High Strain, High Strain Rate Forming of Difficult to Deform Tubular Parts

High demand for formed tubular components and the necessity to increase their strength to weight ratio have established a need for new, effective, and low cost forming technologies. This work investigates the application of a propellant-driven water stream to the formation of high tensile strength alloys such as stainless steel 321, Inconel 625, and Ti-3Al-2.5V. The proposed forming technology is based on the utilization of high pressure developed in liquid flowing through a tubular work piece. This pressure results from superposition of compression waves generated in the course of the impact of the liquid by products of propellant combustion. An experimental setup, used for the study of the technology in question, consisted of a tubular component, inserted into a split die assembly, and a combustion chamber, which generated gas, driving water through a work piece. This setup was successfully used for high strain, high strain rate forming of tubular components. In particular, the formation of various shapes in the course of an expansion of seamless tubing was examined. Despite large strains, exceeding in some cases the static test elongation limit, the generated samples were characterized by a uniform wall thinning and structural integrity. For example, a 55% expansion of Ti-3Al-2.5V tube was attained using a simple setup. The acquired experimental data show that the technology can be applied to form alloys characterized by high tensile strength, low static elongation limits, and low modulus of elasticity. Simplicity and low capital cost of the process determine its competitiveness in comparison to conventional quasistatic hydroexpansion, hot forming, and high-energy rate explosive forming processes.