Vacuum bag molding

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  • 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 aclamping method that uses atmospheric pressure tohold the adhesive or resin-coated components of alamination in place until the adhesive cures.•(When discussing composites, “resin” generally refersto the resin system— mixed or cured resin.)
  • 7. Vacuum Bagging - Advantages• Even Clamping pressure• Control of resin content• Custom shapes• Efficient laminating
  • 8. Vacuum bagging -Equipment
  • 9. Vacuum Bagging - Materials• Release fabric• Perforated film• Breather Material• Vacuum bag• Mastic sealant• Plumbing system• Mold release
  • 10. 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 highvacuum pressure is used with slow curing resin system(or) thin laminates.
  • 11. Breather material:•(or) bleeder cloth.•Allows air from all parts of the envelope – to be drawnto a port (or) manifold by providing slight air spacebetween the bag and laminate.Vacuum bag:•If vacuum pressure less than 5psi(10 hg) at roomtemperature – 6mil polyethylene plastic can be used.•Clear plastic material is preferable as compared toopaque - for easy inspection
  • 12. • 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.
  • 13. Plumbing system:•Provides an airtight passage from vacuum envelope tovacuum 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 vacuumbag.•Control valve – control of airflow at the envelope.
  • 14. • 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.
  • 15. 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 layerbefore each new part is molded)•Also use PVA in wax.•Fine detail gloss level obtained by the use of wax.
  • 16. 2. Semi permanent formulation: •Liquid release system. •Fine detail and gloss level are obtained aswell as texture. 3. General contaminant variety: •Grease, vaseline, toilet bowl wax, hair spray,hair gel.
  • 17. Example: Step 1
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  • 25. Challenges:
  • 26. Example 2: Step 1
  • 27. Step 2:
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  • 32. Step 7: