Traditional Manufacturing Processes
Casting
Forming
Sheet metal processing
Powder- and Ceramics Processing
Plastics processing
Cutting
Joining
Surface treatment
FUNDAMENTALS OF METAL
FORMING
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Overview of Metal Forming
Material Behavior in Metal Forming
Temperature in Metal Forming
Strain Rate Sensitivity
Friction and Lubrication in Metal Forming
Metal Forming
Large group of manufacturing processes in which
plastic deformation is used to change the shape
of metal workpieces
• The tool, usually called a die, applies stresses
that exceed yield strength of metal
• The metal takes a shape determined by the
geometry of the die
Stresses in Metal Forming
• Stresses to plastically deform the metal are usually
compressive
– Examples: rolling, forging, extrusion
• However, some forming processes
– Stretch the metal (tensile stresses)
– Others bend the metal (tensile and compressive)
– Still others apply shear stresses
Material Properties in Metal
Forming
• Desirable material properties:
– Low yield strength and high ductility
• These properties are affected by temperature:
– Ductility increases and yield strength
decreases when work temperature is raised
• Other factors:
– Strain rate and friction
Bulk Deformation Processes
• Characterized by significant deformations and
massive shape changes
• "Bulk" refers to workparts with relatively low
surface area-to-volume ratios
• Starting work shapes include cylindrical billets
and rectangular bars
Basic bulk deformation processes: (a) rolling
Basic bulk deformation processes: (b) forging
Basic bulk deformation processes: (c) extrusion
Basic bulk deformation processes: (d) drawing
Material Behavior in Metal
Forming
• Plastic region of stress-strain curve is
primary interest because material is
plastically deformed
• In plastic region, metal's behavior is
expressed by the flow curve:
  K
n
where K = strength coefficient; and n = strain hardening exponent
• Stress and strain in flow curve are true stress and true strain
Flow Stress
• For most metals at room temperature,
strength increases when deformed due
to strain hardening
• Flow stress = instantaneous value of
stress required to continue deforming
the material
Yf  K n
where Yf = flow stress, that is, the yield strength as a function of strain
Temperature in Metal Forming
• For any metal, K and n in the flow curve
depend on temperature
– Both strength and strain hardening are
reduced at higher temperatures
– In addition, ductility is increased at higher
temperatures
Cold working is metal forming performed at room temperature.
Advantages: better accuracy, better surface finish, high strength and hardness of the part, no
heating is required.
Disadvantages: higher forces and power, limitations to the amount of forming, additional
annealing for some material is required, and some material are not capable of cold working.
Warm working is metal forming at temperatures above the room temperature but bellow the
recrystallization one.
Advantages: lower forces and power, more complex part shapes, no annealing is required.
Disadvantages: some investment in furnaces is needed.
Hot working involves deformation of preheated material at temperatures above the re
crystallization temperature.
Advantages: big amount of forming is possible, lower forces and power are required, forming
of materials with low ductility, no work hardening and therefore, no additional annealing is
required.
Disadvantages: lower accuracy and surface finish, higher production cost, and shorter tool life.
Friction in Metal Forming
• In most metal forming processes, friction is
undesirable:
– Metal flow is retarded
– Forces and power are increased
– Wears tooling faster
• Friction and tool wear are more severe in hot
working
Lubrication in Metal Forming
• Metalworking lubricants are applied to tool-work
interface in many forming operations to reduce
harmful effects of friction
• Benefits:
– Reduced sticking, forces, power, tool wear
– Better surface finish
– Removes heat from the tooling
Considerations in Choosing a
Lubricant
• Type of forming process (rolling, forging, sheet
metal drawing, etc.)
• Hot working or cold working
• Work material
• Chemical reactivity with tool and work metals
• Ease of application
• Cost
Definitions
Plastic Deformation Processes
Operations that induce shape changes on the work piece by plastic deformation under forces applied
by various tools and dies.
Bulk Deformation Processes
These processes involve large amount of plastic deformation. The cross-section of workpiece
changes without volume change. The ratio cross-section area/volume is small. For most
operations, hot or warm working conditions are preferred although some operations are carried
out at room temperature.
Sheet-Forming Processes
In sheet metalworking operations, the cross-section of work piece does not change—the material
is only subjected to shape changes. The ratio cross-section area/volume is very high.
Sheet metalworking operations are performed on thin (less than 6 mm) sheets, strips or coils of
metal by means of a set of tools called punch and die on machine tools called stamping presses.
They are always performed as cold working operations.
Bulk Deformation Processes
Rolling: Compressive deformation process in which the thickness of a plate is
reduced by squeezing it through two rotating cylindrical rolls.
Forging: The workpiece is compressed between two opposing dies so that the die
shapes are imparted to the work.
Extrusion: The work material is forced to flow through a die opening taking its
shape
Drawing: The diameter of a wire or bar is reduced by pulling it through a die
opening (bar drawing) or a series of die openings (wire drawing)
Rolling
Definition
Rolling is a Bulk Deformation
Process in which the thickness
of the work is reduced by
compressive forces exerted by
two opposing rolls
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Rolling
Rolling
Important Applications:
Steel Plants,
Raw stock production (sheets, tubes, Rods, etc.)
Screw manufacture
Rolling Basics
Sheets are rolled in multiple stages (why ?)
tf
to
Vf
to
tf
Vf
Vo
Vo
stationary die
Screw manufacture:
rolling die
thread rolling machine
Reciprocating flat thread-rolling dies
Forging
Definition
Forging is a Bulk Deformation Process
in which the work is compressed
between two dies. According to the
degree to which the flow of the metal
is constrained by the dies there are
three types of forging:
 Œ
Open-die forging
 •Impression-die forging
 ŽFlash less forging
Forging
Stages in Open-Die Forging
(a) forge hot billet to max diameter
(b) “fuller: tool to mark step-locations
(c) forge right side
(d) reverse part, forge left side
(e) finish (dimension control)
[source:www.scotforge.com]
Stages in Impression-die (Closed-Die) Forging
[source:Kalpakjian & Schmid]
Stages in Impression-die (Closed-Die) Forging
Flash less forging
Forging grain flow
Quality of forged parts
Surface finish/Dimensional control:
Better than casting (typically)
Stronger/tougher than cast/machined parts of same material
[source:www.scotforge.com]
A material is pushed or drawn through a die of the desired crosssection .Any solid or hollow cross-section may be produced by
extrusion, which can create essentially semi-finished parts. The
metal can forcing through a die in the same direction or opposite
direction.
Extrusion
Typical use: ductile metals (Cu, Steel, Al, Mg),
Plastics, Rubbers
Common products:
Al frames of white-boards, doors, windows, …
Extrusion: Schematic, Dies
chamber
die
extruded shape
hydraulic
piston
stock
chamber
Exercise: how can we get hollow parts?
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The cross-sections that can be produced vary from solid round,
rectangular, to L shapes, T shapes.
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Extrusion may be continuous (theoretically producing indefinitely
long material) or semi-continuous (producing many pieces).
Extrusions can be done with the material hot or cold.
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Commonly extruded materials include metals, polymers,
ceramics, and foodstuffs.
Extruded products
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Typical products made by extrusion are railings for sliding doors,
tubing having carious cross-sections, structural and architectural
shapes, and door and windows frames.
Extruded products
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Direct extrusion: A metal
billet is located into a
container, and a ram
compresses the material,
forcing it to flow through
one or more openings in a
die at the opposite end of
the container.
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Indirect extrusion: The die
is mounted to the ram
rather than at the opposite
end of the container. One
advantage of the indirect
extrusion process is that
there is no friction, during
the process, between the
billet and the container
liner
.
Drawing
Similar to extrusion, except: pulling force is applied
stock (bar)
die
wire
F (pulling force)
Commonly used to make wires from round bars
WHAT is DRAWING?
Drawing is an operation in which the cross-section of solid
rod, wire or tubing is reduced or changed in shape by pulling
it through a die.
The principle of this procedure consist of reducing the
thickness of a pointed ,tapered wire by drawing it through a
conical opening in a tool made of a hard material.The wire
will take shape of the hole.
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Drawing improves strength and hardness when these properties
are to be developed by cold work and not by subsequent heat
treatment
Where is it used?
This process is widely used for the production of thicker walled
seamless tubes and cylinders therefore; shafts, spindles, and small
pistons and as the raw material for fasteners such as rivets, bolts,
screws.
DRAWING TOOLS
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The most important tool in the drawing process is without
doubt the drawplate.This consist of a plate of high grade steel
into which similar shaped holes have been placed whose size
in evenly reduced from one hole to another.
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The most common drawplate have round holes and are used
to reduce the size of round wire.
Drawing wire with the draw tongs
drawbench
How such a drawplate hole is made