Single-sided Spot Welding Research Articles

Robustness and reliability assessment of Single-Sided Spot Welding as a process for sheet to closed profile joining for Body in White vehicle structures

The application of high performance steels in combination with rolled profiles, hydro-formed or tailored tubes (TT) can create a stiffer and safer vehicle structure. However, it presents some challenges regarding the joining process, once accessibility to both sides of the surface to be joined is limited. The Single-Sided Spot Welding (SSSW) is an alternative to Resistance Spot Welding (RSW), as it only requires access to just one side of the joint to weld it. In order to validate SSSW as a robust and reliable welding process for automotive manufacturing, this work encompassed experiments comparing SSSW and RSW under manufacturing conditions and tolerance problems, such as sheets and electrode misalignment, gaps or shunt current conditions, using DX54D steel sheets, and steel profiles made of press-hardened 22MnB5 and S355J2 + N. The experimental parameters in this study were current, electrode force, geometry and misalignment angle. The performed tests were lap shear tensile strength, analyses of weld nugget quality and the measurement of spot diameters by chisel testing. The obtained results show that SSSW can meet RSW requirements regarding mechanical properties and quality standards, overcoming the set manufacturing tolerance issues, without reducing the spot diameter and with similar mechanical properties of RSW joints.

Simulation Analysis on the Contact Status during Sheet-to-Tube Single Sided Spot Welding Process

Single sided resistance spot welding (SSRSW) developed from RSW is a feasible plan to join vehicle structure to closed-form tube and is increasingly used in automobile manufacturing. During the process of SSSW, large deformation and complex contact status of the workpieces occur because there is no inside support. The complex contact status has directly influence on the size of the nugget which is critical to the quality of welding. In this study, the contact statuses during the current stage of sheet-to-tube spot welding were researched by numerical method. It was found that the widths of the contact regions of electrode to sheet and sheet and sheet to tube have dynamic change during welding process which decided the size and speed of the nugget formation. The results have direct guiding significance to the study on ring nugget formation during sheet-to-tube welding.

Estimation of the weldability of single-sided resistance spot welding

A single-sided spot welding technique is investigated by numerical analysis using a commercial CAE package to estimate the weldability. The reliability of the method is verified by the welding experiment performed under conditions similar to those of a real product. Several conditions are analyzed to find an optimal condition set, including the boundary condition for the ground location and the electrical contact resistance. The resulting Lobe curve with respect to welding time and current is obtained. The weldability of the single-sided spot welding specimen is estimated through the tensile strength test. A certain level of tensile strength can be obtained at the range of welding variables for the optimal nugget sizes, which supports the reliability of the single-sided RSW.

Numerical Simulation of Sheet to Cylindrical Tube Single-Sided Spot Welding

With the promotion of lightweight structure, hydroformed tubes have been widely used in the automobile industry. In order to join different parts, sheet to tube single-sided spot welding (SSSW) is proposed. In the present study, numerical simulation method is employed, and an electrical-thermal mechanical coupled finite element model is established for predicting the nugget size and shape of sheet to cylindrical tube SSSW. Because of the welding deformation, doughnut weld nugget is formed and the course of the welding deformation can be reflected by the electrode displacement.

Investigations on the weldability of high-strength steels sheet to cylindrical tube single-sided spot welding

With the promotion of weight reduction, hydroformed tubes have been widely used in vehicle construction. Because of different section shapes in hydroformed tubes, sheet to cylindrical tube joining process by single-sided spot welding (SSSW) is proposed in the present paper. However, because of line contact status and low structural stiffness, welding deformation often occurs. As a result, doughnut weld nugget is formed, and welding quality is affected. In this study, the microstructure and microhardness of the doughnut weld nugget are investigated, and the weldability of high-strength steels sheet to cylindrical tube SSSW with different electrode force, tube thickness, and radius is explored, respectively, through the analysis of dynamic electrical resistance. Because of special structural characteristics, the weld lobe for sheet to cylindrical tube SSSW is very narrow. Owing to high dynamic resistance, the weld lobe is moved to the left with small electrode force or high tube thickness, and the weld lobe is expanded with thick cylindrical tube. With the decrease of tube radius, crack or expulsion easily occurs, and the weld lobe gets narrow. Welding time is also found to be an important parameter, which influences the weldability because proper welding time can enlarge the weld lobe.

Strength prediction of sheet to tube single sided resistance spot welding

Single-Sided Spot Welding (SSSW) procedure is considered as a feasible method to join hydroformed or closed section parts to others in vehicle productions. A ‘doughnut’ shaped or ring nugget can be formed between the two workpieces during this process. The strengths of conventional button spot welds can be determined by the attributes of weldments and many functions that link weld diameter, sheet thickness and material properties to weld strength have been established. For welds of sheet to tube joining, the strength prediction model is greatly different from that of conventional welds for the completely different nugget form. In this study, computer experiments were conduced using the concept of design of experiments (DOE) and the method of finite element used to simulate the tensile-shear tests. The stress and strain distribution contour clouds during tensile-shear process were analyzed and quantitative relationship models were established to link a weld’s geometric and material properties to its tensile-shear strength. The results can give a simple judgment whether a ring spot weld was good only by its appearance.

Numerical analysis of single sided spot welding process used in sheet to tube joining

As a new kind of lightweight structure, hydroformed tubes are now widely used in vehicle bodies. The single sided spot welding (SSSW) is a variation of resistance welding used in joining hydroformed closed tubular parts and vehicle structures. During the process of SSSW, large deformation and complex contact status of the workpieces occur because there is no inside support. The time variation of the contact region and pressure distribution changes the flow paths for electric current timely and brings a fierce shunting at the position far away from the axis line, which prevents the heat concentration at the faying surface of workpieces. The characteristics of SSSW different from those of classical resistance welding mentioned above make it difficult to determine rational welding processing parameters for SSSW. In the present paper, a comprehensive structural–thermoelectric model is established. Using the incrementally coupled analysis of finite element analysis, the electrical, thermal and mechanical aspects of sheet to tube process using SSSW are investigated. The mechanical characteristic of specimens during the squeeze and welding progress, the electric current density transient distribution, the nugget formation process, and the effects of welding parameters for SSSW are discussed. It is found that ring nugget is obtained by sheet to tube SSSW. Modifying electrode force during welding cycle is a valid method to obtain acceptable nugget with shorter welding time or less energy. The calculated results of nugget size and location are in good agreement with those of experimental observations.