Determination of energies in high-speed blanking

Abstract

High speed blanking is a process in which the speed of the punch exceeds a specific material threshold to produce localization phenomena in the blanking clearance, leading to thermal softening and eventually to a shear band formation. The analysis of the formation of these shear bands requires the analysis of the energies for the initiation of shear bands for the mechanical and thermal boundary conditions, and the knowledge of the amount of energy for maintaining the localized deformation until material separation. This paper presents an approach to determine the available process energy for a high-speed blanking process, and the energy dissipated for high carbon steel C75 and a AA5083 aluminum alloy. With these energies the material-independent efficiency of the tool (28%) and the material-dependent efficiency of the blanking process (2.6 - 71.8%) are calculated, leading to a total efficiency between 0.73% to 20.1%. This approach provides a basis to compare various investigations on high speed blanking. Using process forces and strain formulation, an instability criterion identifies instability points, approximating energy dissipation pre- and post-instability for blanking. It was found, that the energy required for deformation from the instant of instability until material separation increases as the tool speed increases. When ASB are formed, the evaluation of these energies shows increased energy dissipation per volume by a factor of 20 or more. For all blanking experiments a peak acceleration larger than 26,120 g was measured, revealing the dynamic nature of this impact process.