Influencing Factors on the Strength of Electromagnetically Produced Form-Fit Joints using Knurled Surfaces

Abstract

Joining by electromagnetic forming is a non-contact assembling method that is especially suitable for connections in aluminum space frame structures. By reason of increased joint strength along with lower charging energies, form-fit connections are favored over interference-fit connections for this joining process. In contrast to conventional form-fit concepts, in which the inner joining partner has grooves or pockets, the use of knurled surfaces offers several advantages like easier machinability or the resistance against combined axial and torsional loadings. The objective of this paper is to identify the influencing geometry and process parameters on the joint strength of tubular joints using mandrels with knurled surfaces, with tube and mandrel being made of the same aluminum alloy AA6060-T6. For that reason, experimental studies were conducted: In addition to pull-out tests to determine the axial strength of joints, first computed tomographic images and, afterwards, micrographs of joined components were produced to analyze the contact zone between tube and mandrel and the deformation behavior of the inner joining partner by non-destructive and destructive means. Based on the detailed knowledge of the influencing variables, guidelines for joint and process design are derived.