Spot Weld Nugget Research Articles

Effect of Al-Si coating weights on weldability of hot-stamped ultra-high-strength steel (UsiborR 1500) used in automotive structures

ABSTRACT Automotive industries have seen increased demands for indirect hot-stamped pre-coated ultra-high-strength steel 22MnB5 due to its excellence. This paper presents the results of experimental investigation of the effect of Al-Si coating weights AS150 (150 g/m2) and AS80(80 g/m2) and spot-welding process parameters of indirect hot-stamped Usibor 1500 to further understand which coating weight perform better for automotive application. The resistance spot welding experiments were conducted with a medium-frequency direct control (MFDC) machine. The MFDC resistance spot-welding machine had two G20 electrodes with a 458 truncated cone designed with a diameter of 4.9 mm. The results show that the nugget diameter increases with increasing weld current, better spot-weld nugget diameter is recorded at weld currents above 7.5 kA for both AS80 and AS150 coating weights, and the weld current range decreases with increase in coating weight and with increase in the interdiffusion layer. Heat treatment dwell time has a remarkable influence on weld current range for both AS150 and AS80 coating weights. AS80 coating weight has a slightly higher weld current range of 2.1 KA than AS150 coating weight with weld current range of 1.8 KA. Tensile shear strength for AS150 and AS80 increases nonlinearly with increase in weld diameter.

Measurement of spot welding nugget diameter using power spectral density variation of laser ultrasonic Lamb wave

In applications of spot welding, the nugget determines reliability of the material joining, which is characterized by nugget diameter. However, the conventional methods are complex and rough to measure the diameter of the nugget. This paper aims to propose a novel convenient method for measuring the diameter of spot welding nugget. The characteristic curve of laser ultrasonic Lamb waves in nugget area are obtained by laser ultrasonic detection technology under completely non-contact conditions. The variation characteristics of power spectral density in nugget area are analyzed by Fast Fourier Transform, to determine the geometric relationship between the scanning area and the nugget diameter, and the nugget diameter are obtained by further calculation. Experiments show that the accuracy of the proposed method is within 0.2 mm, and the relative errors of experimental data are within 3%. This paper provides an alternative method for the measurement of spot welding nugget diameter, and has great significance for the application of laser ultrasonic detection in spot welding.

Peculiarities of Pressure Welding of Pd Foil to Stainless Steel

The peculiarities of joining a palladium alloy foil to 12Cr18Ni10Ti stainless steel by diffusion and resistance welding are considered. It is shown that both technologies can be realized only using an intermediate nickel layer with a thickness of 0.1 mm, which provides uniform strength and joint tightness and also prevents the formation of brittle intermetallic compounds. Diffusion welding allows one to obtain high-quality joints of palladium alloy to stainless steel, but this process proceeds at relatively high (950°C) temperatures and takes a long time. Resistance welding does not have these disadvantages, but the outcome significantly depends on the correct choice of welding conditions, upon which the spot weld nugget must be displaced as much as possible toward the stainless steel and the intermediate nickel layer. The connection of the palladium alloy to the intermediate layer occurs owing to mutual diffusion occurring during the passage of the welding pulse.

Effect of external magnetic field on resistance spot welding of aluminum alloy AA6061-T6

An external magnetic field is applied in resistance spot welding (RSW) of 3 mm thick AA 6061-T6 sheets to improve the weld quality. Under the action of the external magnetic field, an additional circumferential flow is generated, resulting in the reduction of cooling rate and the change of solidification mode, and it finally influences the nugget profiles, microstructural evolutions, and mechanical properties. The profile of the magnetically assisted resistance spot welding (MA-RSW) nugget became more regular and freer of defects, e.g., the internal shrinkage defects and eyelash-like hot cracks. Moreover, a double-layered columnar grain zone and a nearly single-structured equiaxed grain zone were finally obtained. The tensile properties of the MA-RSW welds were significantly improved by increasing nugget diameter, eliminating defects, and complicating the crack propagation path. As a result, the application of the external magnetic field could achieve an energy-saving effect.

Optimization on strength spot welding joint trough finite element modelling indentation approach

Failure behaviour of spot welding are important in order to design the weld strength on dissimilar spot welded joint as a significant step to reduce vehicle weight in the development of urban transportation systems. Environmental friendly. Including in this case to take positive measures to reduce CO2 emissions and reduce fuel consumption. The material failure behaviour, properties parameter of plastics materials and fracture of materials can be easily determined when the specimen material standards (i.e parent metal) but for the results of spot welding joint testing standards are not applicable to characterize the HAZ and spot welding nugget because it is constrained by a complex structure and a small sample size. One potential approach to be developed in the behaviour of material failure, parameter plastic properties of material is to combine the numerical-experimental method. Where ph-curve indentation experimental results combined with numerical approach through Finite Element (FE) modelling. Approach was established to be used for reverse (inverse) testing of the nature of constitutive material (i.e the yield stress (σy), the coefficient of strain hardening (n)) for nugget, HAZ and the parent material (base). In this approach the Load data of material deformation used as input data for finite element model (FE) which simulates the geometry and boundary conditions of the experiment. Finite element model (FE) Model-based approaches are developed, validated then used to predict the effect of nugget size and thickness of the sheet metal on the strength of the weld joint points with different materials (dissimilar material).

Resistance spot weldability of galvannealed and bare DP600 steel

Resistance spot welding (RSW) of galvannealed and bare dual phase (DP600) steel is a challenging task as it involves the additional complexity of zinc coating layer. This study is focused on optimization of spot welding parameters, viz., welding current and time to achieve maximum load bearing capacity in tensile-shear and coach-peel configurations. Study revealed a minimum critical nugget diameter is needed above which favorable pull-out failure is observed. Critical nugget diameter for pull-out failure is determined to be 4.4 mm. Applicability of different empirical and metallurgical models for determination of critical nugget diameter were assessed. Transition from partial interfacial to pullout failure mode has been explained on the basis of combined effect of increased nugget diameter and micro-mechanism of fracture. It was observed that the there was an increase in nugget diameter and load bearing capacity of the spot welds with an increase in welding current as well as welding time. Best fit equations have been proposed for maximum load bearing capacity as a function of spot welding parameters and nugget diameter. Microstructural evolution and hardness variation across different welding zones have been presented in detail. Redistribution of zinc in different zones of welding has been evaluated using electron probe micro-analysis.

Influence of Nitrogen Atmosphere on Weld Nugget Morphology during Resistance Spot Welding of 304L Stainless Steel

The Resistance Spot Welding is most widely used as a joining process for stainless sheets. AISI 304L austenitic stainless steel offers the optimum combination of corrosion resistance and mechanical strength. Improving the microstructure of the spot-welded nugget has a great effect on the quality of sheet weld joints. The current research presents the influence of using nitrogen atmosphere on macro and microstructure morphologies of the spot-welded nugget of AISI 304L stainless steel. Results show that using nitrogen atmosphere as shielding gas improves the appearance and color matching of the welded nugget with base, but on the other hand, nitrogen atmosphere reduces the nugget size. In addition to the reduction of the total ferrite in the spot weld nugget, Skeletal d-ferrite / total ferrite ratio increases by using nitrogen shielding gas due to nitrogen diffusion in fusion welded nugget zone.

Elastic analytical solutions and angular distributions near spot weld nugget in lap-shear specimens

Spot welding has been a remarkably important joint method for automotive body engineering. Based on a simplified two-dimensional analytical model in a lap-shear specimen, the elastic analytical solutions near spot weld nugget are theoretically derived to analyze stress distributions. A Cartesian coordinate system is centered at the center of the nugget, and the shear or resultant force acting on the nugget is marked as the positive x-direction. The results show that the normalized radial and hoop stresses are negative at the angle intervals between [66.25°, 113.75°] and [246.25°, 293.74°], while the normalized shear stress is negative at the angle intervals between [0°, 90°] and [180°, 270°]. It can be observed that the locations with the initial yielding failure change gradually from the normalized radial distance of 1.34 to the circumference of the spot weld nugget, and finally to the infinity as the angle increases. The normalized effective stress could approach to 1.84 as the normalized radial distance goes to infinity. In addition, the obtained analytical solutions are validated in the comparison with numerical results. The locations with peak Von Mises stresses along the circumference of the spot weld nugget have a good agreement with the analytical solutions. It indicates that the initial yielding locations would likely occur at the four special angles of the spot weld nugget. Therefore, the derived stress distributions in this study are beneficial for analyzing yielding failure behavior or evaluating damage evolution on engineering structures jointed with spot welds.

Ultrasonic C-scan detection for stainless steel spot welding based on wavelet package analysis

An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish the nugget from the corona bond. The 2D C-scan images produced by ultrasonic C scan which contribute to quantitatively calculate the nugget diameter for the computer are further analyzed. The spot welding nugget diameter can be automatically obtained by image enhancement, edge detection and equivalent diameter algorithm procedure. The ultrasonic detection values in this paper show good agreement with the metallographic measured values. The mean value of normal distribution curve is 0.006 67, and the standard deviation is 0.087 11. Ultrasonic C-scan test based on wavelet packet signal analysis is of high accuracy and stability.

Study on Flow Phenomenon in Spot Welding Nugget of Dissimilar Materials

Flow phenomenon in spot welding nugget of dissimilar materials was studied. Metallographs in the course of welding nugget formation were observed and analyzed, through which it was indicated that: in the early stage of welding nugget formation, spot welding of dissimilar materials made liquid metals in the nugget produce a violent stirring action because the electrodynamic force overcame the medium resistance, causing unevenness of elements and compositions in the welding nugget; and then the unevenness was represented by vortex flow by means of different resistances to corrosion. It was proposed that the formation law of welding nugget could be recognized according to the formation law of vortex flow, and the vortex flow often moved from later-molten metal to former-molten metal. The property of welded joint with vortex flow was poorer than that without vortex flow.

Nondestructive Evaluation of Spot Weld in Stainless Steel Using Ultrasonic Immersion Method

This paper describes quantitative evaluation of the nugget size and shape of resistance spot welds on stainless steel using ultrasonic pulse-echo amplitude. Here an empirical formula has been derived for predicting spot weld nugget diameter for sample having different thickness. The reliability as well as the accuracy of the empirical equation has been verified by comparing the calculated results based on ultrasonic response with the results obtained by X-ray (Radiography) and destructive testing.

Failure analysis for resistance spot welding in lap-shear specimens

Abstract Based on the elasticity theory and finite element method, this paper aims to explore the failure incidence of resistance spot welding in dual-phase lap-shear specimens. The stress function approach is adopted to derive an analytical solution to a lap-shear specimen containing a spot weld nugget subjected to the uniformly distributed loading condition, which provides a means to exploring the stress distributions near the spot weld nugget. The normalized effective stress obtained indicates that the initial yielding failures likely occur at four specific angles of 38.02°, 141.98°, 218.02°, and 321.98° along the spot weld nugget in the lap-shear plate. In addition, the contours of normalized stress are also plotted in the polar system to understand the surrounding stress distributions, which reveals that the locations of the maximum and minimum values of normalized radial, hoop, and shear stresses are located at angles 0°/180° and 90°/270°, 90°/270° and 0°/180°, 135°/315° and 45°/225°, respectively, as the normalized radial distance r / a goes to infinity. The elasto-plastic finite element analysis (FEA) is also conducted to analyze the initial necking or thinning phenomenon. It is found that the angular locations of the maximum equivalent plastic strain or initial necking failure points are located at four angular intervals for the advanced high strength steel (AHSS) plate with a spot weld nugget. The derived stress distributions allow predicting failure behavior and evaluating damage evolution on many engineering structures jointed with spot welds.

Spot Welding Quality Prediction Model Based on Partial Least-Squares Regression

The relationship between spot welding process parameters and nugget diameter was selected and synthesized by partial least squares. The partial least squares regression model of spot welding quality was established. And the nugget diameter was predicted based on the model mentioned above. The results show that this model can be used to predict the spot welding quality.

Critical Nugget Diameter of Resistance Spot Welded Stiffened Thin Plate Structure

Stiffened thin plate structure which is mostly applied to the car body structures consists of frame and sheet. It is a low cost method to reach a high-performance vehicle structure because of requirement low volume materials. Frame is thicker than sheet, so it acts as the reinforcement of this structure. The resistance spot welding (RSW) is generally used to join it. In this study failure modes of resistance spot welded thin plate structure, pullout and interfacial failure modes, were investigated based on thickness of joined plates and load secondary voltage to determine the critical nugget diameter. Three pairs of joined plates thickness of 1-1, 2-1 and 3-1 mm were spot welded using varied voltage in a range of 1.6 V to 2.3 V. The spot weld nugget of the stiffened thin plate structure joint were asymmetric form. Increasing welding voltage made the shear load bearing capacity of RSW joint increase. In the pullout failure, the bearing capacity increased if the thickness of joined materials increased. The experimental critical nugget diameter to guarantee pullout failure mode in the unequal sheet thickness joint of the stiffened thin plate structure decreased if the sheet thickness of joined materials increased. It was higher than nugget diameter obtained by AWS formula. AWS formula should be used carefully in the dissimilar sheet thickness joint of the stiffened thin plate structure.

Assessment of Nugget Size of Spot Weld using Neutron Radiography

Resistance spot welding (RSW) has been widely used for many years in the fabrication of car body structures, mainly due to the cost and time considerations. The weld quality as well as the nugget size is an issue in various manufacturing and processes due to the strong link between the weld quality and safety. It has led to the development of various destructive and non-destructive tests for spot welding such as peel testing, ultrasonic inspections, digital shearography, and infrared thermography. However, such methods cannot show spot weld nugget visually and the results are very operator’s skill dependent. The present work proposes a method to visualize the nugget size of spot welds using neutron radiography. Water, oil and various concentrations of gadolinium oxide-alcohol mixture were evaluated as a contrast media to obtain the best quality of radiography. Results show that mixture of 5 g gadolinium oxide (Gd 2 O 3 ) in 25 ml alcohol produces the best contrast. It provides the possibility to visualize the shape and size of the nugget spot weld. Furthermore, it can discriminate between nugget and corona bond. The result of neutron radiography evaluation shows reasonable agreement with that of destructive test. Received: 13 October 2010; Revised: 25 August 2011; Accepted 26 August 2011

Study of Friction Stir Spot Welding of Steel/ Magnesium

Dissimilar metal of Steel and Magnesium alloy by friction stir spot welding is studied. Based on using orthogonal test method to optimize the process parameters and get satisfactory joint, SEM is used to observe the features of joint, fracture morphology, and XRD is used to determine the joint phase, and the results show that: the design of rotating tool without pin is reasonable and it can form satisfactory joints without keyhole for spot welding; spot welding nugget zone on the magnesium side shows the phenomenon of melting and solidification in the range of hundreds microns, and its microstructure appears a structure of dendrites; The fracture mode of spot welding joint is a mixed mode of cleavage and dimpled rupture.

Fatigue Properties of Spot Welded and Spot Weld-Bonded Joints of Steel Sheet

In this paper, fatigue tests are carried out on spot welded and spot weld-bonded joints of mild steel and ultra-high strength steel plates. The fatigue strength of the spot weld-bonded joints is higher than that of the spot welded joints. On the spot weld-bonded specimens, the strain distribution around the bonded area during fatigue tests is measured by using strain gauges to investigate the interfacial debonding behavior of adhesive bonding. According to the strain distribution measurement, the debonding initiates from the edge of the adhesive bonding, and propagates to the spot weld nugget. The fatigue strength is improved because the stress concentration of the nugget edge is considerably reduced in large part of fatigue life.

Simulação numérica do crescimento da lentilha de solda obtida pelo processo de soldagem a ponto por resistência elétrica no aço inox AISI 304

O crescimento das lentilhas de solda obtidas pelo processo de soldagem a ponto por resistência elétrica em chapas de aço inoxidável AISI 304 foi analisado através de simulação numérica com o método de elementos finitos, sendo utilizado para essa finalidade o programa comercial ANSYS. O modelo matemático utilizado considerou: acoplamento entre os campos elétricos e térmicos em regime transiente; a variação das propriedades elétricas e térmicas do aço AISI 304 com a temperatura e condições de contorno térmicas de convecção. A geometria tridimensional analisada, axissimétrica, permitiu a simplificação para uma geometria bidimensional. Os resultados obtidos com o modelo foram comparados com resultados experimentais apresentados na literatura. Foram consideradas espessuras de chapas de 1, 2 e 3 mm, e diferentes diâmetros de face para os eletrodos. As simulações determinaram os tempos necessários de aplicação de diferentes valores de corrente para obtenção dos diâmetros e penetração das lentilhas de solda recomendados em cada situação. Os resultados mostraram também que com o uso de maiores correntes menos energia é consumida na formação da lentilha de solda.

Fatigue Life Prediction of Spot-Welded Structure under Different Finite Element Models of Spot-Weld

In order to accurately and conveniently simulate spot-weld in FEA, based on the typical specimen of stainless steel, three typical finite element models (FEM) of spot-welds have been created as analysis objects. Firstly, based on the calculation theory of the spot-weld fatigue, two sets of analytical solution, which were the maximum principle stress of the specimen around the spot-weld nugget, were obtained under the action of stretching and shearing, respectively. Then, their linear elastic FEM were established, and the stress states around the spot-weld nugget and the adjacent sheets were analyzed. Finally, according to the results compared between the analytical solution and simulation solution, it can be seen that, when the specimen was stretched, using the brick model to simulate the nugget can get the smallest absolute error of the principle stress, so its spot-weld fatigue damage is the most consistent with the actual situation, a stiff beam model followed, and an umbrella model is the worst; when the specimen was sheared, using the brick model to simulate the nugget can also get the smallest absolute error of the principle stress, so its spot-weld fatigue damage is also the most consistent with the actual situation, the umbrella model is followed, and the stiff beam model is the worst. The results show that appropriate selection of spot-weld FEM is extremely essential for fatigue life prediction under the initial design of products.

Resistance spot welding processing monitoring based on electrode displacement curve using moving range chart

Electrode displacement curve is an ideal monitoring parameter which can directly reflect spot weld nugget formation in resistance spot welding (RSW) process. The current RSW quality monitoring systems based on electrode displacement curve mainly focus on the low frequency information of the curve, such as the curve’s shape. Variation of the curve that represents process consistency is little studied. Based on on-line measured electrode displacement curve, statistical process control method is introduced to analyze the process consistency by employing moving range (MR) chart. The moving range method implemented the RSW process monitoring through providing the high frequency information of the curve. The results of this research will enhance the understanding of the electrode displacement curve, and help systematically design better on-line RSW quality monitoring systems. A case study demonstrates the validity and effectiveness of the methodology.