The Calibration of High Energy-Rate Impact Forging Hammers by the Copper-Column Upsetting Method and High Speed Camera Measurements

Abstract

The hammer forging is a well-known technology to incrementally produce geometrically complex forgings by compressing the material against the dies using several forming blows. When forging aeronautical components with this technology, it is crucial to control the final grain size of the part since this variable highly influences the high temperature low cycle fatigue properties. Nowadays, it is common practice to use the finite element models coupled with recrystallization models to optimize the process parameters and strategy. However, a very important variable to conduct these simulations is the real available hammer energy, which must be calibrated, not being an easy task since very high forces are generated in the impact of the anvils. In the present paper, the copper-column upsetting method is compared with a novel method where a high speed camera has been used to compute the anvils’ velocity and corresponding energies. The compressive behavior of the copper samples has been characterized using Rastegaev compression tests. The experimental and calculated results using the high speed camera are compared to the ones obtained using high purity copper samples. These measurements have enable to quantify the influence the friction and the elastic rebound have during the energy transfer from the anvils to the billet. This makes possible a precise future characterization of hammers using the conventional copper-column upsetting method if high speed cameras are not available in workshop.