Molding or extrusion
Metal Pressing - a technology, wherein the preform, generally circular cross-section, extruded rod press - ram - under high pressure through a special instrument - the matrix - in one or more profile extruded products - rods, wire, tubes or profiles. This technology is also referred to as extrusion. It is used mainly for the production of rods, wire, tubes and profiles of aluminum and copper alloys. However, pressing (extrusion) is also used for the production of small quantities of stainless steel pipes., steel profiles and semi-finished products from other metals .
Forward and reverse pressing
The figure below shows the two most important pressing methods:
- direct pressing;
- reverse pressing.
Figure - Pressing methods:
a) direct pressing; b) back pressing 
When direct compression ram, usually mounted on a front end of the press washer, pushes the billet from the container through the stationary forming tool - matrix. In this method, a relative movement occurs between the workpiece and the container.
In the reverse extrusion, conversely, matrix of a front hollow ram and its forced through the workpiece during translational motion muffled rear container. In this case, there is no relative movement between the workpiece and the container.
Pressure and temperature
During compaction the preform is generated inside the uniform compression stress state, which enables the development of large strain with a low risk of cracking. The ratio between the cross sectional area of the preform and the molded profile called reduction ratio or compression ratio. Typically, this value is between 10 to 100. In some cases,, for example, when pressing a brass wire, compression ratio can reach 1000. However, this requires a low yield strength material to be pressed, and, Moreover, high specific pressing pressure - up 1000 N / mm2 .
For these reasons, metal pressing is usually done at high temperatures:
- aluminum alloys - generally ranging from 400 to 500 ºS;
- copper alloy - in the range of 600 to 900 ºS;
- stainless steels and special alloys - up 1250 oC.
It should be noted, that there are also other except for the forward and reverse pressing, special, pressing methods, which are used in much smaller quantities:
- hydrostatic pressing;
- Conform method;
- cable sheaths manufacturing method.
Pressing on the rod-profile press used in the production of wire, bands, bars, solid and hollow profiles. The English term "rod extrusion" corresponds to the rod-shaped pressing [1, 2]. In this case, the hollow profiles, including, tubes, pressed through a matrix with so-called welding chamber. In these chambers the material is welded in the process of deformation within the matrix. This is called "pressure welding". Therefore, hollow profiles, including, tubes, which make this method of pressing, have welds.
On truboprofilnyh presses produce tubes and hollow profiles, who do not have welds. These tubes are called "seamless pipes". For this, special mandrels are used (“needle”), which pass through the workpiece - “stitch” her. Wherein the mandrel forms the inner contour of the tube, and the matrix - the outer. Pipe extrusion corresponds to the English term "tube extrusion" [1, 2].
1. Extrusion: Second Edition / M. Bauser, G. Sauer, K. Siegert – ASM International, 2006
2.Pressing of nonferrous metals and alloys / Grabarnik LM, Nagaytsev AA. - M .: Metallurgy, 1991