Showing papers on "Electric resistance welding published in 1999"

Material flow behavior during friction stir welding of aluminum

Abstract: Friction stir welding (FSW) is a new technique for joining aluminum alloys. Invented in 1991 at The Welding Institute (Ref. 1), this technique results in low distortion and high joint strength compared with other techniques, and is capable of joining all aluminum alloys. To date, the majority of research has concentrated on developing the tools and procedures for making reliable welds in a variety of alloys, on characterizing the properties of welds and on developing design allowables (Refs. 2-7). However, very little is known about material flow behavior during welding. The purpose of the current study is to document the movement of material during friction stir welding as a means of developing a conceptual model of the deformation process. In this paper, two new techniques for visualizing material flow patterns in friction stir welds are presented. Based on measured results in welds of 6061 and 7075 aluminum, material movement within friction stir welds is by either simple extrusion or chaotic mixing, depending on where within the weld zone the material originates. These results impact the development of welding procedures and suggest ways to model the process for predicting welding tool performance.

Current issues and problems in laser welding of automotive aluminium alloys

Abstract: The automotive industry is facing demands simultaneously to increase its fleet average fuel economy and to reduce the emission of greenhouse gases by its products. In order to meet these new standards, the industry is increasingly aiming to decrease the weight of vehicles through the use of new materials, especially lightweight aluminium alloys. Laser welding is a critical enabling technology in reducing the weight of the body structure through increased use of aluminium and tailor welded blanks. In this review the available research on the laser welding of 5xxx, 6xxx, and some 2xxx series automotive aluminium alloys is critically examined and interpreted from different perspectives. First, the current understanding of the important physical processes occurring during laser welding of these alloys such as energy absorption, fluid flow and heat transfer in the weld pool, and alloying element vaporisation are examined. Second, the structure and properties of these weldments are critically evaluated....

Prediction of nugget development during resistance spot welding using coupled thermal–electrical–mechanical model

Abstract: An axisymmetric finite element model employing coupled thermal–electrical–mechanical analysis of resistance spot welding is presented. The welding parameters considered include: heat generation at the faying surface and the workpiece–electrode surface; Joule heating at the workpiece and the electrode; and the thermal contact conductance between the electrode and the workpiece. The latent heat of phase change due to melting is accounted for. The effect of friction coefficient on the workpiece interface is also studied. The computed results agree well with the experimental data. Heat generation at the faying surface in the initial stages of welding dominates the nugget development, and Joule heating at long times governs the weld nugget growth. A parametric study is carried out for the nugget growth with specific consideration of resistance spot welding of Al alloys. Process control and modelling of resistance spot welding of Al alloys is more difficult than that for steel because of their high elec...

Hybrid welding with arc and laser beam

Abstract: This paper deals with a combination of two different welding processes, i.e. the synergic action of two different heat sources for fusion welding. The major part of the paper is focused on the combined action of a welding arc and a laser beam. The main advantage of the use of both heat sources is more efficient use of the energy supplied. With certain parameters, the quantity of molten material increases by 100% compared with the sum of the individual quantities of molten material in the individual processes. The paper further presents several practical applications of the combined welding process. Eventually, development of arc augmented laser welding may progress in two directions; the first being the synergic effect of a laser beam and plasma welding arc and the second the combination of tandem laser welding and consumable electrode welding. This paper presents two such cases schematically.

An Experimental Study of Resistance Welding of Carbon Fibre Fabric Reinforced Polyetherimide (CF Fabric/PEI) Composite Material

Abstract: This paper presents an experimental investigation of resistance welding of carbon fibre fabric reinforced polyetherimide composites (CF fabric/PEI). The heating elements were made from a single CF fabric/PEI prepreg sheet with neat PEI films co-moulded to both surfaces. Welding was conducted on a welding area of 25 mm × 12 mm. The quality of the welded specimens was studied using a non-destructive evaluation technique (C-scan) as well as a mechanical test (lap shear strength). The relationships between input power, input energy, welding time and consolidation pressure were studied. Experimental results indicated that sufficient joining was obtained at a power level from 80 to 160 kW/m2, under an initial welding pressure of 0.15 to 0.40 MPa. The maximum lap shear strength achieved through resistance welding was equivalent to that of the compression moulded benchmark. The fracture surfaces of welded specimens showed mostly cohesive-failure or intralaminar failure. An optimum processing window is proposed for the resistance welding of CF fabric/PEI composite system.

Static and Fatigue Behavior of Spot-Welded 5182-0 Aluminum Alloy Sheet

Abstract: There is a strong interest in the use of aluminum alloy sheet for vehicle applications, particularly the body, where resistance spot welding is the principal joining method. It is important that the particular discontinuities that are often found in aluminum alloy spot welds do not adversely affect the weld properties. The objectives of this work were to provide information about the effect of excessive porosity and surface indentation and the effect of weld size on the fatigue performance of spot welds in aluminum alloy sheet. Trials were conducted on 1.2-mm-thick 5182-0 aluminum alloy in the mill-finished condition. Static shear and fatigue tests were conducted on welds over a range of welding conditions to simulate severe weld discontinuities. The work indicated that nugget porosity, up to about 40% of the weld diameter, deep surface indentation and variation in weld size had no major impact on the fatigue properties of the welds.

Process behavior and stability in short circuit gas metal arc welding

Abstract: In this paper, the results of an investigation dealing with short circuit gas metal arc welding with the emphasis on process stability are presented. Welding runs were made under different conditions and, during each run, the different process parameters were continuously monitored. It was found that maximum process stability is reached under specific welding conditions. Outside this maximum, either irregular material transfer takes place with a tendency for open arc droplet transfer or stubbing of the welding wire in the weld pool starts to occur, accompanied by highly irregular melt-off behavior. The results show that process stability is directly related to weld pool oscillation. More specifically, it appears that process stability is maximum when the short circuit frequency equals the oscillation frequency of the weld pool. Under these conditions, the weld pool touches the droplet at the end of the electrode at every oscillation, which results in regular droplet transfer and high stability of the overall welding process.

Laser welding of thin sheet steel with surface oxidation

Abstract: The joining of thin sheet steel generally involves conduction mode welding, in which the reflection of the laser beam by the sheet surface is high. The absorption of laser energy by the workpiece increases significantly during keyhole laser welding, in which a vapor-plasma-filled cavity is formed. The reflectivity of cold-rolled thin sheet steel was found to be in the range of 65--80% in CO{sub 2} laser welding. The reflectivity decreased to about 30% when the sheet surface was oxidized before laser welding. In the laser welds with surface oxidation, the oxygen inclusions and porosity were not found, but the grain size was large. However, the tensile strength of all welds--with or without surface oxidation--was higher than the base metal. The toughness of the welds with surface oxidation degraded, because of the small amount of oxygen content, but it was still comparable to the toughness of the welds without surface oxidation. The oxygen content in the welds with surface oxidation was found to be slightly higher than in the welds without surface oxidation. The mechanical properties of the welds with surface oxidation were found to improve when steel powders consisting of manganese and silicon were used during welding.

Heat treatment for weld beads

Abstract: Two parts are welded together at a weld spot in a groove. A spot adjacent the weld spot is heated simultaneously and independently of the welding so that the heating and welding form a heat-treated weld bead along the groove. Preheat treatment, postheat treatment, or both, may be used simultaneously with welding to maximize performance of the resulting weld joint. Preheat and postheat treatment may be performed using lasers while the welding may be performed by TIG welding or laser welding. The welding torch and preheat and postheat lasers are coplanarly aligned.

Welding system and method

Abstract: A welding system (10) which allows a single welding operator to perform quick, easy and high quality vertical welds comprises a welding fixture (12) with a pair of opposing, positionally adjustable welding shoes, and lock screws for attaching to a workpiece (56) such as an I-beam. Welding fixture (12) is located adjacent the end of an articulating boom (20), and includes a welding torch (14) and oscillator (48). A rotary straight wire feeder (18) removes the cant and helix from welding wire as it is fed to the welding torch (14). The welding torch (14) prevents welding wire from fusing to a guide tube. A distributed welding control system comprising a plurality of controller modules (46, 48, 50, and 52) is interfaced with a common bus (54) and allows a welding operator to program automated welding cycles for various welding operations. The welding system (10) is particularly useful for installing stiffener plates (58) onto structural beams (56).

Resistance spot welding of steel and aluminium sheet using insert metal sheet

Abstract: The present paper reports the resistance spot welding of steel and aluminium sheets using aluminium clad steel sheets as insert metals. Intermetallic compound layers were formed in the weld zones in direct spot welding of steel sheets to aluminium sheets. Thus, the strength of these joints was lower than that of aluminium to aluminium joints. Intermetallic compound layers were also formed at the steel/aluminium interfaces of the insert metal in welding of steel to aluminium using an insert metal sheet. However, the strength of these joints was of the same order as that of the aluminium joints. The fracture mode of these joints varied with the welding current. The suitable welding current for steel to aluminium joints varied between the values suitable for steel to steel and aluminium to aluminium joints. The fatigue strength of joints using insert metals was somewhat lower than that of the aluminium joints.

Method and apparatus for feeding welding wire

Abstract: A welding wire feeding system feeds welding wire from a barrel to a welding gun. The system includes a feed mechanism for drawing welding wire from the barrel and advancing the welding wire toward the welding gun. A free-wheeling wheel is disposed between the barrel and the feed mechanism and is freely rotatable about an axis. The welding wire is wound around the wheel, whereby a curvature is imparted to an otherwise-straight welding wire. Also, any twists generated in the welding wire at the welding gun will be stopped at the wheel before reaching and fouling the barrel.

Friction stir weld system for welding and weld repair

Abstract: A friction stir weld system for welding and weld repair has a base foundation unit connected to a hydraulically controlled elevation platform and a hydraulically adjustable pin tool. The base foundation unit may be fixably connected to a horizontal surface or may be connected to a mobile support in order to provide mobility to the friction stir welding system. The elevation platform may be utilized to raise and lower the adjustable pin tool about a particular axis. Additional components which may be necessary for the friction stir welding process include back plate tooling, fixturing and/or a roller mechanism.

Laser Transmission Welding of Thermoplastics: Analysis of the Heating Phase

Abstract: In laser transmission welding, the parts to be joined are brought into contact prior to welding, and the heating and joining phase take place simultaneously. The laser beam of the Nd:YAG laser pene...

Method of solid state welding and welded parts

Abstract: A method of solid state welding for joining metal parts having opposed planar and parallel surfaces which includes quickly heating the opposed surfaces of the metal parts with a high frequency induction heater to the hot working temperature of the metal parts in a non-oxidizing atmosphere, continuously moving at least one of the parts relative to the other part generally parallel to the parallel surfaces of the parts, and quickly bringing the opposed surfaces of the parts together with an axial force approximately equal to the conventional friction welding forging force while continuing the relative motion of the parts until the absorbed kinetic energy is approximately equal to ten percent of the energy input required by conventional friction welding The resultant weld is of a quality equal to or greater than normal friction welding but has a much smaller volume of flash and requires significantly less kinetic energy than conventional friction welding and is performed at rotational velocities well below the normal critical surface velocity of friction welding The welded metal part includes a generally planar flash extending radially from the inner section of the opposed planar welded surfaces having a volume corresponding to a combined loss of length of less than 02 axial inches per inch of wall thickness Thus, the disclosed solid state welding method is substantially more efficient than prior friction or other welding methods and results in an improved product

Modified friction stir welding

Abstract: A modified method of friction stir welding of members applying a non-consumable rotating probe further comprises a preheating of the assembled members prior to the welding operation. A welding apparatus is also disclosed provided with a primary heat source attached to the probe, preferentially a high frequency moving induction coil.

Laser welding superalloy articles

Abstract: A process is provided for laser welding a nickel or cobalt based superalloy article to minimize cracking by preheating the entire weld area to a ductile temperature, maintaining such temperature during welding and solidification of the weld, with the welding utilizing a powder alloy feed and the speed of the laser controlled to less than 10 inches per minute.

Dynamic welding of silver contacts under different mechanical bounce conditions

Abstract: Mechanical parameters were correlated with dynamic contact welding for a hard silver contact alloy The study was conducted with a model switch that simulated an automotive relay The switching tests conducted at 13 VDC for rigid and flexible blades correlated contact bounce to weld strength The weld strength was shown to be highest for single bounces of very short duration and contact gap Flexible contact springs were shown to create weak welds by mechanical adhesion

Analysis of mechanism of plasma and spatter in CO2 laser welding of galvanized steel

Abstract: In laser welding, quality, reproducibility and formability are required. That is the great problem in the automation of the laser welding process. Therefore, construction of an on-line process monitoring system of high accuracy is requested. The light which is emitted from plasma and spatter in laser welding was detected by photo-diodes. It was found that the light intensity depends on welding speed, laser power and flow rate of assist gas. The relationship between the plasma and spatter and the bead shape, and the mechanism of plasma and spatter were analyzed for on-line laser weld monitoring systems.

Battery tab attachment method

Abstract: The difficulties encountered with attaching tabs to very thin metal layer. e. g., a layer of gold from 0.3 μm to 50 μm thick are severe. Typically, in the uses envisioned for the thin metal layer, which is for a compact battery, a plastic sheet such as polyimide underlies the thin metal layer. Polyimide has a relatively low melting point. The thin polyimide substrate melts when resistance welding is used. Ultrasonic welding doesn't work because the sound wave energy is absorbed by the polyimide. This invention solves the attachment problem by using wire bonding to the thin metal sheet and to its tab. The tab attachment for a thin metal layer comprises a thin metal layer, a metal tab, and a wire and the wire is bonded to the thin metal layer and the wire is bonded to the metal tab. The thin metal layer may be gold; the thickness of the gold is between 0.3 μm and 50.0 μm.

Statistical models for spot welding of commercial aluminium sheets

Abstract: The present paper reports experimental investigations on the spot welding of commercial aluminium sheets. Experiments were carried out to study the influence of spot welding parameters (welding current, welding time, electrode force and sheet thickness) on the strength of spot welded aluminum sheets with commercial purity. Experiments were planned on the basis of response surface methodology (RSM) technique. The mathematical models (failure load and nugget area) correlating process parameters and their interactions with response parameters have been established. These models have been used in selecting the optimum process parameters for obtaining the desired spot welding quality at the least possible consumed power.

Quantitative evaluation of softened regions in weld heat-affected zones of 6061-T6 aluminum alloy : Characterizing of the laser beam welding process

Abstract: In welding 6061-T6 aluminum alloy, softening caused by the dissolution of strengthening β″ (Mg2Si) precipitates occurs in heat-affected zones (HAZs). Laser beam welding is advantageous in view of narrower softened regions. The width of the softened region in a laser beam weld with a welding speed of 133 mm/s is 1/7 that of a tungsten inert gas (TIG) weld with a speed of 5 mm/s. The hardness distributions and width of softened regions in the HAZ have been quantitatively predicted to characterize the laser beam welding process. To this end, a kinetic equation describing the dissolution of age precipitates has been established and has been applied to 6061-T6 aluminum weldments. The hardness profiles and the width of softened zones have been successfully predicted in both welding processes. Prediction of the width of softened regions with varying power inputs and welding speeds reveals that a high energy density and a high welding speed in laser beam welding result in significantly narrower softened regions, in which the width is insensitive to variations in welding parameters compared to that of TIG welding.

Welding of die-casted magnesium alloys for production

Abstract: The importance of light weight magnesium alloys, especially for the automotive industry, has grown significantly during the last years. To fully benefit from the whole designing potential of this material, joining processes have to be developed. Laser beam welding turns out to be very suitable to join magnesium parts. The results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view. The determination of the process window by analyzing the influence of laser type, power, welding velocity, and shielding gas, as well as the influence of the base material, leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are e...

Metal sheet piling

Abstract: A metal sheet pile comprises a cold formed wall section to the longitudinally extending side edges of which are secured hot formed clutch sections (12). The clutch sections (12) may be produced by hot rolling, extrusion or other hot forming process and are preferably welded to the side edges of the pan or web by, for example, laser, submerged arc or resistance welding. Cold forming of the wall section from steel plate may be effected in a press, or by passing steel plate between or around cold bending rolls.

Welding machine and method for assembling same

Abstract: In the resistance welding machine, an arm 2 including one electrode tip 3, a drive unit 4 including a linear guide for driving the other electrode tip 5 corresponding to one electrode tip 3, and a welding unit 7 including a welding transformer T for passing a secondary current through a gun bracket 13 for supporting the present resistance welding machine on a robot and/or the present resistance welding machine can be mounted and removed individually as a unit with a common base 6 or a rail main body 8 including the linear guide as the reference thereof