Numerical Simulation of the Parallel Gap Resistance Welding Process of a Solar Cell and Mo/Pt/Ag Interconnector

Energy for space vehicles in low Earth orbit(LEO) is mainly generated by solar arrays, and the service time of the vehicles is controlled by the lifetime of these arrays, which depends mainly on the lifetime of the interconnects. To increase the service life of LEO satellites, molybdenum/platinum/silver(Mo/Pt/Ag) laminated metal matrix composite(LMMC) interconnectors are widely used in place of Mo/Ag LMMC and Ag interconnectors in solar arrays. A 2D thermal-electrical-mechanical coupled axisymmetric model was established to simulate the behavior of the parallel gap resistance welding(PGRW) process for solar cells and Mo/Pt/Ag composite interconnectors using the commercial software ANSYS. The direct multicoupled PLANE223 element and the contact pair elements TARGE169 and CONTA172 were employed. A transitional meshing method was applied to solve the meshing problem due to the ultrathin(1 μm) intermediate Pt layer. A comparison of the analysis results with the experimental results revealed that the best parameters were 60 W, 60 ms, and 0.0138 MPa. The voltage and current predicted by the finite element method agreed well with the experimental results. This study contributes to a further understanding of the mechanism of PGRW and provides guidance for finite element simulation of the process of welding with an ultrathin interlayer.

Repairing of exit-hole in friction-stir-spot welded joints for 2024-T4 aluminum alloy by resistance welding

The exit-hole in friction stir spot welded(FSSWed) 2024-T4 aluminum alloy joints was successfully repaired by using a three-phase secondary rectification resistance spot welding machine, which is termed as filling exit-hole based on resistance welding(FEBRW). The filling dynamic behavior of force was recorded by a device monitoring. Optical microscope(OM), electron backscatter diffraction(EBSD), and tensile shear tests and finite element modelling were conducted to investigate the repairing stages and bonding mechanisms of the repaired joints in detail. Results showed that exit-hole was completely filled and repaired experiencing three stages. Metallurgical bonding was achieved between plug and exit-hole wall in two forms, including melting bonding in the middle of the joints and partial diffusion bonding on both the upper and bottom of the joints. The highest tensile shear strength of the repaired joints was 7.43 kN, which was 36.3% higher than that of the as welded joints. Resistance welding paves an efficient way to repair the exit-hole in FSSWed joints.

Characteristics and Weldability of Resistance Plug Welding of Dissimilar Steels

TRIP980 high-strength steel plate/SPCC low-carbon steel plate were welded by RPW. The key factors such as size and material of filler were studied, and the structure, fusion ratio and mechanical properties of the RPW joint were analyzed. The experimental results show that the calculation formulas of the length and diameter of the filler were designed reasonably. Q235 as a filler for RPW of TRIP980 high-strength steel plate/SPCC low-carbon steel plate is suitable according to schaeffler organization chart. The deposited metal of RPW joint is in the shape of “spool”,and the base metal and cap of deposited metal are alternately combined. The deposited metal has the characteristics of “locking” as rivets, which is beneficial to the improvement of mechanical properties of RPW joint. The nugget of RPW joint is uniform without deviates. TRIP980 high-strength steel plate, SPCC low-carbon steel plate, and filler were metallurgically bonded in the RPW joint.

Multi-field dynamic modeling and numerical simulation of aluminum alloy resistance spot welding

In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.

Lap-Shear Performance of Weld-Bonded Mg Alloy and Austenitic Stainless Steel in Three-Sheet Stack-Up

With the growing interest in utilizing Mg and austenitic stainless steel(ASS)in the automotive sector,joining them together in three-sheet configuration is inevitable.However,achieving this task presents considerable challenges due to the large differences in their physical,metallurgical and mechanical properties.To overcome these challenges,the feasibility of using weld-bonding to join Mg alloy/ASS/ASS was investigated.The nugget formation,interface characteristics,microstructure and mechanical properties of the joints were investigated.The results show that the connection between the Mg alloy and upper ASS was achieved through the combined effect of the cured adhesive and weld-brazing in the weld zone.On the other hand,a metallurgical bond was formed at the ASS/ASS interface.The Mg nugget microstructure exhibited fine columar grains composed predominantly of primaryα-Mg grains along with a eutectic mixture ofα-Mg andβ-Mg17Al12.The nugget formed at the ASS/ASS interface consisted largely of columnar grains of austenite,with some equiaxed dendritic grains formed at the centerline of the joint.The weld-bonded joints exhibited an average peak load and energy absorption of about 8.5 kN and 17 J,respectively(the conventional RSW joints failed with minimal or no load application).The failure mode of the joints changed with increasing welding current from interfacial failure via the Mg nugget/upper ASS interface to partial interfacial failure(part of the Mg nugget was pulled out of the Mg sheet).Both failure modes were accompanied by cohesive failure in the adhesive zone.

Microstructure and mechanical properties of dissimilar steel plate resistance plug welding joints

A new type of hybrid welding method called resistance plug welding （RPW） was firstly adopted to achieve the connecting of dissimilar steel, mainly as for the poor welding characteristics of high strength steel produced by increasing carbon, manganese, silicon, etc. Microstructures and mechanical properties of RPW joint were analyzed by optical microscope,micro-hardness test and shear tensile measurement. Experimental results indicate that the RPW joint has a rounded rectangle nugget ^ and the size is larger than elliptical nugget of resistance spot welding （RSW） jo in t; the hardness value of RPW joint is evenly distributed, accordingly there is no hard brittle phases ; the shear tensile strength o f RPW joint increases by 20% in comparison with RSW joint under the same welding conditions.

Study of joining mechanism of ABS polymer and steel/aluminum by resistance spot welding

The joining of metal and polymer is an increasingly important method to get lightweight components in the development of manufacturing industry- nowadays. In this artiele, metal and polymer lap joint was achieved by means of resistance spot welding （RSW） and ultrasonic assistance welding （UAW）. The joining mechanism of lap joint was analyzed by OM, TEM on microstructure at the interface of lap joints and XPS and IR spectra was discussed based on the following different ones： mechanical-interlocking, diffusion bond and coordination bond. The results showed that it was the combined action that played an important role in the effective joining work. Besides, ultrasonic assistance was used in the study to aid welding process based on its high-frequency ultrasonic vibration, which made joints shaping better and improved tensile strength visibly contrast to joints with the same lower heat input parameters.

Numerical simulation on temperature field for resistance spot welding of non-equal thickness stainless steel

An axisymmetric finite element model is developed to simulate the temperature field of resistant spot welding according to the process characters of nugget formation of non equal stainless steel sheets. A simulation method of the interaction of electrical and thermal factors is presented. The spot welding process of nugget formation is simulated using hard and soft welding technique norms. The heating characters of soft and hard norms determine the differences in the process of nugget formation and determine the finally shape and offset of nugget. Experimental verification shows that the model prediction agrees well with the practical.

Comparative study of resistance spot welding performance between cold-rolled DP980 and Q&P980 steels

Advanced high strength steel (AHSS) has been widely used in the automobile industry.The resistance spot welding performance of DP980 and Q&P980 steels was studied through comparing the two steels’welding current range,tensile shear strength (TSS),cross tension strength (CTS),weld spots’microhardness,etc.The following conclusions were achieved:It is easy for both DP980 and Q&P980 steels to get a nugget size bigger than 4 mm,they all have welding current ranges exceeding 2 kA and high weld strength.

Filling technique for keyhole of friction stir spot welding based on the principles of resistance spot welding

Keyhole at the end of a weld prepared by friction stir welding(FSW)is one of the major issues that impede the application of FSW.To address this issue,a keyhole filling technique was proposed in this paper,which is based on the principles of resistance spot welding(RSW).A three-phase secondary rectifier resistance spot welder was applied as the experimental instrument for filling the keyhole in the center of friction stir spot weld(FSSW).The test sheet is a 2024-T4 aluminium alloy with a thickness of 6.0mm.The experiments results show that the filled joint strength is improved by 26.12%since the area is increased for the plug in the keyhole.And there are two kinds of dimples in the tensile fracture-equiaxial dimples and long dimples.The filled joint involves the fusion welding zone(FWZ),pressure welding zone(PWZ),melted plug zone(MPZ),and plastic deformation zone(PDZ).The FWZ and the PWZ is the melting bond and diffusion bond between the plug and keyhole,respectively.The MPZ is the center part and the PDZ is upper or lower part of the plug.

A MULTI-COUPLED FINITE ELEMENT ANALYSIS OF RESISTANCE SPOT WELDING PROCESS

A two-dimensional axisymmetric finite element model is developed to analyze the transient thermal and mechanical behaviors of the Resistance Spot Welding （RSW） process using commercial software ANSYS. Firstly a direct-coupled electrical-thermal Finite Element Analysis （FEA） is performed to analyze the transient thermal characteristics of the RSW process. Then based on the thermal results a sequential coupled thermo-elastic-plastic analysis is conducted to determine the mechanical features of the RSW process. The thermal history of the whole process and the temperature distribution of the weldment are obtained through the analysis. The mechanical features, including the distributions of the contact pressure at both the faying surface and the electrode-workpiece interface, the stress and strain distributions in the weldment and their changes during the RSW process, the deformation of the weldment and the electrode displacement are also calculated.

Interfacial microstructure and property of resistance spot welding joints of titanium to stainless steel

Commercially pure titanium and stainless steel sheets were welded using the technique of resistance spot welding with an aluminum alloy insert. The interfacial microstructure of the joint was observed and analyzed using electron microscopy; the tensile shear strength was investigated. An approximate 160 nm thick layer of Al solid solution supersaturated with Ti was observed at the interface between titanium and aluminum alloy. The solid solution layer contained the precipitates TiAla. And an approximate 1. 5 μm thick serrate reaction layer was observed at the interface between stainless steel and aluminum alloy. The maximum tensile shear load of 5.38 kN was obtained from the joint welded at the welding current of 10 kA. The results reveal that the property of the joint between titanium and stainless steel can be improved by using an aluminum alloy insert.

Resistance welding of carbon fibre reinforced polyetheretherketone composites using metal mesh and PEI film

Weldability of polyetheretherketone(PEEK) with polyetherimide(PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.

Dynamic simulation of resistance spot welding of zinc-coated steels

A model was developed to simulate the temperature distribution and nugget formation during resistance spot welding （ RS1V） of zinc-coated steels. It employs a coupled thermal-electrical-mechanical analysis simulating the dynamic RSW process. Temperature-dependent thermal-electrical-mechanical material properties were considered including contact-resistance. The contact area was determined from a coupled thermal-mechanical analysis. A layer of transition elements was used to represent the change of contact area by killing or activating elements. The heat generation and temperature field were computed in a coupled thermal-electrical model. All these analyses were solved using the commercial finite element method （FEM） based on ANSYS code, and some advanced functions were used by writing a paragraph of codes by the authors. Compared with the results from only coupled thermal-electrical model in which contact area was uniform during the whole process, the result matches better to the experimental results.

A cooperative control strategy of resistance spot welding process by combining the constant current control with the DRC method

The modeling control method based on the dynamic resistance characteristics of good nuggets, that is the DRC method, is an improvement on the dynamic resistance threshold method for the quality control of resistance spot welding. But there is still a control blind area in the initial four cycles. For this reason, the quality of every weld nugget could not be fully ensured. Thus a new fuzzy cooperative control method is put forward. It uses a multi-information time-control mechanism by combining the constant current control technology with the DRC method in a relay way. This whole-process control strategy has led to a good control effect and produced the dual-identical results in the weld nugget quality and the welding time.

Quality estimation of resistance spot welding of stainless steel based on BP neural network

The end value of the dynamic resistance curve of stainless steel was proved to have strong correlation with nugget size by experiments, so it was an important factor for estimation of weld quality. BP neural network was employed to estimate the weld quality, The end value of the dynamic resistance curve, welding current and welding time were selected as the input variables while the nugget diameter, which is closely related to weld quality, was selected as the output variable. Testing results shows that such network has fine fault tolerance and real-time quality estimation is possible.

Deformation at Room and Low Temperatures and Martensite Transformation in Resistance Spot Welding Duplexγ&α(δ) Materials of 301L Stainless Steel

Transformation induced plasticity （TRIP） and twinning induced plasticity （TWlP） effects had been widely studied in single austenite steel. But in duplex γ ＆ α（δ） phase, such as welding materials of stainless steel, they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy （SEM） as well as X-ray diffraction （XRD） were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4% α（δ） ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.

Characterization of electrical properties of resistance welding machines

Due to the individual electrical and mechanical characteristics of resistance welding machines, choice of the right machine and welding parameters for an optimized production is often difficult. This is especially the case in projection welding of complex joints. In this paper, a new approach of characterizing the electrical properties of AC resistance welding machines is presented, involving testing and mathematical modelling of the weld current, the firing angle and the conduction angle of silicon controlled rectifiers with the aid of a series of proof resistances. The model predicts the weld current and the conduction angle （or heat setting） at each set current, when the workpiece resistance is given.

Study on the resistance spot welding technology of 22MnMoB hot stamping quenched steel

In this paper, the spot welding technology of a new kind of 22MnMoB hot stamping quenched steel sheet was systematically studied by power frequency spot welder. Through a series of technology and test experiments, we have obtained the optimal spot welding technological parameter condition. According to the results, the relations among spot welding technological parameter, welding nugget, mechanical property and fracture mode were discussed. The effects of all the welding parameters such as welding current, welding time and electrode force on the quality of joint can be boiled down to one thing--the diameter of welding nugget. The experimental results showed that welding nugget diameter determines the mechanical property of spot welding joint and the relation between welding nugget diameter and the mechanical property of joint presents a kind of linear mathematic representation. There are two typical fracture models of 22MnMoB hot stamping quenched steel sheet, i.e., interracial fracture and nugget pullout. Other than mild steel or normal high strength steel, in the shearing tensile test, hot stamping quenched steel has a great tendency to fail in interfacial mode due to the effects of high strength matrix structure, welding soft zone and the porosity level of fusion zone.

Electrical-thermal interaction simulation for resistance spot welding nugget process of mild steel and stainless steel

A three dimensional finite difference electrical thermal model for resistance spot welding nugget process of mild steel and stainless steel is introduced. A simulation method of the interaction of electrical and thermal factors is presented. Meanwhile, calculation method of contact resistance and treatment method of heater structure is provided. The influence of the temperature dependent material properties and various cooling boundary conditions on welding process was also taken into account in the model. A method for improving the mild steel and stainless steel joint was analyzed in numerical simulation process. Experimental verification shows that the model prediction agrees well with the practice. The model provides a useful theoretic tool for the analysis of the process of resistance spot welding of mild steel and stainless steel.