With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets.

In recent years, with the rapid advancement of automotive lightweight technology, the mechanical clinching process between aluminum alloy and ultra-high-strength steel sheets has received extensive attention. However, the low ductility of ultra-high-strength steel sheets often results in conventional mechanical clinching processes producing joints that either fail to establish effective interlocks or cause the steel sheets to fracture. To address this issue, a novel mechanical clinching process is presented, called center-punching mechanical clinching (CPMC). This innovative process employs a method of punching, flanging, and bulging gradation to achieve the mechanical clinching of aluminum alloy and ultra-high-strength steel sheets in a single step. In order to determine the effects of different parameters on the quality and strength of the joint, an experimental study was carried out for various die depths and diameters based on the condition of constant punch size. Based on tensile and shear tests, the static strength and failure modes of CPMC joints were analyzed. The results indicated that the CPMC process significantly enhances the connectivity of joints for AA5052 aluminum alloy and DP980 ultra-high-strength steel. Optimal tensile and shear strengths of 1264 and 2249 N, respectively, were achieved at a die depth of 2.2 mm and a diameter of 10.4 mm. The CPMC process provides new ideas for the mechanical clinching of aluminum alloy and ultra-high-strength steels.

When analyzing the strip coiling process, the finite element (FE) method is closer to the actual working conditions compared to the analytical method. However, due to the large number of strip elements and contact elements, it often leads to problems such as long-time consumption and non-convergence. Meanwhile, traditional FE methods are still unable to solve the problem of additional contact deformation between layers. Therefore, in order to overcome the shortcomings of the above methods, the FE software MSC Marc is used to establish a strip coiling model. The distribution pattern of interlayer friction and contact stress are analyzed to propose a new step-by-step bonding FE model, which greatly reduces the computing time. Through laminated compression experiments, the variation curve between additional contact deformation and pressure is obtained. The curve is introduced into the gasket elements to consider the additional contact deformation between the layers, and the effect of additional contact deformation between the layers on the stress of the coil and the pressure on the mandrel is studied. Finally, the analytical solution is compared with the FE solution proposed in this paper, and the errors generated by the analytical method are analyzed.

During the coiling process of a hot-rolled strip, with the increasing layers the temperature and stress distribution inside the coil constantly change and interact with each other. Due to the contact with the sleeve and the transition of the heat exchange state, it is inaccurate to consider the temperature of the whole coil as the coiling temperature set by the process requirement. Meanwhile, due to the periodic interlayer contact in the radial direction, the relation between stress and deformation is nonlinear. For the coiling process, it is difficult to consider the above factors using conventional methods. Therefore, an incremental model has been established to couple the temperature and stress of the coil. In order to obtain the mechanical properties of the strip and radial elastic modulus of the coil, tensile tests and laminated compression experiments are conducted at different temperatures. The effects of changes in strip thickness, coiling tension, and initial temperature of the sleeve on the stress and the temperature inside the coil are studied. Finally, by comparing the model results with measurements and analytical solutions, the effectiveness of the incremental coupled model is verified and the errors caused by the analytical method are analyzed.

As research on new, lightweight energy vehicles continues to develop, the application of high-strength steel sheets with tensile strength greater than 1 GPa and their mechanical clinching technology, which is associated with aluminum alloys, has emerged as a new research focus. However, due to the challenges associated with the cold deformation of high-strength steel, conventional mechanical clinching processes often fail to establish effective joint interlocking, resulting in weak connections. This study proposes a center-punching mechanical clinching process for connecting DP980 high-strength steel to AL5052 aluminum alloy. The mechanical evolution during the forming process was analyzed via finite element simulation. An orthogonal experimental design was employed to optimize key geometric parameters of the punch and die, yielding the optimal configuration for the mold. Mechanical testing of the joint demonstrated average pull-out force and pull-shear forces of 1124 N and 2179 N, respectively, confirming the proposed process’s ability to successfully connect high-strength steel and aluminum alloy.