Apport de la simulation numérique et de l'expérience pour la compréhension des phénomènes de frottement en emboutissage et hydroformage

Abstract : The sheet metal forming industry uses more and more the numerical simulation computer codes in order to minimize the development time and the cost of trial and error loops. Friction which has a major influence on the product quality is usually described by a constant Coulomb friction coefficient. The validity of this very simplified description of the real frictional behaviour is discussed in this thesis. The first part focuses on the stamping process. A new frictional device is developed based on a flat/flat tribometer. It allows measuring either static or dynamic friction coefficient. Experiments on coated and non coated steel sheet demonstrate that the static friction coefficient is significantly higher than the dynamic one on the whole range of contact pressures. The influence of a local and time variable friction coefficient on the result of the stamping operation is discussed using several friction models based on tribometry results and implemented in two numerical codes (FORGE2® et ABAQUS®): The static to dynamic transition of the friction coefficient described as a function of the sliding length underlines the role of the static coefficient of friction on the beginning of sliding under the blank holder and also on the thickness distribution under the punch where small relative sliding occurs. A pressure and sliding speed friction model describes well the influence of the heterogeneity of these quantities. For higher punch speeds, the difference of the results obtained with a constant and a variable friction coefficient decreases. The use of two constant friction coefficients, the punch friction being higher than the blank-holder friction, improves significantly the results.The Devine's model which describes the influence of the microscopic history of the contact (microplasticity, hydrodynamic effects) has been improved. It is an interesting alternative model which provides also an estimation of the evolution of friction with the plateaux upsetting and the onset of galling.The second part is dedicated to the friction in hydroforming of tubes. We develop a frictional device and apply it to AA 6060 tubes. The Coulomb friction coefficient increase from typical values of 0,03 for greases to 0,3 for other lubricants (oil, solid lubricants). Finite elements calculations show the huge influence of the friction coefficient on the thickness distribution in the case of plane strain forming.
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Gérard Steinmetz. Apport de la simulation numérique et de l'expérience pour la compréhension des phénomènes de frottement en emboutissage et hydroformage. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 2005. Français. ⟨pastel-00001514⟩

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