Characterization and modelling of backward cold flowforming of Ti-6Al-4V

TitleCharacterization and modelling of backward cold flowforming of Ti-6Al-4V
Publication TypeThesis
Year of Publication2014
AuthorsDepriester, D
Academic DepartmentCenter for Material Forming (CEMEF)
Date Published208
UniversityEcole Nationale Supérieure des Mines de Paris
Thesis TypePhD thesis
Keywordscold plastic deformation, flowforming, microstructure, numerical simulation, Ti-6Al-4V, titanium

Flowforming is a means to produce seamless tubes by plastic deformation at room temperature. It consists in a tubular part, mounted on a mandrel, and a couple of rollers. While the mandrel is rotating, the roller translate along the tube axis. Because of the conical shape of the roller, the tube thickness reduces by cold plastic deformation, thus the tube elongates. Thanks to the high compressive stresses and to the incremental nature of the deformation process, flowforming can lead to a high thickness reduction and thus to high elongation of the deformed tubes.

Ti-6Al-4V (also known as Ti64) is an α − β titanium alloy. Because of its high strength and its low density, Ti64 is the most widely used titanium alloy in aerospace industry. Nevertheless, flowforming of this alloy is a great challenge, considering its well known poor ductility at room temperature.

In order to increase the “tube spinnability” of Ti64, first the flowformed material has been extensively investigated at microscopic scale (SEM, EBSD) as well as at macroscopic scale (mechanical properties). In addition, an experimental flowforming machine, equipped with load sensors, has been designed. It has provided valuable informations about the strain mechanism occuring during flowforming; furthermore, this experimental set-up has allowed to buid an adequate constitutive law for the plastic flow. Then, this law has been used to optimize the processing parameter, in order to avoid failure during the process.

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