Transcript MSE 440/540: Processing of Metallic Materials

MSE 440/540: Processing of Metallic Materials
Instructors: Yuntian Zhu
Office: 308 RBII
Ph: 513-0559
[email protected]
Lecture 9: Forging
Department of Materials Science and Engineering
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Forging
Deformation process in which work is compressed
between two dies
• Oldest of the metal forming operations
– Dates from about 5000 B C
• Products: engine crankshafts, connecting rods, gears,
aircraft structural components, jet engine turbine parts
– Also, basic metals industries use forging to establish basic
shape of large parts that are subsequently machined to final
geometry and size
http://www.youtube.com/watch?v=Fa0FVYxbVWk (Axe, 5.5 min)
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Classification of Forging Operations
• Cold vs. hot forging:
– Hot or warm forging – advantage: reduction in
strength and increase in ductility of work metal
– Cold forging – advantage: increased strength due
to strain hardening
• Impact vs. press forging:
– Forge hammer - applies an impact force
– Forge press - applies gradual force
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Types of Forging Operations
• Open-die forging - work is compressed between two
flat dies, allowing metal to flow laterally with minimum
constraint
• Impression-die forging - die contains cavity or
impression that is imparted to workpart
– Metal flow is constrained so that flash is created
• Flashless forging (closed die forging) - workpart is
completely constrained in die
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Open-Die Forging
Compression of workpart between two flat
dies
– Deformation operation reduces height and
increases diameter of work
– Also called upsetting or upset forging
http://www.youtube.com/watch?v=dK6eZGeDjZg (Sword, 3 min)
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Open-Die Forging with No Friction
• (1) Start of process with workpiece at its original length
and diameter, (2) partial compression, and (3) final size
True strain:
ho
  ln
h
Quiz: What is engineering strain?
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Open-Die Forging with Friction
Actual deformation of a cylindrical workpart in open-die
forging, showing pronounced barreling: (1) start of
process, (2) partial deformation, and (3) final shape
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Impression-Die Forging
Compression of workpart by dies
• Flash is formed by metal that flows beyond die cavity
into small gap between die plates
• Flash must be later trimmed, but it serves an important
function during compression:
– As flash forms, friction resists continued metal flow into gap,
constraining metal to fill die cavity
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Impression-Die Forging Practice
• Several forming steps are often required
– With separate die cavities for each step
• Beginning steps redistribute metal for more
uniform deformation and desired metallurgical
structure in subsequent steps
• Final steps bring the part to final geometry
http://www.youtube.com/watch?v=mySkT0Gw_X0 (1 min)
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Advantages and Limitations of
Impression-Die Forging
• Advantages compared to machining from solid stock:
–
–
–
–
Higher production rates
Less waste of metal
Greater strength
Favorable grain orientation in the metal
• Limitations:
– Not capable of close tolerances
– Machining is often required to achieve accuracies and
features needed
Quiz: why forging improve the strength?
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Flashless (closed die) Forging
Compression of work in punch and die tooling whose
cavity does not allow for flash
• Starting work volume must equal die cavity volume
within very close tolerance
• Process control more demanding than
impression-die forging
• Best suited to part geometries that are simple and
symmetrical
• Often classified as a precision forging process
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Flashless Forging (Closed Die Forging)
• (1) Just before contact with workpiece, (2)
partial compression, and (3) final punch and
die closure
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Upset Forging
•
Upset forging to form a head on a bolt or similar
hardware item: (1) wire stock is fed to stop, (2) gripping
dies close on stock and stop retracts, (3) punch moves
forward, (4) bottoms to form the head
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Heading (Upset Forging)
•
Examples of heading operations: (a) heading a nail using
open dies, (b) round head formed by punch, (c) and (d) two
common head styles for screws formed by die, (e) carriage
bolt head formed by punch and die
http://www.youtube.com/watch?v=218nPKuoKSM (Nail, 1.5 miin)
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Swaging
Accomplished by rotating dies that
hammer a workpiece radially inward to
taper it as the piece is fed into the dies
• Used to reduce diameter of tube or solid
rod stock
• Mandrel sometimes required to control
shape and size of internal diameter of
tubular parts
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Swaging and Radial Forging
• Swaging process to reduce solid rod stock; dies rotate as they
hammer the work
• In radial forging, workpiece rotates while dies remain in a fixed
orientation as they hammer the work
http://www.youtube.com/watch?v=ilL8ViUDUKc (cartoon, 1.5 min)
http://www.youtube.com/watch?v=o1ZU6Yh0ce4 (37 sec)
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HW assignment
• Reading assignment: Chapters 13
• Review Questions: 13.10, 13.11, 13.12,
13.14,
• Problems: 13.10, 13.12, 13.14
Department of Materials Science and Engineering
17
NC State University