Joining by forming with a flat counter tool - A new way of joining magnesium components

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 degrees C or more is required to form joints without cracks. State-of-the-art joining by forming methods (such as clinching or self-pierce riveting) are usually working with a contoured die as a counter tool. 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. In this paper two new clinching methods "dieless clinching" and "dieless rivet-clinching" shall be introduced. Both methods work with a flat anvil as a counter tool, thus offering important advantages for the application in joining of Mg/Mg, Al/Mg or Fe/Mg joints. In joining by forming with a flat counter tool the proportion of crack inducing tensile stresses in the bottom part during the joining process is very low. Moreover the heat transfer between the heated anvil and the parts is comparatively fast. That makes it possible to decrease the heating time in joining by forming with a flat counter tool to only one second or less. The dieless clinching process was simulated using the Finite Elements Method (FEM) to analyze the influence of geometrical parameters of the punch and the process parameter clamping force. Furthermore the limitations of the new dieless joining method were investigated.