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