Alternative Control of an Electrically Assisted Tensile Forming Process Using Current Modulation

Abstract

Electrically assisted forming is a technique whereby metal is deformed while simultaneously undergoing electric current flow. Using this process, electric current level becomes a new degree of freedom for process control. In this work, we present some alternative control architectures allowing for new avenues of control using such a process. The primary flndings are architectures to allow for forming at constant force and forming at constant stress levels by modulating electric current to directly control material strength. These are demonstrated in a tensile forming operation, and found to produce the desired results. Combining these control approaches with previous and contemporary efforts in modeling of the process physics will allow for system identißcation of material response properties and model-based control of difficult-to-observe process parameters such as real time temperature gradients. Model-Based Manufacturing Process Control. Model-Based Control (MBC) is a term incorporating a number of approaches Journal of Manufacturing Science and Engineering

Influence of stacking fault energy in electrically assisted uniaxial tension of FCC metals

“…EPE has been observed in materials possessing different crystal structure, electrical resistivity and thermal conductivity, and deformed under different conditions. 1–24 In a recent work, 20 a decrease of the electrical threshold as the material resistivity increased has been noted, but no relations between lattice type and EPE were revealed; this reduction in the threshold value may support the theory of localised heating from electrons scattering-off from lattice obstacles, allowing the lattices to expand easier. Further, in some cases, it has been observed a possible effect on the material flow stress that appears to be solely due to the electrical influence, beyond what would be expected from the temperature effects.…”

“…In the past years, many efforts have been spent on the study of the effect of electricity within metals during deformation, in order to understand in which extent the application of continuous and pulsed electrical current can induce enhancements on their formability. Starting from the pioneering works of Conrad and Troitskii, 1–3 the researchers involved in the study of the so-called electroplasticity have performed numerous experiments on a wide range of metals and alloys, 4–24 leading to the development of theories explaining the phenomenon known as electro-plastic effect (EPE). These works have revealed that the passage of electricity can cause a modification of the materials flow properties by improving their workability, therefore making this method suitable to be adopted in forming operations.…”

“…However, even if EPE has been found to be more significant in BCC materials respect to FCC ones, 16 a direct correlation among crystal structure, electrical resistivity and EPE seems not to be the key point for the occurrence of electroplasticity . On the contrary, by analysing the available literature data on EAM, 4–24 a metallurgical parameter that is likely to be more connected to EPE could be the stacking fault energy (SFE) of the tested material – or that of the constituting phases. SFE is a property of the considered metal or alloy and it depends on the electron-to-atom ratio (i.e.…”