Spot-welded Joints Research Articles

Comparison of Properties on Withdrawing and Refill Friction Stir Spot Welding Joints

The 2 mm sheet of 6082 - T6 aluminum alloy was carried to develop refill friction stir welding and withdrawing friction stir spot welding,the forming of solder joints , the cross-sectional microstructure and fracture morphology of welding joints were observed and analyzed, the cross-sectional microhardness of welding joints were tested. Tensile shear load and fracture mode were contrasted simultaneously. The results showed that smooth surface and free of macroscopic defects of welding joints could be obtained in both welding type. Tensile shear load of WFSSW was up to 10.28kN under the optimal process parameters greater than RFSSW’s 8.62kN.

The optimisation of process parameters for friction stir spot-welded AA3003-H12 aluminium alloy using a Taguchi orthogonal array

The aim of the present work is to optimise the welding parameters for friction stir spot welded non-heat-treatable AA3003-H12 aluminium alloy sheets using a Taguchi orthogonal array. The welding parameters, such as the tool rotational speed, tool plunge depth and dwell time, were determined according to the Taguchi orthogonal table L9 using a randomised approach. The optimum welding parameters for the peak tensile shear load of the joints were predicted, and the individual importance of each parameter on the tensile shear load of the friction stir spot weld was evaluated by examining the signal-to-noise ratio and analysis of variance (ANOVA) results. The optimum levels of the plunge depth, dwell time and tool rotational speed were found to be 4.8mm, 2s and 1500rpm, respectively. The ANOVA results indicated that the tool plunge depth has the higher statistical effect with 69.26% on the tensile shear load, followed by the dwell time and rotational speed. The tensile shear load of the friction stir spot welding (FSSW) joints increased with increasing plunge depth. Additionally, examination of the weld cross-sections, microhardness tests and fracture characterisation of the selected friction spot welded joints were conducted to understand the better performance of the joints. All the fractures of the joints during tensile testing occurred at stir zone (SZ), where the bonded section was minimum. The tensile shear load and tensile deformation of the FSSW joints increased linearly with increasing the bonded size. The finer grain size in the SZ led to the higher hardness, which resulted in higher fracture strength. When the tensile shear load of the joints increased approximately 3-fold, the failure energy absorption of the joints increased approximately 15-fold.

Assessment of resistance spot welding quality based on ultrasonic testing and tree-based techniques

Classification and regression tree (CART) and random forest techniques were proposed as pattern recognition tools for classification of ultrasonic oscillograms of resistance spot welding (RSW) joints. The results showed that CART models produced an acceptable error rate with high interpretability. These features may be used to understand and control the decision processes, instruct other human operators, compare margins of safety or modify them depending on the criticality of the industrial process. Compared with CART trees, random forests reduced the error rate at the cost of decreasing decision interpretability. The use of the agreement of the forest was proposed as a measure to reduce the workload of human operators, who would only have to focus on the analysis of ultrasonic oscillograms that are difficult to interpret.

피로손상의 누적에 따른 강성변화를 고려한 점용접부의 진동피로해석

본 논문의 목적은 진동 피로해석 기법을 적용하여 다수의 용접점을 포함하고 있는 점용접 구조물의 강성변화를 고려하여 피로수명을 평가하는 것이다. 먼저 모재부 인장특성 및 점용접부의 인장 및 피로특성을 획득하였다. 유한요소법을 적용하여 S-N 선도를 획득하여 피로해석에 적용하였다. 주파수 응답해석을 수행하여 구조물의 전달함수를 획득하였고, 주파수영역에서 0.11의 PSD를 선정하여 수행하였다. 강성변화 및 고유진동수의 변화를 알아보기 위하여 점용접부의 총 6개 지점 중 최소수명이 발생하는 지점을 기준으로 1개씩 제거하여 반복 해석을 수행하였다. 따라서 강성이 낮아질수록 고유주파수도 낮아지는 것을 확인하였다. 이러한 조건하에서 진동피로해석을 수행하여 피로손상의 누적에 따른 전달합수의 변화를 고려한 진동피로해석을 수행하였다. The purpose of this paper was to evaluate the fatigue life to apply the vibration fatigue analysis considering the stiffness change of the spot welding due to fatigue damage accumulation. For this, the mechanical and fatigue properties of base and spot welded standard specimens were obtained through the tensile and constant amplitude fatigue test. The transfer function of the spot-welded structure was obtained from the frequency response analysis and fatigue analyisis was performed under the condition of PSD=0.11. A vibration fatigue analysis that considered changes in the frequency response due to the fatigue damage that is, failure of some wleding point was conducted on spot-welded structure. The fatigue life of the spot-welded structure was determined by combining the transfer function, the S-N curve of the tensile-shear spot-welded joint and the input PSD.

Development of a Procedure for the Acoustic-Emission Checking of Resistance Spot Welding

We study the possibility of application of the acoustic-emission method for the monitoring of resistance spot welding. We develop a specialized system for the reception and processing of acoustic emissionsignals and criteria for synthesizing the quality index of a spot-welded joint. For the formation of the quality index of spot-welded joint, it is proposed to use the method of convolution of the template signal and a signal obtained by checking of the current weld spot.

GS06 二段多重変動振幅荷重下のスポット溶接継手の疲労寿命評価

In this paper, the possibility of fatigue life prediction of spot-welded joint under two steps variable amplitude load was investigated. The constant amplitude load fatigue tests for the spot-welded tensile shear specimen and peeling specimen were carried out and the results were arranged by using the nominal structural stress. As a result of prediction using Miner's rule, the fatigue life of spot-welded joint under two steps variable amplitude load could be estimated by the nominal structural stress considering average load and fatigue crack closure. Further, it was suggested to be able to estimate the fatigue life without depending on the joint form. Therefore, the nominal structural stress parameter showed the possibility of evaluating the fatigue life of spot-welded joint under actual variable load.

Ultrasonic Spot Welding of Aluminum to High-Strength Low-Alloy Steel: Microstructure, Tensile and Fatigue Properties

The structural applications of lightweight aluminum alloys inevitably involve dissimilar welding with steels and the related durability issues. This study was aimed at evaluating the microstructural change, lap shear tensile load, and fatigue resistance of dissimilar ultrasonic spot-welded joints of aluminum-to-galvanized high-strength low-alloy (HSLA) steel. Two non-uniform layers were identified in between Al and HSLA steel via SEM/EDS and XRD. One was an Al-Zn eutectic layer and the other was a thin (<2 μm) layer of intermetallic compound (IMC) of Al and Fe in the nugget zone. The lap shear tensile testing gave a maximum load of 3.7 kN and the sample failed initially in between the Al-Zn eutectic film and Al-Fe IMC, and afterward from the region containing Al on both matching fracture surfaces. The fatigue test results showed a fatigue limit of about 0.5 kN (at 1 × 107 cycles). The maximum cyclic stress at which transition of the fatigue fracture from transverse through-thickness crack growth mode to the interfacial failure mode occurs increases with increasing energy input.

Tensile strength and failure simulation of simplified spot weld models

A simple model for spot weld joints is desirable in body-in-white automotive structures which contains thousands of them. Hence, comparative performance and failure prediction study of six simplified spot weld models in terms of their geometric and constitutive properties are presented in this paper. The stiffness characteristics of these models under tensile loading condition were compared with the experimental results. It was found that the current spot weld modelling practice in the automotive industry predict the strength with 45.33% of error. To simulate the joint failure a material damage criterion correlating ultimate tensile strength of material was implemented in the developed models. The comparative study with respect to the accuracy was also related with the computational cost incurred by the different models. Hence, suitable modelling conditions to design a finite element model for spot welded joints are established which is very simple to develop, relatively cheap in terms of computational costs but yet predicts reasonably accurate results.

Stored Energy Welding Technology of Ultra-Thin Sheet Stainless Steel

Considering the characteristics of the multilayered ultra-thin sheet stainless steel, by chosen the proper equipments and stored energy welding technology, the optimizing welding parameters are got from the condenser discharge spot welding experiments. The energy stored in the capacitor group is controlled by the energy required during welding and the discharge current is controlled by the size of dynamic resistance in resistance spot welding. So those control ways can better solve the hard problem of choosing welding parameter. The joint strength of ultra-thin sheet stainless steel is ensured by the reasonable quality assessment methods. The processed spot-welded joints are of good quality and appearance.

Experiment Research on Tensile-Shear Behavior of Spot-Welded Lap Joints of Ultra-High Strength Steel with Common Steel

The welding spot of Ultra-high strength steel of 22MnB5 and common steel of St16 were the investigative objects, the intermediate frequency inverter &amp; electric servo welding system was used to weld the sheets. Electrical measuring test method was used on spot-welded joint under tensile-shear load to determinate the strain of different positions, including the strain of weld nugget, the stain around the nugget and the base metals strain near the weld nugget. The deformation regularity of spot welding joints surrounding and base metal were analysed according to the data. The test provided a reference for the numerical simulation of spot welding model. Test results show that the strain distribution on spot welding joint is not uniform, the strain of the weld nugget center is relatively small, large deformation exists mainly in the heat affected zone. That is to say, the area near the spot-welding joint heat affected zone is prone to yield. The base metal area near the weld nugget is mainly affected by tensile strain, and the strain increases with the increasing of the load. The force condition of the specimen is complicated around the nugget, the relationship between the load and the strain is erratic. The strain of the weld nugget will gradually change from axial compressive strain to axial tensile strain. The strain of spot welding specimen made of dissimilar materials (22MnB5&amp; ST16) is negative, and almost linearly.

A Nondestructive Evaluation Method: Measuring the Fixed Strength of Spot-Welded Joint Points by Surface Electrical Resistivity.

Destructive tests are generally applied to evaluate the fixed strength of spot-welding nuggets of zinc-plated steel (which is a widely used primary structural material for automobiles). These destructive tests, however, are expensive and time-consuming. This paper proposes a nondestructive method for evaluating the fixed strength of the welded joints using surface electrical resistance. A direct current nugget-tester and probes have been developed by the authors for this purpose. The proposed nondestructive method uses the relative decrease in surface electrical resistance, α. The proposed method also considers the effect of the corona bond. The nugget diameter is estimated by two factors: RQuota, which is calculated from variation of resistance, and a constant that represents the area of the corona bond. Since the maximum tensile strength is correlated with the nugget diameter, it can be inferred from the estimated nugget diameter. When appropriate measuring conditions for the surface electrical resistance are chosen, the proposed method can effectively evaluate the fixed strength of the spot-welded joints even if the steel sheet is zinc-plated.

Ultrasonic Nondestructive Testing on False Welding Joint of Spot Welding for 00Cr18Ni10N Stainless Steel

00Cr18Ni10N stainless steel spot-welded joints were inspected by ultrasound in transmission mode under the water. By comparing and studying ultrasonic transmission wave signals of the spot welded joint of existing nugget and the false welded joint which were received by digital oscilloscope, we find that there are differences in degree of attenuation between multi transmitted wave and primary transmitted wave of two kinds of joints. The degree of attenuation of multi transmitted wave of false welded joint is obviously less than that of the joint with nugget. Therefore, false welded joint can be judged and identified through the degree of attenuation of multi transmitted wave relative to primary transmitted wave, and the dissection results verify the feasibility of this test method.

Fatigue Strength under Optimal Conditions of Spot Weldment Using GA and FEM

High tensile strength steel (HS40R) and galvanized steel (EZNCEN) are extensively used as components of vehicle bodies because they satisfy environmental standards and improve fuel economy. Because vehicle body sheets are becoming thinner and stronger, it is difficult to satisfy the design standards of spot welding joints. This research presents the optimization of the welding condition for various welding variables of a spot welding specimen by genetic algorithm (GA). When the welding condition optimization of spot weldment is performed using finite element method. The fatigue strength prediction method using FEM is useful for the prior evaluation technique that can predict the fatigue strength of spot weldment.

GS28 スポット溶接継手の疲労寿命に及ぼすナゲット径と打点位置変動の影響

In this paper, the influence of variation of nugget diameter and spot welding location on fatigue life of the spot-welded joints was investigated. The relationship between nominal structural stress, which is used as fatigue life estimation parameter, and influence factors of fatigue life on single spot-welded joints under eccentric tensile shear and triple spot-welded joints under peel load was quantitatively clarified, and fatigue tests of these specimens were conducted. Following the increase of the distance of eccentricity of spot welding location from the center line of tensile shear specimen, the influence factors of fatigue life became highly sensitive. The sensitivity of peel specimen was larger than one of tensile shear specimen.

GS26 二段多重変動振幅荷重下のスポット溶接継手の疲労寿命評価

In this paper, the possibility of fatigue life prediction of spot-welded joint under two steps variable amplitude load was investigated. The constant amplitude fatigue tests for the spot-welded tensile shear specimen were carried out and the results were arranged by using the nominal structural stress. As a result of prediction using Miner's rule, the fatigue life of spot-welded joint under two steps variable amplitude load could be estimated by Miner's rule considering fatigue crack closure. Therefore, the nominal structural stress parameter showed the possibility of evaluating the fatigue life of spot welded joint under actual variable load.

Structural performance of adhesive and weld-bonded joints in AHSS

A study was performed to compare the properties of weld-bonded joints in several zinc-coated high-strength (H260LAD GI) and advanced high-strength steels (DP600 GI and DP800 GI) with spot-welded and adhesive bonded joints. Both the microstructure of the spot-welds and the mechanical properties of the joints were evaluated. Joints were tested under varied static loading conditions and, to a more limited extent, under crash and fatigue loading conditions. The results indicate that weld-bonding of zinc-coated steel does not result in any significant absorption of detrimental components from the adhesive into the weld zone. In addition, a greater joint failure strength for all static mechanical loading types was achieved with weld-bonding across the range of AHSS materials tested. Weld-bonding also increases the fatigue and crash performance compared with conventional spot-welded joints.

Formation of Micro Spot-Welding Joint of Rapidly Solidified Ni-19.8%Sn Alloy Foils

In this study, the spot welding of rapidly solidified Ni-19.8%Sn alloy foils has been conducted by a micro-type capacitor discharge welder. The configuration and microstructural morphology of the joint were examined experimentally and he temperature of the micro nugget was analyzed numerically. The results show that the micro-joint consists of an oblate spheroid nugget and a 2.0~3.0 m thick bond zone. The microstructure of the joint is fine and homogeneous and there is no coarsening sign in the parent materials near nugget. During solidification, the cooling rate of nugget is so high to the order of 106K/s that the eutectic reaction of L  α-Ni + Ni3Sn was suppressed or at least partly suppressed and almost all of the liquid within the joint solidified into supersaturated α-Ni. Therefore, the joint microstructure which is consistent with the microstructure of the alloy foils shows the characteristics of rapid solidification. In addition，a kind of streamline due to vortex flow in micro nugget, with dispersed dross distributes in cluster along the streamline, is formed under electromagnetic force and electrode pressure.

Vibration fatigue analysis for multi-point spot-welded joints based on frequency response changes due to fatigue damage accumulation

This study conducted a vibration fatigue analysis that considered changes in frequency response resulting from the cumulative fatigue damage to multi-point spot-welded joints in an automotive body. The S–N curve was obtained using a fatigue test for tensile-shear spot-welded (single-point) joint under constant amplitude load and a finite element analysis based on the Rupp/LBF model. In addition, a vibration fatigue analysis that considered changes in the frequency response due to the fatigue damage was conducted on multi-point spot-welded joints. The fatigue life of the spot-welded joints was computed by combining the transfer function, the S–N curve of the tensile-shear spot-welded joint and the input PSD. Furthermore, a vibration fatigue test using an electronic dynamic shaker was conducted to verify the results of the analysis. The fatigue life by the proposed method was in conformance with the test results.

원격 CO2레이저 용접이음에 대한 피로시험과 해석

A remote laser system can rapidly change both the distance and the direction of the laser beam by moving a lens and rotating mirrors. It is then easy to weld complex patterns of weld lines. A conventional spot weld joint specimen and a remote laser weld joint specimen with complex weld line patterns were prepared and tested both statically and dynamically. The relationships between the fatigue strength, i. e. the maximum cyclic force, and the fatigue life were obtained. The fatigue strength of the tested welded joints at two million cycles was found to be approximately 10% of the static strength. Furthermore, it was observed that the fatigue fracture mode changed with the level of the applied cyclic force. The fatigue crack origins were confirmed as the highest stress points found in the structural analysis. The maximum cyclic stress for different weld patterns converges as the fatigue life approaches two million cycles.

Design of an in situ mechanical test for spot-welded joints

Facing the need of a better understanding of spot-weld strength and failure mechanisms of advanced high strength steels, we have developed a novel test for the in situ failure analysis of spot-welded joints. Providing loading conditions similar to the standard cross tension test, this new test is based upon the use of wedges to peel plates apart in a welded sample that has been cut in half, revealing the weld in the scanning electron microscope. We first perform finite element modeling and show why the wedge test approach is suitable for our purpose. We then perform experimental tests and observe failure in the scanning electron microscope chamber. We are able to both follow crack propagation and control the failure mode. As a corollary, this approach enables the use of local strain mapping, using digital image correlation, to measure local strains in the vicinity of the crack path. The wedge test should be valuable for assessing failure processes in spot-welded joints.