Vacuum bag molding is an open mold technique used for thermoset composites involving hand layup and vacuum bagging. Vacuum bagging uses a vacuum bag to apply even pressure over composite materials to consolidate them. It involves placing release fabrics, breather materials, and vacuum bags over molds with resin-coated components. Applying vacuum pressure draws air out and uses atmospheric pressure to hold components in place until the resin cures.

1. Vacuum bag molding

2. • Vacuum bag molding
• Also known as vacuum bagging.
• Open mold techniques for thermoset composites.
• Hand lay-up: The application of reinforcement along
with a polyester or epoxy resin by hand.
• Vacuum bagging: The use of a vacuum bag to apply
an even pressure over the composite to consolidate
the material.

3. Hand layup

4. Hand Layup

5. Hand Layup

6. What is vacuum bagging?
•Vacuum bagging (or vacuum bag laminating) is a
clamping method that uses atmospheric pressure to
hold the adhesive or resin-coated components of a
lamination in place until the adhesive cures.
•(When discussing composites, “resin” generally refers
to the resin system— mixed or cured resin.)

8. Vacuum Bagging - Advantages
• Even Clamping pressure
• Control of resin content
• Custom shapes
• Efficient laminating

9. Vacuum bagging -Equipment

10. Vacuum Bagging - Materials
• Release fabric
• Perforated film
• Breather Material
• Vacuum bag
• Mastic sealant
• Plumbing system
• Mold release

11. Release fabric:
•Smooth woven fabric – not bond to epoxy.
•Used to separate breather and laminate.
•Excess epoxy can wick through release fabric.
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.

12. 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.
Vacuum bag:
•If vacuum pressure less than 5psi(10 hg) at room
temperature – 6mil polyethylene plastic can be used.
•Clear plastic material is preferable as compared to
opaque - for easy inspection

13. • For high pressure and temperature applications –
specially manufactured vacuum bags can be used.
• Vacuum bag should always larger than mould.
Mastic sealant:
• Provide a continuous air tight sealant between bag
and mold.
• Also used to seal the point where the manifold enters
the bag and to repair leaks in the bag.

14. Plumbing system:
•Provides an airtight passage from vacuum envelope to
vacuum pump – allowing pump to remove air.
•A basic system consists of flexible (or) rigid hose pipe,
a trap, a port that connects pipe to the envelope.
•Vacuum hose designed specially for this.
•Vacuum port connects the exhaust tubing to vacuum
bag.
•Control valve – control of airflow at the envelope.

15. • Trap incorporated into the line as close as possible to
the envelope.
• Vacuum gauge – is necessary to monitor the level.
The reading of negative pressure inside the bag is
equal to the net pressure of the atmospheric pressing
on the outside of the bag.

16. Mold release:
•Necessary to prevent epoxy from sticking.
•Three types of mold release:
4.Carnauba based paste wax
•(usually 5 layers for new mold and atleast one layer
before each new part is molded)
•Also use PVA in wax.
•Fine detail gloss level obtained by the use of wax.

17. 2. Semi permanent formulation:
•Liquid release system.
•Fine detail and gloss level are obtained as
well as texture.
3. General contaminant variety:
•Grease, vaseline, toilet bowl wax, hair spray,
hair gel.

21. Example: Step 1

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29. Challenges:

30. Example 2: Step 1

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36. Step 7: