Metal Forming- manufacturing Process

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 a standard form
such as plates, sheets, rods, tubes, and structural sections.

Primary Metal Forming Processes
􀂄Rolling
􀂄Forging
􀂄Extrusion
􀂄Tube and wire drawing
􀂄and Deep drawing
􀂄Although Punching and Blanking operations are
not metal forming processes however these will be
covered due to similarity with deep drawing
process.

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
the thickness of the material or changes its cross-sectional
area
􀂄The geometry of the product depending 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.

􀂄In rolling the crystals get elongated in the rolling direction. In cold
rolling crystal more or less retain the elongated shape but in hot
rolling they start reforming after coming out from the deformation
zone
􀂄The peripheral velocity of rolls at entry exceeds that of the
strip, which is dragged in if the interface friction is high
enough.
􀂄In the deformation zone, the thickness of the strip gets reduced
and it elongates. This increases the linear speed of the at the
exit.
􀂄Thus there exist a neutral point where roll speed and strip
speeds are equal. At this point the direction of the friction
reverses.
􀂄When the angle of contact α exceeds the friction angle λ the
rolls cannot draw the fresh strip
􀂄Roll torque, power, etc. increase with the increase in roll work
contact length or roll radius.

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