Showing papers on "Spot welding published in 2004"
TL;DR: In this paper, the importance of welding machine characteristics relative to weld growth is highlighted, particularly the effect of electrode diameter and the rigidity of the machine coupled with the weight and frictional effects developed in the electrode head assembly are shown to be important factors influencing weld growth.
Abstract: Resistance spot welding is the principal method of welding sheet steel products. In practice, the manufacture of welds of acceptable quality depends on the definition of optimum welding parameters and the implementation of suitable controls to ensure constant weld quality over a long production run. The ability to make a weld is best defined by a weldability lobe outlining the available manufacturing tolerances between minimum and maximum limits. Both two- and three-dimensional weldability lobes exist defined in terms of weld time, welding current and electrode force. Production variables influencing weld growth are discussed, particularly the effect of electrode diameter. The importance of welding machine characteristics relative to weld growth is highlighted. In particular, the rigidity of the machine coupled with the weight and frictional effects developed in the electrode head assembly are shown to be important factors influencing weld growth. Also important are the electrical characteristics of the machine, including transformer configuration current waveform and current ‘off’ time in the nonconducting part of the waveform. A reliable control philosophy is an essential requirement of any inprocess feedback system if high quality spot welds are to be produced in high volume. Various model simulations indicate that changes, with time, in electrode/sheet and sheet/sheet interfacial resistances control weld nugget formation and growth. The relative contributions of these resistances are discussed. Heat generation and temperature distribution in the weldare determined by the current and force distribution across these interfaces. One-, two- and three-dimensional models have been developed to describe the temperature distribution in the weld zone and weld nugget growth. These models have limited application due to inadequate input data to describe the transient conditions appertaining in the weld zone. Current waveform, inductance effects, and friction/rigidity of the electrode head assembly, are not considered. Neural networks and fuzzy logic control have shown promise in classifying weld quality into predetermined groupings. The way forward is to adopt a multidisciplinary approach, taking into account the various interactions between the thermal, electrical, mechanical and metallurgical phenomena developed during the welding process. Models describing these phenomena should be interlinked to simulate heat generation and growth in the weld zone. The resulting model could be coupled with experimentally developed trends to optimise inputs to a neural network, the output of which is used, through a fuzzy logic controller, to take appropriate corrective action to ensure the required weld quality. It is stressed that any mathematical simulation or control system must take into account changes that occur at the welding electrodes as a consequence of electrode wear. The latter are discussed in Part 2 of this review.
167 citations
TL;DR: In this article, the authors present an experimental study on the resistance spot weldability of galvanized interstitial free (cold formable) steel sheets with austenitic stainless steel sheets.
99 citations
TL;DR: In this paper, a general finite element formulation of the electrothermal contact is proposed in order to accurately account for the relative displacements of contact surfaces, and a finite element simulation of the welding of three steel sheets is presented.
80 citations
TL;DR: The results show that the LVQ neural network is able to detect the expulsion in different materials and points to the welding force signal as the most important indicator of the expulsion occurrence.
Abstract: Resistance spot welding is one of the most important welding procedures. Therefore, a strong emphasis is placed on the quality of the welds. One of the phenomena that causes the deterioration in quality is the eruption of molten material, the so-called expulsion. Expulsion can be avoided with appropriate parameter selection. The problem, however, lies in the fact that the best quality welds are made with parameters just below the expulsion area. Therefore, for any successful control scheme an efficient and dependable expulsion detection is needed. A linear vector quantization (LVQ) neural network system is proposed to achieve this goal. The network is analysed with different sensor combinations and different materials. The results show that the LVQ neural network is able to detect the expulsion in different materials. The experiment also points to the welding force signal as the most important indicator of the expulsion occurrence.
76 citations
01 Feb 2004
TL;DR: In this article, the velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer, and the peak temperature and velocity increased significantly with laser power density and pulse duration.
Abstract: Alloying element loss from the weld pool during laser spot welding of stainless steel was investigated experimentally and theoretically. The experimental work involved determination of work-piece weight loss and metal vapor composition for various welding conditions. The transient temperature and velocity fields in the weld pool were numerically simulated. The vaporization rates of the alloying elements were modeled using the computed temperature profiles. The fusion zone geometry could be predicted from the transient heat transfer and fluid flow model for various welding conditions. The laser power and the pulse duration were the most important variables in determining the transient temperature profiles. The velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer. The peak temperature and velocity increased significantly with laser power density and pulse duration. At very high power densities, the computed temperatures were higher than the boiling point of 304 stainless steel. As a result, evaporation of alloying elements was caused by both the total pressure and the concentration gradients. The calculations showed that the vaporization occurred mainly from a small region under the laser beam where the temperatures were very high. Themore » computed vapor loss was found to be lower than the measured mass loss because of the ejection of tiny metal droplets owing to the recoil force exerted by the metal vapours. The ejection of metal droplets has been predicted by computations and verified by experiments.« less
72 citations
Journal Article•
TL;DR: In this paper, an expulsion criterion was proposed by comparing the electrode force with that from the liquid nugget: expulsion occurs when the latter exceeds the former, and an effective electrode force, instead of an applied/nondeterministic electrode force was used in the criterion.
Abstract: An expulsion model has been developed for resistance spot welding, based on consideration of the interaction between mechanical and metallurgical processes during welding. An expulsion criterion is proposed by comparing the electrode force with that from the liquid nugget: expulsion occurs when the latter exceeds the former. An effective electrode force, instead of an applied/ nominal electrode force, is used in the criterion. This force can be calculated based on the applied electrode force and its offset from the liquid nugget force, which can be obtained through knowledge of the internal pressure and the dimensions of a nugget. Pressure components in a molten metal include those due to melting, liquid expansion, vapor pressure, and decomposition of surface agents, and are formulated by thermodynamic considerations. Experiments have been conducted to verify the model on an aluminum alloy (AA5754), and good agreement was achieved. The model can also be used to develop guidelines for electrode force selection.
69 citations
TL;DR: In this paper, the dynamic resistance curve can be divided into the following stages based on physical change in the workpieces: as perity heating, surface breakdown, asperity softening, partial surface melting, nugget growth and expulsion.
Abstract: The dynamic resistance has been investigated during small scale resistance spot welding (SSRSW) of Ni sheets. Electrical measurements have been correlated with scanning electron microscope images of joint development. The results show that the dynamic resistance curve can be divided into the following stages based on physical change in the workpieces: asperity heating, surface breakdown, asperity softening, partial surface melting, nugget growth and expulsion. These results are also compared and contrasted with dynamic resistance behaviour in large scale RSW.
69 citations
Journal Article•
TL;DR: In this article, resistance spot welding was used to weld aluminum alloy to steel from process development to performance evaluation, and the results showed that the alloy was more robust to steel than aluminum.
Abstract: Summary of work on resistance spot welding aluminum alloy to steel from process development to performance evaluation.
66 citations
TL;DR: In this article, the authors highlighted the factors influencing the formation and growth of the weld nugget in resistance spot welding and highlighted the application of artificial intelligence techniques in overcoming the problems encountered.
Abstract: The factors influencing the formation and growth of the weld nugget in resistance spot welding have been highlighted in Part 1 of this review. While various techniques based on theoretically derived models have been used for the control of weld growth, very few have found widespread application in any production control philosophy. The application of artificial intelligence techniques has proved only partially successful in overcoming the problems encountered. A limiting factor in manufacturing using spot welding is the life of the welding electrodes. A short life necessitates frequent electrode dressing or changing, resulting in lower production rates and higher costs. Also, weld quality is more variable towards the end of the life of an electrode, particularly when welding coated steels. Electrode deterioration causes growth of the electrode tip diameter, which has been shown to be dominant in determining the deterioration in weld quality in production operations. The process of electrode wear h...
65 citations
TL;DR: In this article, the characteristics of electrode degradation in resistance spot welding of aluminium and its influence on weld quality were investigated based on analysis of electrode life test results, in which three parameters were defined to represent the tip surface characteristics, namely, relative radius, edge concentration and eccentricity.
Abstract: A study was carried out of the characteristics of electrode degradation in resistance spot welding of aluminium, and its influence on weld quality. Based on analysis of electrode life test results, an imaging approach was developed to determine quantitatively the status of electrode degradation, in which three parameters were defined to represent the tip surface characteristics, namely, relative radius, edge concentration, and eccentricity. This image analysis revealed a clear relationship between these defined electrode surface features and the weld quality, based on which a reasonable understanding was achieved of the causes of weld quality deterioration in electrode life tests. STWJ/404
64 citations
TL;DR: A quality estimation system of resistance spot welding has been developed using a dynamic resistance pattern and the Hopfield neural network classifies the pattern vectors and utilizes them to estimate weld quality.
Abstract: A quality estimation system of resistance spot welding has been developed using a dynamic resistance pattern. Dynamic resistance is monitored in the primary circuit of the welding machine and is mapped into a bipolarized vector for pattern recognition. The Hopfield neural network classifies the pattern vectors and utilizes them to estimate weld quality. Weld strength measurements have been made to examine the performance of the estimation system. Good agreement is obtained between the classified results and tensile-shear strengths. For a better understanding of the estimation process of the network, an example in which the dynamic resistance is classified into the stored pattern is also illustrated.
TL;DR: In this paper, the effect of thickness dissimilarity on the peel and shear strength of spot-welded dissimilar thickness joints was investigated, and it was shown that thickness similarity magnifies the stress concentration located at the boundaries of the weld nugget.
TL;DR: In this paper, the authors investigated the metallurgical interactions between the copper electrode and aluminum alloy sheet using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) and Xray diffraction (XRD).
Abstract: Electrode pitting was investigated in resistance spot welding of 1.5-mm-thick sheet aluminum alloy 5182 using a medium-frequency direct-current welder and electrodes with a tip face curvature radius of 50 mm and tip face diameter of 10 mm. Detailed investigation of the metallurgical interactions between the copper electrode and aluminum alloy sheet was carried out using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results indicated that electrode degradation, which eventually leads to weld failure, proceeded in four basic steps: aluminum pickup, electrode alloying with aluminum, electrode tip face pitting, and cavitation. Since pitting and cavitation result from Al pickup and alloying, periodic electrode cleaning could extend electrode tip life by limiting the buildup of Al on the tip face. This work is part of the effort to improve electrode tip life in resistance spot welding of aluminum alloys for automotive applications.
TL;DR: In this article, the techniques of model updating in structural dynamics are used to analyse and improve CWELD and ACM2 models, and guidelines are given for their optimum implementation, and it is shown that the natural frequencies of the benchmark structures are very sensitive to some parameters characterising these models.
TL;DR: In this paper, a medium-frequency direct-current welder was used for resistance spot welding of aluminum alloy 5182 sheets and both displacement and force experienced a sudden drop when weld metal expulsion occurred, but the rate of increase in displacement did not reach zero during welding even for joints with sufficient nugget diameter.
Abstract: Dynamic electrode displacement and force were characterized during resistance spot welding of aluminum alloy 5182 sheets using a medium-frequency direct-current welder. It was found that both electrode displacement and force increased rapidly at the beginning of the welding stage and then at a reducing rate. Rates of increase in electrode displacement and force were both proportional to welding current. And both electrode displacement and force experienced a sudden drop when weld metal expulsion occurred. However, the rate of increase in electrode displacement did not reach zero during welding even for joints with sufficient nugget diameter while electrode force peaked when a large nugget diameter was produced. Possible strategies for process monitoring and control were also discussed.
TL;DR: In this article, the behavior of thin welds of different grades of steels in dynamic loading conditions such as those experienced in automotive crash test is investigated. And the evaluation of resistance to dynamic failure will be studied through impact tensile test (ITT).
TL;DR: In this paper, the axial compression tests of thin-walled beams joined by spot welding were performed and the effect of the size of the weld's diameter and the pitch of the welding on the amount of absorbed energy was studied.
TL;DR: In this paper, the impact tensile test (ITT) was used to examine the mechanical and metallurgical behavior of the weld bead, heat affected zone (HAZ) and base metal for thin sheet steels used in the car industry.
01 Apr 2004-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, a three-dimensional transient model to solve heat transfer, fluid flow, and species conservation during laser welding of dissimilar metals is presented, which is based on a control volume formulation with an enthalpy-porosity technique to handle phase change and a mixture model to simulate mixing of molten metals.
Abstract: A three-dimensional transient model to solve heat transfer, fluid flow, and species conservation during laser welding of dissimilar metals is presented. The model is based on a control volume formulation with an enthalpy-porosity technique to handle phase change and a mixture model to simulate mixing of molten metals. Weld pool development, solidified weld pool shape, and composition profiles are presented for both stationary as well as continuous laser welding in conduction mode. Salient features of a dissimilar Cu-Ni weld are summarized and thermal transport arguments are employed to successfully explain the observations. It is found that the weld pool shape becomes asymmetric even when the heat source is symmetrically applied on the two metals forming the couple. It is also observed that convection plays an important role in the development of weld pool shape and composition profiles. As the weld pool develops, the side melting first (nickel) is found to experience more convection and better mixing. Results from the case studies of computation are compared with corresponding experimental observations, showing good qualitative agreement between the two.
TL;DR: In this article, the authors analyse spot-welded dissimilar material joints and show that the stresses are more concentrated towards the member that has the lowest melting point in the joint.
Journal Article•
TL;DR: In this article, the authors examined the effects of fusion zone size on failure modes, static strength, and energy absorption of aluminum spot welded samples using a combined experimental, statistical, and analytical approach.
Abstract: This paper examines the effects of fusion zone size on failure modes, static strength, and energy absorption of aluminum spot welded samples using a combined experimental, statistical, and analytical approach. The main failure modes for aluminum spot welds are nugget pullout and interfacial fracture. First, static strength tests using coupon configurations of lap shear, cross tension, and coach peel were performed on the joint populations with a controlled fusion zone size. Thirty replicate static strength tests were performed for each coupon configuration. The resulting peak load and energy absorption levels associated with each failure mode were studied using statistical models. Next, an analytical model was developed to determine the failure mode of an aluminum resistance spot weld based on limit load analyses. It was found that fusion zone size, sheet thickness, and the level and location of weld porosity/defects are the main factors influencing the cross-tension failure mode of an aluminum spot weld. Two additional spot weld populations with different fusion zone sizes were then fabricated to validate the analytical failure mode model. Static cross-tension tests were again performed, and the experimental observations confirmed the analytically predicted failure modes for each population.
TL;DR: A threefold method of testing the performance of an array-based ultrasonic tool for nondestructive testing of spot welds is described and its capabilities, use, and advantages over existing counterparts are described.
Abstract: This paper describes a threefold method of testing the performance of an array-based ultrasonic tool for nondestructive testing of spot welds. The tool is described in its capabilities, use, and advantages over existing counterparts. Performance testing for and the results from carrying out the testing are described. The three performance testing methods include 1) the use of calibrated samples, 2) comparisons with actual spot-welds, and 3) a performance evaluation of the embedded fitting software. The test of the fitting software was carried out by a comparison of results with reference fits supplied by the National Institute of Standards and Technology.
TL;DR: In this article, an in-process tempering of weld martensite was performed on a TRIP steel to modify the hardness of the weld and the results showed that the weld hardness could be reduced to approximately 350 HV.
Abstract: In recent years new types of sheet steels, combining higher strength with better ductility have been developed. Some of these steels have shown limited weldability compared to mild steels. The hardness of the welds for these steels stretches from 380 HV for DP 600 to approximately 500 HV for TRIP (Transformation Induced Plasticity) and boron steels. Static peel tests of eight types of steels resulted in plug failures for the DP 600 steels, but some interfacial failures for higher strength steels. Generally, welds with a hardness exceeding 400–450 HV caused unstable fractures. To modify the hardness of the weld an in-process tempering of weld martensite was performed on a TRIP steel. Guidance to a proper tempering pulse was obtained through simulation of phase transformation and cooling of the weld. Welding experiments showed that the weld hardness could be reduced to approximately 350 HV, i.e. below the limit where interfacial failures start to occur.
TL;DR: In this article, a set of test fixtures were designed and used to obtain failure loads of mild steel spot weld specimens under combined opening and shear loading conditions, and three different impact speeds were applied to examine the effects of separation speed on failure loads.
Abstract: Failure loads of spot weld specimens are investigated under impact combined loading conditions. A set of test fixtures was designed and used to obtain failure loads of mild steel spot weld specimens under combined opening and shear loading conditions. Three different impact speeds were applied to examine the effects of separation speed on failure loads. Micrographs of the cross-sections of failed spot welds were obtained to understand the failure processes in mild steel specimens under different impact combined loads. The experimental results indicate that the failure mechanisms of spot welds are very similar for mild steel specimens at various impact speeds. These micrographs show that the sheet thickness can affect the failure mechanisms. For 1.0 mm specimens, the failure occurs near the base metal in a necking/shear failure mode. For 1.5 mm specimens, the failure occurs near the heat-affected zone in a shear failure mode. Based on the experimental results, the effects of the inertia force, the separation speed, and the loading angle on the failure loads of spot welds are investigated. Failure criteria are proposed to characterize the failure loads of spot welds under impact combined opening and shear loads for engineering applications. The failure load can be expressed as a function of the tensile strength of the base metal, the nugget size, the sheet thickness, the maximum separation speed, the loading angle, and empirical coefficients for a given welding schedule.
TL;DR: In this article, a high-speed video imaging system was employed to directly measure the electrode displacement of the small scale resistance spot welding (SSRSW) process, which eliminates a number of potential error sources inherent in other electrode displacement measuring techniques.
Abstract: A high-speed video imaging system was employed to directly measure the electrode displacement of the small scale resistance spot welding (SSRSW) process. This measurement technique was chosen because it eliminates a number of potential error sources inherent in other electrode displacement measuring techniques. Careful observation of the heating and cooling portions of the electrode displacement curves revealed that each is comprised of two identifiable segments. Distinct high-velocity segments of the displacement curves were thought to correspond to solid-liquid phase transitions in the weld nugget, while lower-velocity portions corresponded to thermal expansion or contraction of solid material. It was found that the magnitudes of the high speed portions of the electrode displacement were more closely correlated with the weld nugget thickness than was the overall magnitude of the electrode displacement. Furthermore, all measures of electrode displacement were more closely correlated to weld nugget thickness than to nugget diameter.
TL;DR: In this paper, seam welding of Al/Fe sheets is reported to be difficult and little reported in literature, and it is recommended to use seam welding rather than spot welding in order to ensure good weld strength and joint tightness.
Abstract: Aluminium (Al), despite its low melting point, has a high electric conductivity and thermal conductivity but poor heating efficiency, ranking as a hard-to-weld material. It is routinely necessary to weld aluminium sheets to sheets made of a dissimilar metal, such as steel sheets (Fe). In this case, it is advisable to use seam welding than spot welding in order to ensure good weld strength and joint tightness. However, seam welding of Al/Fe sheets is difficult and little reported in literature.
Patent•
03 Jun 2004TL;DR: In this paper, a two-dimensional array of ultrasonic transducers arranged with a delay line for positioning adjacent a surface of a weld is used to evaluate the size and/or quality of a spot weld.
Abstract: A method and apparatus for evaluating the size and/or quality of a spot weld. The apparatus includes a two-dimensional array of ultrasonic transducers arranged with a delay line for positioning adjacent a surface of a weld. A layer of gel is placed between the delay line and the weld surface. The array of transducers emit ultrasonic waves that pass into the weld. The reflected waves are received by the transducers and relayed to a central processing unit that analyzes the time delay, amplitude, and amplitude attenuation to calculate the border of the weld nugget, the thickness of the welded material, the thickness of the gel layer, and other factors contributing to weld quality.
Patent•
10 May 2004TL;DR: In this article, the formation of spot welds in high strength steel workpieces is improved by using welding electrodes with annular, or donut shaped welding tips for forming the molten metal weld pool at the weld site.
Abstract: The formation of spot welds in high strength steel workpieces is improved by using welding electrodes with annular, or donut shaped welding tips for the formation of the molten metal weld pool at the weld site. The annular poll solidifies to form an annular weld nugget. Preferably the donut shaped nugget has an internal diameter that is no more than three-quarters of the outside diameter. The method is applicable to carbon steel workpieces with allowing elements for strengthening, and to thick sheets of mild carbon steels.
TL;DR: In this article, the authors used X-ray imaging to determine the fatigue crack growth behavior and failure mechanisms of spot welded specimens and showed that the natural frequencies of these joints nonlinearly decrease with the growth of fatigue cracks.
Abstract: X-ray imaging has been used to determine the fatigue crack growth behavior and failure mechanisms of spot welded specimens. Cracks critical to final failure of the tensileshear specimens studied are through-thickness plate cracks, which are usually initiated about 0.2–1.0 mm away from the edge of the nugget. In addition, frequency response functions (FRFs), obtained by impact hammer-accelerometer experiments throughout the fatigue process, show that the natural frequencies of these joints nonlinearly decrease with the growth of fatigue cracks. The three-dimensional finite-element analysis results for FRFs of uncracked and cracked spot welded joints are shown to be in good agreement with the experimental data. It is also shown that the fatigue cracks have different degrees of influence on different natural frequencies because of the location of cracks and vibrating modes. The results by both experiment and finite element analysis indicate that analysis of the variation of natural frequencies and vibrating modes may be used to study the fatigue crack propagating shape and the location of the fatigue crack.
Journal Article•
TL;DR: In this paper, a cold-rolled clad material was introduced as a transition to aid the resistance welding process and optimal welding parameters and electrode selections were established using experimental approaches The welded samples' mechanical behaviors were then evaluated using static and dynamic weld strength tests as well as cyclic fatigue tests.
Abstract: This paper summarizes our work to date on resistance spot welding of aluminum alloy to steel, from process development to performance evaluation Since aluminum alloys and steel cannot be readily fusion welded together due to their drastically different thermal physical properties, a cold-rolled clad material was introduced as a transition to aid the resistance welding process The optimal welding parameters and electrode selections were established using experimental approaches The welded samples' mechanical behaviors were then evaluated using static and dynamic weld strength tests as well as cyclic fatigue tests The weld strength, failure mode, and fatigue life were then compared with self-piercing rivets of the same dissimilar metals combination Statistical analyses were also performed to analyze the effects of different failure modes on samples' peak strength and energy absorption