[China Aluminum Industry Network] I: positive extrusion (positive extrusion)
The extrusion method in which the extrusion direction of the product is the same as the extrusion axis is called positive extrusion, as shown in Figure 1-2a. Positive extrusion is a more basic extrusion method, and it has become one of the more widely used methods in the forming and processing of aluminum and aluminum alloy materials due to its mature technology, simple process operation, high production flexibility, and availability of products with excellent surfaces. . The positive extrusion can be further subdivided according to the other classification methods shown in Fig. 1a, such as flat deformation extrusion, axisymmetric deformation extrusion and general three-dimensional deformation extrusion, or divided into cold extrusion, warm extrusion and Hot extrusion and so on.
The basic feature of positive extrusion is that there is relative sliding between the billet and the barrel during extrusion, there is a large external friction, and in most cases, this friction is harmful, it makes the metal flow rate uneven Therefore, the quality of the extruded product is adversely affected, resulting in uneven tissue properties at the head and tail of the extruded product, the surface layer and the center; and the energy consumption of the extrusion is increased. In general, the inner surface of the tube is squeezed. Friction energy consumption accounts for 30%-40% of the energy consumption of extrusion, and even higher; due to the strong friction and heat, the extrusion speed of aluminum alloys and aluminum alloys is limited, and the extrusion die wear is accelerated. .
II: Reverse extrusion (back extrusion)
The extrusion of the extrusion of the metal when the extrusion direction of the product is opposite to that of the extrusion axis is called reverse extrusion, as shown in Figure 1-2b. Reverse extrusion is mainly used in aluminum and aluminum alloys (in which the application of high-strength aluminum alloys is relatively more) hot extrusion molding of pipes and bars, and cold extrusion forming of various aluminum alloy parts. In reverse extrusion, there is no relative sliding between the metal blank and the extrusion cylinder, the required extrusion force is small, and the energy consumption of the extrusion is low. Therefore, in the same capacity of the device 7, the back extrusion can achieve a greater degree of deformation. Pressure deformation, or extrusion deformation of the higher resistance of the alloy. Different from the positive extrusion, when the back extrusion is performed, the metal flow is mainly concentrated in the area near the die hole, so that the deformation of the metal is more uniform along the longitudinal direction of the article. However, the back extrusion technology and operation are more complex, the gap length is longer than the positive extrusion, the surface quality of the extruded products is difficult to control, and special extrusion equipment and tools are needed. The application of back extrusion is limited. However, in recent years, with the development of special anti-extrusion presses and the development of tooling and die technology, the reverse extrusion of aluminum alloys has become more and more widely used. 2.3 Composite Extrusion Compound Extrusion Combines the characteristics of forward extrusion and reverse extrusion to produce double cups and cups with round, square, hexagonal, toothed, petal-shaped cross-sections. Class and rod extrusions can also produce asymmetric extrusions with equal sections. The composite extrusion method is such that the direction of the flow of a part of the metal of the billet is the same as the direction of the movement of the pressing shaft during the positive extrusion, and the flow direction of the other part of the metal is opposite to the direction of the movement of the pressing shaft.
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