Contact pressure, sliding velocity and viscosity dependent friction behavior of lubricants used in tube hydroforming processes

Lander Galdos,Nagore Otegi,Joseba Mendiguren,Javier Trinidad,Eneko Saenz De Argandoña

doi:10.25518/esaform21.2081

Abstract

The final quality of sheet and tube metal formed components strongly depends of 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. 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 major effect on friction. This last dependency on temperature is attributed to the viscosity change of the lubricant with temperature. In this work, three lubricant having different viscosity have been characterized using the tube sliding test. The final aim of the study is to obtain friction laws that are contact pressure and sliding velocity dependent for their use in tube hydroforming modelling. The tests, performed at various contact pressures and velocities, demonstrate that viscosity has a major effect on friction. As shown in the literature, the friction coefficient is also varying with the contact pressure and sliding velocity.Abs

Highlights

Tube hydroforming is a well-known technology for the production of lightweight, high strength and complex shape hollow components
The minimum friction coefficient is observed for the highest viscosity lubricant but the maximum sliding velocity, small difference is observed in comparison to the lowest velocity of the same condition
The results clearly show that friction coefficient decreases when the contact pressure, the sliding velocity and the viscosity increase

Summary

Introduction

Tube hydroforming is a well-known technology for the production of lightweight, high strength and complex shape hollow components. During the tube hydroforming operation the tube is sealed by two axial cylinders Lateral forces of these cylinders avoid the leakage of pressurized water-oil emulsion and feed material from the guiding or feed zones to the expansion zones. One can understand this working principle as it is similar to the deep drawing, where material is fed from the blank-holder zone to the die cavity. At this stage, the reader may have already noticed that friction is very critical in tube hydroforming. The rest of the needed axial force is proportional to the internal pressure used in the process, which needs to be counteracted by the external

Objectives

Results

Conclusion