Simulation of the Final Stage of the Direct Extrusion Method of Large-Size Rods at Small Elongations
Tóm tắt
A simulation of the direct extrusion method of large-size rods with diameters of 188, 214, 252, 283, 326, and 560 mm made of alloy 7075; coefficients of friction of 0 and 0.5; and die cone angles of 80° and 90° from a container with a diameter of 800 mm using a 200-MN press with the help of the DEFORM-2D software package is performed. The distribution of radial velocities of metal flow on a working surface of a pressure pad depending on the contact friction, die cone angle, and elongation ratio at the main and final stages of extrusion is found. The butt-end height at the beginning instant of funnel formation is accepted equal to the distance between the pressure pad plane and input plane of extruded metal into a screw channel of flat or cone dies. The combined effect of the elongation ratio, coefficient of friction, and die cone angle on the butt-end height, extrusion force, intensities of strain rates and stresses, and temperature on the die orifice edge is investigated. Numerical experiments are performed according to the complete factorial plan 23 for variability intervals of parameters: Х1 = 3–9, Х2 = 0–0.5, Х3 = 80°–90°. Friction between the tool and the billet at the final stage of extrusion plays a negative role, noticeably decreasing the radial velocity. This leads to the earlier onset of the formation of the central funnel. Extrusion into a conical die and an increase in the elongation ratio, on the contrary, increase the radial flow velocity and provide the later onset of formation of a central funnel. The main factor that determines the butt-end height is the elongation ratio. A mathematical model is proposed to select the butt-end thickness for concrete extrusion conditions of large-dimensioned rods with small elongation ratios.
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