New Tool Concept for Internal-High-Pressure Forming of Long Thin-walled Tubes

摘要

The objective of presented study is to establish a new tool concept for axial feeding of long thin-walled tubes based on Internal-High-Pressure (IHP) forming.As in IHP forming processes, load application on inner side of tube is achieved by high fluid pressure up to 4000 to 6000 bar, final workpiece dimensions result from superposition of tensile and shear stress, generated by the axial feeding and radial expansion of tube.For long thin-walled tube dimensions, having a length to outer diameter ratio larger than 10, any axial feeding is very demanding although the friction force is increasing proportionally to the internal pressure.This effect may lead to high risk of buckling of tube wall in the forming zone.To cope with this problem, a special IHP tool concept for axial feeding of long thin-walled tubes was developed at the Institute for Metal Forming (IFU) at University of Stuttgart/Germany.In order to overcome friction force during pressure increase the mentioned tool concept was equipped with moveable sleeves to enclose tube along large fractions, so no relative motion of tube wall is observed within sleeve.Axial feeding is managed by two hydraulic cylinders acting in opposed direction.After simulating this IHP metal forming process with LS-Dyna code, the tool was built and experiments were performed.These experiments were conducted for different tube materials and numerous die inserts to get sufficient proof of chosen concept.During the experiments additional measurements of the energy consumption were conducted to analyse the single process.By using this new tool concept it was possible to significantly reduce the friction force for all materials tested during the experiments.Measurement and simulation results presented in this paper will disclose proper feasibly of developed tool concept and will lead to new possibilities in IHP forming of long thin-walled tube cross sections.