Compound extrusion (compound extrusion) is an extrusion method in which metal flows in two opposite directions simultaneously in the space between the extrusion rod and the extrusion barrel and the extrusion die hole during cold extrusion. A typical cup-rod type compound extrusion is shown in the figure. In the first stage of the extrusion process
(a), the ingot is upset and fills the cavity of the extrusion barrel; in the second stage
(b), the deformed metal flows into the annular gap between the extrusion rod and the extrusion die and the exit of the extrusion die at the same time, and starts to flow in both directions, and the extrusion force P reaches the maximum value; in the third stage
(c), the metal flows in a balanced and free direction along the upper (B1) and lower (B2) directions, and the pressure changes smoothly; to the fourth stage
(d), leave the pressure surplus in the post-extrusion stage (see squeeze residue) (S1), take S1≥S0 and S1>1/2d for cup-rod products; take S1≥2S0 for cup-cup products.
This method can be used to extrude products with circular, square, hexagonal, tooth-shaped and petal-shaped cross-sections, as well as asymmetric products with such cross-sections.