On a reshaping method of clinched joints to reduce the protrusion height

The existence of relatively high protrusions above the sheets on most of the clinched joints could sometimes bring about an undesired result in the subsequent processing and, therefore, the application of the clinching technologies might be restricted. The current study proposed a countermeasure by imposing compression on the joints with a pair of contoured tools and then obtaining a controlled local plastic deformation of the joints, resulting in a reduction of the protrusion height. A typical two-layer clinching of 6063 aluminum alloy sheets with the thickness of 0.8 mm was employed to study the successional processes of clinching, reshaping, and separation. Geometrical parameters of the reshaping tools were optimized in terms of pull-out strength on the basis of numerical simulation and orthogonal design. It was found that diameter d of the truncated cone end on the reshaping die, inclination alpha of the truncated cone, and then fillets of the die and punch are of important influence on the connecting strength. Moreover, connecting strengths of the clinched joints before reshaping and after reshaped with the optimal parameters of the tools were compared experimentally. The results show that the protrusion height of the clinched joints can be reduced dramatically by the method without decreasing the connecting strength. In the example, the protrusion height of the clinched joint decreased from 1.7 to 0.68 mm, while the average pull-out strength of the joints increased from 230.8 to 331.4 N, and the shear strength increased from 559.7 to 657.5 N.