inside the tubing to support the tube during the drawing operation.
This forces the metal to flow between the die and the mandrel and
controls the wall thickness and the inside and outside tube diameters.
Stamping and Pressing.
Stamping and pressing sheet metal into
molds or dies are methods of shaping or forming various-sized parts
or complete pieces.
In a broad sense, the two terms have little
difference in meaning.
However, stamping is generally applied to
forming small objects that can be shaped by one rapid blow of a
machine.
Pressing, on the other hand, describes the process that
uses a slow, steady stroke or movement to form a large piece or
section.
Making parts by stamping and pressing brings the aviation
industry one step nearer to mass production.
However, constant
changes in aircraft design make it necessary to alter or replace dies
frequently.
SUMMARY
In general, most alloys consist of two or more metals.
Other
elements such as carbon, silicon, and sulfur may be present.
Industrial alloys are classed as ferrous (iron based) and non-
ferrous. Ferrous alloys with less than 0.13 percent carbon by weight
are steels.
Cast and wrought iron have 2 to 5 percent carbon by
weight. Alloy steel and special steel have relatively large amounts
of chromium and nickel.
The aircraft industry requires lightweight
alloys such as aluminum and magnesium; titanium and titanium-based
alloys are much used.
Alloys are usually prepared by
melting the constituent metals
together. The melting can be done
in furnaces fired by gas, coke, or
oil.
Electrical heating is also
used.
Some alloys, such as pig
iron, are prepared directly by the
process used to extract the metal
from the ore.
A metal can be made harder, stronger, and more resistant to impact by
controlled heating and cooling. Heating (annealing) can make a metal
softer. Metal properties are often improved at the expense of other
properties. Heat-treating processes differ in three important ways:
the temperature to which the metal is treated, the rate at which it
is cooled, and the properties possessed by the finished metal.
The
most common forms of metal heat treatment are hardening, tempering,
normalizing, case hardening, and hot working. Hardening consists
of heating the steel to the appropriate temperature and then
cooling it rapidly by quenching.
Heating the steel below the
critical point and then cooling it in still air tempers it.
Annealing requires heating the metal to the proper temperatures,
holding that temperature for the required time, and cooling the metal
to room temperature. Normalizing consists of heating metal to the
27
AL0992
Previous Page
