Experimental Investigation of Grain and Specimen Size Effects During Electrical-Assisted Forming

Abstract

Alternative manufacturing processes such as hot working and Electrical-Assisted Forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable affects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore the dislocation density, related in part by the grain size, appears to be a factor in the EAF process.

Effect of current density and zinc content during electrical-assisted forming of copper alloys

“…This could relate to the required energy to allow dislocations to move past barriers. Similar threshold effects were found in studies of other materials as well [3][4][5][6].…”

“…The electrical current was applied to the specimen using a Llamda 6 V, 200 A power supply. The current output of this device was verified by an amp meter in series and also by the measured voltage drop across a shunt resistor [6]. The current entered through the upper platen, passed through the specimen, and exited through the lower platen.…”

“…Furthermore, microstructural changes do not occur in the material due to the heating which could also affect the material behaviour (e.g., studies of Al5754 [5] and Cu101 [6]). Thus, EAF produces increased formability and decreased elastic recovery of materials without the drawbacks associated with forming at elevated temperatures such as microstructural changes which could adversely affect the material properties.…”

“…For example, Siopis and Kinsey [6] studied the effect of grain size and specimen size during axi-symmetric compression of Cu101 (commercially pure, 99.99% Cu). As the grain boundary area increased, the flow stress reductions increased.…”

A review of electrically-assisted manufacturing

“…Moreover, the threshold current density significantly affected stress reduction in the compression of a Cu 260 alloy. In addition, Siopis et al 64 reported that larger grain sizes of copper in the compression test were less affected by electroplasticity than were fine grain sizes due to the small surface area of the grain boundaries. Higher continuous electric currents were necessary to aid the motion of dislocations at the boundaries.…”