抄録
The behaviors of impact extrusion in three kinds of metals with different density were investigated at impact velocities from 4.5 to 6.2 m/sec and varying extrusion ratios of 2.6 to 60.0. It was found that the observed initial punch pressure at high extrusion ratio became exceedingly large due to the inertia resistance force pR of ρ(vR)2⁄2g, where ρ is the density of metal, v the punch velocity, R the extrusion ratio and g the gravity constant, respectively. On the contrary, the observed final punch pressure for the high extrusion ratio was found to decrease by the inertia drawing force of ρaRl⁄g which is the tensile stress acting on the load cell system (the punch) and arises due to the inertia force of the running extruded rod of length l at the decelerating rate of a·R, (a is the decelerating rate of the punch).
In the impact extrusion of metals with high density at a high extrusion ratio, these two kinds of extra force become important and usually the punch pressure decreases rapidly with the punch stroke (or time). The critical velocities vc·R at which the inertia parting takes place are found to be 320 m/sec for Al at room temperature and 120 m/sec for Cu at 600°C, respectively. In other words, the tensile stress due to the inertia force exceeds the tensile strength of Al and Cu at R=60 and 35, respectively, when they are extruded at the punch velocity of 6.2 m/sec. In the case of Pb the inertia parting takes place more easily due to the large density and the low tensile strength of this metal. Due to the easiness for the inertia parting to occur in this case, the effect of inertia force on the final punch pressure does not appear.
