Extrusion press stretching machine: theory and practice

Press line for aluminum extrusion except the extrusion press includes a considerable number of pieces of equipment throughout the processing chain of production of aluminum profiles, how to press, and after the press. stretching machine, which is located at the exit of the press, is one such piece of equipment [1].

Technological operation profiles Changes

after extrusion,, ie after exiting the die, extruded length whip 50 m changes usually require dilation. Therefore, these lashes are transmitted to the receiver through a cooling table to table tenter.

Editing stretching produce is almost at "room" temperature, When profiles have cooled enough to work safely with them. The amount of residual elongation profile Percentage changes after surgery, usually, from 1 by 3 %.

Editing is an almost obligatory process step, since under the influence of non-uniform plastic deformation during extrusion and uneven cooling during quenching profiles having residual stresses. These stresses cause warping of the finished profiles of camber and twist.

Stretching machine extrusion press

The stretching machine of the extrusion press has two main functions:

  • edit profile after the extrusion process, to bring it into line with the requirements of standard tolerances sizes and shapes, including, straightness and twisting;
  • remove or reduce the maximum residual stress, are formed in the aluminum profiles during manufacture.

The figure 1 Stretching is a company car Tecalex, known manufacturer of equipment for extrusion presses.

Figure 1 - Stretching Machine Company Tecalex [1]

The main technical characteristics of a modern stretching machine are as follows [1]:

  • Stretching profiles made between the two heads, fixed and mobile. The movable head is automatically set to the length of the expandable Profile.
  • Clips have a special shape, which excludes slippage of the profiles in the heads during their stretching (Figure 2).
  • Profiles smoothly supplied to each head of the machine by means of walking beams.
  • The machine has the ability in various modes:
    – two operators, one on each head;
    – one operator on a fixed head with a control panel (figure 3) and a surveillance camera on a movable head (figure 4);
    – fully automatic operation without operator.
  • Infrared communication between the two heads for the transmission of control signals
  • Communication between the two heads via web-cam industrial system.
  • The distance between the heads is controlled laser system.

Figure 2 – Stretching Machine Vise [1]

Figure 3 – Stretcher control panel [1]

Figure 4 – Surveillance camera on the movable head of the stretching machine [1]

Maximum force stretching machine, dependent on the workpiece diameter, which is applied on the press, as well as on the type of aluminum alloys. for instance, press with a pressing force 1350 tons and a diameter of the workpiece 6 inches (152 mm) for pressing soft and medium strength alloys (6xxx series) can be stretched with maximum force 20 tonnes.

The principle of stretching changes

Fixed head can change its position on the frame stretching machine, depending on the length of the expandable Profile. The power stretcher must be greater than, than that required for straightening tensile force. The tensile force is a function of the following factors:

  • cross-sectional area of ​​the profile;
  • yield strength of aluminum alloy, material of the profile in the hardened, but aged condition.

The principle of stretch straightening is shown in Figure 5 [2].

Figure 5 - Principle of profile straightening by tension [2]

The amount of stretching is determined by the amount of permanent deformation in the longitudinal direction:

Stretch = (LS – LE)/LE ×100 %

Where
LS - the length of the extruded lash after stretching;
LE - the length of the extruded whip up tension.

The amount of residual strain is selected for each specific profile depending on a number of factors, which include [2]:

  • cross-sectional shape and dimensions;
  • availability of critical dimensions, such as gaps, cavities or semi-closed cavities ("tongues");
  • tight tolerances;
  • need for applying protective and decorative covering.

The following factors can also affect the quality of stretch straightening (see. Figure 5):

  • vise design for profiles of various shapes;
  • tensile force FS for a given aluminum alloy and profile;
  • stretching speed VS

Changes Mechanics stretching aluminum profiles

The mechanics of the process of stretching aluminum profiles on a stretching machine is similar to the mechanics of testing an aluminum sample during tensile testing [3]. The figure 6 shows a typical diagram for stretching samples of aluminum alloys. The essential difference between the profiles for the stretching process is, it ends much earlier, what starts necking.

Figure 6 - A typical diagram of stretching
when testing aluminum samples [3]

When the load increases in the sample arises voltage level, at which it begins to undergo irreversible plastic deformation. This voltage level is called the yield point or elastic limit. When loading the metal above the yield strain dependence of the voltage stops being linear, as it was in the elastic region of deformation (see. Figure 6).

Process aluminum profiles Changes stretching

The amount of tensile residual deformation is controlled in several ways [4]:

  • "approximately" – at the discretion of the operator with the adjustment of the stretching parameters;
  • by the applied effort;
  • by extension length;
  • Percentage of the total length of elongated whip.

On older presses operators located at both ends of the extruded whip - with head and tail. On new presses stretching machine can be operated with a single operator or without operator, in automatic mode [1].

Usually, however, when frequent changes of species profiles and pressing on the new matrix on tenter should work at least one operator. It's necessary, to solve problems, that can occur with frequent changes of profiles, especially for those, which tend to form along the length of the form "banana". In this case, at the end of the whip, where there is no operator, use remote video monitoring.

accident prevention

To minimize the risk of damage to the operator's hands, Control stretching machine includes dual buttons or switches. Only in case that, when both hands are on the operator control panel, machine vise can clamp the profile.

Sources:

1. http://www.tecalex.net/en/handling-tables-zone.html

2. Aluminum Extrusion Technology / Pradip K. Saha - ASM International, 2000.

3. Evaluation of Process Mechanism and Parameters for Automated Stretching Line /
P. Kazanowski and R. Dickson, Aluminum Extrusion Technology Seminar, Chicago, 2012.

4. The Extrusion Press Maintenance Manual -Chapter 8. Profile Handling Systems / Al Kennedy, 2004