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

Abstract

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.

On the Use of Advanced Friction Models for the Simulation of an Industrial Stamping Process including the Analysis of Material and Lubricant Fluctuations

“…Under the boundary lubrication condition, the friction coefficient is composed of solid and fluid friction coefficients. The local heating effect of the friction at the peak causes the viscosity of the lubricant to decrease, resulting in a decrease in the coefficient of fluid friction [15,16]. The effect of variability on material properties was further analyzed by Harsch et al [17,18], who concluded that material fluctuations contributed significantly to the forming process.…”

Improving Material Formability and Tribological Conditions through Dual-Pressure Tube Hydroforming

“…However, there are ongoing efforts to develop friction models that specifically aim to accurately quantify the nonlinear friction observed at the tube-die interface. A variable friction law that takes into account the sliding velocity, contact pressure and viscosity was developed and implemented in the commercial software Abaqus [16] Another critical design aspect of THF is preforming. Depending on the shape complexity of the tubular part and formability of the tubular material, the incoming straight tube might need to be bent or crushed before the final THF process is carried out.…”

Theoretical and Experimental Study of Conical Tube Hydroforming with One-Sided Axial Feeding

“…The material parameters include mechanical properties of tube material, such as elongation, tensile strength, strain hardening rate, etc., while process parameters represent the load path which is, generally speaking, the loading of internal pressure and the amount of axial feeding. Also, the die's geometric configuration and the status of the lubrication at the specimen -die interface have significant impact on the outcome [10,11].…”

“…One of the significant parameters that influence the quality of the product is the amount of friction between the die and the specimen during the hydroforming process. The friction at the specimen-die interface usually causes a nonuniform distribution in terms of shear stress, as well as variation in the thickness of the formed product along its length [11,[20][21][22]. The degree to which the friction is present depends on the geometrical features and the loading conditions between moving surfaces since hydroforming is an active process of deformation in different directions.…”