Group 9
3 / 1 / 2006
Ch. 15: Extrusion and Drawing of Metal
Ch. 16: Sheet-Metal Forming Process
David Ortegel
Steven Neidigk
Tim Ngo
Jason Maestas
CHAPTER 15
Extrusion and Drawing
Of
Metals
15.1 Introduction
Extrusion
Rooted From Latin Term “Extrudere”(To
Force out).
A Cylindrical Billet is Forced Through A Die
Same Concept as forming Play-Doe
Die Geometry remains constant throughout
the operation
Forms a constant extruded cross-section
Aluminum, copper, Steel Magnesium, lead
are the most common material used in the
Extruding process
Products Made by Extrusions
 Railings for Sliding
Doors
 Window Frames
 Aluminum Ladders
 Extrusions can be cut
into desired lengths,
allowing for discreet
parts such to be
produced as Gears,
and Brackets
Economics of Extrusions
Extrusions can be economical for
Large productions runs as well as
short ones.
Tool cost is generally low
Manufactures are able to produce
quantity because of the ability to cut
individual parts from a single
extrusion
Drawing
 Drawing – Crosssections of solid rod,
wire, or tubing is
reduced or changed in
shape by pulling
through a die.
• Developed between
1000 -1500 AD
• Used to from shafts,
automobile
components, spindles,
fasteners.
 Depending on the ductility pf the
material used extrusions can be caries
out various ways:
1. Cold Extrusion – Extrusion carried out a
ambient temperature. Often combined with
forging operations
2. Hot Extrusions – Extrusions carries out at
elevated temperatures
3. Impact extrusion – punch is rapidly
descends on billet material
4. Hydrostatic extrusion – pressure is applied
by a piston through incompressible fluid
medium surrounding the billet
15.2 The Extrusion Process

3 Basics Types of Extrusion:
• Direct or Forward Extrusion: A billet is
placed in a chamber and forced
hydraulically through a die by a ram. Fig a
• Indirect Extrusion (Reverse, Inverted,
Backward Extrusion): The Die Moves
Toward the billet material. fig b
• Hydrostatic Extrusion:
– A Billet that is smaller that the chamber is used.
– The Chamber is filled with a fluid. Pressure is
then applied to the pressing stem
– There is no friction to overcome
Variables
• Die Angle
• A ۪ – Initial crosssectional Area
• A – Final crosssectional Area
Extrusion Force
 The force required for extrusions
F = A*k*ln( A ۪ / A )
k = Constant determined experimentally
• The force required depends on:
– Strength of Billet Material
–
–
–
–
–
Extrusion Ratio: A ۪ /A
Friction between the billet material and the chamber
Temperature
Speed of the Ram
Type of lubricants used
Extrusion constant k for various metals at different
temperature
Metal Flow
Flow patterns influence the quality
and mechanical properties of the
extruded product
Material flows longitudinally (ex.
Fluid flowing in a channel)
The extruded product has a
elongated grain structure
-
A common technique in investigating a flow is to section the
round billet in half
Dead-Metal Zone – The corner of the material stays
stationary. Bright finishes result due to material flowing
past the die angle
Fig a – flow patterns attained with low friction
Fig b – flow patterns attained with high friction
Fig c – flow pattern attained with high friction or cooling of
the billets outer regions in the chamber
15.3 Hot Extrusion
Extrusions carried out at elevated
temperatures
Used for metals that do not have
sufficient ductility at room
temperature.
Used when wanting to reduce forces
on billet material
Special Requirements
 Due to excessive heat die
wear becomes excessive
and rapid cooling of the
product after extrusion
causes deformations.
 Pre-heated dies
prolong the life of the
die done my hot
forging. This also
reduces rapid cooling if
the material
 Billet develops an oxide
film. Oxides can result in a
finished product that is
unacceptable.
 Placing a dummy
block, a little smaller
than the chamber
ahead of the ram,
results in a thin shell of
the oxide layer left in
the container.
Lead
Aluminum and its alloys
Copper and its alloys
Steels
Refractory alloys
C
200–250
375–475
650–975
875–1300
975–2200
Die Design
Main types of die designs:
1) Square dies: Used in extruding nonferrous
metals
- Develops dead metal zones that form the
dies angle
2) Solid or Hollow Dies: Used in extruding
tubing products
- The ram is fitted with a mandrel that
pierces a hole in the billet
-Wall thickness is limited to 1 mm for
aluminum. 3mm for stainless steels, 5mm
to stainless steels
3) Spider, porthole dies ,and bridge dies:
Used in creating hollow cross-section
extrusions
-Created by welding chamber methods
-Metal divides and flows around the
supports for the internal mandrel
-The extruded strands become welded back
together by the high internal pressure
existing in the chamber
only suitable for aluminum and its alloys
because of their capacity to create strong
welds.

(
a
)

(
b
)

(
c
)
Die Materials
 Hot Worked dies
Steels are used for
hot extrusion
 Coatings such as
zirconia used to
extend die life
• Not suitable for dies
used for complex
shapes because of
the sever stress
gradients that
develop in the die.
Lubrication
 Lubrication Is important in hot
extrusions because of major effects
on:
a)
b)
c)
d)
Material flow
Surface finish on extrusion
Product quality
Extrusion forces
Sejournet process was developed in
the 1940s uses Glass as a lubricant
on high temperature steels.
• A circular glass pad is placed in the
chamber at the die entrance
• The head conducted cause the glass to
melt around the extruded product acting
as a lubricant
Jacketing: also known as canning,
uses softer and lower strength
metals metals such as copper or a
mild steel.
• Used for materials that have a tendency
to stick to the container and die
• Also used or toxic and radioactive
material. The jacket that is formed over
the extruded material acts as a
protected barrier
15.4 Cold Extrusion
 Developed in the 1940’s, are extrusion
produced at ambient temperature.
• Denotes combinations of operations, that
consist of indirect extrusions and forgings
 Cold extrusions are widely used
• Automobile products
• Appliances
• Fasteners
Advantages cold extrusion has over
hot extrusion
- Improved mechanical properties
- Control over dimensional tolerances
- Improved surface finishes
- production rates and cost are
competitive
- magnitude of stress is extremely high
15.5 Extrusion Defects
 Surface Cracking: Cracking on billet
materials occurs due to temperature,
friction, punch speed.
 High Temperatures
• Crack from along the grain boundaries. Typically
occur in aluminum, magnesium, zinc alloys
 Cold Temperatures
• Caused by sticking of billet material at the die land
• Known has the “Bamboo Defect” because of its
similar appearance to bamboo
 Pipe: The metal-flow pattern tends to
draw oxides and impurities toward the
center of the billet
 Internal Cracking: Center of extruded
product develops cracks.
• Attributed to a state of hydrostatic tinsel stress
• Cracks increase with increasing die angle,
impurities, and decreasing extrusion ratio and
friction
15.6 Extrusion Equipment
 Basic horizontal press: Suitable because
the stroke and speed of the press can be
controlled
 Vertical Hydraulic press: used for cold
extrusions. Take up less floor space
15.7 The Drawing Process
 A long rod or wire is reduces or changes
by pulling through a die called a “draw
die”
• Rod and wire is used in many applications such as
drive shafts, machine and structural components,
welding electrodes, spokes.
Drawing Force: used under ideal and
frictionless conditions
F = YA * ln(A
۪ / A)
• Y- average true stress
• A ۪ – initial cross–sectional area
• A – Final cross-sectional area
 Drawing Force used under frictional
forces:
F = Y*A* [(1 + u/s) * ln(A ۪ / A) + (2/3)*s]
• S – Die angle in radians
• U – Frictional forces
15.8 Drawing Practice
Bundle Drawing: Drawing many
wires simultaneously
• Produces wire in polygonal crosssections
• Theses types of wire are cut into many
shapes. Used in medical implant,
electrically conductive material, filter
media
• Reduces cost of production by producing
100 or more.
 Die Design:
• Die angles range from 6 -15 degrees
• Die designs go through many period of trial and error
 Die Materials:
•
•
•
•
Die are made out of typical tool steels and carbides
Cast steels are used for hot extrusions
Diamond dies are used for drawing extremely fine wire
Insert and nibs are used to support carbide and diamond
dies because of their lack of tensile strength
 Lubrication:
• Proper lubrication is essential to improve die
life and product surface finish
• Particular in tube drawing, because of its
difficulty to maintain for a thick lubrication film
at the mandrel
• Wet drawing – Dies and rod are completely
immersed in lubricant
• Dry Drawing – Rod is coated in a lubricant by
passing through a box filled with lubricant
15.9 Drawing Defect and
residual Stresses
Typical defects in a drawn rod or wire
are similar to extrusion
• Internal Cracking with are longitudinal
• Seam may open
• Cold–drawn products have residual
stresses, this causes stress-corrosion
cracking over a period of time
• Quality control becomes a major
problem in drawn defects and residual
stresses
15.10 Drawing Equipment
 Draw Bench:
• Contains a single die, design is long
• Pulling for is supplied by a chain drive that is
hydraulically activated
 Rotating Drum:
• Used in producing long rods and wires of
smaller cross-sections less that 13mm
• A large drum is rotated
Introduction
•
We utilize sheet metal for products such as
–
–
–
–
•
•
Cans
Cookware
Appliances
Car bodies
Low carbon steel is the most commonly used
sheet metal for its strength and formability
The most general sheet forming operations
–
–
Press working
Press forming
Shearing
• Shearing metal is like
punching holes in paper
with a hole punch.
• It can also be compared
to using a cookie cutter
• The punch must be
harder and stronger that
the metal being sheared
Shearing
•Typical features of sheared
edges are not smooth nor
perpendicular to the cutting
plane
•Edge quality can be
improved by increasing
punch speed
•Shearing is most
commonly done with
a punch and die
Shearing
• Having the correct
between the punch and die
is important
– Too much and the sheared
edge can become rough
– Too little and tools can be
damaged
• Burr is a thin edge or ridge
an the punched out piece
of metal
• Can be caused by dull tool
edges
• The size and shape of the
burr can change
subsequent forming
operations
Shearing Operations
• Die cutting- perforating, parting, notching, lancing
– Parts produced by die cutting are commonly used in
assembly with other components
• Fine blanking- used to produce smooth and square edges
• Nibbling- moves a small straight punch up an down rapidly
into a die. One advantage of this technique is intricate
slots and notches.
Shearing Operations
• Slitting- a pair of circular
blades follow a line or
path cutting as they go.
– much like a can opener
• Scrap in shearing- The
sheets of metal that are
not used.
– Can be as large as
30% of large
stampings
– Increases
manufacturing cost
Shearing Operations
• Tailor-Welded Blanks- Can be used of sheet metal with
different shapes and thicknesses (often used in automotive
industry)
– Reduction in scrap
– Eliminate need for subsequent spot welding
– Better control of dimensions
– Improved productivity
Punches and Dies
• Compound dies-Limited to simple shapes
– Several operations on the same sheet may be performed
in one stroke at one station with a compound die
Punches and Dies
• Progressive dies- good for making
parts that require multiple operations
to produce
– Use a series of punches
• Other operations include
– Laser beam cutting
– Water-jet cutting
– Friction sawing
– Flame cutting
Sheet-Metal Characteristics
and Formability
• After a blank is cut into a sheet it is formed into various shapes
• Elongation- Stretching the metal
– High elongation is desirable for good formability
• Yield-Point Elongation- Happens in low carbon steel and
aluminum-magnesium alloys. Causes stretcher-strain marks,
or worms
– Elongations, depressions along the surface
Sheet-Metal Characteristics
and Formability
• Dent-Resistance of sheet metalrefers to the dynamic yield or yield
stress under high rate of deformation
– Ways to improve dent-resistance is to
increase sheet thickness of decrease the
metals elastic modulus
Formability Tests for SheetMetals
• Formability- The ability to
of the sheet-metal to
undergo the desired shape
without failure
– May undergo two basic
modes of deformationstretching and drawing
• Cupping Tests- earliest
tests to determine
formability
• Erichsen test- Sheet
clamped between two
circular dies then a steel
ball of round punch is
forced into the sheet until
it cracks
Formability Tests for SheetMetals
• Forming Limit
Diagrams- They are
made by marking a flat
sheet with a grid
pattern of circles, then
it is stretched over a
punch. The
deformation of the
circles is measured in
regions where the sheet
has failed.
• The information
gathered from the test
is then turned into a
diagram.
Bending Sheets, Plates,
Tubes
• Bending is the most
common industrial
forming operation
• Adds stiffness to the
part without adding
weight (car door
panels)
• Minimum bend
allowance- refers to
the radius at which a
crack first appears at
the outer fibers of a
sheer being bent
Bending Sheets, Plates,
Tubes
• Bendability can be increased by heating the
metal or by bending in a high-pressure
environment.
• Edge cracking can be decreased by minimizing
cold working when the part is sheared.
• Anisotropy of the metal is another important
factor in bendability.
(a)
(b)
Bending Sheets, Plates,
Tubes
• Springback- when a sheet or tube
recovers elastically when load is removed
• Usually compensated for by overbending
the part
Ch.16 Sections 16.6 - 16.9
• 16.6
– Miscellaneous Bending and
• 16.7
• 16.8
• 16.9
– Deep Drawing
– Rubber Forming
– Spinning
Related Operations
16.6 Miscellaneous Bending
and Related Operations
• Press-brake forming. • Dimpling, piercing,
and flaring.
• Bending in a fourslide machine.
• Bulging.
• Roll bending.
• Stretch forming.
• Beading.
• Flanging.
• Roll forming.
• Tube bending and
forming.
• Press-brake forming.
– Easily bends sheet
metal or plates that
are 7m (20ft) or
longer, which is
suitable for small
production runs.
– This machine uses
long dies in a hydraulic
press, to create an up
and down motion to
bend the metals.
– Material of the die:
Hardwood – used
for low strength
materials and small
production runs;
Carbides- used for
strong and abrasive
sheet materials and
last longer than
other dies. Carbonsteel and gray iron
is the most
commonly used.
• Bending on a four-slide machine.
– Uses dies to bend short pieces of metal into
tubing and conduits, bushings, fasteners, and
various machinery components.
• Roll bending.
– Plates are bent using a
set of rolls.
– By adjusting the rolls
various curvatures can
be obtained.
– The metals created can
be use for boilers,
cylindrical pressure
vessel, and other curved
structures.
• Beading.
– A technique utilizing
the cavity of a die to
bend the periphery of
the sheet metal.
– The purpose of the
bead is to create
stiffness and better
appearance of the
part and eliminates
hazardous sharp
edges.
• Flanging.
– A process of bending the
edge of a sheet metal into
a 90o angle.
– Periphery wrinkling may
occur in shrink flanging,
due to excessive
compressive hoop stress.
– Periphery cracking may
occur in stretch flanging,
due to excessive tensile
stress.
• Dimpling, piercing, and flaring.
– Dimpling is a type of flanging operation
that punches a hole in the sheet metal
and expanded into a flange with a
shaped punch.
• Roll forming.
– Process where sheet metal strips are passed
through consecutive set of rolls and bent in
consecutive stages and then sheared into specific
lengths and stacked continuously.
– Sheet thickness: 0.125 – 20mm(0.005–0.75 in.)
– Forming speed: below 1.5 m/s (300 ft/min)
– Examples: Door panels, picture frame, and
gutters.
• Tube bending and forming.
– Several methods are implemented to prevent
buckling and folding of the tubes, such as filling
the tubes with sand or the use of mandrels.
– Relatively thick tubes have a low tendency to
buckle so it can be bent safely without the use
of fillers.
• Bulging.
– Process involving the
expansion of a polyurethane plug within
the tube, and once
the punch retracts,
the plug goes through
elastic recovery.
– Examples: coffee or
water pitchers, beer
barrels and bellows.
• Stretch Forming
– Process where a
sheet metal is
clamped along it’s
edges and
stretched over a
male die (form die
or form punch).
– Examples: aircraft
wing-skin panels,
fuselages, and boat
hulls.
16.7 Deep Drawing
•
•
•
•
•
•
•
•
Blanking
Deep Drawing
Redrawing
Ironing
Doming
Earing
Necking
Seaming
• Process in Manufacturing an Aluminum Can
• Deep Drawing
– Process where a round sheet-metal blank is
placed over a circular die and is held in place
with a blank-holder, which is then forced
downward into a die cavity by a punch;
forming a cup.
• Redrawing
• Ironing
– Operations used to
redraw containers that
are too difficult to draw
in one operation.
– If clearance between
the punch and the die is
sufficiently large, the
drawn cup will have
thicker walls at its rim
than its base.
– The thickness can be
controlled by ironing, a
process which the
drawn cup is pushed
through one or more
ironing rings
• Earing
– A phenomenon where
the edges of cups
become wavy during
the drawing process.
– The ears have to be
trimmed off since it
serves no useful
purpose and interferes
with further processing
of the cup.
– Earing is caused by
planar anisotropy of the
sheet.
• Hemming and Seaming
– Hemming
• Sheet metal is folded
over itself.
• Increases stiffness,
improves appearance
and eliminates sharp
edges.
– Seaming
• Joining two edges of
sheet metal by
hemming.
• Double seaming.
16.8 Rubber Forming
• Rubber Forming
– One of the dies in the set is made of
polyurethane membrane, which is a type of
flexible material.
– Polyurethane is resistant to abrasion, cutting
or tearing by the metal, and has a long
fatigue life.
16.9 Spinning
• Conventional Spinning
– Process where a circular
piece of sheet metal is
placed and held against
a mandrel and rotated
while a rigid tool
deforms and shapes the
material over the
mandrel.
– May be performed at
room temperature or at
higher temperature for
thicker metal.
• Sheer spinning
– Also called power
spinning, flow turning,
hydrospinning, and spin
forging.
– Process used to create
axisymmetric conical or
curvilinear shape,
reducing the sheet’s
thickness while
maintaining its
maximum diameter.
– Applications: Rocket
motor casings and
missile nose cones.
• Tube Spinning
– The process where
cylindrical blanks
are reduced or
shaped by spinning
them on a solid,
round mandrel
using rollers.
– Applications:
Rocket, missile, and
jet engine parts,
pressure vessels,
and car and truck
wheels.
Diffusion Bonding/Superplastic
Forming
Figure 16.43 Types of
structures made by
diffusion bonding and
superplastic forming of
sheet metal. Such
structures have a high
stiffness-to-weight ratio.
Source: Rockwell
International Corp.
Specialized Forming Processes
• Explosive forming
•
•
•
•
Magnetic-pulse forming
Peen forming
Laser forming
Microforming
• Electrohydraulic forming
Explosive forming
• First used to form metals in the 1900’s. A sheet metal blank is
clamped over a die, and the entire assembly is lowered into a tank
filled with water. The air in the cavity is evacuated, and an
explosive is detonated at a certain height above.
Magnetic-pulse forming
• Also called electromagnetic forming. Energy stored in a capacitor
bank is discharged rapidly through a magnetic coil. Magnetic field
crosses metal tube (conductor) creating eddy currents which have
an opposing magnetic field.
(a)
(b)
Figure 16.45 (a) Schematic illustration of the magnetic-pulse forming process used to form a
tube over a plug. (b) Aluminum tube collapsed over a hexagonal plug by the magnetic-pulse
forming process.
Other forming processes
• Peen forming – A cast-iron or steel shot is discharged from
a rotating wheel or by an air-blast from a nozzle. It is used
for complex curvatures on thin sheet metals.
• Laser forming – Laser beams are directed in certain regions
causing thermal stresses , which are high enough to cause
localized plastic deformation of the sheet.
• Microforming – More recently developed for very small
metallic parts and components. Typical components made
include small shafts for micromotors, springs, screws, and a
variety of cold-headed, extruded, bent, embossed, coined,
punched, or deep-drawn parts.
• Electrohydraulic forming – Also called underwater spark or
electric discharge forming. In this process, the source of
energy comes from a spark between two electrodes
connected by a thin wire.
Manufacturing of Metal Honeycomb
Structures
Figure 16.46 Methods of manufacturing honeycomb
structures: (a) Expansion process; (b) Corrugation
process; (c) Assembling a honeycomb structure into
a laminate.
Design Considerations in Sheet-Metal
Forming
• Blank design – Material scrap is the primary
concern. Poorly designed parts will not nest
properly.
• Bending – Bending can cause material fractures
or wrinkles. This is prevented with a flange, or
relief notch which limit the stresses from
bending. Do not put bends next to places with
high-stress concentrations such as holes. A tab or
ear can be used.
• Stamping and progressive-die operations – Limit
features so that tooling and machining costs are
minimal. Narrow cuts and protrusions must be
are also problematic.
Equipment for Sheet-Metal Forming
• Type of forming operation, size and shape of the
die, and tooling required.
• Size and shape of workpiece.
• Length of stroke, number of strokes per minute,
operating speed, and shut height.
• Number of slides.
• Maximum force required.
• Type of controls.
• Safety features
Economics of Sheet-Forming
Operations
•
•
•
•
•
Die and equipment cost
Labor and skill required
Time
Machining and tooling operations
Level of automation and computer control
required
References
•
•
•
•
•
•
•
•
•
http://www.amcastle.com/HTML/am_pr_alloy_tubing.html
http://www.e6.com/e6/page.jsp?pageid=600406065
http://www.brass.org/Training/Lecture/sld043.htm
http://www.ionbond.com/standard.cfm?ID_n=28&unter=28
&haupt=2&language=1
http://www.noktametal.com/extrusionpress.htm
http://www.benchtest.com/504_11.html
http://science.howstuffworks.com/gear.htm
http://www.sundram.com/ce_product.htm
http://www.webcastgroup.com/client/start.asp?wid=087072
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