Aluminum extrusion: a brief introduction

 

Aluminum extrusion (or aluminum extrusion) is an industrial molding process for the production of long aluminum profiles with a constant cross section. Under the brand aluminum intended to be unalloyed aluminum, and aluminum alloys.

The following summarizes the aluminum pressing process. It is designed as an introduction of technical personnel press production with this technology, and may also be useful as information for management and support staff.

extrusion press

Aluminum cylindrical rods - preform - is heated and pressed through a die having one or more openings, to obtain a profile with a predetermined cross-section. The most common type of molding is compression molding, when the press ram pushes the aluminum billet through the stationary (stationary) die. Most of the presses for this technology are horizontal hydraulic presses. Capacity depends on the size press matrices used, which may have a diameter of 100 to 1000 mm. For the majority of extruded aluminum products used matrix diameter of 175 to 250 mm. For matrices such diameter are required extrusion presses with a force of 1500 to 2000 tonnes.

compression molding

Scheme typical extrusion press for direct compression aluminum is shown in Figure 1.


1 - press stamp; 2 - press washer; 3 – container; 4 - feeder; 5 - the matrix; 6 - lining;
7 - bolster; 8 - matrix holder; 9 - the holder die assembly

Figure 1 - Diagram of direct extrusion of aluminum [1]

The ram (1) transfers the force from the main cylinder of the extrusion press to the aluminum billet, which is loaded into the container (3). A steel press washer is installed on the ram (2). Press washer included in the container with a very small gap, which prevents aluminum (shown in black) from being squeezed into the container. Matrix (5) is part of the matrix set, which is made of a heat-resistant tool steels. Lined (6), bolster (support ring) (7) and die holder (8) and die set holder (9) support the die under the influence of pressing force. A feeder (4) can be installed in front of the die, to expand the flow of aluminum from the container to a wider portion of the matrix.

Pressing without lubrication

Since the direct compression aluminum lubricant is not applicable, the outer layer of the workpiece is cut under the influence of friction on the wall of the container. This has a positive effect on the quality of pressed aluminum products. The thing is, in that the outer layer of cast billets has a higher content of iron-containing intermetallic particles and Mg2Yes [1]. These contaminants can be a source of surface defects on the finished extruded aluminum product. When direct compression without the lubrication they accumulate at the end of the blank.

Press and the rest of the transverse weld

This part of the workpiece, which is called the press residue, cut off before, as a new workpiece is loaded in the press. During the next working stroke of the press from a new aluminum preform under the influence of high pressure and high temperature welded to aluminum from the previous workpiece, which remained in the matrix. This creates a continuous extruded aluminum product. Place the welding of two adjacent blanks called transverse weld. Since near this seam has reduced mechanical properties, and unsatisfactory appearance, it is usually cut and shipped to the smelter.

Heating of the workpiece and the pressing tool

Before loading to press the aluminum billet is heated to 400-500 ° C depending on the alloy. This facilitates the deformation and minimizes the strain hardening aluminum. The heated workpiece is in a plastic (but not liquid) state. Container and also heated matrix, to prevent the workpiece podstuzhivanie. The dimensions of the matrix holes make some more, than the cross-sectional dimensions of the finished pressed Profile, since aluminum is reduced while cooling longer, than tool steel, which is made of matrix.

types of matrices

The most widely used types of dies for aluminum extrusion are flat (solid) dies and porthole dies.. Flat matrix consist of only one steel flat disk and their use, to press solid profiles (figure 2 (and)). Matrix "porthol" consists of two parts, matrix disk and a mandrel part. This allows hollow profiles to be pressed (figure 2 (b)) and semi-hollow profiles (figure 2 (in)). Both types of matrices may have multiple channels pressing, so it can be pressed simultaneously several identical profiles.

a - solid profile; b - hollow profile; c - semi-hollow profile

Figure 2 - Three types of extruded profiles [1]

flat matrix

Flat (solid) matrix is ​​shown in the figure 3. The most important characteristics of a flat matrix are:

  • fork camera (1), pocket in front of the work belt; applies when necessary;
  • work belt (2);
  • flared outlet (3).


Figure 3 - Flat (solid) matrix [1]

Work belt - is that part of the matrix, where aluminum gets its final shape. Safety belt does not pass through the entire thickness of the matrix, and have a length 15 mm or less. It is necessary, to minimize the required pressing force.

The function of the expanding output of the matrix - to provide the necessary power support running web, but without coming out of contact with the aluminum matrix. To the output part of the walls are at an angle of about 5º and, Moreover, it usually has some shoulder immediately behind the working belt.

The function of a special pocket – prechamber - to protect the "breakable" working belt from damage during separation of the discard, and to facilitate welding the workpiece residue in the matrix with the next workpiece. Moreover, prechamber used as alumina flow control means.

Matrix "porthol"

The figure 4 shows an array of "porthol". As I mentioned, it consists of two parts, matrix disk (a) and mandrel part (b).

Figure 4 - Matrix "porthole" [1]

The mandrel can have one or more mandrels (1) with working belts, which form the inner contour of the aluminum profile. The mandrels are connected to the mandrel body by means of bridges (2). Aluminum streams flow around these bridges through feed holes (ports) (3) and rejoin in the welding chambers (4). The final formation of the profile takes place simultaneously on the working belts of the mandrel and the matrix disk (5).

Dies Correction


Figure 5 – Methods for slowing down or accelerating the flow of metal through an extrusion die [2]

A source:

  1. CAD Implentation of Design Rules for Aluminium Extrusion Dies / Gijs van Ouwerkerk, PhD Thesis, the University of Twente, Enschede, The Netherlands, 2009
  2. TALAT 1302