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Forging of Metals
By Nadun Kuruppumullage
Deparment of Mechanical Engineering
Most of the slides are work of Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ.
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Outline
• Introduction to forging
• Open – Die Forging
• Impression Die & Closed – Die Forging
• Forging Machines
• Forging Practice and Process Capabilities
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What is Forging ?
• Forging is a process in which the workpiece is shaped by compressive forces applied through various dies and tools.
• Dating back to 4000 B.C.
• First used to make jewelery, coins etc.
• Typical forged items- Rivets, Bolts, Connecting rods,Gears
• Simplest Forging – Hammer & Anvil ( Blacksmith‘s work)
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Forged Components
(a) Schematic illustration of the steps involved in forging a knife. (b) Landing-gear
components for the C5A and C5B transport aircraft, made by forging. (c) General
view of a 445 MN (50,000 ton) hydraulic press.
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Metal flow of Forging
• Forged parts have good strength and toughness due to metal flow & grain structure can be controlled in forging.
• Forged parts can be used in highly stresssed and critical applications.
• Because of higher strength of the material, forging may require greater forces.
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Microstructure as a Function of Manufacturing Method
Schematic illustration of a part made by three different processes showing grain
flow. (a) Casting (b) Machining form a blank, and (c) forging. Each process has
its own advantages and limitations regarding external and internal characteristics,
material properties, dimensional accuracy, surface finish, and the economics of
production.
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Characteristics of Forging Process
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Open – Die Forging
• Solid work piece placed between two flat dies and reduced in height by compressing.
• This is also called as upsetting or flat die forging.
• The Open Die forging may have simple cavities to produce relatively simple forgings.
• Barrelling and cogging....
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Upsetting with Barreling
Solid cylindrical billet upset between two flat dies. (b) Uniform
deformation of the billet without friction. (c) Deformation with friction.
Note the barreling of the billet caused by friction forces at the billet-die
interfaces.
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Cogging Operation on a Rectangular Bar
(a) Schematic illustration of a cogging operation on a rectangular bar. Blacksmiths
use this process to reduce the thickness of bars by hammering the part on an anvil.
Reduction in thickness is accompanied by barreling, (b) Reducing the diameter of a
bar by open-die forging; note the movements of the dies and the workpiece. (c) The
thickness of a ring being reduced by open-die forging.
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Impression – Die Forging & Closed –Die Forging
• The work piece acquires the shape of the die cavities while being forged between two shaped dies.
• Flash can be formed.
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Impression-Die Forging
(a) through (c) Stages in impression-die forging of a solid round billet. Note the
formation of flash, which is excess metal that is subsequently trimmed off. (d)
Standard terminology for various features of a forging die.
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Die Inserts
Die inserts used in forging an automotive axle
housing.
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Forging a Rod, Fullering, and Edging
(a) Stages in forging a connecting rod for an internal combustion engine. Note the
amount of flash required to ensure proper filling of the die cavities. (b) Fullering
and (c) edging operations to properly distribute the material when preshaping the
blank for forging.
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Trimming Flash After Forging
Trimming flash from a forged part. Note that the thin
material at the center is removed by punching.
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Closed-Die Forging Versus Flashless Forging
Comparison of closed-die forging with flash (left side of each illustration) and
precision or flashless forging (right side) of a round billet
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Precision Forging
• Operations in which part formed is close to the final dimensions of the desired component.
• Having greater accuracies
• Requre less machining
• High capacity machines are required.
• E.g. Gears, Turbine Blades, housings..
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The Coining Process
(a) Schematic illustration of the coining process. The earliest coins were made by
open-die forging and lacked precision and sharp details. (b) An example of a
modern coining operation, showing the work piece and tooling. Note the detail
and superior finish that can be achieve in this process..
(b)
• Coining is a closed die forging process typically used in minting coins.
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Heading
(a) Heading operation to form heads on fasteners, such as nails and rivets. (b)
Sequence of operations to produce a typical bolt head by heading.
• Heading is an upsetting operation performed at the end of a round rod or wire in order to produce a large cross section.
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Stepped Pin
(a) The stepped pin (b) Illustration of the manufacturing steps used to produce
the stepped pin.
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Radial Forging
• In radial forging or swagging, a solid rod or tube is subjected to radial impact forces by a set of rollers in a cage.
• Action is similar to roller bearing.
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Swaging
(a) Schematic illustration of the rotary-swaging process. (b) Forming internal
profiles on a tubular work piece by swaging. (c) A die-closing swaging machine
showing forming of a stepped shaft. (d) Typical parts made by swaging.
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Swaging with and without a Mandrel
(a) Swaging of tubes without a mandrel; note the increase in wall
thickness in the die gap. (b) Swaging with a mandrel; note that the
final wall thickness of the tube depends on the mandrel diameter. (c)
Examples of cross-sections of tubes produced by swaging on shaped
mandrels. Rifling (internal spiral grooves) in small gun barrels can be
made by this process.
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Metals in Decreasing Order of Forgeability
• Forgeability is the capacity of a material to undergo defromation without cracking.
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Defects in Forged Parts
Examples of defects in forged parts. (a) Laps formed by web buckling during
forging; web thickness should be increased to avoid this problem. (b) Internal
defects caused by an oversized billet. Die cavities are filled prematurely, and the
material at the center flows past the filled regions as the die closes.
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Principles of Various Forging Machines
Schematic illustration of the principles of various forging machines.
(a) Mechanical press with an eccentric drive; the eccentric shaft can be
replaced by a crankshaft to give the up-and-down motion to the ram.
(b) Knuckle-joint press. (c) Screw press. (d) Hydraulic press.
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Cost-per-piece in Forging
Typical (cost-per-piece) in forging; note how the setup and the tooling costs-per-
piece decrease as the number of pieces forged increases if all pieces use the
same die.
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Costs of a Rod Made by Forging and Casting
Relative unit costs of a
small connecting rod made
by various forging and
casting processes. Note
that, for large quantities,
forging is more
economical. Sand casting
is the most economical
process for fewer then
about 20,000 pieces.
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Lotus Elise Series 2 and Vertical Suspension Uprights
(a) The Lotus Elise Series 2 Sport scar; (b) illustration of the original design
for the vertical suspension uprights, using an aluminum extrusion; (c) retrofit
design, using a steel forging; (d) optimized steel forging design for new car
models.
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Comparison of Suspension Designs for the Lotus