06-07-2012, 12:07 PM
Metal Forming Processes
Metal%20Forming%20Processes.pdf (Size: 9.01 MB / Downloads: 1,991)
Introduction
Practically all metals, which are not used in cast form are
reduced to some standard shapes for subsequent processing.
Manufacturing companies producing metals supply metals
in form of ingots which are obtained by casting liquid metal
into a square cross section.
Slab (500-1800 mm wide and 50-300 mm thick)
Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to cast
the liquid metal into slabs, billets or blooms.
These shapes are further processed through hot rolling,
forging or extrusion, to produce materials in standard form
such as plates, sheets, rods, tubes and structural sections.
Salient points about rolling
Rolling is the most extensively used metal forming
process and its share is roughly 90%
The material to be rolled is drawn by means of friction
into the two revolving roll gap
The compressive forces applied by the rolls reduce the
thickness of the material or changes its cross sectional
area
The geometry of the product depend on the contour of
the roll gap
Roll materials are cast iron, cast steel and forged steel
because of high strength and wear resistance
requirements
Hot rolls are generally rough so that they can bite the
work, and cold rolls are ground and polished for good
finish
Pressure during rolling
Typical pressure variation along
the contact length in flat rolling.
The peak pressure is located at
the neutral point. The area
beneath the curve, represents
roll force.
Direct and Indirect Extrusion
In direct extrusion metal flows in the
same direction as that of the ram.
Because of the relative motion between
the heated billet and the chamber walls,
friction is severe and is reduced by using
molten glass as a lubricant in case of
steels at higher temperatures. At lower
temperatures, oils with graphite powder
is used for lubrication.
In indirect extrusion process metal
flows in the opposite direction of the
ram. It is more efficient since it reduces
friction losses considerably. The process,
however, is not used extensively because
it restricts the length of the extruded
component.