Cold and Warm Kinetic Heading of Hexagonal Bolt-Heads onto Cylindrical Mild Steel Rod

Abstract

Results of experiments are reported in which ‘cold’ (room temperature) and ‘warm’ (460 and 650°C) low-carbon steel billets were injected at high speed (at velocities of up to approx. 300 m/s) into a closed die-set having the form of a hexagonal bolt head. Under the inertia forces developed upon its arrest, the material at the head of the billet flows to assume the form of the die cavity. Earlier work has indicated that in the forming of such components there are two distinct phases of deformation: the first phase is essentially only velocity dependent, and is associated with absorbing the high radial momentum which is imparted to the billet head upon impact, whilst the second lower-speed “barrelling” phase is dependent also on the total mass of the billet. The present work attempts to establish the conditions necessary to ensure the forming of components that are both to form, and metallurgically sound. The equipment used is described, and photographs and photomicrographs of typical formed specimens are provided to illustrate the response of the forming process to changes in the major parameters. Features associated with the forming of metals at such high speeds are discussed, and conclusions are drawn as to the practical limitations and the prospects for the process.