Comparison of dieless clinching and dieless rivet clinching of magnesium

Joining by forming of magnesium alloys is restricted by the limited forming capability of magnesium at room temperature. For this reason heating of the parts to temperatures of 220 °C or more is required in state-of-the-art joining methods using a contoured die (like clinching or self-pierce riveting) to form joints without cracks. Researches on these joining methods have shown that a minimum heating time of 3 to 6 seconds is needed to achieve joints of acceptable quality. Dieless clinching and dieless rivet clinching are new joining by forming methods, where a flat anvil is used as a counter tool instead of a contoured die. In this methods the crack inducing tensile stresses in the parts are reduced considerably during joining. Although crack-free joining without heating of the magnesium parts has not been successful so far, a heating of the magnesium parts to temperatures of about 150 °C often is sufficient in the dieless joining methods. Moreover the heat transfer from a flat anvil to the parts can be much faster than from a contoured die of the same diameter. The combination of both effects make it possible to decrease the heating time to only one second or less. Dieless clinching and dieless rivet clinching, both methods were simulated using the Finite Elements Method (FEM) to analyze the influence of the geometrical parameters of the punch in dieless clinching and of the rivet in dieless rivet clinching. In this paper new results of investigations on the two processes are introduced.