Joining thin-walled structures without protuberance by two-strokes flattening clinching process

Clinching technology has better performance in joining different sheet materials. However, the protuberance and mechanical behaviors of clinched joints have always been needed to be improved. In this paper, a new clinching method, named the two-strokes flattening clinching (TFC) process, was proposed to improve the mechanical behaviors of joints and flatten the protuberance. Mechanical testing including tension-shearing tests was employed under quasi-static conditions to evaluate the different mechanical behaviors between TFC and conventional clinched joints. The influences of the different forming forces on mechanical response of these joints were studied. The static strength, energy absorption, material flow, and failure modes of TFC and conventional clinched joints were investigated comparatively. The experimental results demonstrated that the tension-shear strength of TFC clinched joints was increased by 30.3% compared with conventional clinched joints at the forming force of 30 kN. Furthermore, the material flow analysis showed that the thickness and interlock of TFC clinched joints were increased by 79% and 45.9%, respectively. The energy absorption of TFC clinched joint was increased by 82%. In addition, the TFC process did not change the failure mode of clinched joints, and the failure mode of all clinched joints was neck fracture.