Showing papers on "Electric resistance welding published in 1998"

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...

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.

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.

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.

Method and system for gas metal arc welding

Abstract: An improved method of gas metal arc welding (GMAW) is disclosed. The method includes utilizing a pulsed current having a variable waveform to ensure the detachment of one-droplet-per-pulse of current. During the welding process, the current is sufficient to produce a droplet at the end of a consumable electrode wire. After the droplet reaches a desired size, the current is lowered to induce an oscillation in the droplet. The current is then increased which, in combination with the momentum created by the oscillation, effects droplet detachment. The oscillation may be monitored by observing the arc voltage to determine a preferred detachment instant. A computer implemented method allows for the adaptive control of the current waveform to accommodate for anticipatable variations in the welding conditions, while maintaining ODPP transfer and a constant pulse period. An accompanying system is disclosed for implementing the method of adaptive welding.

Investigation into properties of laser welded similar and dissimilar steel joints

Abstract: Laser beam welding is currently used in the welding of steels, aluminium alloys, thin sheets, and dissimilar materials. This high power density welding process has unique advantages of cost effectiveness, deep penetration, narrow bead and heat affected zone (HAZ) widths, and low distortion compared to other conventional welding processes. However, the metallurgical and mechanical properties of laser welds and the response of conventional materials to this new process are not yet fully established. The welding process may lead to drastic changes in the microstructure with accompanying effects on the mechanical properties and, hence, on the performance of the joint. The thermal cycles associated with laser beam welding are generally much faster than those involved in the conventional arc welding processes. This leads to the formation of a rather small weld zone that exhibits locally a high hardness in the case of C–Mn structural steels owing to the formation of martensite. It is currently difficult ...

Friction plug welding

Abstract: Friction plug welding (FPW) usage is advantageous for friction stir welding (FSW) hole close-outs and weld repairs in 2195 Al—Cu—Li fusion or friction stir welds. Current fusion welding methods of Al—Cu—Li have produced welds containing varied defects. These areas are found by non-destructive examination both after welding and after proof testing. Current techniques for repairing typically small (<0.25″) defects weaken the weldment, rely heavily on welders' skill, and are costly. Friction plug welding repairs increase strength, ductility and resistance to cracking over initial weld quality, without requiring much time or operator skill. Friction plug welding while pulling the plug is advantageous because all hardware for performing the weld can be placed on one side of the workpiece.

Mechanisms of electrode degradation when spot welding coated steels

Abstract: The present work compares the behaviour of precipitation hardened and dispersion strengthened electrodes during the manufacture of resistance spot welds in coated steel sheet. The primary mechanism causing the failure of spot welding electrodes was growth of the electrode tip. Under normal welding conditions electrode tip growth was primarily dependent on local alloying morphology so that deterioration was mainly a function of the type of coating present on the steel. However, welding with high currents or use of current stepping programmes could extend electrode performance such that softening became a more dominant electrode degradation mechanism. Under these conditions, use of dispersion strengthened material could extend electrode campaign life.

Characteristics of resistance welding of lap shear coupons.: Part II. Consolidation

Abstract: A consolidation model based on transient three-dimensional heat transfer for the resistance welding of thermoplastic-matrix composite lap-shear specimens is established. The consolidation occurring in the resistance welding process was studied in terms of intimate contact and autohesion processes. Effects of power level on the time to achieve full intimate contact were determined. The influence of the consolidation pressure on the degree of intimate contact was investigated. Different welding configurations of lap-shear specimens were evaluated, i.e. APC-2 laminate/PEEK film, APC-2 laminate/PEI film and CF–PEI laminate/PEI film. The bonding time was compared with experimental electrified times, and close agreement was obtained. Local thermal degradation in the heating element was discussed for high power levels. A processing window for the CF–PEI/PEI configuration was established, which showed close agreement with that determined experimentally.

Solid electrolyte capacitor

Abstract: A solid electrolyte capacitor has a metal case 3 housing a capacitor element 1 and closed by a hermetic seal structure. More specifically, the case 3 has an opening closed with a seal plate 4 of nickel alloy. The capacitor element 1 has a pair of lead wires 15, 15 which are joined at their outer end faces respectively to lower end faces of a pair of lead pins 2, 2 by resistance welding. The lead pins 2, 2 are inserted through holes 41, 41 in the seal plate 4, with an insulating glass seal 5 filled in a clearance in each of the holes 41, 41 around the lead pin 2. The opening-defining edge of the case 3 and the outer peripheral edge of the seal plate 4 are joined to each other by resistance welding. Consequently, the capacitor retains high reliability over a prolonged period of time.

Weld pool oscillation as a tool for penetration sensing during pulsed GTA welding

Abstract: This paper deals with weld pool oscillation during pulsed gas tungsten arc (GTA) welding of unalloyed steel. Experiments were carried out in which the weld pool was triggered into oscillation during both the base time and the pulse time by short current peaks, superimposed on the pulsed welding current. The arc voltage was continuously measured during welding and the oscillation frequency spectrum was calculated on-line from the voltage variations by means of Fast Fourier Transform analysis, using a computer program. It was found that the obtained frequency distribution gives direct information about the penetration of the weld pool and can serve as a basis for sensing and in-process control of weld penetration.

Effects of welding parameters on hard zone formation at dissimilar metal welds

Abstract: An experimental study was conducted to determine effects of welding parameters and to optimize those parameters that have the most influence on eliminating or reducing the extent of hard zone formation at dissimilar metal welds (DMWs). Preheat, base metal thickness and welding electrode composition were found to have the most influence. Maintaining an optimum preheat for a given base metal thickness and controlling the maximum interpass temperature throughout welding resulted in drastic reduction and often complete elimination of hard zones at DMWs fabricated with ENiCrFe-3 electrodes, but not those welds fabricated with E309 stainless steel electrodes. This finding indicates that depending on the cooling rate and composition of the welding electrode, hard zones in DMWs can be eliminated. The cooling rate must be slow enough to avert formation of hard allotropic structures (i.e., martensite) and fast enough to avoid precipitation of hard intermetallic phases. The optimum welding electrode composition is one that will retard formation and precipitation of intermetallic phases during welding while the preheat needed to prevent the formation of allotropics is being maintained. Unfortunately, this unique characteristic is not available in most, if not all, austenitic stainless steel electrodes; nickel-based welding electrodes have been demonstrated to be more receptive.

Method and apparatus for friction stir welding

Abstract: The invention concerns a friction stir welding method according to which the workpieces (2, 3) to be welded are positioned on a work-table (7) and by means of clamping means (5, 6) clamped to one another and/or to the work-table during the welding. A rotating welding means (12, 13) is arranged to move along a joint between the workpieces while being pressed against said workpieces during the welding. Additional heat is supplied to the joint prior to and/or during the welding operation, in excess of the frictional heat generated in the joint from the rotation of the welding means and of any other heat that may be supplied to the joint in any other manner by the welding means. The invention likewise concerns an apparatus for friction stir welding, comprising a heating element (70) for supply of additional heat to the joint prior to and/or during the welding operation, in excess of the frictional heat generated in the joint from the rotation of the welding means and of any other heat that may be supplied to the joint in any other manner by the welding means.

Apparatus for welding thermoplastic materials

Abstract: An improved apparatus and method for joining two or more thin sheets of thermoplastic materials along a welded seam includes a welding assembly and a means for feeding the thermoplastic sheets to the working area of the welding assembly. The welding assembly includes a heated platen welding press coupled with a welding tool, an energy generator electrically connected to the welding tool and control means electrically connected to the welding press, the welding tool and the energy generator. The welding press includes a pair of opposed platens, means for heating each of the platens and pressing means for displacing at least one of the opposed platens in the thickness direction of the thermoplastic sheets. Pressure is applied to the thermoplastic sheets by using the pressing means to displace at least one of the heated platens in the thickness direction of the thermoplastic sheets. Heat produced by the heating means is then transferred to the thermoplastic sheets by the heated platens to raise the temperature of the thermoplastic sheets in the area of the welded seam to a first predetermined temperature which is below the softening temperature of the thermoplastic materials. High frequency energy produced by the energy generator is then conducted to the thermoplastic sheets by the welding tool to raise the temperature of the thermoplastic sheets in the area of the welded seam to a second predetermined temperature which is above the softening temperature but below the melt point of the thermoplastic materials. Conduction of the high frequency energy is then discontinued so that the thermoplastic sheets fuse together along the welded seam under applied pressure. Application of the pressure is then discontinued so that the welded thermoplastic sheets may be removed from the welding assembly.

Characteristics of resistance welding of lap-shear coupons. Part III. Crystallinity

Abstract: A transient three-dimensional heat-transfer, consolidation and crystallinity model for the resistance welding of thermoplastic-matrix composite lap-shear specimens is established. The heat-transfer model assumes orthotropic heat conduction in the composite parts and includes heat losses by radiation as well as natural convection. For the APC-2 laminate/PEEK film welding configuration, three crystallisation kinetics models are compared during the cooling stage of the resistance welding process. Cooling rates are predicted for natural cooling and the total processing time is determined. A coupled crystallisation kinetics/crystal-melting model is developed to predict the final crystallinity level in the welded joint. The effect of power level on the final crystallinity in the joint is investigated. Latent heat due to crystallisation and crystal-melting events is predicted and taken into account in the heat-transfer model. The influence of the environmental temperature on cooling rates and on the final crystallinity level in the joint is discussed. For the CF–PP laminate/PP film welding configuration, final crystallinity levels are predicted and compared with experimental data.

Weld quality measurement

Abstract: This invention concerns weld quality measurement. In particular it concerns an apparatus and a process for measuring on-line, while the welding process is under way, the quality of the resulting weldment. The invention is applicable to spray-transfer gas-metal arc welding, short-circuiting transfer gas-metal arc welding, pulse welding, radio-frequency resistance welding and submerged arc welding. It involves the measurement of voltage or current and the generation of an artificial signal for the other. A two dimensional signal analysis then produces data for comparison with data obtained from a high quality weld.

Method and apparatus for evaluating quality of resistance welds

Abstract: A method for evaluating quality of a resistance weld is provided, in which a nugget generation state during a welding process is evaluated by observable numerical values based on physical phenomena, and which can afford a wide application range in welding material as well as a capability of accurate knowledge as to the nugget generation state of the weld. Based on that a specific resistance value of a metal material to be welded has a temperature dependency in a conduction state of AC or current-pulsated welding current, a rate of change of inter-chip dynamic resistance instantaneous value during a current changing period is determined, a changing state of the dynamic resistance instantaneous value is further calculated, and a heat-generating state of a weld zone, i.e., a nugget formation state is estimated. Thus, a quality evaluation of a weld is performed accurately.

Hybrid welding apparatus

Abstract: A hybrid welding apparatus for subjecting a base metal to gas-shielded arc welding and laser welding comprises a laser generator for emitting a laser beam and a condenser optical system for condensing the laser beam to laser weld the base metal. The condenser optical system includes a plurality of lenses, each having a hole portion in the center thereof. A tubular supply holder for supplying a welding wire is passed through these respective hole portions of the lenses and located substantially coaxially with the axis of the condenser optical system. The laser beam and welding wire to be applied to the base metal are arranged coaxially, so that laser-welding and arc-shielded welding can be simultaneously performed with a wide angle between the welding head and a bevel of the base metal, thereby deepening penetration of the weld at an increased welding speed.

Finite element analysis of electrode wear mechanisms: face extrusion and pitting effects

Abstract: Resistance spot welding is one of the major Joining methods widely used in automotive body fabrication and assembly. Electrode wear has been a major concern in resistance spot welding of galvanised steel and in this paper advanced finite element techniques were used to simulate the thermomechanical interactions between the electrode and the workpiece during welding. First, the coupled electric–thermal–mechanical process associated with nugget formation was studied. The cumulative effects on electrode face deformation were then simulated over a large number of welds. Electrode face pitting effects were also examined. It was found that welding process parameters, such as holding time and pressure trace, played a key role in electrode face extrusion. Any pitting on the electrode tended to accelerate the face extrusion process.

Resistance welding system with a self-contained close-loop cooling arrangement

Abstract: A resistance welding system with a self-contained close-loop cooling arrangement which includes a chiller, a welding transformer, a cable and a welding gun. The chiller has a feed-port and return-port for the cooling fluid. The welding transformer has an inlet and outlet for a defined cooling path and the inlet is coupled with the feed port of the chiller while the outlet is coupled with the return port of the chiller. One end of the cable is connected to one side of the transformer, for carrying the welding current. The cable is capable of being coupled to the chiller in a manner to internally transfer the cooling fluid in either direction. The welding gun is connected to the other end of the cable and has a pair of electrodes for applying the current through a pair of workpieces. The welding gun also has a built-in cooling system which is capable of receiving, circulating and returning the cooling fluid to the chiller without external fittings and hoses.

Method and device for welding arc ignition for arc welding apparatus

Abstract: Method and device for welding arc ignition of an arc welding apparatus providing a reduced level of high frequency disturbances. A welding electrode and a workpiece are connected with a welding power source and to at least two additional high voltage power sources. A short a periodic high voltage pulse is transmitted from the first high voltage power source to a gap present between the welding electrode and the workpiece, to break down the air present between the welding electrode and the workpiece, and to create a current conducting duct therebetween. The current output of the high voltage power source is restricted in amplitude and rate of rise. The short non-periodic high voltage pulse is superimposed by another, long, high voltage pulse from the second high voltage power source. The long pulse has a current rate of rise not exceeding that of the short pulse, and the open circuit voltage of the second high voltage power source is lower than that of the first high voltage power source. A stretched pulse appears, and the duration of the current discharge increases. The current conducting duct is heated, its electric resistance decreases and an arc is ignited. When the voltage in the current conducting duct decreases to a value less than that of the open circuit of the welding power source, the current starts flowing through the welding electrode and arc to the workpiece, resulting in a welding arc burning from the welding power source.