Metallic Forging Using Electrical Flow as an Alternative to Warm/Hot Working

Abstract

Manufacturing processes (e.g., forging, rolling, extrusion, and forming) rely on heat to reduce the forces associated with fabricating parts. However, due to the negative implications associated with hot working, another more efficient means of applying energy is desired. This paper investigates material property changes of various metals (aluminum, copper, iron, and titanium based alloys) in response to the flow of electricity. Theory involving electromigration and electroplasticity is examined and the implications thereof are analyzed. It is shown that, using electrical current, flow stresses are reduced, resulting in a lower specific energy for open-die forging. It is also shown that an applied electrical current increases the forgeability of materials, allowing greater deformation prior to cracking. Moreover, the changes caused by the flow of electricity are significantly greater than those explained by resistive heating. Additionally, elastic recovery is decreased when using electrical flow during deformation. Finally, for most materials, these effects were dependent on strain rate. Overall, this work demonstrates that substantial increases in the forgeability of metals are achieved by deforming the material while applying an electrical current. These improvements exceed those achieved through comparable increases in workpiece temperature and demonstrate that this method provides a viable alternative to warm/hot working.

A review of electrically-assisted manufacturing

“…As recently reported by Ross et al 14 and Perkins et al, 15 the presence of a continuous electric current during plastic deformation of a metal may significantly reduce the flow stress of the metal. Under compression, the formability of a metal is significantly enhanced with application of a continuous electric current.…”

“…3. Perkins et al 15 reported the results for various materials investigated in electrically-assisted compression tests such as 304 stainless steel, 360 brass, and 6061 T6511 aluminum alloys. The contribution of electroplasticity of these materials decreased the total required energy versus current density.…”

“…Under compression, the formability of a metal is significantly enhanced with application of a continuous electric current. 15 Studies have shown that the disadvantage of the reduced maximum elongation of metals under tension with a continuous electric current 14 can be overcome by applying an electric current periodically (a pulsed electric current) instead of continuously.…”

“…The thermal (Joule heating) and athermal (electroplasticity) effects of a continuous electric current were studied by comparing the results of electrically-assisted forming by applying electric currents to metals during deformation with the results of conventional oven heating 15 or hot working 38 at temperatures equal to or higher than the temperature applied during the electricallyassisted forming. According to Perkins et al, 15 even at lower temperatures, the stress reduction during the electrically-assisted compression of aluminum, copper, iron, and titanium-based alloys was clearly higher than that of conventional compression at elevated temperatures. Also, according to Dzialo et al, 38 the temperature increase obtained during electrically assisted compression of copper alloys was lower than that during a hot working process at the same reduction of stress.…”

The Effect of Electric Current on Metals

“…• Threshold versus resistivity relation [22] • Dislocation density versus temperature relation (stationary-electrical tests) [4] • Springback elimination in sheet bending [23] • Dislocation density versus EEC (EAF tests) [4] Experimental work supports the theory of localized resistive heating due to the applied electricity. From this previous work, a threshold current density value has become apparent which is specific to each metal tested [22].…”