Introduction to Manufacturing
Chapter 14: Forging
Forging
• Metal-forming process in which the
workpiece is shaped by compressive forces
applied through various dies and tools.
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Forging
• Cold Forging
• Requires greater forces and workpiece materials
must have sufficient ductility at room
temperature; good surface finish and
dimensional accuracy.
• Hot Forging
• Requires smaller forces, not as good finish or
dimensional accuracy; usually require additional
machining.
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Forging
• Forgeability
• Capability of a material to undergo
deformation without cracking.
• Forging is a discrete (individual) parts
process
• Forging is a near net shape process
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Open-Die Forging
• (upsetting or flat-die forging)
• Simplest forging process.
• Solid workpiece is set between two flat dies
and reduced (height) through compression.
• Barreling (outward bowing of material)
minimized with the use of lubricants.
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Cogging:
• Drawing out
• Operation where the thickness of a bar is
reduced by successive forging steps at
certain intervals.
• Typical for parts such as I-beams which must
be pre-shaped before rolling
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Impression-Die Forging
• Work piece forms in between shape of die
cavities (impressions).
• Flash: material which flows out from dies
(frictional resistance causes material to fill
the inside of the die cavity).
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Impression-Die Forging
(Cont.)
1. blank (part which has been cropped or
cut from bar stock).
2. blocking (rough shaping with dies).
3. finishing (using impression dies, forging
the final part shape).
4. trimming (removing the flash).
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Closed-Die Forging
• flashless forging (flash does not form).
• workpiece completely fills the die cavity. Volume
of material is precise.
• Precision Forging: near-net-shape, net-shape
forging – (volume control – gears, connecting
rods)
• Coining: pressures five to six times the strength
of material.
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Related Forging Operations
• Heading
• upsetting operation, usually performed at the
end of a round rod or wire to produce a large
cross section (bolts, rivets); warm, cold, or hot
process. (Fig. 14.11)
• Piercing
• indenting, without breaking, the surface of a
workpiece with a punch to produce a cavity or an
impression (pressure is usually 3-5 times the
strength of material). (Fig. 14.12)
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Related Forging Operations
• Hubbing
• pressing a hardened punch into the surface of a
block of metal to produce a cavity (create dies
for tools, tableware, etc.).
• Roll Forging
• the cross section of a bar is reduced or shaped
by passing it through a pair of rolls with shaped
grooves (leaf springs, hand tools). (discrete
parts)
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Related Forging Operations
• Skew Rolling
• similar to roll forging
• Ball bearing production
• Orbital Forging
• upper die moves along an orbital path
above the part which is also spinning.
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Related Forging Operations
• Incremental Forging
• process where a blank is forged into a
shape in several small steps (the die
penetrates the blank at different depths
across the surface). Similar to cogging.
• Isothermal Forging
• Hot die forging
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Related Forging Operations
• Rotary Swaging
• Radial Forging (circular shaped parts)
• Use reciprocating dies controlled by a cam
• Tube swaging
• Mandrel and dies
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Forging Machines
• Presses
• hydraulic
• mechanical
• screw
• Hammers
•
•
•
•
gravity drop
power drop
Counterblow (two hammers)
high-energy-rate Machines (pneumatic)
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