Cold Extrusion of Metals
is the process by which long straight metal parts can be produced.
The cross-sections that can be produced vary from solid round,
rectangular, to L shapes, T shapes. Tubes and many other different
types. Extrusion is done by squeezing metal in a closed cavity
through a tool, known as a die using either a mechanical or
produces compressive and shear forces in the stock. No tensile
is produced, which makes high deformation possible without
tearing the metal. The cavity in which the raw material is
contained is lined with a wear resistant material. This can
withstand the high radial loads that are created when the
material is pushed the die.
cold extrusion, which is used for the manufacture of special
sections and hollow articles, the material is generally made
to flow in the cold condition by the application of high pressure,
which forces it through the cavity enclosed between a punch
and a die. A distinction is to be made between forward extrusion
(Fig.2), in which the extruded metal flows in the direction
of movement of the punch, and backward extrusion (Fig.1),
which is characterized by the opposite direction of flow.
The two techniques may be used in simultaneous combination
(Figs 3 & 4), Cold extrusion can be used with any material
that possesses adequate cold work–ability; e.g., tin,
zinc, copper and its alloys, aluminum, and its alloys and
it is for these metals that the process is most widely adopted.
Low carbon soft-annealed steel can also be cold-extruded.
If the product cannot be fully shaped in a single operation,
the extrusion process may be performed in several stages.
The solid or hollow products that can be made by cold extrusion
are relatively limited in size.
cold extrusions are produced consists of round blanks, lengths
cut from bars, or specially performed blanks. The punches
and dies used in cold extrusion are subject to severe working
conditions and are made of wear-resistant tools steels; e.g.,
high-alloy chromium steels. To reduce friction, the tool surfaces
are polished. In the cold extrusion of steel the blank may
additionally be given a phosphate coating to minimize friction.
widely used cold extrusion method is impact extrusion. It
is used for making collapsible tubes of lead, tin, zinc and
aluminum. E.g., toothpaste tubes. Zinc battery cans are also
produced in this way. A pointed punch descends swiftly on
to a disc-shaped blank arranged in a die, causing the metal
to flow upwards and around the punch.
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