A New Approach for Void Closure in Bulk Metal Forming

At present, the discussion about pores/ voids in large ingots is still actual. Researchers investigated the closing behavior during the open die forging process. Mostly, the approaches take the account into void closure with artificial pores. But artificial pores do not reflect the real closing behavior. This is caused in the surface/ structure of inner voids. During drilling and heating, the voids got a smooth surface and have contact to the atmosphere. Therefore, the material oxidizes on surface and the closing behavior is not similar to the real process. Real pores show a fractal surface with dendrites. And the inner of voids contains a vaccum. In the framework of a new approach, for void closure cast ingots with pores were generated and the structure and the closing behavior were investigated.The final goal is to find out a global closing function “Z”. This closing function should improve the understanding of void behavior and in the future the industrial process. The function depends on different parameters, like yield strength of material (Pkf), the pore size (AEq), the pore structure (Pstruct) and process parameters (Pproc), such as tool geometry or bite ratio. Finally, there is a parameter Pdisturb. This parameter works against the final closure and is important for the understanding of the process, because it represents the influence of dendrites. Furthermore the closing behavior is not comprehensible without the consideration of recrystallization.