PRODUCTION OF METALS
The term metal production refers to all of the
processes involved in the conversion of a raw
material, such as a metallic ore , to a final form in
which the metal can be used for some commercial
or industrial purpose. In some instances, metal
production involves relatively few steps since the
metal already occurs in an elemental form in
nature. Such is the case with gold, silver, platinum,
and other so-called noble metals. These metals
normally occur in nature uncombined with other
elements and can therefore be put to some
commercial use with comparatively little additional
treatment.
In the majority of cases, however, metals occur in
nature as compounds, such as the oxide or the
sulfide, and must first be converted to their
elemental state. They may then be treated in a
wide variety of ways in order to make them usable
for specific practical applications.
Metal Manufacturing Processes
Casting Processes : Metal casting processes
involve pouring molten metal into a mold cavity
where, once solid, the metal take on the shape of
the cavity. They can be divided into two categories
based on the type of mold:
Expendable Mold Casting: where the mold must be
destroyed in order to remove the part
Permanent Mold Casting: for which the mold is
fabricated out of a ductile material and can be
used repeatedly.
Powder Metallurgy: In powder metallurgy a metal
powder is compacted into the desired shape and
heated to cause the particles to bond into a rigid
mass.
Deformation Processes : Deformation processes
include metal forming and sheet metalworking
processes. These processes use plastic
deformation resulting from the use of a tool that
applies stresses to the piece which exceed the
yield stress of the metal. There are two types of
deformation processes:
Bulk Processes: Bulk deformation processes are
characterized by large deformations and shape
changes and by the fact that the surface area to
volume ratio is relatively small. Bulk processes
include rolling, forging, extrusion and wire and bar
drawing.
Sheet Metalworking: Sheet metalworking
processes are performed on metal sheets, strips
and coils having a high surface area to volume
ratio. These operations use a punch and die to
form the workpiece. Bending, drawing and shearing
are types of sheet metalworking processes.
Material Removal Processes : These processes
remove extra material from the workpiece in order
to achieve the desired shape and include:
Machining Operations: These are cutting
operations using cutting tools that are harder than
the metal of the product. They include turning, drilling, milling, shaping, planing, broaching and
sawing.
Abrasive Machining: In these methods material is
removed by abrasive particles that normally form a
bonded wheel. Grinding, honing and lapping are
included in this category.
Nontraditional Processes: These methods use
lasers, electron beams, chemical erosion, electric
discharge and electrochemical energy instead of
traditional cutting and grinding tools.
Joining and Assembly Processes: In these
operations multiple parts are connected either
permanently or semipermanently to form a new
entity.