Showing papers on "Spot welding published in 2000"

Numerical Simulation of Resistance Spot Welding Process

Abstract: This paper develops a model to predict the nugget development during resistance spot welding (RSW) of Al-alloys. The model employs a coupled thermal-electrical-mechanical analysis and accounts for phase change and convective transport in the weld pool. The contact area and the pressure distribution are determined from a coupled thermal ? mechanical model. The model calculates time varying interface pressure. The knowledge of interface pressure allows for accurate prediction of interfacial heat generation. Temperature-dependent thermal-electrical-mechanical properties are used. The predicted nugget shape and size agree well with experimental data. The proposed model can be applied to predict the effects of the welding parameters and the electrode shapes on the nugget development.

Method and apparatus for electric arc welding

Abstract: An electric arc welding apparatus for depositing molten metal from an advancing welding wire into a weld puddle in an open root between two juxtapositioned plates where the root extends in a welding path and is formed by converging walls terminating in generally parallel walls spaced to define a gap, which apparatus comprises a contact holder with a wire outlet, a switching power supply directing welding current to the wire as the wire passes from the outlet toward the open root, with the advancing wire defining an electrode stick out between the contact holder and the weld puddle, a circuit for sensing the length of the stick out, and control means for adjusting the welding current as a function of the sensed stick out length.

New technology for measuring dynamic resistance and estimating strength in resistance spot welding

Abstract: Because welded structures such as automotive bodies have become smaller and lighter, a strong emphasis is being placed on the quality of the welds. Over the years many quality estimation systems have been developed by several researchers in order to ensure that welds are of high quality. The dynamic resistance signal, which is closely related to the nugget formation of the weld, has been used very effectively for this purpose, together with the electrode displacement signal. However, in previous research, the dynamic resistance was calculated using process parameters that were measured in the secondary circuit of the welding machine, causing many in-process problems. In this study, the process variables, which were monitored in the primary circuit of the welding machine, are used to obtain the variation of the dynamic resistance across electrodes. This allows the dynamic resistance monitoring system to be applied to the in-process system without any extra monitoring devices in the secondary circuit. Also, in order to test the reliability of such a system, an artificial intelligence algorithm to estimate the weld quality using the primary dynamic resistance is proposed.

Analysis of aluminum resistance spot welding processes using coupled finite element procedures

Abstract: A comprehensive analysis procedure has been developed to perform the incrementally coupled thermal-electrical-mechanical analysis to simulate the resistance spot welding process of aluminum alloys. Because aluminum has high thermal conductivity, low melting temperature and low yield strength, deformation resulting from resistance spot welding is expected to be more severe than for steel. Compared with most of the published work in this area, this paper takes into account the incremental changes in sheet-deformed shape, contact area and current density profile as well as large deformation effects. The present analysis procedures consider electrical contact resistivities to be not only functions of contact temperature but also functions of pressure. Joule heating at the contact surfaces is computed using an equivalent surface heat generation concept. This new procedure is suitable for analyzing many important parameters such as contact area changes, electrode movement and dynamic resistance, as well as other factors that contribute to weld quality such as weld size, weld indentation, sheet separation and weld residual stresses. It can also be used to study nugget development and analyze the mechanisms of electrode wear and weld cracking.

Weldability of thin sheet metals during small-scale resistance spot welding using an Alternating-Current power supply

Abstract: The resistance weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding (SSRSW) was studied. The effects of electrode materials and process parameters on joint strength and nugget size were investigated. The welding current ranges for SSRSW of the sheet metals were determined based on the minimum current that produced a required nugget diameter and maximum currents that did not result in electrode-sheet sticking or weld metal expulsion. A qualitative analysis indicated that resistance weldability of the metals is not only determined by their resistivity (or thermal conductivity) but is also affected by other physical properties (such as melting point, latent heat of fusion and specific heat).

A new approach to the numerical fatigue‐life prediction of spot‐welded structures

Abstract: From the numerical evaluation of the experimental data for the double-cup specimens (DC specimens) under cross-tension, a new and simple fatigue parameter is derived which is based on the nominal radial stress at the tip of the spot weld and the thickness of the sheets. The new parameter is especially suitable for use in the context of a FE calculation. The relation of the proposed fatigue parameter to the stress intensity factor is shown by a simple example. The results show that, instead of the nominal stress, the notch effect (or the singularity due to a spot weld) has to be considered in order to characterize the fatigue behaviour of the weld. This is supported by the evaluation of the same test data using notch stresses. A FE model for the spot weld is presented which can be used to determine the nominal stress around a spot weld. Using this model, the experimental results for H-type specimens under tensile-shear can be evaluated subsequently, and hence the viability of the new parameter demonstrated.

On-line Quality Estimation in Resistance Spot Welding

Abstract: A neural network model is developed for on-line nugget size estimation in resistance spot welding. The variables used consist of features extracted from both controllable process input variables and on-line signals. A systematic signal and feature selection procedure is developed. The three commonly observed on-line signals, dynamic resistance, force, and electrode displacement, have been proven to carry similar information. Thus, only dynamic resistance is used in the model. The obtained model has been demonstrated to be robust over various welding conditions including electrode wear.

Cracking in spot welding aluminum alloy AA5754

Abstract: The phenomenon of cracking was observed during resistance spot welding a commercial aluminum alloy AA5754, and mechanisms of cracking and healing are discussed in this paper Metallographic study of welded coupons revealed cracks located on only one side of a weldment in the heat-affected zone (HAZ), with respect to the welding sequence. Cracks are visible from longitudinal cross sections only. Some of them are partially or fully filled. Crack appearance and orientation are fairly repeatable and their intergranular characteristics and dendritic fracture surface morphology prove they were formed at elevated temperatures in the presence of liquid metal. The discussion of metallurgical factors considering the Al-Mg equilibrium phase diagram and the possible temperature histories of various zones in a weldment during spot welding elucidated the approximate conditions for cracking during spot welding and for mending the structure. A thermomechanical analysis revealed a high possibility for tensile stress huildup on the cracked side of the weldments as a result of material flow, thermal stress development and localized straining.

A statistical analysis of expulsion limits in resistance spot welding

Abstract: Expulsion is an important phenomenon in resistance spot welding. It involves loss of metal from the liquid nugget, which often results in the reduction of weld strength. Various models have been proposed to understand expulsion mechanisms. In these models the occurrence of expulsion is often treated as a deterministic event, and depicted by a line (boundary) in conventional lobe diagrams. In this study, statistical analysis is employed to explore expulsion with consideration of the influence of random factors. Models are built based on experimental data, and one steel and two aluminum alloys are used as examples. Expulsion probabilities are presented as a function of electrode force, welding current, and time. Analytical models and their graphical form of expression (contours and surfaces) are created to present expulsion limits under various combinations of welding parameters. This study provides not only quantitative model predictions on expulsion limits for the materials studied, but also a generic statistical methodology that can be used for analyzing expulsion in various material systems.

Statistical investigation of resistance spot welding quality using a two-stage, sliding-level experiment

Abstract: Quality variation in resistance spot welding is a major concern in the automotive industry. The relationship between weld quality and various process conditions, including abnormal process conditions, has not yet been systematically studied. This paper investigates this relationship using a newly developed two-stage, sliding-level experiment. In the experiment, welding current is treated as a slid factor whose settings are determined based on those of other process variables. Engineering knowledge is applied in statistical model selection. From the analysis, it is found that abnormal process conditions, such as axial misalignment, angular misalignment, poor fitup, edge weld, and electrode wear, significantly affect weld size and thus cause large variation in the weld quality. Although they may help increase the weld size in some cases, abnormal process conditions generally lead to a less robust process. In order to minimize the effects of the abnormal process conditions, a robust parameter design is formulated using the statistical models developed from the experimental data. The analysis suggests that high current and large electrodes should be used for reducing the weld quality variation. Developed in this study, the new experimental design and analysis procedures can also be applied to other processes, where the process variables are inter-dependent.

Force characteristics of resistance spot welding of steels

Abstract: Welding force is an important parameter of resistance spot welding (RSW). Ideally controlled as constant, the force changes during welding. The change is affected by several factors, including welding schedules and welding machine characteristics. In this article, the welding force change is investigated through experiments. Observations, of the force characteristics are presented under various welding conditions, and the mechanism of the change is discussed.

Friction stir spot welding method and apparatus

Abstract: Modified method for friction stir welding process where the shoulder (2) being independently movable of the pin (1) exercises controlled and variable forces on the assembled joined-to-be members so that the down force under retraction of the pin exceeds the plasticity limit of excess material collected under the shoulder.

Method for spot welding of high strength steel plate

Abstract: PROBLEM TO BE SOLVED: To provide a method for spot welding high-strength steel plates, from which a weld joint can be obtained that is superior in static strength and fatigue strength and has an excellent delayed fracture property, even when resistance spot welding high-strength steel plates of tensile strength equal to or greater than 750 MPa.SOLUTION: In resistance spot welding two high-strength steel plates 1 together, of which at least one steel plate has a tensile strength of 750 to 1850 MPa among high-strength steel plates consisting of two or more thin steel sheets, and which have a plate thickness of 0.8 to 3.6 mm respectively, and in which a carbon equivalent Ceq is 0.22 to 0.55 mass%, the following steps are executed after carrying out welding energization under pressure force EF1 represented by the following formula {1.96*t≤EF1≤3.43*t}: setting to a pressure force PEF1 represented by the following formula {1.2*EF1≤PEF1≤2.4*EF1}; carrying out post-energization by using a post-energization current PC1 represented by the following formula {0.60*WC≤PC1≤0.95*WC} and at a post-energization time Pt1 represented by the following formula {30≤Pt1≤200}; and then carrying out electrode holding at electrode holding time Ht represented by the following formula {0≤Ht≤200}.

Numerical Thermal Model of Resistance Spot Welding in Aluminum

Abstract: A three-dimensional thermal model for resistance spot welding in aluminum is presented. The numerical model, validated with experimental findings, considered phase change and the associated weld pool convection. A parametric study was performed to determine the influence of welding features such as welding current, faying surface (workpiece contact surface) electrical contact resistance, and electrode-workpiece (E/W) thermal contact conductance. These parameters have significant effects on the nugget and heat-affected-zone geometry. The phase change morphology, including melting and solidification rates and weld pool dynamics, was also significantly influenced by the parameters studied. The strongest convection was observed at the center of the molten pool in a vertical plane, aligned with gravity. Although two prominent convection cells developed, the phase change morphology was not significantly affected by convection due to the short welding time (less than 0.1 s) and low fluid velocity (smaller than 0.01 mm/s). The nugget grew nonlinearly with increasing current and faying surface electrical contact resistance, whereas it diminished with increasing E/W thermal contact conductance. The influence of electrical contact resistance at the faying surface on nugget size was less pronounced than that of the other parameters. The length of time that the weld pool existed was directly proportional to current and indirectly proportional to E/W thermal contact conductance.

Fatigue life predictions of spot welds using coarse FE meshes

Abstract: A new engineering method for fatigue life prediction of spot welds is presented. The method starts with a coarse finite element representation of each spot weld using shell elements and one beam element. Forces and moments at the spot weld are calculated using the finite element method and used in an analytical calculation of the stresses around the spot weld. Mode I and II stress intensity factors are calculated from these stresses. Thereafter, an equivalent stress intensity factor is calculated and the fatigue life prediction is made using one unique ΔK-N curve for spot welds. Good agreement is found between a ΔK-N curve derived from the Paris law and several experimental results from the literature, although in order to achieve this, a shear correction factor is required. This factor is discussed in relation to results from the literature.

Analysis and optimisation of electrode life for conventional and compound tip electrodes during resistance spot welding of electrogalvanised steels

Abstract: Rapid electrode wear is the major concern in resistance spot welding of galvanised steels. The electrode life in such instances is tremendously influenced by the continuous alloying reactions that occur between the molten free zinc and the copper electrodes. It is shown in the present work that the use of compound electrodes can considerably enhance the effective electrode life. The compound electrodes are fabricated by introducing a tungsten insert at the tip of conventional circular face electrodes. The performance of these new electrodes has been investigated under laboratory conditions during multispot welding. It is observed that the compound tip electrodes can offer superior electrode life only for a small insert size. A finite element method based numerical simulation has simultaneously been carried out. The results of the numerical calculation also indicate that the optimum design of the compound tip electrode depends on the insert size.

Projection welding of an aluminum sheet

Abstract: A projection coined onto a metal sheet, preferably an aluminum sheet, for projection welding the sheet to an adjacent metal sheet. The projection has a thickness greater than the thickness of the sheet on which it is formed. The wall of the projection surrounds a first recess and a second recess is formed in a side of the sheet opposite the projection from which the metal cold flows to form the projection. A welding gun assembly having an improved low interia, fast response to the collapse of the projection welding the sheet having the projection to the adjacent sheet.

Gap Inspection and Alignment Using a Vision Technique for Laser Butt Joint Welding

Abstract: The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and penetration. Laser butt joint welding is one of the most accurate welding processes, because the laser ,spot size and welding gap are only 0.1-0.2 mm, and sometimes even smaller. It usually takes a long time to set up the welding operation, because the focused laser beam must be aligned with the centre of the welding gap, and the gap should be smaller than half the beam diameter. During the actual operation of laser butt welding, the laser beam must be properly aligned at any welding position. Also, the gap size must be maintained at a reasonable size or inspected on-line to make sure that it is small enough so that the laser beam cannot pass straight through the welding gap. This criterion limits the applicability of laser butt joint welding. A CCD camera and several image process techniques were employed in this research to capture the welding seam track, and determine the proper welding path and gap size. The results showed that the laser beam can be automatically aligned with the centre of the welding gap at any welding position, and the gap size can be inspected to make sure that it is always smaller than half the spot size.

Study of voluminal defects observed in laser spot welding of tantalum

Abstract: Significant problems in deep laser spot welding are the formation of welding defects, and particularly porosities in the case of tantalum joining. In this study, we investigate and model porosity formation and trapping. Two types of porosity are observed. (1)?Small porosities are round shape bubbles of less than 250??m diameter. These defects may come from gas bubbles generated following hydrogen rejection during solidification or they may come from bubbles induced by both an intense evaporation inside the keyhole and a turbulent flow in the molten pool. (2)?Large porosities are voids generated in the bottom of the welded zone. They arise from a lack of matter inside the weld as if the molten metal had not had enough time to fill up the keyhole completely before it solidified. We elaborated a numerical model for the comprehension of small porosities trapping by comparing the calculated spot weld solidification time with the rise time of bubbles in the liquid phase. We also studied the melt flow back into the keyhole in order to explain the formation of the large voids observed. These two models are in good agreement with experimental observations, in particular with x-ray radiographs achieved during the solidification of tantalum spot welds.

GHTA Welding Experiments under Simulated Space Environment in Flying Laboratory.

Abstract: GHTA (Gas Hollow Tungsten Arc) welding experiments were performed in a simulated space environment using aircraft. A vacuum chamber for GHTA welding test was placed in the cabin of the aircraft and the microgravity environment was produced by a parabolic flight of the aircraft.Spot welding tests on stainless steel plates and girth welding tests of stainless steel pipes were performed in the vacuum chamber under microgravity condition.The results are summarized as follows, (1) GHTA method makes it possible 'to form a stable arc and weld stainless plates and pipes in the simulated space environment.(2) Experimental results show that the arc configuration and the melting characteristics of GHTA are insensitive to the gravity.(3) The weld bead formation is affected significantly by the gravity. The flat weld with full penetration, as is expected, is formed both in the spot welding and the girth welding under the microgravity condition.(4) The butt joints of pipes welded by GHTA process in the simulated space environment have no defect good joint strength and the bead appearances is quite satisfactory.

Spot welding joint and spot welding method

Abstract: PROBLEM TO BE SOLVED: To provide a spot welding joint and a spot welding method to obtain a spot welding joint which imparts a high joint strength and reduces strength fluctuation and stably holds a good joining state, by only conducting tight fit of a tight fit pin of a rotary tool for friction welding. SOLUTION: For metal plate material 2, 3 stacked in plural, the tight fit pin 5 of a friction welding tool 4 harder than the plates is tight fitted/agitated, a stir part 6 is pressed with a shoulder part 7 which forms a base part of the tight fit pin 5, a tight fit hole by the tight fit pin is formed, the stacked plural metal plates are joined near the tight fit hole. Formation of a step part 9 around the tight fit hole 8 generated by tight fit of the tight fit pin and pressing of the shoulder part is further preferable for obtaining the joining joint with reduced fluctuation. COPYRIGHT: (C)2001,JPO

Analysis of weld image to determine weld quality

Abstract: A system and method of determining the quality of a spot weld based on a set of image data includes separating the weld data from the background data and estimating a diameter of a weld (e.g., the nugget diameter of a spot weld) based on the weld data. The image data (e.g., a digital image) represents an image of the weld and includes weld data and background data. The estimation indicates the quality of the weld. In one embodiment, the surface brightness of the image data attributable to the spot weld is used to estimate the inner diameter of the spot weld.

Spot welding device

Abstract: PROBLEM TO BE SOLVED: To provide a spot welding device capable of spot welding in good condition SOLUTION: By performing preheating for t1 hour, a work 20, 21 are warmed up and a gap 30 formed at the welding part of the work 20, 21 is disappeared After preheating is finished, the preheating is suspended for t2 hours and a pre-current flowing is performed for t3 hours to make a resistance stable between an electrode 11 and 12 Thereafter, the pre-current flowing is suspended for t4 hours, a current flowing is performed so that the heating value Q of the work 20, 21 reach a target heating value Q3 for the prescribed current flowing t4 hours by controlling a welding electric current Since the welding electric current is controlled to make the heating value Q of the work 20, 21 to the target heating value Q3 after the gap 30 is disappeared by preheating, there is no bad welding occurred even in case of having a gap between the work 20 and 21

Connection structure between cells, and connection method

Abstract: PROBLEM TO BE SOLVED: To provide a connection structure between cells and connection method enabled to surely secure a good welding quality at all time by easily and surely performing a projection welding, and enabled to joint adjacent two single cells in a good connection state without apprehension of leakage. SOLUTION: A plurality of welding protrusions 29, 30 for a projection welding are formed on both surfaces of a connector 27 respectively. An electrode plate 22 of a sealing body 20 of one cell Ba1 out of adjacent two cells, is jointed to one surface of the connector 27 by projection welding through the welding protrusion 29 for projection welding, and a cell case 19 of the other cell Ba2 is jointed to the other surface of the connector 27 by projection welding through the welding protrusion 30 for projection welding, thus, a plurality of cells Ba1-Ba6 are serially connected.

Apparatus for monitoring spot welding process and method of the same

Abstract: The present invention discloses an apparatus and a method for monitoring the quality of a spot welding process. The measured electric current and voltage signals between electrodes of a spot welding system are converted into digital data first. Then the two digital data are processed to obtain their complex forms via Hillbert transform respectively to construct their imaginary part. Finally, the electrical impedance Zin is obtained from dividing the complex form of digital voltage by the complex form of digital current. The electrical impedance Zin can be applied to compare with historical data to diagnose the quality of spot-welding points.