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Advanced Composite

Processes

Dr. S. Nagaraja RaoPrincipal, PG Section,

G.T.T.C, Mysore


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Advanced composite ProcessesCommon feature to all polymeric composite processes:Combining resin, curing agent, reinforcing fiber,

and in some cases a solvent.

Heat and pressure: Shape and "cure" the mixture into a

finished part.

Resin : Hold the fibers together, protect them & transfer

the load to the fibers in composite part.

Curing agent/ hardener: Acts as a catalyst and helpsin curing the resin to a hard plastic.

Reinforcing fiber: Imparts strength and other required

properties


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Major Processes

Processes:

Automated

Manual

Combined


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Basic process types

Formulation:

Mixing of resin, curing agent, and anyother component required

May involve adding the componentsmanually into a small mixing vessel

or

In case of larger processes componentsmay be pumped into a mixing vessel


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repregg ng Resin and curing agent mixture are impregnated into

the reinforcing fiber.

Prepregs main forms:

1. woven fabrics

2. roving

3. unidirectional tape.

Fabrics and tapes -continuous rolls in widths up to

72 inches and lengths up to several hundred feet. Fabric or tape thickness constitutes one ply in the

construction of a multi-ply lay-up.

Impregnated roving is wound onto cores orbobbins

prepreg must be stored in a refrigerator or freezeruntil use

cold storage prevents the chemical reaction fromoccurring prematurely.

Prepreg materials used in advanced compositeindustry- aircraft and aerospace.


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PREPREG MANUFACTURE


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Open Molding processes

part being manufactured is exposed to the

atmosphere.

worker typically handles the part manually

Higher potential for exposure

The resin mixture may be a liquid being

formed onto a reinforcing material

or prepreg material being formed for finalcure.


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Open Molding process


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Closed Molding processes

All or part of the manufacture takes place in a

closed vessel or chamber.

The liquid resin mixture or prepreg material may

be handled or formed manually into the

container for the curing step.

Liquid resin mixtures pumped into the container,

usually a mold of some type, for the curing step.


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Sequential or batchprocesses

Manufacture of a single part at a time, insequence.

This type of process is usually required:

Part being made is small complex in shape

curing phase is critical

finishing work must be minimized

small number of parts


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Continuous processesare typically automated to some degree

and are used to produce larger numbers

of identical parts relatively quickly.

These processes are typified by

pumping of the resin mixture into the

mold, followed by closed curing.


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Resins

The resin systems used to manufacture

advanced composites are of two basictypes: thermosetting and thermoplastic.

Thermosetting resins predominate

today, while thermoplastics have only a

minor role in advanced composites

manufacture.


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Thermosets

Thermoset resins require addition of a curing agentor hardener and impregnation onto a reinforcingmaterial, followed by a curing step to produce acured or finished part. Once cured, the partcannot be changed or reformed, except forfinishing.

Common thermosets :

Epoxies

Polyurethanes

Phenolic and amino resins Bismaleimides (BMI, polyimides)

Polyamides


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EPOXIES Epoxies: Most commonly used in today's PMC industry.

Basic epoxy compounds: reaction product of epichlorohydrin and

bisphenol-A.

Epoxy compounds are also referred to as glycidyl compounds.

Types of epoxy compounds : glycidyl ethers (or diglycidyl ethers),

glycidyl esters, and glycidyl amines.

Several of these compounds are reactive diluents and are sometimesadded to the basic resin to modify performance characteristics.

The epoxy molecule can also be expanded or cross-linked with other

molecules to form a wide variety of resin products, each with distinctperformance characteristics.

These resins range from low-viscosity liquids to high-molecularweight solids. Typically they are high-viscosity liquids.


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Curing agent or hardener:

They control the reaction rate

Determine the performance characteristics of the finishedpart.

These compounds act as catalysts for the reaction

Curing agents :

Aromatic amines.

4,4'-methylene-dianiline (MDA)

4,4'-sulfonyldianiline (DDS).


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Other types of curing

agents&Resins

Aliphatic and cycloaliphatic amines

polyaminoamides

amides

anhydrides.

Note:The choice of curing agent depends on the cure andperformance characteristics desired for the finished part.

Polyurethanes are another group of resins used in advancedcomposite processes.

These compounds are formed by reacting the polyol componentwith an isocyanate compound, typically toluene diisocyanate(TDI);

methylene diisocyanate (MDI) and hexamethylene diisocyanate(HDI) are also widely used.


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RESINS AND CURINGS(CONTD)

Phenolic and amino resins are anothergroup of PMC resins. They are usedextensively in aircraft interiors becaosue

of their exceptional low smoke and heatrelease properties in the event of a fire.

The bismaleimides and polyamides arerelative newcomers to the advancedcomposite industry and are used forhigh temperature applications.


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AUTOCLAVE CURING &

BONDING

Prepreg method adopts both vacuum

bagging & autoclave for consolidation &

curing.

Autoclave

Pressure Temperature (Heat)


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AUTOCLAVE CURING


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AUTOCLAVE CURING &

BONDING


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Advantages

Superior Products

Complex parts can be producedProblems:

Heat loss

ControlCostly


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Filament Winding

Winding Methods

Wet Dry Post Impregnation


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Filament Winding


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Winding Types

Hoop

CircumferentialRadial

Helical

AxialPolar


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Process of Winding

A continuous wire or tape or mat of

fibrous material is dipped in a resin bathand wound on a mandrel in the desired

orientation and desired thickness.


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Resins used

Epoxy --- most common

Polyester --- most commonPhenolic

Silicon

Thermoplastics


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Examples of combination

Graphite for longitudinal stiffness, Fiberglass

to resist hoop direction.

Carbon for strength, Aramid for impact

strength.


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Desirable Factors

Proper control of resin viscosity,

consistency TemperatureTension control

Proper shape of mandrels

Rotational speed of mandrelsPost curing

Ch t i ti f fil t


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Characteristics of filament

wound parts

Voids minimum

FlexibilityJoints between the composite and metal

can be made easily


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Advantages

Varying size

High strength in desired directions

Less material wastage

Forming shapes easy Panels and fittings can be included during winding

Parts with high pressure ratings can be made

Continuous process and thus faster production

Overall production cost is lower


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PULTRUSION

Continuous reinforcement fibers areimpregnated with resin shaped by drawingthrough a die.

Types of die:

Fixed High pressure

Floating Low & Medium pressures

Multiple


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PULTRUSION


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PULTRUSION


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Applications

Building panels

Electrical insulators

Supports & panels for truck trailers

Door support for automobiles Ladder rails

Pressure tanks (Trunk portion)

Aircraft flooring

Rods, Stringers, Stiffness for aircraft and automobileleaf springs (Shock absorbers)


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Advantages (contd.)

Storage tanks

Pipes

Chimney liners Lightening arresters

Springs

Shafts Wind turbine blades

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