Friction Modelling for Tube Hydroforming Processes-A Numerical and Experimental Study with Different Viscosity Lubricants

The final quality of sheet and tube metal-formed components strongly depends on the tribology and friction conditions between the tools and the material to be formed. Furthermore, it has been recently demonstrated that friction is the numerical input parameter that has the biggest effect in the numerical models used for feasibility studies and process design. For these reasons, industrial dedicated software packages have introduced friction laws which are dependent on sliding velocity, contact pressure and sometimes strain suffered by the sheet, and currently, temperature dependency is being implemented as it has also a major effect on friction. In this work, three lubricants having different viscosity have been characterized using the tube-sliding test. The final aim of the study is to fit friction laws that are contact pressure and sliding velocity dependent for their use in tube hydroforming modeling. The tests performed at various contact pressures and velocities have demonstrated that viscosity has a major effect on friction. Experimental hydroforming tests using the three different lubricants have corroborated the importance of the lubricant in the final forming of a triangular shape. The measurement of the axial forces and the final principal strains of the formed tubes have shown the importance of using advanced friction laws to properly model the hydroforming process using the finite element modeling.

Automated summary

The quality of sheet and tube metal-formed components depends heavily on the tribology and friction conditions between tools and materials. Friction is the most influential parameter in numerical models for feasibility studies and process design. Industrial software packages have introduced friction laws that consider sliding velocity, contact pressure, and sometimes strain and temperature dependence. This study characterizes three lubricants with different viscosities using tube-sliding test and aims to determine friction laws for tube hydroforming modeling. The results show that viscosity has a major effect on friction, which is further confirmed by experimental hydroforming tests. Advanced friction laws are important for accurately modeling the hydroforming process using finite element modeling.