Analytical model for friction coefficient determination in tube hydroforming process

The influence of friction on load of die in hydroforming process has a major impact. Regardless that hydroforming process is considered to be the process with reduced friction or very low intensity of friction, still this phenomenon in hydroforming process is field of interest for many scientist. Many authors have been defined analytical models for friction coefficient determination for symmetrical shapes. These analytical models gives different values then real measured ones therefore in these models was not included influence of workpiece free expansion zone. In this paper analytical model for friction coefficient determination is given depending on flowing parameters: workpiece material, tube wall thickness, fluid pressure and workpiece deformation ratio. Analytical model is practical for application and describes real hydroforming process. In paper experimental method for friction coefficient measuring is given for tube hydroforming.