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VACUUM BAGGING TECHNIQUE

AND COMPRESSION MOULDING

TECHNIQUE

NAME: N.K.NAGARAJAN

ROLL NO: 11 MT66ASSIGNMENT PRESENTATION I

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WHAT IS VACUUM BAGGING ?

Vacuum bagging (or vacuum bag laminating) is

a clamping method that uses the atmospheric

pressure to hold the adhesive or resin coated

components of a lamination in place until the

adhesive cures

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Vacuum Bagging Advantages

Even clamping pressure

Control of resin content

Custom shapes Efficient laminating

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Vacuum bagging

Vacuum bagging is the modification of hand-

layup

Lay-up(necessarily smaller) is completed and

placed inside a bag made of flexible film and

all the edges are sealed.

Then the bag is then evacuated so that the

pressure eliminates voids in laminate, forcing

excess air and resin from the mould.

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Steps in vacuum bagging process

Lay-up

Preparation of bleeder system

Baggaging operation

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Requirements for proper bagging

Bag to be impervious to air pressure

Bag to uniformly apply cure pressure

The bag used in this method had two fold

advantages.

1. It provides a means for removing volatileproducts during cure

2. It provides a means for application ofpressure of one atom which is adequate forsome materials.

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Vacuum bagging materials

Release fabric

Perforated film

Breather material Vacuum bag

Mastic sealant

Plumbing system Mold release

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Release fabric

1. Smooth woven fabric

it should not bondto epoxy resin.

2. Used to separate breather and laminate

3. Excess epoxy can wick through releasefabric

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Perforated film

Used in conjunction with release fabric

This film helps to hold the resin in laminate,

when high vacuum pressure is used with slow

curing resin system (or) thin laminates

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Breather material

(or) bleeder cloth

Allows air from all parts of the envelope to

be drawn to a port (or) manifold by providing

slight air space between the bag and laminate

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Vacuum bag

If vacuum bag pressure less than 5 psi at room

temperature 6 mil polyethylene can be used.

Clear plastic material is preferred as compared

to opaque for easy inspection

Specially manufactured vacuum bag can be

used for high pressure and temperature

applications.

It should always larger than mould

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Mastic sealant

To provide continous air tight between bag

and mould.

Also used to seal the point where the

manifold enters the bag and to repair leaks in

the bag.

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Mold release

Necessary to prevent epoxy from sticking

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Vacuum Bag moulding Advantages

-as for hand lamination, except

1. Higher fibre volume fraction

2. Lower void contents3. Heavier fabrics can be wet out

4. Improved mechanical properties due to

higher fibre volume fraction5. Volatile organic compounds are largely

contained during the curing stage

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Vacuum Bag moulding Advantages

6. The additional consolidation pressure can

help the reinforcement to conform to tight

curvatures.

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Vacuum Bag Moulding Disadvantages

Higher labour skills for the bagging stage

Low production rates due to bagging stage

Joining bagging film for large items Mould tool must be vacuum tight

Cost of consumables and equipment

Consumable material compatible with resin Consolidation pressure limited to 1 atm

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Applications

Widely used in high performance mouldings

such as for aerospace applications.

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Compression Moulding

It is a process whereby a stack of

preimpregnated layers are

compressed betweeen a set matcheddies using a powerful press, and then

cured while under compression.

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Applications

This method is often used to manufacture

small quantities of high quality components

such as crash helmets and biccycle frames.

Due to the use of matched dies, the

dimensional tolerances and mechanical

properties of finished components are

extremely consistent.

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Compression moulding

However, the requirement to trim the

component after curing and the need for a

large press means that this method is

extremely expensive. Also, it is very difficult to

make components where the plies drop off

consistently within the component.