Post on 03-Feb-2022
Processing and Manufacturing
Antonio Miravete, Stanford University
September 22, 2009
Outline
Laws for Composite Materials Processing
* Physical and Constitutive laws
Introduction to Manufacturing
Pultrusion: How to produce low cost, constant cross-section parts
Infusion: How to produce large parts with just one smooth surface
RTM: How to produce medium/large parts with two smooth surfaces
SMC: How to produce short cycle time (< 1 min) parts
Prepregging: How to produce high performance parts
Filament Winding: How to produce bodies of revolution
PHYSICAL LAWS FOR COMPOSITES PROCESSING
(GOVERNING EQUATIONS)
•Conservation of Mass
Rate of Mass Increase=Rate of Mass Inflow-Rate of Mass outflow-Rate of Mass lost due to a sink
•Conservation of Momentum
Inertia Force=Hydrodynamic Force + Force due to stresses + Body Forces
•Conservation of Energy
Rate of increase = Inflow flux + Inflow flux +Rate of energy + Rate of energy + Rate of energy
of internal and of internal and of heat increase due to increase due to generation
Processing Introduction
kinetic energy kinetic energy total stresses body forces
CONSTITUTIVE LAWS FOR COMPOSITES PROCESSING
(CONSTITUTIVE EQUATIONS)
Constitutive equations are empirical relations between parameters of interest:
•Resin Viscosity
•Reaction Kinetics
•Permeability
•Fiber Stress
Processing Introduction
CONSTITUTIVE LAWS FOR COMPOSITES PROCESSING
•Resin Viscosity
1 10 100 1000 Temperature ( C)
Viscosity (Pa.s)
1000
100
10
Thermoset resins
Processing Introduction
CONSTITUTIVE LAWS FOR COMPOSITES PROCESSING
•Reaction Kinetics or Curing
1 10 t (sec)
Degree of cure
0.9
0.5
0.1
T= 125 C
T= 25 C
Processing Introduction
CONSTITUTIVE LAWS FOR COMPOSITES PROCESSING
•Permeability
Darcy s law:
Q=K A dP
dxη
Q: flow rate across the section A
η: viscosity of the resin
: driving pressure gradient
K : permeability of the porous medium
dPdx
Processing Introduction
CONSTITUTIVE LAWS FOR COMPOSITES PROCESSING
•Fiber stress
Processing Introduction
Pultrusion Vacuum bag
OPEN MOLD:
INFUSION,
PREPREG/AUTOCLAVE,
FILAMENT WINDING,…
Manufacturing Processes Introduction
CLOSED MOLD:
RTM, SMC,
PULTRUSION,..
SMOOTH SURFACE
FIBER
PROCESSING
COMPOSITE
PART
RESIN
Fiber
impregnationConsolidation
(pressure)
Curing
Manufacturing Processes Introduction
Manufacturing Processes Why Composites?
“One shot” RTM
Source: Volkswagen
Manufacturing Processes Introduction
Consolidation by
vacuum (bag)
Consolidation by
resin pressure
Consolidation
by press
Three types of consolidation
Manufacturing Processes Introduction
How to produce low cost,
constant cross section
parts in an efficient way?
Pultrusion Introduction
How to produce low cost, constant cross
section parts in an efficient way?
Pultrusion Raw Materials
• Most fibers are suitable for this process.
Most used are glass and carbon.
• Material forms can also be used at the
inlet to the die when materials such as
mats, weaves, or stitched materials are
used.
Fibers and matrices used:
• Resins must be fast curing because of process speeds. Most
used are polyester, vinyl ester, epoxy and phenolic.
• Higher resin reactivity, lower filler loadings, and thicker parts
contribute to higher exotherms and faster cure, but potentially
higher shrinkage.
Pultrusion Processing Parameters
Key Parameters:
• Typical speeds are 0.4 - 1m/min
• Wide up to 3 m
• Die lengths are 0.6 – 1.5 m
• Fiber Volume fractions range between 30 to 65%
• Voids usually range between 1 to 5%
• Pulling forces range between 45 to 90 KN
Viscosity and Temperature changes of a
thermosetting resin along a pultrusion die
Pultrusion Processing Parameters
Pultrusion Die Technology
Dies are metallic
(heated)
Dies may be fixed,
floating and multiple
Pultrusion 4 types in terms of impregnation
1) Open bath1 2
43
Pultrusion Applications
B C
D
A B
C D
Pultrusion Future trends
A major problem of the
pultruded parts is their
constant cross-section
VARIABLE CROSS-SECTION
Two future trends consist of
using sliding parts in the die
or molding after pultruding.
Manufacturing Processes Introduction
How to produce large parts
with just one smooth
surface in an efficient way?
How to produce large parts
with just one smooth
surface in an efficient way?
The part is consolidated by
means of a vacuum bag
The mold is usually heated
for curing purposes
Infusion Introduction
The fiber is impregnated
by the vacuum pressure
Infusion Introduction
High fiber fraction
Low tooling cost
Complex process
Low viscosity resin
Infusion Types
a) Longitudinal flow
b) Transverse flow with surface
medium
c) Transverse flow with grooved
cores
d) Transverse Interlaminar flow
This is a basic and low-cost infusion process
Requires high permeability fabrics
Also, the resin viscosity must be low ( 20 – 400 cps)
Infusion Longitudinal flow
Infusion Longitudinal flow
Darcy s Law:
Permeability test
L
pK
A
Q
Q: resin flow
A: transverse section
: viscosity
L: preform length
K: permeability
ΔP: pressure difference
Fiber fractions are higher than the obtained with longitudinal flow.
The final composite material has higher quality.
A peel ply is needed to separate the distribution nets.
Higher viscosity resins may be used.
Cost of auxiliary materials is higher.
The process is more repetitive.
Infusion Transverse flow
Infusion Applications
Infusion Future Trends
* Implementation of hybrid
materials: carbon and glass
* Implementation of hybrid
processes: infusion and
prepregging
Processing Homework#4
1. What type of pultrusion would you use for a profile to be
implemented in an aerospace application?
Open bath
Enclosed bath
Injection
Preimpregnated reinforcements
2. What type of infusion would you use to make a large boat
hull?
Longitudinal flow
Transverse flow with surface medium
Transverse flow with grooved cores
Transverse interlaminar flow
RTM Introduction
How to produce
medium/large parts with
two smooth surfaces in an
efficient way?
RTM Introduction
The part is consolidated
by the resin pressure
The part is usually cured by
oven or heated mold
How to produce
medium/large parts with
two smooth surfaces in an
efficient way?The fiber is impregnated
by the resin pressure
RTM Introduction
RTM Standard RTM Light
Closed cavity bag molding
RTM Types
Infusion
1. Placing the preform3. Injection2. Closing the mold
5. Demolding4. Curing
1 2 3 4 5
RTM Processing steps
Plain Twill 8-H Satin
RTM Preforms: drapability
RTM Preforms: permeability
A. Closed fabric
K = 1x10-6 cm2
B. Open fabric
K = 9x10-6 cm2
C. Standard fabric
K = 5x10-6 cm2
Permeability
testresin
RTM Resin: flow
VISCOSITY OF THE RESIN
RTM requires low viscosity resins to get an adequate flow and good wetability of the resin (between 50 and 300 cps)
Some examples of viscosity:
cps Similar to
1 Water
40 Polyester
150 Epoxy
500 Auto oil
2500 Pancake syrup
RTM Applications
3D BRAIDINGUD LAMINATE
Y=55 MPa
X=850 MPa X=635 MPa ( =25 )
X=545 MPa ( =30 )
Y=110 MPa ( =25 )
Y=165 MPa ( =30 )
[0] 40% Vf
Carbon Fiber HTA-6K/novolac
[0 50% , 50% ] 40% Vf
Carbon Fiber HTA-6K/RTM-6
x
y
z
RTM Future trends
How to produce short cycle
time (< 1 min) parts in an
efficient way?
How to produce short cycle
time (< 1 min) parts in an
efficient way?
SMC Introduction
First, a subproduct is
made: the SMC
Second, the SMC is consolidated
and cured in a hot press
SHEET MOLDING COMPOUND (SMC)
Chopped glass+ polyester+ fillers
SMC or Sheet Molding
Compound is a combination of
chopped glass strands and
filled polyester resin, in the
form of a sheet. The additives
allow the compound to be
stored for months before
processing.
SMC Introduction
There are three types of SMC in
terms of its density:
STANDARD SMC -1.9 g/cc (Renault
Laguna)
LOW DENSITY - 1.3 g/cc (Corvette
Chevrolet)
LITE SMC -1.6 g/cc (Ford Mustang)
SMC Introduction
SMC Step 1: The sub-product
SMC Step 2: The part
Composite tail gates
Megane cc
SMC Auto applications
SMC Future Trends
Vipper 2003: carbon fiber/vinyl ester SMC
Processing Homework#5
A constant cross-section 1 meter long part, must be injected
by RTM standard. The resin pressure is 7 bars and the
viscosity of the resin is 120 cps.
The injection time must be less than 45 minutes. There are
two fabrics available:
A) E-glass, cost: $ 1.5/kg and permeability: 1.5 x10-6 cm2
B) E-glass, cost: $ 1.7/kg and permeability: 2 x10-6 cm2
Which fabric would you use (A or B) ?
Would it be possible to use RTM light and meet the time
requirement?
Prepregs Introduction
How to produce high
performance parts in an
efficient way?
Prepregs Introduction
How to produce high
performance parts in an
efficient way?
First, a subproduct is
made: the prepreg
Second, the prepreg is consolidated
and cured by autoclave (T and P)
Pros
• The composite material is controlled in terms of thickness and fiber fraction,
which is very high, about 70% in volume. Porosity is very low (< 1%).
•Processing is easy since the resin is already present in the prepreg.
•Mechanical performance is very high, due to the high fiber fraction and
control.
Cons
• Refrigerated storage and transportation are required.
•Cost of the parts made out of prepregs are higher than other processes
since two steps are needed for their processing: production of the prepreg
and manufacturing of the part.
Prepregs Introduction
1. Cutting
2. Collation3. Vacuum
4. Autoclave
5. Trim 6. Inspection
7. Assembly
1 2 3 4 5 6
Prepregs Production scheme
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
• Release film: prevents the resin to reach the bleeder fabric but not the volatiles.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
• Release film: prevents the resin to reach the bleeder fabric but not the volatiles.
• Bleeder fabric: takes out
the excess of resin in
order to get the desired
fiber fraction.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
• Release film: prevents the resin to reach the bleeder fabric but not the volatiles.
• Bleeder fabric: takes out
the excess of resin in order
to get the desired fiber
fraction.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
• Release film: prevents the resin to reach the bleeder fabric but not the volatiles.
• Bleeder fabric: takes out
the excess of resin in order
to get the desired fiber
fraction.
• Breather fabric: makes
the vacuum uniform along
the part.
Prepregs Consolidation
Vacuum bagging
After ply collation the lay-up is sealed in a plastic bag for curing. The lay-out is composed of the
following components:
• Release agent: facilitates the extraction of the part.
• Peel ply: leaves the part surface apt to be bonded or painted.
• Prepreg.
• Release film: prevents the resin to reach the bleeder fabric but not the volatiles.
• Bleeder fabric: takes
out the excess of resin
in order to get the
desired fiber fraction.
• Breather fabric:
makes the vacuum
uniform along the part.
• Vacuum bag/seal:
seals the cavity to be
vacuumed.
Prepregs Consolidation
Curing by autoclave
Prepregs Curing
Prepregs Prepregging vs RTM
60+ % of Volume
fiber fraction
Most structural
composite parts
are made out of
prepregs
No countermold
is required
More suitable for
parts loaded in
one direction
Unidirectional
system provides
the best property
Requires
autoclave
Strict
Room
Conditions
High Cost
Less
efficient
load paths
ADVANTAGES OF Prepregs DISADVANTAGES
Prepregs Prepregging vs RTM
Complex geometries
High dimensional accuracy
Tight thickness control
Good surface quality.
Recommended for parts with
several surfaces to be adjusted
Integration of several parts in a
single one
High drapability
Does not require autoclave
Less strict room conditions
More efficient load paths
A mold and a countermold
are required
Fabrics are crimped in
some cases
Most structural composite
parts are made out of
prepregs
Impregnation process must
be carefully studied and
performed
Parts loaded in one
direction are more efficiently
designed and manufactured
by using prepregs.
ADVANTAGES OF RTM DISADVANTAGES
Prepregs Applications
Fiber Placement and Automated Tape Laying
Prepregs Future Trends
Photographs by MTorres
Filament Winding Introduction
How to produce bodies of
revolution, such as
cylinders, cones and
spheres in an efficient way?
Filament Winding Introduction
How to produce bodies of
revolution, such as
cylinders, cones and
spheres in an efficient way?
In-line impregnation by drawing the
fibers through a bath of resin
Consolidation ( fiber tension ) by
pulling the fibers through a number
of fiber guides
The part is usually cured by oven
1. Spool of fibers2. Impregnation
3. Fiber tension
4. Winding around
the mold
6. Demolding5. Curing
Filament Winding Production scheme
There are three main variants in terms
of winding patterns:
a) Helical winding
b) Polar winding
c) Hoop winding
Filament Winding Introduction
Filament Winding Degrees of freedom
Helical winder machines may have as many as six axes of movement:
1) Mandrel rotation, generally constant
2) Carriage linear movement, also
generally constant
3) Horizontal cross-feed, used to position
the winding pay-out band close to the
part at the end domes
4) Vertical cross-feed, same as horizontal
5) Pay-out rotation, used to allow the winding pay-out to keep the
band normal to the winding surface
6) Yaw, used to allow the pay-out band to be rotated in a 90º plane to
give additional control over the band placement
Processing Homework#6
Wind Turbine Blades use spar caps to
carry the majority of the load in the soft
or “flap” direction. The spar caps are
held apart by one or two shear webs.
The skins are thin except for the blade
root, which usually exhibits very thick
skins. Would you use prepreg or 3D
fiber infusion?Spar caps Shear webs Tip skins Blade root skins
Prepreg
3D fiber infusion
Filament Winding Applications
Driveshaft
Cylinders
Space launcher structuresBicycle fork
Carbon Fiber Applications
Glass Fiber Applications in Chemical, Oil and Water Industries
Filament Winding Applications
Filament Winding Future trendsReusable mandrels with shape memory polymers
Shape memory
polymer mandrel.
Mandrel is placed in a clamshell
mold, heated above its transition
temperature, and blown into its
complex shape under air pressure.
Under air pressure, the mandrel
is cooled in its new shape. Once
cooled, it is removed from the
mold and installed on a winder.
The rigid
mandrel is
filament-wound.
After the part cures, the mandrel is
heated above its transition temperature
to return to its initial tubular shape. The composite part
is completed.
Source: CRG