Abstract
A new high strain rate forming process for titanium alloys is presented and named High Pressure Pneumatic Forming (HPPF), which might be applicable to form certain tubular components with irregular cross sections with high efficiency, both with respect to energy cost and time consumption. HPPF experiments were performed on Ti-3Al-2.5V titanium alloy tubes using a square cross-sectional die with a small corner radius. The effects of forming of pressure and temperature on the corner filling were investigated and the thickness distributions after the HPPF processes at various pressure levels are discussed. At the same time, the stress state, strain and strain rate distribution during the HPPF process were numerically analyzed by the finite element method. Microstructure evolution of the formed tubes was also analyzed by using electron back scattering diffraction (EBSD). Because of different stress states, the strain and strain rate are very different at different areas of the tube during the corner filling process, and consequently the microstructure of the formed component is affected to some degree. The results verified that HPPF is a potential technology to form titanium tubular components with complicated geometrical features with high efficiency.
Highlights
In comparison with liquid-based forming operations, in the area of forming at elevated temperatures, gas offers the chance to provide higher temperatures due to its high temperature resistance in contrast to most liquids
There are many kinds of forming processes on pneumatic forming at elevated temperatures, e.g., super-plastic forming (SPF), quick-plastic forming (QPF), hot metal gas forming (HMGF)
Drossel and Pierschel [11] developed a measuring instrument to determine the temperature variation curve of the gas in the tube with a measuring frequency of at least 1 Hz during high pressure pneumatic forming of high strength steel. They confirmed that it was possible to determine the temperature variation curve of the gas and the maximum temperature of the active media was up to 500 °C. He [12] measured the formability of TA2 pure titanium at different temperatures and determined the best forming parameters, the results showed that a good formability could be attained at the proper temperature, at which the uniform elongation has the biggest value, but not the total elongation with necking
Summary
In comparison with liquid-based forming operations, in the area of forming at elevated temperatures, gas offers the chance to provide higher temperatures due to its high temperature resistance in contrast to most liquids. There are many kinds of forming processes on pneumatic forming at elevated temperatures, e.g., super-plastic forming (SPF), quick-plastic forming (QPF), hot metal gas forming (HMGF). Among the studies of the QPF process, Jarrar et al [2] found that a common failure mode during QPF of non-ferrous materials in plane strain was splitting (or rupture) in the vicinity of the die entry radius and major contributing factors were sheet-die friction and die geometry. Wu et al [5] performed tensile tests and shallow pan rapid gas blow forming to explore the deformation behavior of AZ31B Mg alloy sheet and found that the fillet radius of the rectangular pan to be one of the key factors influencing forming time on closed die gas blow forming
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