Showing papers on "Spot welding published in 1998"

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

Ultimate Strength of Resistance Spot Welds Subjected to Combined Tension and Shear

Abstract: A new test setup and data concerning the ultimate strength behavior of resistance spot welds in a mild strength steel subjected to combined tension and shear loads are presented. A test plan based on a design of experiments (DOE) with three design factors (coupon width, coupon length, and nugget diameter) was conducted to investigate the influence of the factors on the ultimate strength of the resistance spot welds under different loading angles. In this program, test loads were monotonically applied to the resistance spot weld at a specific angle until the load carrying capacity of the resistance spot weld was exceeded. It was found that the nugget diameter contributes the most (more than 70%) to the total variation of the recorded ultimate strength and that the coupon length has little effect. A deterministic ultimate strength model was proposed to take into account the interaction of in-plane shear and 90° out-of-plane tensile loading in the resistance spot weld. A reliability model was also demonstrated to evaluate the ultimate strength of a single resistance spot weld.

The effect of surface roughness, oxide film thickness and interfacial sliding on the electrical contact resistance of aluminium.

Abstract: Contact resistance measurements were made on aluminium alloy sheet with a configuration relevant to electrical resistance spot welding. Previous work has shown that a small amount of sliding is required at the interface to break down contact resistance when the material has a thin, insulating coating. Sliding on a macroscopic scale occurs at the electrode-sheet interface but not at the faying surface. For this reason, the contact resistance at the faying surface is high and its behaviour with applied force is observed to be anomalous. However, local sliding on a microscopic scale can occur at the faying surface, depending on the surface roughness. The effect of surface roughness and oxide film thickness was investigated in the present work. In addition, the degree of sliding required to break down contact resistance was quantified in experiments in which relative rotation was induced at the faying surface. It is estimated that a sliding displacement of only about 10 μm is required to produce a dramatic reduction in contact resistance. The results are interpreted in terms of Holm's constriction resistance theory of microscopic spots of metal-to-metal contact within a mechanical contact area largely insulated by the presence of the surface oxide films.

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.

An Improved Numerical Modeling for Resistance Spot Welding Process and Its Experimental Verification

Abstract: A numerical model of resistance spot welding with spherical tip electrode is developed to incorporate the electro-thermal aspect as well as thermo-elasto-plastic behaviour inherent in this process. The electro-thermal aspect includes the Joule's resistive heating along the contact surfaces and within the sheet-electrode system due to nonuniform current density distribution in the sheet-electrode. The elasto-plastic deformation of the sheet-electrode interface at higher temperature is included in the thermo-mechanical analysis. The interdependence of those two analyses has been taken care of The model is used to simulate the spot welding in low-carbon steel sheets of I mm and 2 mm thickness and HSLA steel sheet of 1 mm thickness. The results are compared with experimental data obtained as a part of this work and also with literature data. The comparison has shown a good agreement in all the cases. The results are later used to draw the thermal cycle curves at different location along the faying surface.

Spot welding method

Abstract: PROBLEM TO BE SOLVED: To obtain a spot welding method of high quality by preventing the formation of burrs due to intermediate dispersion. SOLUTION: In a spot welding method, plural metal members 1, 2 with different melting points are overlapped, nipped between a pair of electrodes comprising the first electrode 13 and the second electrode 4, pressurized, and energized, so as to be joined. A concave part 14 on a surface of the first electrode 13 contacts with the metal member 1 with low melting point, and the metal members 1, 2 with different melting points are held between a pair of the electrodes 4, 13. Under such a condition, pressure and current are applied to the metal members for joining.

Penetration in spot GTA welds during centrifugation

Abstract: Convective flow during arc welding processes mainly depends on electromagnetic force, Marangoni force, and buoyancy force. The Marangoni flow (caused by surface tension gradient,dγ/dT)and the buoyancy driven flow are the major factors in controlling weld penetration in austenitic stainless steels, such as types 304 and 316. Alloys 304 and 316 were subjected to a 7 s spot gas-tungsten arc (SGTA) welding at 1 g (g = 9.8 m/s2)and 5 g accelerations. The welds at 5 g were performed on Clarkson University’s multigravity research welding system (MGRWS). The cross sections of the fusion zones were polished/etched, and their depth (D)and width (W)were measured to ± 0.025 mm. It was determined that the depth/width ratio (D/W)of the welds decreased as the acceleration increased from 1 to 5 g. This result indicates that increase in buoyancy driven flow will produce wider but shallower welds during SGTA welding.

Device for assembling motor-vehicle bodies by spot-welding

Abstract: There is described a device for welding motor-vehicle bodies, comprising a welding station provided with welding programmable robots, to which the floor panels of the bodies to be welded are fed along a vertical direction by a lifting device. The component elements of the sides of the body to be welded are brought to the assembling position by means of two locating gates, provided with self-propelled lower carriages, which are movable on rails between a working position, at the two sides of the floor panel of the body to be welded, and a waiting position, in which they may receive the component elements of the body sides. The elements of the rear part of the body are carried by a third locating frame arranged transversally between the two guiding rails of the side locating gates.

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.

Bioabsorbable two-dimensional multi-layer composite device and a method of manufacturing same

Abstract: This invention relates to bioabsorbable multi-layer two-dimensional composite devices and their method of manufacture by spot welding the layers of the device at designated points, which devices can easily be cut into any desirable form by a surgeon during operation on a patient.

A method for resistance electric spot welding of a first sheet of non weldable material to a second sheet of weldable metal material

Abstract: A sheet (1) of a material which cannot be electrically welded is connected to a second sheet (2) of a weldable material by providing a through hole (3) in the first sheet having a transverse dimension substantially greater than the transverse dimension of the tips of the electrodes (8) which are used for carrying out the electric welding spot. Within the hole (3) there is provided an insert (4) of a material which can be electrically welded. The two electrodes (8) are applied so as to cause welding of the insert (4) to the second sheet (2). The insert (4) has a stop surface (7) which prevents the first sheet (1) from separating from the second sheet (2) after welding. The difference of the transverse dimensions of the tip of each electrode (8) and the insert (4) avoids any possible overheating up to the melting point of the material constituting the first sheet (1) while welding is carried out.

Method of controlling electrode force of spot welding gun

Abstract: In a spot welding gun which is made up of a gun main body (2) which is operated for equalization by a driving source (6), a stationary electrode tip (3) which is immovable relative to the gun main body (2), and a movable electrode tip (5) which is connected to a pressing source (4), both electrode tips (3, 5) are pressed to a workpiece (W) with an even force, to thereby perform a high quality spot welding. The driving source (6) is controlled such that the electrode force of the stationary electrode tip (3), by the driving source (6), to the workpiece (W) becomes substantially zero. In this manner, there occurs no difference in the electrode forces by both the electrode tips (3, 5) to the workpiece (W).

Spot welding system and spot welding method and nugget diameter estimation system and nugget diameter estimation method

Abstract: A welding spot is held between electrodes either biased with a controlled pressure, having a controlled voltage applied thereacross, and variations of an inter-electrode distance are detected for a welding quality control, in which the distance variations are time-integrated, a nugget size is estimated on a basis of the integration, and a decision is made of a conformity of welding quality based on an estimated nugget size.

Application of artificial intelligence techniques to resistance spot welding

Abstract: Despite decades of research, controlling the spot welding process is a difficult task, particularly with the increased use of zinc coated steels. Conventional control techniques have been limited by the fact that many weld quality monitoring signals are prone to changes in their profile as a result of electrode wear, leading to misinterpretation of the signals. Current stepping has been introduced to maintain consistent weld quality by increasing the welding current in predetermined steps to compensate for reduced current density with the growth of the electrode tip. However, the optimum current stepping programme is difficult to establish in practice. To overcome the present limitations of spot welding control systems, greater effort needs to be applied to develop intelligent control systems. Artificial intelligence (Al) techniques, relying less on mathematical process representation, may be ideal for controlling this highly non-linear process. The development of a neural network based process model for weld size prediction is described. Taguchi techniques have been used to establish the optimum network parameters, and weld nugget diameter has been classified from electrical welding data and information regarding the condition of the welding electrodes. Based on the results of the investigation and a recent review, it is felt that a combination of the neural network, with its mapping and pattern recognition capabilities, and a fuzzy logic controller, with its ability to handle vague and imprecise data, is likely to offer greatest benefits in overcoming the limitations of existing control systems.

Pulsed thermographic inspection of spot welds

Abstract: In automotive manufacturing, the lack of nondestructive methods for assessment of spot weld integrity has been a critical shortcoming, with enormous economic consequences for both domestic and foreign auto makers. At present, auto body welds are subjectively evaluated using destructive pull tests, or visual examination after the weld has been mechanically separated using an impact tool. Pulsed thermographic evaluation of spot welds offers a fast, noncontact method for quantitative assessment of the weld nugget. The technique can be applied using either one or both faces of the weld. Results on steel resistance welds will be presented, along with correlation to weld process parameters.

Apparatus for controlling the quality of a resistance spot weld and method therefor

Abstract: A resistance spot welding apparatus having a primary circuit, a secondary circuit and a transformer for controlling the quality of a resistance spot weld, wherein a voltage is applied to the primary circuit to thereby generating a welding current, includes a current sensor for sensing the weld current from the primary circuit, a power factor calculator, a dynamic resistance calculator, a nugget estimator and a weld current controller. In the welding apparatus, the power factor calculator calculates power factors based on the welding current. And, the nugget estimator estimates a nugget size and nugget penetration from an dynamic resistance curve by using a Hidden Markov Model method, wherein the dynamic resistance curve is obtained by the power factor calculator. The quality of the resistance spot weld is controlled by changing the welding current based on the nugget size and the nugget penetration.

Aluminum alloy sheet for spot welding

Abstract: An aluminum alloy sheet for automotive use is provided which comprises a starting aluminum alloy sheet which has an alloy composition containing from 2 to 6 % by weight of Mg, 0.15 to 1.0 % by weight of Fe and from 0.03 to 2.0 % by weight of Mn, and a surface layer disposed over one surface of the starting alloy sheet to be pressed against electrodes for use in welding, the surface layer containing a particulate intermetallic compound which has a particle diameter of 0.5 µm or more and a density of 4,000 pieces of particles per one mm2 or more. The product alloy sheet ensures least deformation of an electrode and stable weldability by means of continuous resistance spot welding.

Spot welder for making small electrical contacts

Abstract: A capacitive-discharge spot welder is described which is primarily intended for making electrical connections between small (<25–150 μm diameter) wires and samples of metallic materials, although it can be used in many applications where miniature welds must be made. It has been particularly useful in allowing low resistance (several mΩ) contacts to be created on samples of rare earth and actinide intermetallic compounds which are highly resistant to soldering. The device has a minimum time constant of about 25 μs and can deliver a maximum of between 700 μJ and 400 mJ of energy to the weld region, depending on the resistance of the latter. A suitable electrode holder is also described, and considerations for choosing the electrode materials, selecting the contact wires, preparing the sample, and creating a weld are discussed.

A robust in-process monitoring of pulsed laser spot welding using a point infrared sensor

Abstract: Many manufactured goods employ pulsed laser spot welding in joining and it is important to monitor the weld quality. The weld quality is highly related to the thermal history of the weld an...

Method and device for series spot welding

Abstract: PROBLEM TO BE SOLVED: To provide a method and a device for the series spot welding, by which defective welding does not occur. SOLUTION: The applied current of initial welding is made two times a steady state current and the pressurizing forces of electrode tips 30A and 30B to plates 40 and 44 are made 1.25 times steady state pressurizing forces. That is, by increasing the pressurizing forces in the initial welding, the contact resistance of the plates 40 and 44 is decreased. Simultaneously with that, by making a high current to flow, the current is made to flow through the plate 44 on the opposite side of the electrode tips, and weld nuggets are produced at contact points of the plates 40 and 44. And, after the weld nuggets is produced once, the steady state current is made to flow, and by decreasing the pressurizing forces, the weld nuggets are grown up, and both plates 40 and 44 are welded.

Current stepping programmes for maximising electrode campaign life when spot welding coated steels

Abstract: Improvements in electrode life are possible when resistance spot welding coated steels, through the application of current stepping techniques. The present investigation has evaluated a number of criteria for establishing optimum rates of current increase. The most significant improvements in welding performance were obtained when the current was increased as a function of electrode tip growth. It was found that electrode softening occurred at a faster rate when current stepping, compared to welding using standard conditions. This softening was caused by recrystallisation of the base electrode material and resulted in a fast tertiary stage of electrode tip growth. The practical implications of the work are discussed.

Resistance welding method

Abstract: When a workpiece (W) which is made up by laminating a plurality of plates of different thicknesses is welded by using a spot welding gun (G) having a pair of electrode tips (3, 5) the electrode force to the workpiece (W) by one of the electrode tips (5), which is positioned on the side of a thinner plate, is made larger than the electrode force to the workpiece (W) by the other of the electrode tips (3). The contact pressure on the side of the thinner plate becomes larger with the result that the contact resistance decreases. Therefore, the nugget on the side of the thinner plate becomes smaller than the nugget on the side of the thicker plate.

Influence of microstructure on the properties of resistance spot welds

Abstract: An integrated model approach was proposed for relating resistance welding parameters to weldment properties. A key element of the approach is microstructure modeling. It was demonstrated that existing process models and microstructure models can be used to determine the spatial distribution of microstructures and properties in resistance spot welds of a plain carbon steel. It was also shown by finite element analysis that the existence of microstructure gradients in the welds is expected to reduce their ability to support shear loads by about 50%.

Manufacture of vending machine

Abstract: PROBLEM TO BE SOLVED: To provide a method for manufacturing a vending machine capable of shortening process for correcting surface after spot welding, preventing deteri oration of working environment, and securing reliability. SOLUTION: A state that an epoxy adhesive material 8 is applied on a steel plate 7 in a shape of two lines of bead is shown (a), a state just before starting welding with a spot welding electrode 9 with one more sheet of steel plate 7 lapped on the applied epoxy adhesive material 8 is shown (b), a state of completion of welding through pressing, energizing and welding with a spot welding electrode 9 is indicated where two sheets of steel plates 7 are joined at a welded part 10 (c), and an example is shown that two sheets of steel plates 7 are torn off after spot welding and a state of epoxy adhesive material 8 is observed and that the adhesive material has no generation of damage by burning because the epoxy adhesive material 8 is not applied directly below the spot welding electrode 9 (d).