Showing papers on "Electric resistance welding published in 2001"

Advances in fusion bonding techniques for joining thermoplastic matrix composites: a review

Abstract: Joining composite materials is an issue because traditional joining technologies are not directly transferable to composite structures. Fusion bonding and the use of thermoplastic films as hot melt adhesives offer an alternative to mechanical fastening and thermosetting adhesive bonding. Fusion bonding technology which originated from the thermoplastic polymer industry has gain a new interest with the introduction of thermoplastic matrix composites (TPC) which are currently regarded as candidates for primary structures. The improvement of thermoplastic polymer matrices, with the introduction of recent chemistries such as PEEK, PEI and PEKEKK. exhibiting increased mechanical performance, service temperature and solvent resistance (for the semi-crystalline systems) also supported the growth of interest for fusion bonding. This review looks at the state of the art of fusion bonding technology and focuses particularly on the three most promising fusion bonding techniques: ultrasonic welding, induction welding and resistance welding. Physical mechanisms involved in the fusion bonding process for modelling purposes are discussed including heat transfer, consolidation and crystallinity aspects. Finally, the application of fusion bonding to joining dissimilar materials, namely thermosetting composites (TSC)/TPC and metal/TPC joints, is reviewed.

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.

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...

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.

Recent developments in underwater wet welding

Abstract: Developments in underwater wet welding processes over the past 25 years are reviewed. Shielded metal arc welding with rutile base coated electrodes is still by far the most common wet welding process in use. Research and development of wet welding electrodes has led to improvements in the control of hydrogen content, porosity, chemical composition, and microstructure of the weld metal. Additional work is required to develop welding consumables with improved control over diffusible hydrogen and porosity. Development of techniques such as temper bead welding has allowed successful wet welding repairs on steels having carbon equivalents greater than the traditional limit of 0.40. Alternative wet welding processes such as flux cored arc welding and friction welding are under development, but have yet to become widely accepted.

Marangoni effect in laser deep penetration welding of steel

Abstract: In welding, the resulting weld-seam geometry may vary significantly although using constant process parameters and steels with the same material number. One likely reason for this are small variations in the concentration of sulfur, phosphorus, oxygen, and other chemical elements that are well within the tolerance of the standard of a specific alloy. These substances act as surfactants and even marginal changes strongly effect the temperature-dependent coefficient of surface tension. In simulations of conventional electric arc welding and laser heat conduction welding, the effect of the temperature-dependent coefficient of surface tension (Marangoni effect) has been identified as one of the primary driving forces of the liquid melt. In laser deep penetration welding simulations this effect has been widely neglected, so far. In this contribution, simulations of flow fields in the weld pool resulting from different temperature dependencies of the coefficient of surface tension are presented. The simulations...

Friction stir welding of polymeric materials

Abstract: A method and apparatus for welding thermoplastic materials with a stir welding system using a rotating element pin or element with a geometry to induce frictional energy from the rotating element. A floating constraining surface that has a motion independent of the rotation the pin (preferably stationary) is used to constrain ejection of material from the zone where the weld is being formed. Molten material is retained in the weld region, avoiding weakness and voids at the weld joint. Optionally a system for introducing thermal energy into the weld zone in addition to the frictional energy is used. The system for introducing the thermal energy may be in association with the constraining shoe and/or the rotating tool, or a system independent of these.

Resistance welding of thermosetting composite/thermoplastic composite joints

Abstract: An investigation of the resistance welding between carbon fibre (CF)-reinforced polyetherimide (PEI) and CF-reinforced epoxy laminates is presented. A three-dimensional transient finite element model (FEM) featuring heat transfer, consolidation and thermal degradation was used for simulating the process. A hybrid interlayer made of a glass fibre (GF) fabric essentially impregnated with PEI on one side and with epoxy resin on the other side was produced to provide mechanical interlocking between the thermoplastic (TP) and the thermosetting (TS) systems. The ‘optimal’ resistance welding time based on the maximum lap shear strength (LSS) was determined for three power levels and correlated to the time required to achieve bonding predicted by the FEM. Consolidation quality and failure mechanisms were discussed in relation with processing parameters. Experimental and simulated processing windows were constructed and correlated to each other. However, thermal degradation as predicted by the model did not correlate to a reduction in performance of the joint.

Computer Simulation of Residual Stress and Distortion of Thick Plates in Multielectrode Submerged Arc Welding : Their Mitigation Techniques

Abstract: Welding is the main joining method used in shipbuilding. A multi-electrode submerged arc welding is usually applied to long joints of massive components since the early 1950s.The problem of welding ...

Welding superalloy articles

Abstract: A process is provided for welding a nickel or cobalt based superalloy article to minimize cracking by preheating the entire weld area to a maximum ductility temperature range, maintaining such temperature during welding and solidification of the weld, raising the temperature for stress relief of the superalloy, then cooling at a rate effective to minimize gamma prime precipitation.

Quality and productivity improvement in aluminium alloy thin sheet welding using alternating current pulsed metal inert gas welding system

Abstract: An alternating current (ac) pulsed metal inert gas (MIG) welding power source has been developed for welding thin sheets of aluminium alloys and the process features are investigated. Advantages such as high wire melting coefficient, low heat input, shallow penetration, and increased reinforcement height are obtained at high values of electrode negative ratio (ratio of electrode negative current integration to electrode negative plus electrode positive current integration over one pulse cycle). These features successfully counteract the problem of burnthrough in welding of thin sheet joints and greatly improve the bridging ability for wide gap joints. Thin sheet joints can be welded at high speed and with low distortion. By integrating the present welding power source with a welding robot, welding process and current waveform parameters can be defined by key operations in the teach pendant. It is possible to switch between welding processes such as ac pulsed MIG, direct current (dc) pulsed MIG, lo...

Modeling Dynamic Electrical Resistance During Resistance Spot Welding

Abstract: Dynamic electrical resistance during resistance spot welding has been quantitatively modeled and analyzed in this work. A determination of dynamic resistance is necessary for predicting the transport processes and monitoring the weld quality during resistance spot welding. In this study, dynamic resistance is obtained by taking the sum of temperature-dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface within an effective area corresponding to the electrode tip where welding current primarily flows. A contact resistance is composed of constriction and film resistances, which are functions of hardness, temperature, electrode force, and surface conditions. The temperature is determined from the previous study in predicting unsteady, axisymmetric mass, momentum, heat, species transport, and magnetic field intensity with a mushy-zone phase change in workpieces, and temperature and magnetic fields in the electrodes of different geometries. The predicted nugget thickness and dynamic resistance versus time show quite good agreement with available experimental data. Excluding expulsion, the dynamic resistance curve can be divided into four stages. A rapid decrease of dynamic resistance in stage I is attributed to decreases in contact resistances at the faying surface and electrode-workpiece interface. In stage 2, the increase in dynamic resistance results from the primary increase of bulk resistance in the workpieces and an increase of the sum of contact resistances at the faying surface and electrode-workpiece interface. Dynamic resistance in stage 3 decreases, because increasing rate of bulk resistance in the workpieces and contact resistances decrease. In stage 4 the decrease of dynamic resistance is mainly due to the formation of the molten nugget at the faying surface. The molten nugget is found to occur in stage 4 rather than stage 2 or 3 as qualitatively proposed in the literature. The effects of different parameters on the dynamic resistance curve are also presented.

Resistance Welding of Metal/Thermoplastic Composite Joints

Abstract: An investigation of the resistance welding between carbon fiber (CF) rein-forced polyetherimide (PEI) and aluminium substrates (7075-T6 grade alloy) is presented. A three-dimensional transient finite element model (FEM) featuring heat transfer, consolidation and thermal degradation was used for simulating the process. Two mechanisms are distinguished in the consolidation model: (1) removal of the initial surface profile of the laminate modelled by the establishment of intimate contact between the two substrate surfaces and (2) penetration of the thermoplastic (TP) polymer in the micro-pores of the aluminium oxide surface modelled using a capillary flow model. The “optimal” welding time based on the maximum lap shear strength (LSS) was determined for various power levels and correlated to the bonding time predicted by the FEM. Consolidation quality and failure mechanisms were discussed in relation to processing parameters. The effect of the welding operation on overaging (annealing) of the aluminium alloy ...

Method for the control and/or regulation of a welding process

Abstract: The invention relates to a method for the control and/or regulation of a welding process, whereby on striking an arc (15), a welding process, adjusted according to various different welding parameters, is carried out. The control and/or regulation of the welding process is carried out by means of a control device (4) and/or a welding current source (2). During the welding process, the welding device (1) may be switched, in particular the functions and/or the operation types and/or the welding parameters and/or the welding programmes may be switched, without interrupting the welding process, in particular, without interrupting the arc (15), by means of a particular movement of the welding lance (10). For carrying out the switching, a welding parameter, in particular a welding or arc voltage and/or arc current is monitored and on exceeding and/or falling below a threshold value for the welding parameter, the switching of the welding device (1) is carried out by the welding controller.

Microresistance spot welding of Kovar, steel, and nickel

Abstract: Microresistance spot welding of 0.2–0.5 mm thickness Kovar, steel, and nickel using different types of power supply was investigated. The effects of process parameters (welding current/pulse energy, electrode force, and welding time/pulse width) on joint strength and nugget diameter were studied. The maximum values of welding current and nugget diameter that did not result in weld metal expulsion and/or electrode–sheet sticking were determined. The difference between micro- and ‘large scale’ resistance spot welding was also considered. It was noted that the difference between micro- and large scale resistance spot welding is due not only to the difference in the scale of the joints, but also to the fundamental difference in the electrode forces (pressures) used. Based on the results of the present work, nominal process parameters are recommended for microresistance spot welding of Kovar, steel, and nickel when using different power supplies.

Geometry of laser spot welds from dimensionless numbers

Abstract: Recent computer calculations of heat transfer and fluid flow in welding were intended to provide useful insight about weldment geometry for certain specific welding conditions and alloys joined. However, no generally applicable correlation for the joining of all materials under various welding conditions was sought in previous work. To address this difficulty, computer models of fluid flow and heat transfer were used for the prediction of weld pool geometry in materials with diverse properties, such as gallium, pure aluminum, aluminum alloy 5182, pure iron, steel, titanium, and sodium nitrate under various welding conditions. From the results, a generally applicable relationship was developed between Peclet (Pe) and Marangoni (Ma) numbers. For a given material, Ma and Pe increased with the increase in laser power and decrease in beam radius. For materials with high Prandtl number (Pr), such as sodium nitrate, the Pe and Ma were high, and heat was transported primarily by convection within the weld pool. The resulting welds were shallow and wide. For low Pr number materials, like aluminum, the Pe and Ma were low in most cases, and low Pe made the weld pool deep and narrow. The cross-sectional areas of stationary and low speed welds could be correlated with welding conditions and material properties using dimensionless numbers proposed in this article.

Method for continuously regulating or tracking a position of a welding torch or a welding head

Abstract: The invention relates to a method for continuously regulating or tracking a position of a welding torch (10) or a welding head, in relation to a welded joint which is to be produced on a workpiece (16). According to said method, the welding torch (10) which is positioned at a distance from the workpiece (16) or the welded joint executes a pendulum motion which overlays its linear welding motion, while the state variables that are temporally modified, in particular an ohmic resistance or a current and/or a voltage, are detected. In order to regulate or track the position of the welding torch (10), the lateral deviation of the welding torch (10) in relation to the welded joint, in particular in relation to the centre of the welded joint and/or the height of the welding torch (19) above the workpiece (16) or the welded joint, is derived from the detected actual value or signals. The measured value of at least one measuring signal, in particular of the state variable, is detected based on periodically recurring process phases of a welding process, at defined times and/or states of said periodically recurring welding process.

Method of controlling arc welding processes and welder using same

Abstract: A method of generating a real time control signal (224) for use in an electric arc welding process having welding voltage and welding current, said method comprising: measuring the welding voltage and welding current at a first time (200), momentarily changing either the welding voltage or welding current by less than about 10 %, then measuring the welding voltage and the welding current after the change at a second time (204), determining the welding voltage difference between the first time and the second time (220), determining the welding current difference between the first time and the second time (220), producing a derivative value representing the desired control signal by dividing the welding voltage difference between the first and second times by the welding current difference between the first and second times (220) and generating the control signal (224) by the derivative value.

Laser welding with activating flux

Abstract: The effect on laser welding of activating flux, originally developed to improve penetration depth for tungsten inert gas welding, was investigated. Both mild and stainless steels were tested. Results show that weld penetration capability relates closely to the laser power level and welding speed of the process. Significant improvement in penetration was only observed when laser welding was performed in the conduction mode (i.e. weld aspect ratio <1). For the range of parameters studied, the best penetration capability improvements achievable for mild steel, type 304 stainless steel, and duplex stainless steel were found to be 41, 53, and 63% respectively. These data are of use in the selection of parameters for laser welding with activating flux.

Method and system for hot wire welding

Abstract: A hot wire welding method and system rely upon a welding torch with a non-melting electrode, a melting metal filler wire that is fed into a weld puddle created by welding arc, a microprocessor controller for controlling (i) current of the main welding arc, (ii) filler wire feed speed, and (iii) hot wire current for heating the filler wire. The method and system also rely upon a main welding power supply for supplying the main welding arc and a secondary DC supply for supplying the hot wire current. The hot wire current is automatically controlled by the microprocessor to supply the correct amount of current to the filler wire in response to changes in wire feed speed.

Resistance-welding power supply apparatus

Abstract: Disclosed is a resistance-welding power supply apparatus comprising a large-capacitance capacitor 20 for storing a welding energy in the form of electric charge, a charging unit 18 for charging the capacitor 20 up to a predetermined voltage, a transistor group 22 electrically connected between the capacitor 20 and a welding electrode 24 on one hand, and a control unit 30 for causing a switching action of the transistor group 22 at a predetermined frequency during the weld time to provide a control of a welding current I. The charging unit 18 includes a charging transformer 14 and a rectifying circuit 16. The control unit 30 includes a main control unit 32 for providing a control of the witching action of the transistor group 22 by way of a drive circuit 44. The control unit 30 further includes various sensors, measuring circuits and an arithmetic circuit, for providing a feedback control of the welding current, an interelectrode voltage or a welding power.

Weldability of thin sheet metals by small-scale resistance spot welding using high-frequency inverter and capacitor-discharge power supplies

Abstract: An investigation has been conducted of the weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding using a high-frequency inverter and a capacitor-discharge power supply. The results have been compared to those of previous investigations using a line-frequency alternating current power supply. The effects of electrode materials and process parameters on joint strength, nugget diameter, weld-metal expulsion and electrode-sheet sticking were studied. This work has also provided practical guidelines for selection of power supplies, process parameters (welding current/pulse energy, welding time/pulse width, electrode forces, etc.) and electrode materials for small-scale resistance spot welding of thin sheet aluminum, brass and copper.

Cell, cell production method, welded article production method and pedestal

Abstract: A metallic plate and an electrode of, e.g., a polymer lithium ion secondary cell are welded to each other securely so as to further improve the reliability and durability. An upper metallic plate (7a) and a lower metallic plate (9a) of a positive plate are so welded to an electrode (3) of the positive plate that they vertically sandwich the electrode (3). Similarly, an upper metallic plate (7b) and a lower metallic plate (9b) are so welded to an electrode (5) of a negative plate that they sandwich the electrode (5). Thus defective electric resistance welding is prevented.