Nugget Diameter Research Articles

Research on Resistance Spot Welding Property of Hot-Stamping Quenched Steel Sheets

22MnMoB hot-stamping quenched steel sheets were well welded together by power frequency spot welder with optimization of relevant welding parameters in this paper. According to the experiment results of welding spatter, maximum shearing force and the size of nugget, the effects of welding current, welding time and electrode pressure on weld property were advanced. The results show that while welding current, welding time and electrode pressure are respectively set as 6.0~6.5kA, 0.5~0.7s and 4~7kN, the weld exhibits good mechanical property. The nugget diameter appears approximate linear relationship with mechanical property of weld and determines the fracture model of welds. The novel hot stamping steel sheets exhibit good welding property. The optimizing welding parameters can be used to instruct the practical production.

Joining of Dissimilar alloy Sheets (Al 6063&AISI 304) during Resistance Spot Welding Process: A Feasibility Study for Automotive industry

Present design trends in automotive manufacture have shifted emphasis to alternative lightweight materials in order to achieve higher fuel efficiency and to bring down vehicle emission. Although some other joining techniques are more and more being used, spot welding still remains the primary joining method in automobile manufacturing so far. Spot welds for automotive applications should have a sufficiently large diameter, so that nugget pullout mode is the dominant failure mode. Interfacial mode is unacceptable due to its low load carrying and energy absorption capability. Strength tests with different static loading were performed in, to reveal the failure mechanisms for the lap-shear geometry and the cross-tension geometry. Based on the literature survey performed, venture into this work was amply motivated by the fact that a little research work has been conducted to joining of dissimilar materials like non ferrous to ferrous. Most of the research works concentrated on joining of different materials like steel to steel or aluminium alloy to aluminium alloy by resistance spot welding. In this work, an experimental study on the resistance spot weldability of aluminium alloy (Al 6063) and austenitic stainless steel (AISI304) sheets, which are lap joined by using a pedestal type resistance spot welding machine. Welding was conducted using a 45-deg truncated cone copper electrode with 10-mm face diameter. The weld nugget diameter, force estimation under lap shear test and T – peel test were investigated using digital type tensometer attached with capacitive displacement transducer (Mikrotech, Bangalore, Model: METM2000ER1). The results shows that joining of Al 6063 and AISI 304 thin sheets by RSW method are feasible for automotive structural joints where the loads are below 1000N act on them, it is observed that by increasing the spots per unit length, then the joint with standing strength to oppose failure is also increased linearly incase of interfacial failure mode and non linear for pullout failure mode.

Study on Coating Melting Behavior on Weld Growth Mechanism for Al-Si coated Hot-Stamped Boron Steels in Resistance Spot Welding

The effect of coating melting behavior on nugget growth during resistance spot welding of hotstamped boron steels was evaluated. A comparative analysis of the dynamic resistance for bare hot stamped and Al-Si coated hot stamped boron steels was carried out. The dynamic resistance curve of Al-Si coated hot stamped boron steel was higher than bare hot stamped boron steel during the whole stages of weld time. Higher α-peak and β-peak for Al-Si coated hot stamped boron steel resulted in larger nugget size at higher than 4.0 kA weld current owing to non-linear layer structure of alloyed coating, which appears to restrict the current passage through the faying interface. In the case of Al-Si coated hot-stamped boron steel, most of the Al-Fe intermetallic coatings are expected to be pushed away while in the liquid state at the faying interface. The pressure build up during the early stage of weld pushes the liquid Al-Fe intermetallic coating towards the edge of the faying interface. The continuous liquid state of Al-Fe intermetallic through the faying interface ensures the large contact area for the current passage to enlarge the nugget diameter. †(Received June 1, 2014)

Ultrasonic test of resistance spot welds based on wavelet package analysis

In this paper, ultrasonic test of spot welds for stainless steel sheets has been studied. It is indicated that traditional ultrasonic signal analysis in either time domain or frequency domain remains inadequate to evaluate the nugget diameter of spot welds. However, the method based on wavelet package analysis in time–frequency domain can easily distinguish the nugget from the corona bond by extracting high-frequency signals in different positions of spot welds, thereby quantitatively evaluating the nugget diameter. The results of ultrasonic test fit the actual measured value well. Mean value of normal distribution of error statistics is 0.00187, and the standard deviation is 0.1392. Furthermore, the quality of spot welds was evaluated, and it is showed ultrasonic nondestructive test based on wavelet packet analysis can be used to evaluate the quality of spot welds, and it is more reliable than single tensile destructive test.

Resistance Spot Welding between Copper Coated Steel and Aluminum Alloy

Aluminum alloy A6061 and copper coated steel was welded by resistance spot welding with. The mechanical properties of the joint were investigated; the effects of welding parameters on nugget diameter and tensile shear load of the joints were discussed. The results show that the joint strength and nugget diameter increases with the increase of welding current and welding time and decreases with the increase of electrode force. As a result, copper plating as the middle layer of resistance spot welding is suitable for welding of aluminum alloy/steel.

Resistance Spot Welding between Mild Steel and Stainless Steel

Mild steel Q235 and stainless steel SUS304 were welded using resistance spot welding with an interlayer of Ni. The mechanical properties of the joint were examined, the effects of welding parameters on the nugget size and tensile shear strength were investigated. Both the tensile shear strength and nugget diameter increased with the increasing of welding current and welding time, whereas they decreased with the increasing of electrode pressure. The results indicate that the tensile shear strength of joint welded by resistance spot welding with a Ni interplayer is higher in comparison with that obtained by conventional resistance spot weling.

Properties of Resistance Spot Welded Joint between Mild Steel and Aluminum Alloy with an Interlayer of AlCu28

Aluminum alloy A6061 and mild steel Q235 was welded using resistance spot welding with an interlayer of AlCu28. The mechanical properties of the joint were investigated; the effects of various welding parameters on nugget diameter and tensile shear load of the joints were systematically discussed. The results reveal that it is effective to weld aluminum alloy and mild steel using resistance spot welding with an interlayer of AlCu28.

Study on effect of electrode force on resistance spot welding process

This paper deals with the effect of electrode force on resistance spot welding process. As one of the most important parameters during the process, the electrode force can influence the process in different aspects. Dynamic resistance, which can reflect the internal physical variation of the workpiece, is employed to monitor the characteristic variation of the workpieces. According to theoretical analysis, large electrode force may easily induce surface expulsion. Also, it can decrease the overall dynamic resistance values and postpone the time when first melting point appears, as well as enlarge the duration between times when first melting point and peak value appear. Larger electrode force induces the initial smaller nugget diameter, and then the nugget diameter has a higher growth speed. However, the overall nugget diameter may be smaller and its growth terminates earlier than when smaller electrode force is applied. Final experiments validated all the theoretical analysis.

Electrode life in resistance spot welding of zinc–plated steel sheets

Spot weld electrode life was investigated for various types of 0.8mm thick zinc plated steel sheets which are now widley used in automotive industry. The results were discussed from the point of view of chemical compositions of the plated layer in order to find the desirable zinc plated steel sheet which ensures long electrode life. Electrode life was defined as the number of welds until nugget diameter decreased to 4.5mm in continuous spot welding with 6mm∅ dome type Cu–1%Cr electrode at each fixed welding condition. As a result, the plated sheet steel with nickel in plated layer showed a relativly long life. This efficent effect of nickel was confirmed by an additional spot welding test and investigation of zinc diffusion in the electrode.

Microstructures and properties of friction stir spot welded DP590 dual phase steel sheets

DP590 steel sheets were joined by friction stir spot welding using polycrystalline cubic boron nitride tool with an objective to produce bond diameters similar to conventional spot welding nuggets. A range of spindle rotation (400–2400 rev min−1) and plunge speeds (0·03–3·8 mm s−1) were exercised to attain defect free welds in 1·6 mm thick sheets. A bond diameter of 4t1/2, alike minimum nugget diameter criteria for resistance spot welds, resulted in superior mechanical properties than conventional spot welds. The heat inputs corresponding to different welding parameters influenced the weld microstructure, including grain size, phases and their morphology. The bond diameter was higher for higher heat inputs. However, low heat input welds with weld time cycles ∼4 s produced more refined microstructure and exhibited similar strengths even with reduced bond size. Plug type failure was associated with larger bond diameters (∼7·1 mm), while interfacial failure was observed with smaller welds (∼5·4 mm).

Effect of Welding Current and Time on the Microstructure, Mechanical Characterizations, and Fracture Studies of Resistance Spot Welding Joints of AISI 316L Austenitic Stainless Steel

This article aims at investigating the effect of welding parameters, namely, welding current and welding time, on resistance spot welding (RSW) of the AISI 316L austenitic stainless steel sheets. The influence of welding current and welding time on the weld properties including the weld nugget diameter or fusion zone, tensile-shear load-bearing capacity of welded materials, failure modes, energy absorption, and microstructure of welded nuggets was precisely considered. Microstructural studies and mechanical properties showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Electron microscopic studies indicated different types of delta ferrite in welded nuggets including skeletal, acicular, and lathy delta ferrite morphologies as a result of nonequilibrium phases, which can be attributed to a fast cooling rate in the RSW process. These morphologies were explained based on Shaeffler, WRC-1992, and pseudo-binary phase diagrams. The optimum microstructure and mechanical properties were achieved with 8-kA welding current and 4-cycle welding time in which maximum tensile-shear load-bearing capacity or peak load of the welded materials was obtained at 8070 N, and the failure mode took place as button pullout with tearing from the base metal. Finally, fracture surface studies indicated that elongated dimples appeared on the surface as a result of ductile fracture in the sample welded in the optimum welding condition.

Resistance spot welding macro characteristics of the dissimilar thickness dual phase steels

In the present work, macro characteristics of the dissimilar thickness dual phase steel resistance spot welding joints were described in terms of melting rate, indentation rate, nugget diameter and indentation diameter. The results revealed that the melting rate of the DP600 side was higher than that of the DP780 side and the indentation rate of the DP600 side was lower than that of the DP780 side of the welded joints. The base metal lap order had the important effect on nugget diameter, and the DP780/DP600 spot welded joints tended to get the larger nugget diameter than DP600/DP780 spot welded joints with the same process parameters. The indentation diameters of DP600 and DP780 sides depended on the electrode geometry and force.

On the development of nugget growth model for resistance spot welding

In this paper, we developed a general mathematical model to estimate the nugget growth process based on the heat energy delivered into the welds by the resistance spot welding. According to the principles of thermodynamics and heat transfer, and the effect of electrode force during the welding process, the shape of the nugget can be estimated. Then, a mathematical model between heat energy absorbed and nugget diameter can be obtained theoretically. It is shown in this paper that the nugget diameter can be precisely described by piecewise fractal polynomial functions. Experiments were conducted with different welding operation conditions, such as welding currents, workpiece thickness, and widths, to validate the model and the theoretical analysis. All the experiments confirmed that the proposed model can predict the nugget diameters with high accuracy based on the input heat energy to the welds.

Heat-affected zone liquation crack on resistance spot welded TWIP steels

In this study, the heat affected zone (HAZ) liquation crack and segregation behavior of the resistance spot welded twinning induced plasticity (TWIP) steel have been reported. Cracks appeared in the post-welded joints that originated at the partially melted zone (PMZ) and propagated from the PMZ through the heat affected zone (HAZ) to the base metal (BM). The crack length and crack opening widths were observed increasing with heat input; and the welding current was identified to be the most influencing parameter for crack formation. Cracks appeared at the PMZ when nugget diameter reached at 4.50mm or above; and the liquation cracks were found to occur along two sides of the notch tip in the sheet direction rather than in the electrode direction. Cracks were backfilled with the liquid films which has lamellar structure and supposed to be the eutectic constituent. Co-segregation of alloy elements such as, C and Mn were detected on the liquid films by electron-probe microanalysis (EPMA) line scanning and element map which suggests that the liquid film was enrich of Mn and C. The eutectic constituent was identified by analyzing the calculated phase diagram along with thermal temperature history of finite element simulation. Preliminary experimental results showed that cracks have less/no significant effect on the static cross-tensile strength (CTS) and the tensile-shear strength (TSS). In addition, possible ways to avoid cracking were discussed.

Statistical modeling and optimization of resistance spot welding process parameters using neural networks and multi-objective genetic algorithm

Resistance spot welding (RSW) is a highly used joining procedure in automotive industry. In RSW, after a number of welds the welding electrode starts to wear and its diameter changes. This causes the weld nugget diameter abnormal variations and consequently reduces the weld strength. Therefore the tip of the electrode should be dressed in RSW. Selecting the optimum time for the welding electrode tip dressing operations is very important. In this research three welding parameters including the welding time, the welding current, and the welding pressure were identified as the main effective parameters on the weld nugget dimensions including the weld nugget diameter and height using full factorial design of experiments. Then using hybrid combination of the artificial neural networks and multi-objective genetic algorithm, the optimized values of the aforementioned parameters were specified. Finally experiments were fulfilled to estimate the admissible number of the weld spots which should be done before the electrode tip dressing operation.

Automatic Inspection of Spot Welds by Thermography

The interest for thermography as a method for spot weld inspection has increased during the last years since it is a full-field method suitable for automatic inspection. Thermography systems can be developed in different ways, with different physical setups, excitation sources, and image analysis algorithms. In this paper we suggest a single-sided setup of a thermography system using a flash lamp as excitation source. The analysis algorithm aims to find the spatial region in the acquired images corresponding to the successfully welded area, i.e., the nugget size. Experiments show that the system is able to detect spot welds, measure the nugget diameter, and based on the information also separate a spot weld from a stick weld. The system is capable to inspect more than four spot welds per minute, and has potential for an automatic non-destructive system for spot weld inspection. The development opportunities are significant, since the algorithm used in the initial analysis is rather simplified. Moreover, further evaluation of alternative excitation sources can potentially improve the performance.

Process Parameter Selection for Resistance Spot Welding through Thermal Analysis of 2 mm CRCA Sheets

An attempt is made to arrive at suitable process parameters for resistance spot welding through thermal analysis. 2mm Closed Rolled Closed Anealing (CRCA) sheet metal is selected as work piece. Nugget and electrode diameter are evaluated from emperical relations. Full factorial Design Of Experiment (DOE) is applied for weld current and time. Thermal analysis is carried out for selected DOE values using SYSweld. Temperature distribution, nugget and Heat Affected Zone dimensions are obtained from the analysis. Weld strenght is analysed through experimental trails. Optimum process parameter for spot welding of 2mm CRCA sheet is arrived by comparing simulation and experimental results.

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.

Interfacial microstructure and mechanical property of resistance spot welded joint of high strength steel and aluminium alloy with 4047 AlSi12 interlayer

Dissimilar materials of H220YD galvanised high strength steel and 6008-T66 aluminium alloy were welded by means of median frequency direct current resistance spot welding with employment of 4047 AlSi12 interlayer. Effects of interlayer thickness on microstructure and mechanical property of the welded joints were studied. The welded joint with interlayer employed could be recognised as a brazed joint. The nugget diameter had a decreased tendency with increasing thickness of interlayer under optimised welding parameters. An intermetallic compound layer composed of Fe2(Al,Si)5 and Fe4(Al,Si)13 was formed at the interfacial zone in the welded joint, the thickness and morphology of which varying with the increase of interlayer thickness. Reaction diffusion at the steel/aluminium interface was inhibited by introduction of silicon atoms, which restricted growth of Fe2(Al,Si)5. Tensile shear load of welded joints experienced an increased tendency with increasing interlayer thickness from 100 to 300μm, and the maximum tensile shear load of 6.2kN was obtained with interlayer thickness of 300μm, the fractured welded joint of which exhibiting a nugget pullout failure mode.

Effect of welding parameters on the mechanical properties of AA2024 aluminium alloy joints welded by resistance seam welding

In this study, sheets of aluminium alloy 2024-T6 of 1⋅6 mm thickness were welded using the technique of resistance seam welding (RSEW) with different welding parameters. The peak load, energy absorption and failure mode obtained from tensile shear tests were used to describe the mechanical performance of seam welds. The results revealed that the increase in welding current and time and the decrease in electrode force increased tensile shear strength. The interfacial to pullout transition for the AA2024 seam welds occurred at a critical weld nugget (WN) diameter of 3⋅77 mm. In addition, a hardness evaluation was carried out in order to determine the effect of welding parameters on the welded joints and it was found that the developed heat affected the joint hardness.Dans cette étude, on a soudé des feuilles d’alliage d’aluminium 2024-T6 de 1·6 mm d’épaisseur en utilisant la technique de soudage par résistance en ligne continue avec différents paramètres de soudage. On a utilisé la charge maximale, l’absorption d’énergie et le mode de défaillance obtenus à partir des essais de traction en cisaillement pour décrire le rendement mécanique des soudures en ligne continue. Les résultats ont révélé que l’augmentation du courant de soudage et de la durée ainsi que la diminution de la force de l’électrode augmentaient la résistance au cisaillement par traction. La transition de l’interface à l’arrachement des soudures en ligne continue de l’AA2024 se produisait à un diamètre critique du noyau de soudure de 3·77 mm. De plus, on a évalué la dureté afin de déterminer l’effet des paramètres de soudage sur les joints soudés. On a trouvé que la chaleur développée affectait la dureté du joint.