c FabricationProcesses

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Fabrication methods

CompositesIves De Baere and Joris Degrieck – 2013-2014

Fabrication methods: general

• Basic principles:‣ for thermosets:

‧ impregnate fibres with liquid mix of monomers/ polymersimpregnate fibres with liquid mix of monomers/ polymers and let it “cure”; eventually start from “prepreg” (to be stored at -18ºC)

‧ temperature and pressure may act as catalyst/accelerator

‧ “post-curing” is often applied

f h l i


‣ for thermoplastics:‧ impregnate fibres with liquid or dissolved thermoplastic

to obtain “prepreg”, “semipreg” or granules

‧ next warm up above melting temperature, shape/inject and let cool down

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Fabrication methods: general (2)

• Choice of fabrication method function of:

‣ desired mechanical properties (number of layers, fibre di ti fib f ti )directions, fibre fraction,…)

‣ desired quality (porosity, surface quality,…)‣ selected fibres and matrix‣ complexity and dimensions of product‣ size of production series‣ health and environmental considerations,…‣ …


design and fabrication method always have to go hand in hand !!


• points (of attention) with thermosetting matrices:

‣ possibility of creation of voids (from condensation products

(poly-condensation), solvents, other additives,…)

‣ risk of release of toxic gasses(e.g. styrene with polyester)

‣ use polymer mixture with adapted “pot-life” (time available

for processing before start of effective curing)

‣ use of gel coat (protection layer to be applied before or after


use of gel coat (protection layer to be applied before or after

lamination/curing; is often pure resin with fillers and/or

additives, eventually strengthened with “surface “)

.

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• mould(s)/die(s) always needed (composite material

is formed during fabrication of product)

‣ can be cheap and simple (e.g. for wet lamination, filament

winding,…: wood, plaster, composite, metal) up to complex

and expensive (hot pressing, injection moulding, filament

winding…: aluminium, steel, composite)

‣ always apply a release agent or use a release film


y pp y g

‣ take shrinkage and thermal expansion difference into

account !

Wet Hand Lay-up: principle

resin

ld

laminate

resin

Hand roller


mould

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Wet Hand Lay-up


Current Practices in FRP Composites TechnologyFRP Bridge Decks and Superstructures


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Wet Hand Lay-up


Spray-up


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Spray-up

Applying a gelcoat (surface finish) Spraying the chopped fibres


Automated spray-up of boat hull


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Wet hand lay-up & spray-up

• Pro:‣ Low initial investment‣ Adapted for small series

Hi h fl ibilit i h i d l it‣ High flexibility in shaping and complexity

• Contra:‣ Labour intensive‣ Varying properties and quality‣ Relative low fibre volume fractions(25-40%)‣ Only one finished (smooth) surface


y ( )

• Examples of applications:‣ boats, swimming pools, cars/truck bodies, all types of composites prototypes, …

Vacuum assisted resin infusion/injection


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Vacuum assisted resin infusion/injectionlab setup


Resin injection of hulls


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Example resin flow:boat hull


Example resin flow:boat hull


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Replacing some of the manual labour:automated fibre deposition


Injection and bonding two half blades


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Resin Transfer moulding (RTM)- LightUses vacuum to keep the mould closedvacuum causes the infusion


Resin Transfer moulding (RTM)- Light


http://www.youtube.com/watch?v=yTsXKGUdtCE

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Vacuum Assisted Resin Transfer Moulding (VA)RTM

‘infusie-labo.mov’


Uses mechanical system to keep the mould closed, as resin is injected under pressure, combined with vacuum

Vacuum Assisted Resin Transfer Moulding (VA)RTM


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Resin injection ((VA)RTM(-Light))

• Pro:‣ Relatively low initial investments‣ Adapted for smaller to larger series‣ Adapted for large products/constructionsAdapted for large products/constructions‣ High flexibility in shaping and complexity‣ Reasonable to good and consistent mechanical properties

• Contra:‣ Relatively labour intensive‣ High cycle times (for largers products)‣ Medium fibre volume fractions (is improving)


( p g)

• Examples of applications:‣ boating, pressure vessels, car bodies and components,…

Autoclave processing: principle

Pressure vesselInlet pressurized(hot) gas

Sealant tape Vacuum bag

Stacking sequence


vacuum

Stacking sequenceBleeder, breather ...

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Autoclave processing : extra supplies


Autoclave processing : extra supplies

Release film (perforated)

Release fabric

Release film (perforated)


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Autoclave cycle


Viscosity and cure curves (thermosetting prepreg)


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Autoclave examples

Autoclave at Airbus


Pressure bag technique


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Autoclave processing

• Pro:‣ High and consistent mechanical properties‣ High fibre volume fractions possible (50-70%)

Ad t d f ll i‣ Adapted for small series‣ Relatively high flexibility in shaping and complexity

• Contra:‣ (very) labour intensive‣ (very) high investments and cost of supplies


• Examples of applications:‣ Aeronautics and aerospace, products with very high dimensional tolerances (radars, space mirrors,…)

‘out-of-autoclave’ - methods

OOA curing achieves the desired fiber content and elimination of voids by placing the layup within a closed mold and applying vacuum, pressure, and heat by means other than an autoclave

e g RTM VARTM SQRTMe.g. RTM, VARTM, SQRTM

Same Qualified Resin Transfer Moulding (SQRTM)SQRTM is an RTM process adapted to prepreg technology. The prepreg is placed in a closed mould and during the cure cycle a small amount of resin is injected into the cavity


cycle, a small amount of resin is injected into the cavity through ports positioned around the part. This resin does not go into the laminate, but only presses up against the edge of the laminate in order to establish hydrostatic pressure on the prepreg, similar to the goal of autoclave curing.

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SQRTM – example(source: Radius Engineering)

SARAP fuselage prototype (helicopter)


SQRTM - example

Step 2:The roof skin’s prepreg layup is inplace, and the network of tooling inserts thatwill form the faces of the roof section’sbeams and perpendicular frames are inbeams and perpendicular frames are inposition

St 1 L f th l f t


Step 1: Layup of the complex roof part,shown here in the early stages, involvedplacement of a combination of debulkedprepreg materials and dry preforms(described in step 3) on the lower mold half

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SQRTM - example

Step 4: The layup has been completed,multiple tool inserts installed, and the moldclosed. At this point, injection take place,using the same resin as that incorporated intothe the prepregs to maintain steadthe the prepregs, to maintain steadyhydrostatic pressure within the mold.

Step 3: This close up shows the “pi” preforms


Step 3: This close-up shows the pi preformsused at the intersections of vertical andhorizontal elements. Everywhere a verticalstiffener web meets a beam flange or the partskin, the two legs of the pi preform form aslot that accepts the web while theperpendicular preform element lays flatagainst the horizontal flange or skin.

pultrusion: principle

Yarns

Preforming die

resin

pulling mechanism

Saw


Heated mould

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Pultrusion


Pultrusion

http://www.youtube.com/watch?v=1sH9rIGWNvc

http://www.youtube.com/watch?v=bRjU4na-ol8


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Pultrusion - examples


Pultrusion

• Pro:‣ Continuous production process (up to meters per minute)‣ Not labour intensive

V t t ti d lit‣ Very constant properties and quality‣ Broad range of fibre volume fractions (40-70%)

• Contra:‣ High investments‣ Limited flexibility in shaping and complexity


• Examples of applications:‣ beams, walkways, ladders, poles, (cable) ducts,…, springs,…

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Filament winding : principle


Winding patterns

) i f i la) circumferential

b) Helicoidal


c) polar

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Possible implementations of winding eye


Filament winding


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Filament windinghttp://www.youtube.com/watch?v=V2ZJDqPfiwc&feature=related


Filament winding

• Pro:‣ Not labour intensive‣ Constant properties and quality

Hi h l f ti ibl (50 70%)‣ High volume fraction possible (50-70%)

• Contra:‣ Initial investment‣ Limited flexibility in shaping and complexity


• Examples of applications:‣ Storage tanks, pressure vessels, tubes and ducts, fishing poles, drive shafts, flywheels, rocket cases,…

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Tape laying – fibre placement


Tape laying – fibre placement

Laying the fibres• exactly where you want to• under the exact angle• precuring them during• precuring them during

fibre placement


http://www.youtube.com/watch?v=QDbrVTWnFIU

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Injection moulding : principle

granulates

mould Heated screw/housing


Injection moulding


http://www.youtube.com/watch?v=XqoecH2AtaQ

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Injection moulding

•Pro:‣ Ideal for very high production series (several to many components in one shot)‣ Not at all labour intensive‣ Constant properties and quality‣ High flexibility in shaping and complexity

• Contra:‣ High initial investments‣ Small products (moulds need high injection pressures)‣ Limited fibre volume fraction, medium mechanical properties (short fibres fibre orientation function of flow


properties (short fibres, fibre orientation function of flow pattern)

• Examples of applications:‣ All types of small components, small gears, keyboard components, hinges and handles,…

Compression moulding: principle


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Compression moulding




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• Pro:‣ Adapted for large to very large series‣ Good and consistent quality

T fi i h d f‣ Two finished surfaces‣ Reasonable flexibility in shaping and complexity

• Contra:‣ Very high initial investments (presses and moulds)‣ Dimensions limited by limits on compression forces


• Examples of applications:‣ Automobile, sanitary apparatus, casings and components for electrical installations,…

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