Aluminum extrusion: force and pressure

Aluminum Extrusion Operation

Central operation in the production of aluminum profiles is their compaction extrusion press. The main parameters, which affect the magnitude of the pressing force of a aluminum profile are:

  • type of pressing (direct or reverse);
  • pressing ratio (stretch ratio);
  • pressing temperature;
  • pressing speed;
  • workpiece length;
  • the type and chemical composition aluminum alloy.

See. more Aluminum extrusion: from billet to finished profile

pressure molding

The figure 1 shows the variation of the pressing pressure, depending on the movement of the slide in the container. Pressing pressure - a pressing force, divided by the cross sectional area of ​​the workpiece.

With direct pressing of aluminum profiles, a rapid increase in the pressing pressure at the beginning of the ram movement corresponds to the initial upsetting (unpressurization) of the workpiece, when it fills the container.

Maximum pressure corresponds to the passage of the front end of the blank material through a die. Once the front end of workpiece passes through the matrix required, pressing pressure gradually decreases with decreasing length of the billet in the container.

AND, finally, at the end of the cycle the pressure pressing the workpiece pressing briefly again increases in the formation of the discard, which contains a large amount of oxides and other metal and non-metallic inclusions from the surface layer of the ingot billet.

The maximum preform length

The difference between the maximum and minimum pressure compaction arises from the efforts, which is required to "push" the workpiece through the container in spite of the frictional resistance between the workpiece material and the container wall:

  • the greater length of the workpiece remains in the container, the more force is needed to press.
  • the maximum length of the initial preform is about four pipe diameters.

izmenenie-nagruzki-pressa+ Figure 1

Components of the pressing pressure

Full compaction pressure pfloor it is convenient to conditionally break down into three components:

pfloor = pmat + ptr + psetup.

summand pmat - the pressure, which is necessary for the plastic deformation of the material through a die. It depends on the flow stress, and through him – by deformation, strain rate and temperature.

summand ptr - the pressure, to be added to pmat to overcome the friction in the movement of material along the wall of the container.

Finally, summand psetup – it is part of the pressure, which is necessary to make the work of the internal shear deformation of the material. Its value depends on the current and voltage values ​​cone angle deadband, that depends, first of all, from the pressing ratio (figure 2).

izbytochnaya-rabota-pressovaniyaFigure 2

Figure 2 shows, as the material elements in the center of the workpiece are subjected to a substantially pure elongation with changing cross section of the preform to be pressed aluminum profile. The elements of the work material near the container are subjected to intensive shear strain. This shear deformation requires energy, which not directly linked to the change in the size of the workpiece to the profile, and it is called "excessive" work. At a sufficiently high friction between the container and the workpiece during material is concentrated in the direction center of the preform, and having internal plastic shear plane. It also happens when, when the surface of the heated workpiece is cooled by the colder container. When between the container and the condition of total workpiece occurs "sticking", metal separated within the workpiece along the maximum shear surface, and a thin outer shell of the preform remains on the container wall. Therefore, the entire surface is pressed aluminum profile is formed from pure domestic workpiece material.

Model motion alumina

A deeper understanding of the compaction pressure provides a model of material movement through the container and die under the following simplifying assumptions (Figure 3) [1]:

  • Pdiameter round billet ressovanie DC through a continuous matrix of a belt, located at right angles to her mirror;
  • compressible profile - rod diameter DE;
  • movement of material along the cone of the dead zone - shear deformation;
  • movement of material along the walls of the container - shear deformation.

model-processa-pressovaniyaFigure 3

Under this model, a complete secondary compaction pressure on the workpiece material at a distance FROM from the beginning of the dead zone (cm. Figure 3), taking into account the contribution of the frictional forces of the workpiece against the container, is as follows:

pFROM = 2sf (1 + cos α) / √3) ln (DC/DE) + 4(pf Z) / (√3DC),

Where pf- voltage and current a - cone angle deadband.

The first term gives an estimate of the average pressure, which is necessary for the metal flow only through the deadband cone, that is, when FROM= 0 (cm. Figure 3). It depends on the relationship of pressing, cone angle deadband and flow stress. The second term takes into account the contribution of the frictional resistance of the workpiece against the container: the larger the value FROM, the more pressure is required.

The actual compacting pressure in the range from 450 by 760 MPa, sometimes up 1040 MPa [2]. In practice, the press typically has a maximum force, which is greater than actually required for pressing. This allows, if necessary to lower the temperature and increase the compaction ram velocity for aluminum profiles elevated properties, including, quality surface.

The time required for extrusion of aluminum profiles press force is calculated as the product of the compacting pressure on the cross sectional area of ​​the cavity of the container. press force FP defined as FP = pA1 + p (2A2), Where A1 - sectional area of ​​the primary piston cavity, A2 - the cross-sectional area of ​​the cavity of each of the two side cylinders, and p - supplied hydraulic pressure in the cylinders, as it shown on the picture 4. Usually the operating pressure is about 250 have.

sxema-extrusionnogo-pressaFigure 4

Sources:
1. Saha P.
2. Aluminum and Aluminum Alloys.