According to the stress-strain state of the metal in the extrusion cylinder, the metal flow direction, the lubrication state, the extrusion temperature, the extrusion speed and the structure of the equipment, the type or structure of the tool and die, the shape or number of the billet, the shape or number of the aluminum alloy profile, etc., the extrusion molding methods can be divided into the following (Table 1) shown in a variety of methods; these classification methods are not static, many classification methods can be used as a subdivision of another classification method. For example, forward extrusion and reverse extrusion can be further divided into plane deformation extrusion, axisymmetric deformation extrusion, general three-dimensional deformation extrusion, etc. according to the deformation characteristics. Figure 2 shows several main extrusion methods widely used in the aluminum profile processing industry, namely forward extrusion, backward extrusion, pipe pressurization and continuous extrusion

1. Forward extrusion (forward extrusion)

The extrusion method in which the outflow direction of aluminum profile is the same as the running direction of the extrusion shaft is called positive extrusion, as shown in Figure 2(a). Positive extrusion is the most basic extrusion method, which has become one of the most widely used methods in aluminum and aluminum alloy profile forming and processing because of its mature technology, simple process operation, large production flexibility and excellent surface profile products; positive extrusion can be further subdivided according to other classification methods shown in Table 1, such as plane deformation extrusion, axisymmetric deformation extrusion and general three-dimensional deformation extrusion, or cold extrusion, warm extrusion and hot extrusion;

The basic characteristic of forward extrusion is that relative sliding occurs between the blank and the extrusion cylinder during extrusion, and there is great external friction. In most cases, this friction is harmful, which makes the metal flow uneven, thus adversely affecting the quality of the extruded profile, resulting in uneven organizational properties of the head and tail, surface and center of the extruded profile. Increase extrusion energy consumption, in general, the frictional energy consumption on the inner surface of the extrusion cylinder accounts for 30% to 40% of the extrusion energy consumption, or even higher; due to the strong frictional heating effect, the increase in the extrusion speed of aluminum and aluminum alloy profiles is limited, and the wear of the extrusion die is accelerated;

2. Reverse extrusion (reverse extrusion)

The extrusion in which the outflow direction of aluminum profile is opposite to the movement direction of the extrusion shaft during metal extrusion is called reverse extrusion, as shown in Figure 2 (B). The reverse extrusion method is mainly used for hot extrusion of aluminum alloy profile and pipe, and cold extrusion of various aluminum alloy parts. During reverse extrusion, there is no relative sliding between the metal blank and the wall of the extrusion cylinder, the required extrusion force is small, and the extrusion energy consumption is low. Therefore, the reverse extrusion method can realize the extrusion deformation with greater deformation degree or the profile with higher extrusion deformation resistance. Unlike forward extrusion, the metal flow during reverse extrusion is mainly concentrated in the area near the die hole, so the metal deformation along the length of the profile is uniform. However, the operation of reverse extrusion technology is more complicated, the gap time is longer than that of forward extrusion, and the surface quality of extruded profiles is difficult to control, special extrusion equipment and tools are needed, and the application of anti-extrusion is limited to a certain extent. However, in recent years, with the successful development of special anti-extrusion machines and the development of tool and die technology, the anti-extrusion method of aluminum profiles has been more and more widely used;

3. Conform continuous extrusion

A common feature of the above-mentioned methods is the discontinuity of extrusion production. A series of auxiliary operations such as separation and filling of billets are required between the extrusion of front and rear billets, which affects the efficiency of extrusion production and is not conducive to the production of continuous long-size profile products. Extrusion production really realized continuity and obtained good practical application after D Green of the UK Atomic Energy Agency invented the Conform continuous extrusion method in 1971; as shown in Figure 3(e), the Conform continuous extrusion method uses the friction force between the deformed metal and the tool to realize the extrusion; the circular channel composed of the rectangular section groove on the rotating groove wheel and the fixed die base plays the role of the extrusion cylinder in the common extrusion method. When the groove wheel rotates, the rod-shaped blank is continuously fed in by the friction force on the groove wall to realize the continuous extrusion;

Conform the friction between the billet and the tool surface occurs significantly during continuous extrusion, for aluminum alloy profiles with lower melting point, the temperature of the deformation zone can be raised to 400~500 ℃ without external heating to realize hot extrusion. Conform continuous extrusion is suitable for the forming of cladding materials such as aluminum-clad steel wires, aluminum alloy wires, pipes and profiles with small cross-sectional dimensions. Extending die extrusion technology is adopted, it can also be used for the production of larger cross-section aluminum profiles; in addition, cold extrusion, lubricated extrusion, hydrostatic extrusion and other methods are used inAluminum profileExtrusion also obtained certain application;