Vehicle Body Assembly Research Articles

Resistance Spot Welding of Aluminum Alloy and Carbon Steel with Spooling Process Tapes

Many lightweight materials, including aluminum alloy, magnesium alloy, and plastic, have been used for automotives. Aluminum alloy—the most commonly utilized lightweight metal—has poor resistance spot weldability owing to its inherent properties, which demand the development of welding solutions. Various welding techniques are utilized to improve the resistance spot weldability of aluminum alloy, including DeltaSpot welding. However, the technological development for welding dissimilar metals (aluminum alloy and steel) required for vehicle body assembly is still in its nascent stages. This study proposes DeltaSpot welding (a resistance spot welding process with spooling process tapes) using the alloy combination of 6000 series aluminum alloy (Al 6K32) and 440 MPa grade steel (SGARC 440). The welding characteristics of the main process parameters in DeltaSpot welding were analyzed and the weldability of the combination of the aluminum alloy, Al 6K32, and 440 MPa grade steel was evaluated. In addition, the characteristics of the intermetallic compound layer between the 440 MPa grade steel and Al 6K32 sheets were identified via scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS).

Effects of cone angle of truncated electrode on heat and mass transfer in resistance spot welding

Truncated electrodes with different cone angle are widely used in vehicle body assembly. However, the effect of the cone angle on welding process still keeps unclear. In this paper, a multi-physics finite element model, which considered the coupling of electric field, magnetic field, fluid flow and heat transfer, was used to study the effect of the cone angle variation on resistance spot welding. Four kinds of cone angles, including 15°, 30°, 45°, and 60°, were studied systematically. Research results showed that the cone angle variation affects not only weld quality but also electrode life. Specifically, the lower cone angle, the more severe current density singularity at the tip edge, the stronger electromagnetic stirring in the molten nugget, and thus the stronger fluid flow and more uniform temperature field in the weld nugget, which would produce a positive effect on the weld quality. At the same time, the low cone angles would enhance the cooling ability of the electrode for the increased mass and present lower electrode temperature, and thus have a better electrode life, which was also verified with electrode wear experiments. However, the low cone angle electrodes would produce smaller nuggets and consume more coppers. Moreover, for the small cone angle electrode, a larger welding current has to be applied to compensate the heat dissipated by the electrodes due to their excellent cooling capability. As a result, considering the effects of the electrode cone angle on electrode life, weld quality and production cost, the 30° and 45° cone angle would be recommended in vehicle body production.

Single-sided piercing riveting for adhesive bonding in vehicle body assembly

With increasing use of advanced high strength, lightweight materials and alternative vehicle architectures, materials joining issues have become increasingly important in automotive vehicle body assembly. Among the various joining methods, adhesive bonding is one of the important techniques for joining dissimilar materials in vehicle body assembly. During curing of the adhesive, it is necessary to fix and control the gap between the sheet panels to ensure the bonding strength and geometric quality. In this paper, a novel process, the single-sided piercing riveting (SSPR), is proposed for fixing and controlling the gap between the sheet panels during adhesive bonding of vehicle body assembly. The SSPR is a cold forming process for joining two or more sheet parts by driving a specifically designed U-shaped rivet using an impact force. The SSPR process is easy and convenient to implement without the need of a direct back support, and can meet the limited space requirement of vehicle body assembly. Joining experiments and performance tests were carried out to validate the effectiveness of the SSPR process. Performance comparison with other joining methods shows that mechanical properties of the lap-shear SSPR-bonded joints are superior to that of the SPR and SPR-bonded lap-shear joints.

Spot Weld Property Testing and Simulation Modeling with Failure Criteria

Spot welds have been widely used in vehicle body assembly, and can affect the performance of a vehicle. This paper studies the mechanical properties of spot weld and utilizes those properties in the numerical simulation to predict the failure behavior of a spot-welded component. The mechanical properties of a spot weld are not easy to obtain due to the size of spot weld, and the non-uniformity around the weld zone. The study utilized the hardness measured on and around the spot weld, heat treated samples with the same hardness, and then performed the tensile tests on those heat treated specimens to obtain the corresponding mechanical properties. With those testing data, the numerical simulation model was then created based on the properties obtained. A single-spot-welded part was used to correlate the results of hardware tests and numerical simulation. The study compared the results of three different modeling schemes with those of the hardware test. The results showed that the simulation model with material properties assigned to their corresponding region provided better correlation with the hardware testing results.

Investigation on Joining Method Replacement for Vehicle Body’s Assembly

Various joining methods (i.e., spot welding, arc welding, laser beam welding) have been used for vehicle body assembly. However it is unclear for the equivalent conversion of various joints which has the equivalent joint strength for the vehicle body, such as weld-bonded joint, SPR joint, which have been considered likely to replace RSW in the area of high strength steel’s joining. In order for the flexible design in the auto line of vehicles body’s joining, the equivalent (strength) weld pitch design method for various joints, including the joining of similar and dissimilar materials, is presented in this work. And some primary simulating results are presented and discussed. It is shown that the conversion method for various joints can be established based on the joint’s shear failure criteria. And the conversion results can be influenced by the sheet gage obviously. The failure criteria of various joint still need further investigation based on the simulating and experimental results.

Force characteristics of self-piercing riveting

Self-piercing riveting (SPR) is a high-speed mechanical fastening technique for point joining of sheet-material components. SPR is becoming important in automotive applications for aluminium vehicle body assembly. However, compared with current sheet-metal joining processes in the automotive industry, SPR requires a substantially higher operating force. Reduction of the operating force is one of the key objectives for enhancing the mobility and applicability of the SPR system. In this research, the force characteristics of the SPR process were studied with the aim of reducing the operating force. The effects of various workpiece temperatures and thicknesses and the mechanical properties of the SPR joints were examined. It was found that the operating force of SPR was determined by the rivet deformation force. Under certain process conditions, an increase in temperature in workpiece material could help decrease the operating force as it permits the use of softer rivets.

Clamping and welding sequence optimisation for minimising cycle time and assembly deformation

Elastic Assembly Variation Simulation (EAVS) is a computer program to simulate the dimensional variations of manufacturing process in vehicle body assembly. Welding and clamping are two major operations in the assembly process. The selection of the welding/clamping sequence in the original EAVS is based on minimising the assembly deformation. Cycle time was not considered as a criterion for sequence selection. This paper presents an extension of the original genetic algorithm in EAVS to include cycle time as part of the objective function. Application results show that the new algorithm can effectively minimise deformation and cycle time simultaneously.