Transcript Document

Metal Forming Course
Bulk-Deformation Processes
PROCESS
Forging
Rolling
Flat
Shape
Extrusion
Drawing
Swaging
GENERAL CHARACTERISTICS
Production of discrete parts with a set of dies; some finishing
operations usually necessary; usually performed at elevated
temperatures; dies and equipment costs are high; moderate to high
labor costs; moderate to high operator skill.
Production of flat plate, sheet, and foil at high speeds, and with good
surface finish, especially in cold rolling; requires very high capital
investment; low to moderate labor cost.
Production of various structural shapes, such as I-beams and rails, at
high speeds; includes thread and ring rolling; requires shaped rolls
and expensive equipment; low to moderate labor cost; moderate
operator skill.
Production of long lengths of solid or hollow products with constant
cross-sections, usually performed at elevated temperatures; product is
then cut to desired lengths; can be competitive with roll forming; cold
extrusion has similarities to forging and is used to make discrete
products; moderate to high die and equipment cost; low to moderate
labor cost; low to moderate operator skill.
Production of long rod, wire, and tubing, with round or various crosssections; smaller cross-sections than extrusions; good surface finish;
low to moderate die, equipment and labor costs; low to moderate
operator skill.
Radial forging of discrete or long parts with various internal and
external shapes; generally carried out at room temperature; low to
moderate operator skill.
Metal Forming Course
Open-Die Forging
• (a) Ideal deformation of
a solid cylindrical
specimen compressed
between flat frictionless
dies.
•
(b) Deformation in
upsetting with friction at
the die-workpiece
interfaces.
Metal Forming Course
Grain Flow Lines
• Grain flow lines in
upsetting a solid steel
cylinder at elevated
temperatures. The
highly inhomogenous
deformation and
barreling. The differnet
shape of the bottem
section of the specimen
(as compared with the
top) results from the
hot specimen resting
on the lower, cool die
before deformation
proceeded.
Metal Forming Course
Impression (Closed) Die Forging
• Schematic illustration of stages in impression-die forging. Note
the formation of flash, or excess material that is subsequently
trimmed off.
Metal Forming Course
Load-Stroke Curve in Closed-Die Forging
• Typical load-stroke
curve for closed-die
forging. Note the
sharp increase in load
after the flash begins
to form. In hot-forging
operations, the flash
requires high levels of
stress, because it is
thin-that is, it has a
small h-and cooler
than the bulk of the
forging.
Metal Forming Course
• Schematic
illustration of
orbital-forging
process. The
die is in contact
with only a
portion of the
workpiece
surface. This
process is also
called rotary
forging, swing
forging, and
rocking-die
forging and can
be used for
forming bevel
gears, wheels,
and bearing
rings.
Metal Forming Course
Heading
• Forging heads on
fasteners such as bolts
and rivets. These
processes are called
heading.
Piercing Operations
• Examples of piercing
operations.
Metal Forming Course
Cogging Operation
• Schematic illustration of a cogging operation on a rectangular
bar. With simple tools, the thickness and cross-section of a bar
can be reduced by multiple cogging operations. Note the
barreling after cogging. Blacksmiths use a similar procedure to
reduce the thickness of parts in small increments by heating the
workpiece and hammering it numerous times.
Metal Forming Course
Roll Forging Operation
• Schematic illustration of a roll forging (cross-rolling) operation.
Tapered leaf springs and knives can be made by this process
with specially designed rolls.
Metal Forming Course
Manufacture of Spherical Blanks
• Production of steel balls for bearings
by the skew-rolling process. Balls for
bearings can also be made by the
followingforging process.
•Production of steel balls
by upsetting of a
cylindrical blank. Note the
formation of flash. The
balls are subsequently
ground and polished for
use as ball bearings and
in other mechanical
components.
Metal Forming Course
Internal Defects In Forging
• Laps formed
by buckling of
the web
during
forging.
• Internal defects produced in a forging because of an oversized
billet. The die cavities are filled prematurely, and the material at
the center flows past the filled regions as deformation continues.
Metal Forming Course
Defect Formation In Forging
• Effect of fillet radius on defect formation in forging. Small fillets
(right side of drawings) cause the defects.
Metal Forming Course
Forging A Connecting Rod
• Stages in forging a connecting rod for an internal combustion
engine. Note the amount of flash that is necessary to fill the die
cavities properly.
Metal Forming Course
Features Of A Forging Die
Hot-Forging Temperature Ranges
Metal
Aluminum alloys
Copper alloys
Nickel alloys
°C
400-450
625-950
870-1230
Metal
Alloy steels
Titanium alloys
Refractory alloys
°C
925-1260
750-795
975-1650
Metal Forming Course
Presses Used In Metalworking
• Schematic illustration of various types of presses used in
metalworking. The choice of the press is an important factor in
the overall operation.
Metal Forming Course
Flat-And-ShapeRolling Processes
Metal Forming Course
Flat-Rolling Process
• Schematic illustration of the
flat-rolling process. A greater
volume of metal is formed by
rolling than by any other
metalworking process.
• Relative velocity distribution
between roll and strip surfaces.
Note the difference in the
direction of frictional forces. The
arrows represent the frictional
forces acting on the strip.
Metal Forming Course
Roll Bending and Workpiece Spreading
• (a) Bending of straight
cylindrical rolls because of the
roll force. (b) Bending of rolls,
ground with camber, that
produce a sheet of uniform
thickness during rolling.
•Increase in the width of a
strip (spreading) in flat
rolling.
Metal Forming Course
Defects In Flat Rolling
• Schematic illustration of typical defects in flat rolling: (a) wavy
edges; (b) zipper cracks in the center of strip; (c) edge cracks;
(d) alligatoring.
Metal Forming Course
Shape Rolling
• Stages in shape
rolling of an Hsection part.
Various other
structural
sections, such
as channels and
I-beams, are
also rolled by
this process.
Metal Forming Course
Ring-Rolling
• (a) Schematic illustration of a ring-rolling operation. Reducing
the thickness results in an increase in the part’s diameter. (b)
Examples of cross-sections that can be formed by ring rolling.
Metal Forming Course
Thread-Rolling Processes
• Thread-rolling processes: (a) flat dies and (b) two-roller dies.
These processes are used extensively in making threaded
fasteners at high rates of production.
Metal Forming Course
Machined And Rolled Threads
• (a) Schematic illustration of machined or rolled threads. (b)
Grain-flow lines in machined and rolled threads. Unlike
machined threads, which are cut through the grains of the metal,
rolled threads follow the grains and are stronger, because of the
cold working involved.
Metal Forming Course
Mannesmann Process
• Cavity formation by secondary tensile stresses in a solid round
bar and its use in the rotary-tube-piercing process. This
procedure uses the principle of the Mannesmann mill for
seamless tube making. The mandrel is held in place by the long
rod, although techniques have been developed in which the
mandrel remains in place without the rod.
Metal Forming Course
Types Of Extrusion
• Types of
extrusion.
(a) direct;
(b) indirect;
(c) hydrostatic;
(d) impact.
Metal Forming Course
Extrusion
• Extrusion and examples
of products made by
sectioning off extrusions.
• Schematic illustration of three
different types of metal flow in
direct extrusion.
Metal Forming Course
Cold and Impact Extrusion
• Examples of cold
extrusion. Arrows
indicate the direction of
material flow. These
parts may also be
considered as forgings.
•(a) Impact extrusion of a tube
(Hooker process).(b) Two
examples of products made by
impact extrusion, these parts
may also be made by casting,
forging, and machining,
depending on the dimensions
and materials involved and the
properties desired. Economic
considerations are also
important in process selection.
Metal Forming Course
Chevron Cracking
• (a) Deformation zone in extrusion, showing rigid and plastic
zones. Note that the plastic zones do not meet, leading to
chevron cracking. The same observations are also made in
drawing round bars through conical dies and drawing flat sheet
plate through wedge-shaped dies. (b) Chevron cracking in round
steel bars during extrusion. Unless the part is inspected
properly, such internal detects may remain undetected and
possibly cause failure of the part in service.
Metal Forming Course
Extrusion of Seamless Tube
• Extrusion of a seamless tube. The hole in the billet may be
prepunched or pierced, or it may be generated during extrusion.
Metal Forming Course
Extrusion of Complicated Shapes
• (a) An extruded 6063-T6 aluminum ladder lock for aluminum
extension ladders. This part is 8 mm thick and is sawed from the
extrusion. (b) Components of various dies for extruding intricate
hollow shapes.
Metal Forming Course
Drawing
• Variables in drawing
round rod or wire.
• Variation in strain and flow stress
in the deformation zone in drawing.
Note that the strain increases
rapidly toward the exit. The reason
is that when the exit diameter is
zero, the true strain reaches infinity.
The point Ywire represents the yield
stress of the wire.
Metal Forming Course
Tube Drawing
• Various methods of tube drawing.
Metal Forming Course
Drawing Dies
• Terminology for a typical
die for drawing round rod
or wire.
• Schematic illustration of a
typical wear pattern in a
wire-drawing die.
Metal Forming Course
Swaging
• Schematic illustration of the swaging
process: (a) side view and (b) front view.
(c) Schematic illustration of roller
arrangement, curvature on the four radial
hammers (that give motion to the dies),
and the radial movement of a hammer as
it rotates over the rolls.
• Reduction of outer and inner diameters of
tubes by swaging. (a) Free sinking without a
mandrel. The ends of solid bars and wire are
tapered (pointing) by this process in order to
feed the material into the conical die. (b)
Sinking on a mandrel. Coaxial tubes of
different materials can also be swaged in
one operation.
Metal Forming Course
Cross-Sections Produced By Swaging
• (a) Typical cross-sections produced by swaging tube blanks with
a constant wall thickness on shaped mandrels. Rifling of small
gun barrels can also be made by swaging, using a specially
shaped mandrel. The formed tube is then removed by slipping it
out of the mandrel. (b) These parts can also be made by
swaging.
Metal Forming Course
Forming Processes For Rocket Casings
• The forming processes involves in the manufacture of solid
rocket casings for the U.S. Space Shuttle.
Metal Forming Course
The End