control. The presentation of the physical background of the resistance welding process is followed by the description of the main problems concerning the appurtenant control theory. Solutions to these problems are presented primarily according to the measured signals used and to the type of control strategies.

Interface phenomena in aluminium–magnesium magnetic pulse welding

Abstract: The morphology and structure of the weld interface in magnetic pulse welding of similar and dissimilar metals were investigated. The interface zone of dissimilar metal couples such as Al–Mg, was studied in comparison to Al–Al welds. It was found that intermetallic phases (IMP) of different compositions are created during welding of the Al–Mg couple by rapid solidification of a thin melted layer at the interface. According to the calculated energy balance of magnetic pulse welding (MPW), there is enough energy to melt a thin interfacial layer and create IMP. Intensive characterisation techniques were used, including the focused ion beam (FIB) method that was used to prepare a cross-section of the Al–Mg interface for TEM characterisation. It was established that the jet action plays an important role in the melting process at the bonding zone.

The effect of weld parameters on friction stir welding of brass plates

Abstract: More successful results have been obtained in butt- and overlap-joining of Al-alloy plates by a recently developed solid state joining technique, namely friction stir welding (FSW), than in more conventional fusion welding processes. In this joining technique, no fusion takes place in the joint area of the plates welded. This novel joining method also offers the potential to weld some other materials rather than Al-alloys, such as Mg-alloys, brasses and low strength steels. In this study, the applicability of friction stir welding to brasses, namely 90 %Cu-10 %Zn and 70 %Cu-30 %Zn alloys, has been investigated. The joint performance was determined by conducting optical microscopy, microhardness mesurements and mechanical testing (e.g. tensile and bend tests). The effect of welding speed on the joint quality at a given rotational speed of the stirring pin (i.e. 1600 rpm) was also determined for both alloys. The highest joint performances were obtained at a welding speed of 210 mm/min for both alloys.

Underwater Welding - A Review

Abstract: Underwater Welding - A Review The paper describes principles of underwater welding and recent trends in research works undertaken for enhance welding technology and properties of underwater welds. Department of Materials Technology and Welding at Gdansk University of Technology (GUT) has been involved in underwater welding research for over 25 years. Investigations include technology of underwater welding, and weld properties examinations. All tests have been performed with the use of self designed stands allow to perform welds in shallow depths as well as the depths up to 1000 m. The main investigation directions performed at the Department of Materials Technology and Welding are presented: Weldability of HSLA steel and factors influencing susceptibility to cold cracking of welded joints. The effects of wet welding conditions on diffusible hydrogen amount in the welds. The effects of heat input, underwater welding depths and composition of shielded gases on welds toughness.

Analysis of circumferentially arc welded thin-walled cylinders to investigate the residual stress fields

Abstract: The control of weld-induced imperfections like welding deformations and residual stresses is of critical importance in circumferentially welded thin-walled cylinders due to their wide utilization in high tech engineering applications in aerospace and aeronautical structures, pressure vessels and nuclear engineering fields. The paper presents a computational procedure for the analysis of temperature distributions and the subsequent residual stress fields during the course of arc welding of thin-walled cylinders of low carbon steel. Parametric studies based on numerical simulations are conducted to investigate the effects of critical welding process parameter on weld-induced residual stresses. Temperature-dependent thermo-mechanical behavior for low carbon steel, filler metal deposition along with double ellipsoidal heat source model is incorporated. The accuracy of the developed finite element simulation strategy is validated for transient temperature distributions and residual stress fields through full-scale shop floor welding experiments with proper instrumentation for data measurement. The aim is to present data to confirm the validity of in-process circumferential welding technology for thin-walled cylinders so that the in service failures of these structures due to process specific inherent stresses may be minimized.

Research on laser welding of vehicle body

Abstract: Based on many experiments of CO 2 laser welding of vehicle body, joint microstructure and stress–strain curve of specimen are analyzed. The deep punching performance acquired by adopting Ar as protective gas is better than that of the one acquired by adopting N 2 as protective gas. Meanwhile the percentage of zinc in welding seam can be effectively controlled by means of blowing side protective gas. In this paper, welding penetration and width are shown to vary with laser power and speed of welding. The results indicate that some flaws such as gas hole, crack and softening of HAZ do not appear in laser welding seam in sheet steel of automobile bodies if technology parameters optimizes. The deep punching performance of tailor-welding sheet is fine.

Laser assisted Friction Stir Welding of drawable steel-aluminium tailored hybrids

Abstract: Steel aluminium Tailor Welded Hybrids are still mentioned to be difficult to be joint as intermetallic phases appear during melting welding techniques. These phases are the reason for failure of the joint during loading or forming. As conventional friction stir welding, a solid phase welding technology, is not feasible to join steel and aluminium, laser assistance for preheating the steel sheet is adapted in order to enhance the weldability as well as the welding feed and to reduce the wear at the tool. Tensile tests are performed to achieve mechanical properties of joints, which were welded by systematic variation of process parameters. Finally deep drawing tests are conducted to demonstrate the formability of laser assisted friction stir welded steel aluminium joints.

Numerical and experimental investigation of laser beam welding of aisi 304 stainless steel sheet

Abstract: Laser welding offers the advantage of very low heat input to the weld, resulting in low distortion and the ability to weld heat sensitive components. To obtain good weld bead geometry the selection of input parameters is very important. Laser beam welding trials are carried-out for 1.6 mm thick austenitic stainless steel for different beam power, welding speed and beam angle. The experimental trials for butt-joint configuration are conducted based on three level Box-Behnken design with replication resulting in 15 trials. The transient temperature profiles and weld pool dimensions, depth of penetration (DP) and bead width (BW) of the weld have been calculated using finite element code SYSWELD. A three dimensional Conical Gaussian heat source and the temperature dependent thermo-physical properties of AISI 304 stainless steel sheet are employed for performing a non-linear transient thermal analysis. It is found that the optimized parameters for deep penetration welding are laser power of 1250 Watts, welding speed of 750 mm/min and beam angle of 90o. Finally, the results of the simulation models and the experimental results are compared.