Showing papers on "Spot welding published in 2018"
TL;DR: In this paper, the authors present a state-of-the-art review on the surface cracking properties of Zn-coated high strength steels and present a method to prevent surface cracking.
Abstract: Liquid Zn-assisted embrittlement during resistance spot welding of Zn-coated high strength steels induces risks of surface cracking. This paper presents a state-of-the-art review on the surface cra...
85 citations
TL;DR: In this paper, the effect of ultrasonic spot welded hybrid joints, made of AA5754 aluminum and carbon fiber reinforced epoxy with a co-cured thermoplastic surface layer, was investigated.
Abstract: The mechanical and electrochemical behavior of ultrasonic spot welded hybrid joints, made of AA5754 aluminum and carbon fiber reinforced epoxy with a co-cured thermoplastic surface layer, was studied. The effect of the welding parameters (energy and force) and the thickness of a thermoplastic film, applied as an upper ply in the composite lay-up, on the development of adhesion strength, was investigated. The best mechanical results were obtained when the welding parameters were able to achieve a large bonding area of mechanical interlocking between naked carbon fibers and aluminum and a better load distribution. The electrochemical results excluded the possibility of galvanic corrosion between aluminum and composite adherends thanks to the insulating action provided by the thermoplastic film.
80 citations
30 May 2018-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of parameters such as current density, welding time, electrodes force and holding time after welding on tensile shear strength of dissimilar joint were analyzed.
Abstract: Effect of parameters such as current density, welding time, electrodes force and holding time after welding on tensile-shear strength of dissimilar joint were analyzed. Taguchi method was used to design the experiments and Minitab software was used to analyze the effect of parameters and obtain an optimum condition. The microstructure of the optimum condition was analyzed by Scanning Electron Microscope (SEM). The strength of the join was analyzed by tensile-shear test. Fracture mode was assessed by optical microscope. Results showed that current density, holding time after welding, welding time and electrodes force were the most effective parameters hierarchically. Optimum current density of 8 Kamp, holding time after welding of 40 cycle, 16 cycle welding time and 5 kN electrode force were defined as the optimum parameters to join the sheets. Weld nugget (WN) had a martensitic structure containing a relatively high strength and hardness. Its fracture mode was pullout failure.
74 citations
TL;DR: In this article, the static and fatigue strengths of self-piercing riveting are considerably higher than those of resistance spot welding, and the fatigue strength of mechanical clinching is similar to that of resistence spot welding.
73 citations
TL;DR: In this article, an anodized Al alloy 1050 was also welded to Cu and a recrystallized microstructure with shear texture was formed in the Al matrix.
70 citations
TL;DR: In this article, the current state of joining aluminum alloy by ultrasonic spot welding is summarized with numerous critical issues, such as general process parameters, materials flow, interfacial temperature and interfacial shear force, stress distribution, relative motion, strengthening mechanism, macrostructure, microstructure and mechanical properties.
60 citations
TL;DR: In this article, the authors investigated the LME sensitivity of Zn-coated 22MnB5 press-hardening steel as a function of stress intensity and heat input during laser beam welding.
59 citations
TL;DR: In this article, a third generation Al-Li alloy has been successfully spot welded with probeless friction stir spot welding (P-FSSW), which is a variant of conventional friction stir welding.
56 citations
TL;DR: In this article, a probeless friction stir spot welding (P-FSSW) was used to weld a third generation Al-Li alloy to obtain a symmetric basin shape.
54 citations
TL;DR: In this paper, a 3D fully coupled electro-thermo-mechanical model incorporating an improved electrical contact resistance formula from the literature is developed for resistance spot welding of aluminium-silicon coated hot-stamped boron steel.
49 citations
TL;DR: In this paper, three types of tools with different pin profiles were designed to join aluminum and copper by friction stir spot welding, and they were used to characterize macrostructure and microstructure in welded joints.
TL;DR: In this paper, a carbon fiber-reinforced polyetherimide (PEI) laminate was joined via friction spot welding (FSpW), and the fracture surface morphologies revealed a typical ductile fracture containing the deformation of polymer and the pullout of the carbon fiber.
TL;DR: In this article, a scheme for online quality monitoring of resistance spot welding (RSW) process is proposed to effectively determine the rate of spot weld quality, where a random forest (RF) classification featuring with dynamic resistance (DR) signals which were collected and processed in the production environment was carried out.
Abstract: A scheme for online quality monitoring of resistance spot welding (RSW) process is proposed to effectively determine the rate of spot weld quality. In this work, the random forest (RF) classification featuring with dynamic resistance (DR) signals which were collected and processed in the production environment was carried out. The obtained results demonstrated that the constructed RF model based on DR profile features adequately distinguished high-quality welds from the other unacceptable welds such as inadequate sized welds and expulsions. Variable importance evaluation of RF was implemented against the input features. It showed that two DR slopes for nugget nucleation and growth (v
2
, v
3
) and dynamic resistance (R
γ
) in the final half cycle play the most significant roles in achieving more accurate results of classification, while absolute gradient ∇
max
is useful in detecting minor expulsion from pull-out failure. In addition, shunting effect in consecutive welds was tentatively investigated via the DR curves, accounting for noticeable declines in the stage I of DR. The results revealed that shunted welds beyond minimum weld spacing do not significantly undermine the accuracy of classification. The implementation of RF based on the combination of welding parameters and DR features improves the accuracy of classification (98.8%) with ntree = 1000 and mtry = 4, as weld current significantly distinguished situations where DR features solely achieve accuracy (93.6%). The incorporation of the RF technique into online monitoring system attains a satisfying RSW quality classification accuracy and reduces the workload on destructive tests.
TL;DR: The average absorptances determined optically are compared with calorimetrically determined values, and it is found that the calorimeter severely underestimates the absorbed energy due to mass lost during the spot weld.
Abstract: High-irradiance lasers incident on metal surfaces create a complex, dynamic process through which the metal can rapidly change from highly reflective to strongly absorbing. Absolute knowledge of this process underpins important industrial laser processes such as laser welding, cutting, and metal additive manufacturing. Determining the time-dependent absorptance of the laser light by a material is important, not only for gaining a fundamental understanding of the light-matter interaction but also for improving process design in manufacturing. Measurements of the dynamic optical absorptance are notoriously difficult due to the rapidly changing nature of the absorbing medium. These data are also of vital importance to process modelers, whose complex simulations need reliable, accurate input data; yet, there are very few available. In this work, we measure the time-dependent, reflected light during a 10-ms laser spot weld using an integrating-sphere apparatus. From this, we calculate the dynamic absorptance for 1070-nm-wavelength light incident on 316L stainless steel. The time resolution of our experiment (less than 1 μs) allows the determination of the precise conditions under which several important physical phenomena occur, such as melt and keyhole formation. The average absorptances determined optically are compared with calorimetrically determined values, and it is found that the calorimeter severely underestimates the absorbed energy due to mass lost during the spot weld. Weld-nugget cross sections are also presented to verify our interpretation of the optical results, as well as to provide experimental data for weld-model validation.
TL;DR: Al6022-T4/Al7075-T6 welds were fabricated by refilling friction stir spot welding using different tool designs with identical welding parameters as mentioned in this paper, and cracks and voids were formed in the welds manufactured using a standard tool.
TL;DR: In this paper, the authors studied the weld discontinuities and defects that are likely to occur in resistance spot welding of 1-GPa transformation-induced plasticity steel and found that the rich chemistry and complex thermomechanical processing and thus special thermophysical properties of the alloy have significant impacts on the susceptibility of the welds to defects.
Abstract: To obtain reliable resistance spot welds that guarantees their satisfactory mechanical performance and improved crashworthiness in the vehicle autobody, it is vital to study the causes, conditions, and welding parameters resulting in the formation of defects and discontinuities in the welds This work studies the weld discontinuities and defects that are likely to occur in resistance spot welding of 1-GPa transformation-induced plasticity steel The causes of the formation of weld discontinuities and defects are discussed here It is found that the rich chemistry and complex thermomechanical processing and thus special thermophysical properties of the alloy have significant impacts on the susceptibility of the welds to defects The amount of heat input induced by the welding process also plays an important role on the defect formation From the ductility ratio results, it can be said that there are critical heat input and critical nugget size for occurrence of the weld discontinuities and defects The susceptibility of the resistance spot welds of the experimental alloy to early expulsion, liquation cracking, surface breaking cracks and their consequences on weld quality and performance are discussed here
TL;DR: In this paper, a probeless friction stir spot welding (P-FSSW) was used to produce AA2198 joints using the Coupled Eulerian-Lagrangian technique.
TL;DR: In this paper, regression model, artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) are developed for predicting and simulating the joint strength for the USMW of Al-Cu sheets.
TL;DR: In this article, the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds was addressed.
Abstract: Transformation-induced plasticity (TRIP) steel resistance spot welds are delicate to low-energy interfacial failure via crack propagation through martensitic fusion zone during cross-tension (CT) loading. This paper addresses the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds. Depending on the post weld second pulse current level, three different strengthening mechanisms were found including (i) martensite tempering with reduced hardness, (ii) refining of martensite packets with improved toughness and (iii) nugget re-melting/enlargement combined with possible reduction of grain boundary impurity segregation. All designed in situ PWHTs were enabled to promote pullout failure mode with improved load-bearing capacity and energy absorption capability during CT loading.
TL;DR: In this paper, the authors observed that the amount of iron phase decreased as the IMC thickness grew, and the load bearing capacity of Al/steel interface increased, and that the key point for improving mechanical performance under coach peel loading was to increase the first peak point by reducing Al thinning, increasing the Al nugget size, and limiting the IR layer growth.
TL;DR: In this article, displacement-controlled welding was shown to provide consistent quality welds with a constant set of welding parameters and it was hence identified as the most promising welding strategy for sequential ultrasonic welding of thermoplastic composites.
Abstract: The research in this paper is an essential part of a bigger effort on developing robust sequential ultrasonic welding of multi-spot welded joints in thermoplastic composites. It mainly focused on assessing the impact of the changes in boundary conditions on the welding process and whether it could be circumvented by using an appropriate process control strategy. A two-step approach was followed by investigating: (1) the effect of boundary conditions on displacement- and energy-controlled single-spot welded joints and (2) displacement- and energy-controlled sequential ultrasonic welding of double-spot welded joints. The results showed that previous spots indeed affect the energy required to obtain an optimum new welded spot, which challenges the use of energy-controlled welding for this application. Contrarily, displacement-controlled welding was shown to provide consistent-quality welds with a constant set of welding parameters and it was hence identified as the most promising welding strategy for sequential ultrasonic welding of thermoplastic composites.
TL;DR: In this paper, a single-lap RFSSW joints were made in 0.8- and 1.6-mm-thick sheets, which correspond to the actual thicknesses of welded stringer of aircraft skin.
11 Jan 2018
TL;DR: In this article, a cold-rolled 0.1C5Mn steel with a ferrite matrix plus metastable austenite duplex microstructure was resistance spot-welded with various welding currents and times.
Abstract: The medium Mn steels are gaining increasing attention due to their excellent combination of mechanical properties and material cost. A cold-rolled 0.1C5Mn medium Mn steel with a ferrite matrix plus metastable austenite duplex microstructure was resistance spot-welded with various welding currents and times. The nugget size rose with the increase of heat input, but when the welding current exceeded the critical value, the tensile-shear load increased slowly and became unstable due to metal expulsion. The fusion zone exhibited a lath martensite microstructure, and the heat-affected zone was composed of a ferrite/martensite matrix with retained austenite. The volume fraction of retained austenite decreased gradually from the base metal to the fusion zone, while the microhardness presented a reverse varying trend. Interfacial failure occurred along the interface of the steel sheets with lower loading capacity. Sufficient heat input along with serious expulsion brought about high stress concentration around the weld nugget, and the joint failed in partial interfacial mode. Pull-out failure was absent in this study.
TL;DR: In this article, the authors investigated the underlying factors of the tensile shear strength of automotive steels' resistance spot welds during interfacial failure and found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacer failure mechanism.
Abstract: The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed light on the design of proper post-weld heat treatment for improving the weld mechanical performance.
TL;DR: In this paper, the welding parameters were optimized based on the clamping ring temperature and weld strength, and 85.7% of welds achieved a strength which exceeds the American Welding Society requirement when the clamping ring temperature ranges from 230 to 265°C.
Abstract: Al/steel welds were successfully fabricated by refill friction stir spot welding. The welding parameters were optimised based on the clamping ring temperature and weld strength. 85.7% of welds achieve a strength which exceeds the American Welding Society requirement when the clamping ring temperature ranges from 230 to 265°C. Cracks are formed under the pin and sleeve in the Al substrate at the Al/steel interface, which are associated with the tool sleeve plunging period and attributed to the α-Al + Al–Zn eutectic structure. The interdiffusion between Al and Zn at the steel surface produced an Al–Zn eutectic structure layer at the Al/steel interface, while part of the zinc coating materials is squeezed out of the sleeve periphery, leading to a brazing effect which contributes to weld strength. Nanoscale discontinuous Fe4Al13 and FeAl intermetallics form as a layer localised at the Al–Zn layer/steel substrate interface.
TL;DR: In this article, the weld interface is modeled as rough metallic surfaces in sliding contact, and a junction growth model is used to identify parameter sets for ultrasonic spot welding and ultrasonic additive manufacturing that maximize the weld strength while simultaneously minimizing the thermal excursion at the weld interfaces.
TL;DR: Shunting effect of resistance spot welding is evaluated based on the electrode displacement signals in this article, which showed that the weld spacing and nugget diameter were polynomial-correlated, and the minimum welding spacing of 20 mm can be derived from the results.
TL;DR: Refill friction stir spot welding involves a 3-piece tool consisting of a clamping ring, with rotating inner sleeve and pin components made of tool steel to join thin sheets as discussed by the authors, and during the welding process, the tool and pin component rotate to generate frictional heat, and weld two overlapping Al-alloy sheets.
TL;DR: In this article, the effect of single and double pulse welding on the mechanical behavior of resistance spot-welded DP1000-GI steel is investigated, and the results show that double-pulse welding is more effective than single pulse welding.
Abstract: In the present study, the effect of resistance spot welding scheme (i.e. single and double pulse welding) on the mechanical behaviour of resistance spot-welded DP1000-GI steel is investigated. It i...
TL;DR: In this paper, 1.5mm thick 6061-T6 aluminum alloy plates were subjected to friction stir spot welding (FSSW) at a very low rotation speed of 30, 40 and 50 rpm, aiming to prevent the hardness reduction in the heat affected zone (HAZ) of this precipitate hardening Al joints.