Combination of Hydroforming and Joining

Manufacturing of complex tubular workpieces often requires medium‐based forming processes. Because of the inaccessibility to the inside of the parts, joining of attached parts and part handling are difficult. Loss of accuracy during thermal joining is another disadvantage. A new method of spot‐joining by forming is a combination of hydroforming and clinching or hydroforming and self‐pierce riveting. In contrast to the standard method the clinching or self‐pierce riveting is done without die. A high pressure fluid undertakes the task of the die during joining. This die‐less procedure also extends the range of applications to areas which are not covered by standard techniques. By integrating joining into the hydroforming process, assembly processes can be shortened. In order to exploit velocity dependent material properties, for example increase in formability and decrease of spring back, self‐pierce riveting during the hydroforming process by means of impulse load has also been researched among other conventional quasi‐static force transmissions. Numeric simulations were used for the theoretical description of the procedure. One goal of the simulations is the characterisation of the most influential parameters on the process as a function of the material properties, tool kinematics/‐geometry and of the friction conditions. The simulation results permit not only the characterisation of the process, but also the theoretical predetermination of optimal joining parameters for various material and geometry combinations with fewer experiments.