Quantitative Study on Mannesmann Effect in Roll Piercing of Hollow Shaft

Mannesmann effect is studied using a hollow cylinder model, which is devised to analyze a hole expansion phenomenon in artificial roll piercing of a hollow cylindrical material by two barrel-type rolls without any mandrel and guiding tools. A rigid-thermoviscoplastic finite element method is employed with a special mesh generation scheme which can control the mesh density especially on the small hole surface. No damage model is used to soften the material and the hole expansion simulation is conducted without any additional assumptions about material and process. Artificial roll piercing processes for a wide range of hole diameters with outer diameter fixed are simulated with emphasis on hole expansion. It has been shown that the relative hole expansion ratio of the maximum hole diameter to the initial hole diameter increases as the initial hole diameter decreases, indicating that the hole expansion phenomenon is next to the Mannesmann effect occurring in actual roll piercing. It has been also shown that the hole expansion is related to the cavity formation occurring just after the material passes the mandrel nipple, which leads to the decrease in the pushing force exerted on the mandrel in an actual roll piercing process.