What Is The Special Hot Extrusion Forging Process

The hot extrusion method is also a common process in forging processing. This process is mainly used to manufacture long parts, rods, tubes, profiles, etc. with ordinary cross-sections. These extruded parts can be used directly as structural parts or after cutting.

To be finished as machine parts. For the hot extrusion process, let's introduce it in detail below.

1. The basic concept of hot extrusion

During hot extrusion, the heating temperature is above the recrystallization temperature of the blank metal, and it is compressed in three directions, so many materials can be hot extruded. When squeezing again, the blank is put into the squeeze cylinder, and under the action of the squeeze rod, when the pressure exceeds the resistance of the material, it is deformed through the die hole to obtain the desired shape of the workpiece. Compared with cold and warm extrusion, the deformation force during hot extrusion is small, the deformation is large, and very complex sections can be extruded. However, the mold requirements are high, and the surface roughness of the hot workpiece is also large.

2. Preparation, preheating and heating of the blank

• (1) Preparation of blanks: Almost all metals can be hot extruded. The blanks are generally cast and continuous casting billets and forging billets. Because the cylindrical surface of the blank will become the surface of the extrusion, it is necessary to particularly avoid nominal bubbles and surface cracks.
• (2) Preheating and heating of the blank: Before the hot extrusion, the blank must be preheated. The purpose of preheating is mainly to prevent coarse grains of the billet after extrusion and cracks on the surface, improve productivity and save energy. The preheating temperature varies according to the material, and it is generally preheated to a temperature where there is no severe oxidation.

3. Lubricant and its removal

For some heat-resistant materials such as steel, nickel-based alloys, and titanium alloys, glass lubricants are effective. In addition, soft metal is also used to wrap the surface of the blank to provide lubrication and prevent oxidation and cracking. For example, aluminum alloys are coated with pure aluminum, cast iron, tungsten, uranium, etc. are coated with steel plates, and so on.

4. Hot extrusion die structure and die materials

(1) The structure design of the punch for positive extrusion

The mechanism of the punch for positive extrusion is basically the same as that of cold and warm extrusion. Sometimes the extrusion head is inserted between the blank and the extrusion rod. The extrusion head can prevent the extrusion stem from directly contacting the high-temperature blank, so as to prevent the temperature rise and damage of the front end of the extrusion rod, which is beneficial to extend the life of the extrusion rod. If the gap between the outer diameter of the extrusion head and the inner diameter of the extrusion cylinder is kept small, the gap between the extrusion rod and the extrusion cylinder can be a larger value to reduce the accuracy requirements of the press.

(2) Die for back extrusion

The distance between the top surface of the blank and the upper plane of the cavity after the blank is placed in the cavity is 4 to 5 mm. When the die is relatively small, the whole is used; but if the die needs to be cooled, the hot press fit can be used, and a prestressed ring is added to the die, and there is a spiral cold groove in the prestressed ring. In order to avoid the overall die from cracking under high internal pressure and temperature, it is often reasonably divided into two parts, namely the extrusion cylinder and the die.

(3) Extrusion tube

For hot-extruded steel and refractory alloys, when the metal deformation resistance reaches 1300 MPa, and the diameter of the extrusion cylinder is less than 100 mm, four layers are used. Each layer of prestressed ring has an interference fit, and the axial compression and radial interference can be 25% to 40% of the cold extrusion die.

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