Showing papers on "Spot welding published in 1997"

Stress Intensities at Spot Welds

Abstract: The stress intensities (notch stress, stress intensity factors and J-integral) at spot welds under typical loads of tensile-shear, cross-tension and coach-peel are derived as a number of simple formulas on the basis of an analytic solution where the stress intensities at spot welds are generally determined by the stresses around the spot welds and of some analytic solutions to circular rigid inclusions in plates with the inclusions simulating the weld nuggets. The derived formulas show consistently the trends in the stress intensities with the design parameters for spot welds such as nugget diameter and sheet thickness and additionally with spacing of force for cross-tension spot welds and load eccentricity for coach-peel spot welds. The stress intensities at spot welds under general loading conditions are estimated in terms of the forces and moments transferred by the spot welds based on the derivations. The theoretical predictions from the formulas are compared favorably with the finite element results. As an application example, some fatigue test data for spot welds in the form of load range versus life to failure are transferred into the form of stress intensities range versus life to failure with the scatterband of the fatigue test data being substantially reduced.

Neural network control of spot welding

Abstract: A spot welder comprises a neural network for processing, in real time, current and voltage energizing a weld in progress. The neural network generates a predicted time of optimal weld strength and/or nugget size for the weld in progress. A controller terminates the weld in progress at the predicted time. A method for controlling a spot welder comprises the steps of: sensing in real time current and voltage energizing a spot weld in progress; predicting a time of optimal weld strength and/or nugget size with a neural network responsive to the sensed current and voltage; and, terminating the weld in progress at the predicted time. A sensor for electromotive forces (EMF) induced by the spot welder can generate a signal for canceling out a large fraction of EMF components in at least one or both of the current and voltage signals. EMF components are substantially precluded in the current signal if the current sensor uses a buried shunt. Termination of the weld in progress at the predicted time is prevented when the predicted time precedes a predetermined minimum weld duration. The weld in progress is terminated at a predetermined maximum weld duration when the predicted time is after the predetermined maximum weld duration.

Resistance Spot Weld Failure Loads and Modes in Overload Conditions

Abstract: The failure modes of two single-weld specimens, the coach-peel and the tensile-shear specimens, were studied in detail. Weld overload experiments, along with optical and scanning electron microscopy, revealed that the coach-peel specimen failed by microvoid coalescence (ductile fracture) near the weld nugget/heat affected zone (HAZ) boundary and that the tensile-shear specimen failed predominately by localized necking (shear localization) near the HAZ/base metal boundary. Empirical data extracted from measurements performed on metallurgical cross sections of interrupted coach-peel and tensile-shear specimens established the deformed characteristic material distance (coach-peel) and the existence of a critical thickness strain for localized necking (tensile-shear). These quantities were used to predict weld failure via finite element analysis as described in Ref I. The work presented here is the first step in a larger project that is focused on developing a methodology for predicting spot weld overload failure in detailed finite element simulations of spot-welded joints. This methodology is based upon the failure phenomena (as reported here) and detailed characterization of the HAZ (as reported in Ref I). The main requirement of this predictive methodology is that it be adaptable to any combination of joint configuration and loading direction. This predictive methodology will serve as the basis for the final step of developing a model of resistance spot weld failure based upon a simpler representation of the spot weld that can be used in car crash simulation models.

Method and material for resistance welding steel-base metal sheet to aluminum-base metal sheet

Abstract: The present invention relates to a resistance welding method suitable for use in spot welding between a steel-base metal sheet, which has been plated for rust prevention purposes, and an aluminum-base metal sheet and aims to permit a current to flow at a high density across the plated steel sheet and the aluminum-clad steel sheet, thereby realizing high-quality welding. An aluminum-clad steel sheet comprised of a steel layer having projections and an aluminum layer is interposed between the plated steel sheet and the aluminum-base metal sheet to be welded to each other. An electrode is energized by a predetermined weld current from an alternating power supply. The current path is limited to the area of the projections, and metallic melt formed by melting of the plating is accommodated between the projections, preventing the current-carrying area from being increased. Consequently, the temperature of the interface of the plated steel sheet and the aluminum-clad steel sheet can be efficiently raised, resulting in the formation of a proper nugget on both sides of the aluminum-clad steel sheet.

The effects of process variables on pulsed Nd:YAG laser spot welds: Part II. AA 1100 aluminum and comparison to AISI 409 stainless steel

Abstract: In this two-part article, the weldabilities of AA 1100 aluminum and AISI 409 stainless steel by the pulsed Nd:YAG laser welding process have been examined experimentally and compared. The effects of laser pulse time and power density on laser spot weld characteristics, such as weld diameter, penetration, melt area, melting ratio, porosity, and surface cratering, have been studied and explained qualitatively in relation to material-dependent variables such as absorptivity and thermophysical properties. The weldability of AISI 409 stainless steel was reported in Part I of this article. In the present article, the weldability of AA 1100 aluminum is reported and compared to that of AISI 409 stainless steel. Weld pool shapes in aluminum were found to be influenced by the mean power density of the laser beam and the laser pulse time. Both conduction-mode and keyhole-mode welding were observed in aluminum. Unlike stainless steel, however, drilling was not observed. Conduction-mode welds were produced in aluminum at power densities ranging from 3.2 to 10 GW/m2. The power density required for melting aluminum was approximately 4.5 times greater than stainless steel. The initial transient in weld pool development in aluminum occurred within 2 ms, and the aspect ratios (depth/width) of the steady-state conduction-mode weld pools were approximately 0.2. These values are about half those observed in stainless steel. The transition from conduction- to keyhole-mode welding occurred in aluminum at a power density of about 10 GW/m2, compared to about 4 GW/m2 for stainless steel. Weld defects such as porosity and cratering were observed in both aluminum and stainless steel spot welds. In both materials, there was an increased propensity for large occluded vapor pores near the root of keyhole-mode welds with increasing power density. In aluminum, pores were observed close to the fusion boundary. These could be eliminated by surface milling and vacuum annealing the specimens, suggesting that such pores were due to hydrogen. Finally, excellent agreement was obtained between experimental data from both alloys and an existing analytical model for conduction-mode laser spot welding. Two nondimensional parameters, the Fourier number and a nondimensional incident heat flux parameter, were derived and shown to completely characterize weld pool development in conduction-mode welds made in both materials.

The effect of mechanical loading on the contact resistance of coated aluminium

Abstract: Measurements of contact resistance, related to resistance spot welding, were made using pre-treated (coated) and abraded aluminium alloy strip. With conventional domed electrodes, the contact resistance was much larger at the sheet-to-sheet (faying) contact than at the electrode-sheet contact. The effect is believed to be associated with the role of sliding in breaking down contact resistance of sheet with an insulating surface film. When the coating was removed the difference between faying surface and electrode-sheet contact was much smaller. Macroscopic shear stresses are developed by electrode-sheet contact whereas no shear stresses are present at the faying surface. The hypothesis is supported by experiments made with asymmetrical electrode pairs which give rise to varying shear stresses in faying surface contact. Some implications for the control of spot welding of different aluminium surfaces are discussed.

Device for spot welding of structures constituted by metal elements, particularly motor-vehicle bodies or sub-assemblies thereof

Abstract: A welding station, for example for welding motor-vehicle bodies, receives only a part of the structure to be welded from a conveyor line, the remaining components of the structure being assembled with said part (3) at the welding station itself, by means of two locating gates (6,7) which receive said components from manipulating robots (10), said robots also providing for carrying out the spot welding of the structure once the latter has been assembled and locked in a proper welding position by said locating gates (6, 7). The locating gates are provided with self-propelled lower trolleys guided on rails, in order to be rapidly interchanged with another pair of locating gates adapted to a different type of body.

Universal quality assurance method for resistance spot welding based on dynamic resistance

Abstract: Welding of mild steel is one of the most common processes in spot welding. Numerous methods for ensuring high-quality welds are based on dynamic resistance. However, in general, these methods are only useful over a relatively narrow range of welding parameters. This article presents a universal quality assurance method based on dynamic resistance that is valid over a wide range of welding time, welding current, electrode force and electrode tip geometry (up to and including complete tip mushrooming). This method was constructed on the basis of models describing current density redistribution at the faying surface during the welding process. Validation of the method has been confirmed experimentally. The comparison of results shows that the method provides the maximum nugget size.

Modelling of melting and solidification behaviour during laser spot welding

Abstract: It is well known that rapid solidification and fast cooling rates occur in pulsed laser spot welds. It is particularly difficult, but important, to determine various solidification parameters in terms of development of novel microstructure, prevention of welding defects, and improvement in mechanical properties. Therefore, in this study, a heat conduction and solidification model considering the effects of microsegregation and latent heat is developed to provide a reasonably good knowledge of rapid melting and solidification behaviour in such a spot weld. It was confirmed that the latent heat would greatly affect thermal histories during solidification and growth rates of cellular dendrite tips. Also, microsegregation models on the basis of the pseudobinary phase diagram are proposed for rapid solidification to obtain a better knowledge of thermal histories and growth rates of cellular dendrites. These models could be utilised to reveal variations in a molten pool and a mushy zone region during sp...

Device for spot-welding of motor-vehicle bodies or sub-assemblies thereof

Abstract: There is described a welding station for motor-vehicle bodies or subassemblies thereof in which the body side panels are engaged during welding by locking devices (12) arranged in the space between the body sides and carried by two locating gates (5; 6) which are rigidly connected to each other by means of quick coupling means (14).

Method and apparatus of projection welding

Abstract: A process and apparatus for projection welding of overlapping nonferrous sheets, particularly thin aluminum sheets. One of the sheets is provided with a projection therein, and the sheets are positioned so that the tip of the projection contacts a surface of the other sheet. The sheets are not subjected to surface pretreatment to remove the surface oxides therefrom. A projection welding head assembly is positioned with the electrode thereof engaged with one of the sheets, and the other sheet is positioned against a stationary backup or electrode. The electrode of the welding head imposes, in rapid time succession, a series of welding pulses to the overlapping contacting sheets. The series of welding pulses includes two and preferably three pulses which progressively step up in amperage to provide for precise control of the heating of the projection and the associated contact area on the other sheet to cause heating to the plastic state, and then forging (i.e. collapsing) of the projection with subsequent and progressive creation of the desired weld nugget. The series of weld pulses also preferably includes, at the end of the series, one or two pulses which progressively step down in current magnitude to permit greater control over the plasticity of the projection and the forging together of the overlapping sheets to create the desired weld bead.

Spot welding method and its device

Abstract: PROBLEM TO BE SOLVED: To prevent generation of expulsion and welding defects by actually applying a proper pressurizing force between members in a weld zone, in a spot welding method in which the weld zone of a liquid tank is held between a pair of electrode tips, pressurized and energized for welding. SOLUTION: In the servo gun electrode tips oppositely vertically arranged with a weld zone of a liquid tank in between, the upper electrode tip is advanced by a servo motor, pressurizing a weld zone (S4). With the inter- electrode distance detected based on the output signal of the servo motor (S5), and with the distance equalized to the total thicknesses of a work in the weld zone (S6), the pressurizing force to the weld zone by the electrode is detected and stored (S8). The weld zone is pressurized with the value in which the detected pressurizing force is added to the preset proper pressurizing force required for welding (S9, 10, 11).

Apparatus for measuring the quality of spot welds

Abstract: Apparatus (2) for measuring the quality of spot welds, comprising a housing (4); a fluid medium (6) in the housing (4); transmitter means (8) for transmitting at least one ultrasonic pulse through the fluid medium (6) to a spot weld (10), the ultrasonic pulse then reverberating in the spot weld (10); and receiver means (16) through which the ultrasonic pulse passes on its way to the spot weld (10), the receiver means (16) being ultrasonically sensitive so that it is able to receive echoes from the spot weld (10) by the reverberation of the ultrasonic pulse in the spot weld (10), the receiver means (16) comprising a plurality of ultrasonically sensitive elements (18), and the receiver means (16) being such that during use of the apparatus (2) the receiver means (16) is located adjacent the spot weld (10).

Resistance projection welding system and method for welding a fastener element to a workpiece

Abstract: A system and method is disclosed for monitoring and controlling a resistance projection welder for welding a projection weld nut to a workpiece. A displacement sensor measures the displacement of a welding electrode of a weld gun in real time during the welding procedure. A computer is coupled to the displacement sensor and determines whether the projection weld nut is correctly loaded between the workpiece and the welding electrode. The computer instructs a programmable logic controller (PLC) to trigger a weld controller to apply power to the welding electrode if the projection weld nut is correctly loaded onto the workpiece. The computer instructs the PLC to inhibit power if it determines the projection weld nut to be inverted, missing, or misaligned in order to allow for the removal and replacement of the projection weld nut. The computer further instructs the PLC to control and terminate the power to the welding electrode in real time in order to form a projection weld between the projection weld nut and the workpiece that is substantially similar to a predetermined projection weld. The computer processes the displacement data and provides a fault signal when the projection weld is unacceptable. A marker marks the unacceptable workpieces in response to the fault signal.

Spot welding apparatus

Abstract: An object to the invention is to narrow the region burned by the preheating current at the spot welding. Structure is provided for allowing conventional welding current to be flowed between a first welding electrode tip and a contact member intermittently via an electronic switch until a predetermined current starts to flow between a first welding electrode tip and a second welding electrode tip.

Weld bonding method

Abstract: The present invention is a weld bonding method providing adhesion by both an adhesive and resistance spot welding, and includes application of an adhesive including a thermosetting epoxy resin, a latent curing agent and 1 to 15 vol % of one or more additives selected from the group consisting of conductive metals, metal oxides, metal carbides, metal nitrides, metal borides, and metal silicides, which are in the from of powder having a particle size of 10 μm or less, or in the form of fragments or flakes having a thickness of 0.5 μm or more and a size of 30 μm or less.

Mar resistant, corrosion inhibiting, weldable coating containing iron powder for metal substrates

Abstract: A weldable heat curable liquid coating composition for steel is provided that exhibits improved mar resistance without impairing the weldability characteristics of the coating. To this end, the composition contains a conductive welding aid of iron dust. The weldable coating when applied to steel and cured thereon to a dry film allows for spot welding of the coated steel without requiring special welding equipment and techniques.

Spot welding control method and apparatus

Abstract: The spot welding electrodes are driven by the servomotor (30) so as to be moved to and pressured against a work surface. The welding pressure controller (27) detects welding pressure corresponding to current flowing through the servomotor (30) via a driver (26) and controls the welding pressure so as to be changed according to the set welding pressure condition. The welding current flowing through the spot welding electrodes is controlled by the welding current controller (28). The welding current controller (28) and the welding pressure controller (27) are both controlled synchronously by the robot CPU (20) via the system bus (21). The robot CPU (20) controls the welding pressure and the welding current on the basis of the welding condition data (22) stored in a memory, so as to be changed in synchronism with each other at a plurality of welding stages, respectively. By doing this, it is possible to control the welding pressure and the welding current during the spot welding synchronously and systematically, thus realizing a spot welding control adaptive to work behavior.

Porosity formation in laser welding - Mechanisms and suppression methods

Abstract: The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pulse shaping in spot welding and adoption of optimum pulse modulation. Also, a proper angle of beam incidence is effective to reduce porosity formation.The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pul...

Fuzzy adaptive process control of resistance spot welding with a current reference model

Abstract: This paper describes a fuzzy adaptive process control scheme for resistance spot welding and proposes a new method identifying dynamic welding resistance to estimate the spot welding process. An optimal current reference model is also founded, which would modify its output according to the stages in the spot welding process. Then a fuzzy adaptive real time process control system is developed with a fuzzy controller and the welding current reference model. The results of simulations and experiments show that the fuzzy adaptive process control has better transient performance for the welding process. Through simulation and numerical calculation it is shown that a bigger sound nugget could be obtained by the proposed scheme with the same welding time and input energy as the usual constant current control method. Simultaneously, it is also indicated that the welding current reference model is effective for reducing loss energy and realizing online process control for spot welding.

Spot welding system

Abstract: A spot welding system using parallel link robots disposed close to one another. When a camera (CM) detects the arrival of a work (W) that is being conveyed, a mount moves along a guide and tracking of the work is started. Then, a parallel link having a plurality of contractile arms and robots RB1 to RB4 each having a wrist fitted to the distal end of the link start their operations. A large number of positions of the work are welded by spot welding guns G1 to G4 fitted to the wrists of these robots. The proximal end portion of each contractile arm is supported by a vertical wall of the mount in such a manner as to be capable of swinging, and each robot is so disposed as to protrude from the mount. The parallel link robots may be suspended from the mount close to one another.

Process for manufacturing welding wire

Abstract: A process for manufacturing seamless flux-cored welding wires 0.8 to 4 mm in diameter with excellent cracking resistance and primer proof quality and containing very little diffusible hydrogen suited for the welding of high-tensile steels and steel structures subjected to large restraining forces by dehydrogenating by high-temperature heating comprises the steps of heating a straight wire (1) 8 to 15 mm in diameter by direct electric heating through a first and a second pair of roll electrodes (2, 3) spaced 2 to 5 m apart and a ring transformer (4) disposed therebetween to a temperature between 620 and 1100 °C, cooling the heated wire to a temperature not higher than 500 °C with a coefficient of heat transfer not higher than 250 kcal/m 2 h°C, and drawing to the desired diameter. The welding wire thus obtained a weld containing not more than 5 ml of diffusible hydrogen per 100 g deposited metal.

Electrode for resistance-spot welding of aluminium sheets

Abstract: For welding conductive materials, using conventional copper electrode caps, with a long service life of the welding tool, a foil section is provided between the electrode cap and the surface of the sheet. The foil section is part of a foil strip which is displaceable relative to the electrode cap, and consists of a material with a high nickel content, while silver or a silver metal oxide is provided as a material in the contact area between the electrode cap and the foil section. The electrode cap is preferably coated with this material.

Welding gun for projection welding

Abstract: A welding head for projection welding wherein the spring which biases the electrode is initially preloaded to exert a significant biasing force on the electrode to maintain it against a stop to define the normal fully extended position of the electrode. The spring of the welding head is also initially precalibrated to exert an accurate predetermined biasing force on the electrode when the electrode is depressed inwardly so as to effect compression of the spring by a predetermined distance, which latter distance is of very small magnitude. The welding head is disposed in engagement with overlapping sheets so that the electrode is engaged with the sheets in alignment with a projection thereon, and the electrode is depressed through said predetermined distance so that a uniform predetermined biasing force is applied to the electrode and hence to the projection weld area.

Plasma arc spot welding of car body steels containing vaporizable ingredients

Abstract: Method of one side spot welding of a metallic auto body construction containing vaporizable coatings or ingredients, the construction having overlapping metal plys, comprising: impinging a plasma column on a selected spot of one side of the construction, the plasma column being generated by passing a plasma gas at a predetermined flow rate through an electrical arc created by a predetermined electrical current path; shielding the plasma column in an inert gas containing at least 5-35% by volume of oxygen, the shielded plasma column melting at least the metal on one ply at the spot while the oxygen increases the fluidity and wetablility of the melted metal and reduce its surface tension allowing any vaporization of the ingredients to quiescently escape through the molten metal; and ceasing plasma arc impingement for allowing the molten metal to solidify and complete the spot weld.

Adaptive health monitoring concepts for spot-welded and weld-bonded structural joints

Abstract: The health monitoring of structural joints is a major concern of the engineering community and needs to be addressed with the proper consideration. Among joining techniques, the spot welding and weld-bonding (spot weld + adhesive bonding) methods are of great interest in a number of industries. Spot welding is the traditional assembly method for steel-based automotive structures, while weld-bonding is a novel technique that combines the stiffness and productivity benefits of adhesive bonding with the proventechnology attributes of spot welding. Future trends in the design and construction of vehicular structures indicate a strong diversification of material usage, with aluminum and polymeric composites projected to play a major role. While aluminum is amenable to both spot welding and adhesive bonding, composites will, most likely, be entirely adhesive bonded. Hence, the trends towards weld-bonding and adhesive bonding are clearly visible. The paper first presents a short review of the present trends in joining techniques with special emphasis on those in present and future use in the automotive industry. This will be followed by a short review of the existing non-destructive evaluation (NDE) techniques that may be applicable to the health monitoring of spot welded and weld-bonded structures. Next, novel concepts of health monitoring utilizing an adaptive structures approach are presented. Laser ultrasound techniques; tagged adhesive methods; dielectric response techniques; electric potential methods, etc. are briefly mentioned. Particular emphasis is placed on the electro-mechanical impedance method. This novel method is described in some detail. The electro-mechanical impedance method utilizes the coupled electro-mechanical response of piezo-electric interrogators (sensoractuator crystals) intimately bonded to the monitored structure. An array of such structural interrogators can be envisaged to monitor the incipient local damage and crack growth in spot-welded and weld-bonded structures. Preliminary proof-of-concept demonstration tests performed with this method have shown remarkable features and ease of utilization.

Modeling and fuzzy control of the resistance spot welding process

Abstract: Establishes a welding energy model and describes a fuzzy adaptive process control scheme for a resistance spot welding system. For a welding system, it is not easy to measure online the output, the nugget size, by usual measuring methods. It is also difficult to control the welding process in real time. The paper proposes a method using input welding energy to estimate the nugget size and to assess the welding process. An optimal welding energy reference model is found and compared with different input methods of welding energy. A fuzzy adaptive process control scheme with the model is also described to realize real time control and to improve control performance. The results of simulation and experiments show that the reference model is effective for reducing energy loss and producing a sound nugget and the fuzzy adaptive control scheme may obtain an optimal control process for resistance spot welding.