forming and shaping isat 430 module 7 spring 2001isat 430 dr. ken lewis 2 forming and shaping...
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Forming and Shaping
ISAT 430
Module 7
Spring 2001 ISAT 430 Dr. Ken Lewis 2Module 7
Forming and Shaping Meanings blend Forming means changing the shape of an existing
solid body. Shaping usually involves molding or casting
The resulting product is usually near net shape.
Spring 2001 ISAT 430 Dr. Ken Lewis 3Module 7
Forming and Shaping Processes Rolling -- Flat
Production of flat plate, sheet and foil Long lengths, high speeds Good surface finish Requires
High capital investment Incurs low to moderate labor cost.
Spring 2001 ISAT 430 Dr. Ken Lewis 4Module 7
Forming and Shaping Processes2
Rolling – Shaped Production of various structural shapes
Bars I-beams
High speeds Requires
shaped rolls, expensive equipment Low to moderate labor costs Moderate operator skill
Spring 2001 ISAT 430 Dr. Ken Lewis 5Module 7
Forming and Shaping Processes3
Forging Production of discrete parts with a set of dies. Some finishing operations usually necessary Usually performed at elevated temperatures Die and equipment costs are high Requires
Moderate to high labor cost Moderate to high operator skill
Similar parts can be made by casting and powder-metallurgy techniques
Spring 2001 ISAT 430 Dr. Ken Lewis 6Module 7
Forming and Shaping Processes4
Extrusion Production of long lengths of solid or hollow
products with constant cross section Product is cut into desired lengths Cold extrusion has similarities to forging and is used
to make discrete products. Requires
Moderate to high die and equipment costs Low to moderate labor costs Low to moderate labor skill
Spring 2001 ISAT 430 Dr. Ken Lewis 7Module 7
Forming and Shaping Processes5
Drawing Production of long rod and wire with round or
various cross sections. Smaller cross section than extrusion Good surface finish Requires
Low to Moderate die and equipment costs Low to moderate labor costs Low to moderate labor skill
Spring 2001 ISAT 430 Dr. Ken Lewis 8Module 7
Forming and Shaping Processes6
Sheet metal forming Production of a wide variety of shapes with thin
walls Simple or complex geometries Requires
Moderate to high die and equipment costs Low to moderate labor costs Low to moderate labor skill
Spring 2001 ISAT 430 Dr. Ken Lewis 9Module 7
Forming and Shaping Processes7
Powder Metallurgy Production of simple or complex shapes by
compacting and sintering metal powders Competitive with casting, forging, and machining
processes Requires
Moderate to high die and equipment costs Low labor costs Low labor skill
Spring 2001 ISAT 430 Dr. Ken Lewis 10Module 7
Forming and Shaping Processes8
Processing of plastics and composite materials Production of a variety of continuous or discrete
products Extrusion, spinning, molding, casting
Can be competitive with metal parts Requires
Moderate to high die and equipment costs High operator skill in composite fabrication
Spring 2001 ISAT 430 Dr. Ken Lewis 11Module 7
Forming and Shaping Processes9
Forming and shaping of ceramics Production of discrete ceramic products by a variety
of ways Shaping, drying , firing processes
Requires Moderate to high die and equipment costs Low to moderate labor costs Moderate to high labor skill
Spring 2001 ISAT 430 Dr. Ken Lewis 12Module 7
Rolling Rolling is a process to reduce the thickness of a long
workpiece by compressive forces applied through a set of rolls.
First developed in the late 1500’s
Spring 2001 ISAT 430 Dr. Ken Lewis 13Module 7
Sequence of events A steel ingot is cast into a rectangular mold Placed in a furnace while just solidified and held for
many hours (36) until the temperature is uniform. This process is called soaking
Furnaces are called soaking pits. Implies that properties will be uniform throughout
the ingot and process that way. The rolling temperature for steel is about 1200°C From here the ingot goes to the rolling mill.
Spring 2001 ISAT 430 Dr. Ken Lewis 14Module 7
Rolling Starting material depends upon what you are
producing. Bloom
Square cross section 6 x 6 in or larger Slab
Rolled from an ingot or a bloom Rectangular cross section 10 x 1.5 in or more
Billet Rolled from a bloom Square cross section 1.5 x 1.5 in or larger.
Spring 2001 ISAT 430 Dr. Ken Lewis 15Module 7
Spring 2001 ISAT 430 Dr. Ken Lewis 16Module 7
Metal behavior in forming
An aside
Spring 2001 ISAT 430 Dr. Ken Lewis 18Module 7
Stress -- strain Elasticity below the elastic
limit Strain hardening above it. In the plastic region, the
metal’s behavior is expressed as:
0
, P
StressA
0
0
, l l
Strainl
Elastic Plastic
Fracture
YieldStress
Ultimate TensileStress
E
nK
Where K = strength coefficient psi (MPa)
n is the strain hardening exponent.
Spring 2001 ISAT 430 Dr. Ken Lewis 19Module 7
Flow Stress
As the metal deforms its strength increases (strain hardening)
Thus the stress required to deform must be increased
Flow stress Instantaneous value of
the stress needed to keep the metal “flowing”
fYfY
Y
Shear Rate
Tru
e St
ress
nfY K
Yf = flow stress MPa
Spring 2001 ISAT 430 Dr. Ken Lewis 20Module 7
Average Flow Stress
The average flow stress is the average stress needed over entire strain region.
Just integrate the flow stress over the strain region of interest:
fYfY
Y
Shear Rate
Tru
e St
ress
nfY dY K d
1
n
f
KY
n
Spring 2001 ISAT 430 Dr. Ken Lewis 21Module 7
Effect of Strain Rate In theory, a metal in hot working should be perfectly
plastic with n = 0. The rate of metal deformation is directly related to
the speed of deformation v.
v
h
v is the velocity of the roll or ram
h is the instantaneous height of the piece being deformed.
Spring 2001 ISAT 430 Dr. Ken Lewis 22Module 7
Effect of Strain Rate
Note that if v is constant, the strain rate will increase with decreasing h.
v
h
Spring 2001 ISAT 430 Dr. Ken Lewis 23Module 7
Effect of strain rate
0.1 1.0 10.0 100.0
Strain rate (sec-1)
Flo
w S
tres
s (M
Pa
)
Similar
C is strength constant m is the slope, called the
strain rate sensitivity exponent.
The effect of temperature is pronounced.
mfY C
Spring 2001 ISAT 430 Dr. Ken Lewis 24Module 7
Effect of temperature on stress
0.1 1.0 10.0 100.0
Strain rate (sec-1)
Flo
w S
tres
s (M
Pa
)room temperature
400°C
800°C
1200°C
Spring 2001 ISAT 430 Dr. Ken Lewis 25Module 7
Temperature Cold working (~room temperature)
Advantages accuracy Surface finish Strain hardening increases strength Grain flow can provide directional properties No heating required
Spring 2001 ISAT 430 Dr. Ken Lewis 26Module 7
Temperature Cold working (~room temperature)
Disadvantages Higher forces and power needed Part must be dirt and scale free (stress risers) Ductility and strain hardening limit the amount
forming that can be done without part fracture or cracking.
Spring 2001 ISAT 430 Dr. Ken Lewis 27Module 7
Temperature Warm Working (0.3Tm – 0.5Tm)
Working above room temperature but below recrystallization temperatures.
Advantages Low forces and power More intricate work geometries possible Need for annealing may by reduced
Tm = melting T.
Spring 2001 ISAT 430 Dr. Ken Lewis 28Module 7
Temperature Hot working (0.5Tm – 0.75Tm)
The recrystallization temperature is about one half the melting point. So hot working is above these temperature
Disadvantages Deformation process causes localized heating which can
cause localized melting (bad Ju Ju) Scale formation increases as the temperature increases. Lower dimensional accuracy Poorer surface finish Shorter tool life.
Tm = melting T.
Spring 2001 ISAT 430 Dr. Ken Lewis 29Module 7
Temperature Hot working (0.5Tm – 0.75Tm)
Advantages Can produce SIGNIFICANT PLASTIC
DEFORMATION of the metal. Lower forces and power Brittle metals can be hot worked. Strength properties are usually isotropic No work hardening
Tm = melting T.
Back to Flat Rolling
Spring 2001 ISAT 430 Dr. Ken Lewis 31Module 7
Flat Rolling A strip of thickness h0
enters the roll gap and leaves at a thickness of hf.
The initial velocity V0 increases to Vf at the exit.
Note that because the surface speed of the roll is constant, there must be relative sliding between the roll and the strip
Spring 2001 ISAT 430 Dr. Ken Lewis 32Module 7
Flat Rolling At one point (no slip point),
Vstrip = Vmill.
To the left, the roll moves faster than the strip
To the right the roll moves slower than the strip
Friction is necessary Too much ruins the
surface and costs power Too little and nothing
happens.
Spring 2001 ISAT 430 Dr. Ken Lewis 33Module 7
Flat Rolling The draft is (h0 –hf) The maximum draft is a
function of the coefficient of friction and the big roll radius R
20 fh h R
Higher friction and bigger roll, the greater draft.
Compare Large tires and rough
treads on tractors and off road vehicles.
Spring 2001 ISAT 430 Dr. Ken Lewis 34Module 7
Flat Rolling The roll force F is shown as
perpendicular to the strip (rather than perpendicular to the point of contact) Because R >>> h
The roll force may be estimated as:
avgF LwY
Spring 2001 ISAT 430 Dr. Ken Lewis 35Module 7
Flat Rolling
avgF LwY
L = roll strip contact length 0 fL R h h
w = strip width
Yavg = average true stress on the strip in the roll gap
Spring 2001 ISAT 430 Dr. Ken Lewis 36Module 7
Flat Rolling Equation assumes no friction The higher , the further off the
formula (low side). The power per roll can be
estimated by assuming F acts in the middle of the arc of contact
The torque/roll is F x a so in S. I. Units (Newton, meters, seconds) the power per roll is:
avgF LwY
260,000
FLNPower
kW
F is in Newtons
L is in meters
N is rpm
Spring 2001 ISAT 430 Dr. Ken Lewis 37Module 7
Flat Rolling Equation assumes no friction The higher , the further off the
formula (low side). The power per roll can be
estimated by assuming F acts in the middle of the arc of contact
The torque/roll is F x a so in English Units (Pounds, feet, seconds) the power per roll is:
avgF LwY
233,000
FLNPower
hp
F is in Pounds force
L is in feet
N is rpm
Spring 2001 ISAT 430 Dr. Ken Lewis 38Module 7
Example: An annealed copper strip, 9 in (228 mm) wide, and 1 inch (25 mm) thick is rolled to a thickness of 0.8 in (20 mm) in one pass. The roll radius is 12 in (300 mm), and the rolls rotate at 100 rpm. What is the roll force and power required?
avgF LwY
0 12 1.00 0.80 1.55fL R h h in
From Table 3.4 pg 51 Groover, K = 300 MPa, n = .5
1.00ln 0.223
0.80
.5300 0.223 141.7 20,551nfY K MPa psi
Spring 2001 ISAT 430 Dr. Ken Lewis 39Module 7
Example: An annealed copper strip, 9 in (228 mm) wide, and 1 inch (25 mm) thick is rolled to a thickness of 0.8 in (20 mm) in one pass. The roll radius is 12 in (300 mm), and the rolls rotate at 100 rpm. What is the roll force and power required?
avgF LwY
.5300 0.223 141.7 20,551nfY K MPa psi
1.55 9 20,551 286,688F lb
2 2 (286,688)(1.5/12)100680
33,000 33,000FLN
Power hp hp
But, there are two rolls so the power is: 1360Power hp
Spring 2001 ISAT 430 Dr. Ken Lewis 40Module 7
Effect of rolling on Structure This is a typical ingot
The outer edges have small grains Faster cooling
Note the large interior grains. Slow cooling Plenty of time to grow.
Spring 2001 ISAT 430 Dr. Ken Lewis 41Module 7
Effect of rolling on Structure The normal forces elongate
the grains With enough energy new
smaller grains grow Structure becomes much
more uniform Better strength and
ductility
Spring 2001 ISAT 430 Dr. Ken Lewis 42Module 7
Shape Rolling
Flat rolling is just the start. Straight and long structural shapes
Bars Channels I – beams
The material cross section is reduced non-uniformly The sequence and type of rolls is quite complex.
Spring 2001 ISAT 430 Dr. Ken Lewis 43Module 7
Shape rolling of an H– section part.
Spring 2001 ISAT 430 Dr. Ken Lewis 44Module 7
Ring Rolling Ring is placed between two
rolls, of which one is driven Volume of the ring is
constant to the diameter increases during the process
Ring blanks Cut from a plate Cutting a thick walled
pipe.
Spring 2001 ISAT 430 Dr. Ken Lewis 45Module 7
Ring Rolling -- shapes Shapes can be quite
complex. Uses
Large rings for rockets and turbines
Gearwheel rims Ball bearing races Flanges.
Spring 2001 ISAT 430 Dr. Ken Lewis 46Module 7
Thread Rolling Straight or tapered threads
put in round rods. Most bolts and screws are
made this way. Production rates of up to
80 pieces per second are possible
Spring 2001 ISAT 430 Dr. Ken Lewis 47Module 7
Thread Rolling No loss in material Good strength (cold
working) Surface finish is very good Process induces residual
compressive stresses on surface which improves fatigue life.
Spring 2001 ISAT 430 Dr. Ken Lewis 48Module 7
Thread Rolling
Spring 2001 ISAT 430 Dr. Ken Lewis 49Module 7
Thread properties Machining cuts through the
grains Rolling compresses them
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