Potential of Joining Dissimilar Materials by Cold Formed Pin-Structures

Abstract

• Basic research on the joining of dissimilar metals via cold formed pin-structures. • Cold formed pin-structures are suitable to join dissimilar metals. • Caulking enables higher joint strengths compared to direct pin-pressing. • Significant increase of joint strength by using multi-pin-structures. • Inhomogeneous material flow complicates the forming of multi-pin-structures. Joining dissimilar materials brings established joining techniques to their limits due to different thermal expansion, unequal stiffness/strength and chemical incompatibilities. The use of pin-structures has proven an appropriate strategy to join multi-material-systems in laboratory scale. At present, the industrial application of this joining technology is limited due to the time-consuming pin manufacturing process and the inadequately researched achievable joint strengths. In this study, extrusion of the pin-structures from sheet metal is used to investigate an approach that can be directly integrated into existing production processes and does not require auxiliary joining elements. With direct-pin-pressing and caulking, two different joining strategies are analysed to join multi-material systems of sheet steel (DC04, t 0 = 2 mm) and aluminium (EN AW 6016-T4, t 0 = 2 mm). The basic feasibility of the joining technique is experimentally proven by using single-pin-structures. The joint strength is analysed by tensile shear tests, micro sections and failure patterns. Based on the experimental results, a failure criterion for the joint is defined. Parallel to the experiments, numerical finite element models (FE-models) for the single-pin-joint are developed and validated. In a further step, numerical investigations for multi-pin-structures are carried out in order to derive predictions on achievable joint strengths with this joining technique. It is shown that the form-fit is crucial for the joint strength. Thus, 93 % higher shear strength is achieved for caulked joints. By multi-pin-structures the strength can be increased considerably. For a 5 × 3 pin-structure, shear strength of 9.9 kN can be achieved.