Vacuum Bag Moulding

Vacuum Bag Moulding:

The mechanical properties of open-mould laminates can be improved with vacuum bagging. By reducing the pressure inside the vacuum bag, external atmospheric pressure exerts force on the bag. The pressure on the laminate removes entrapped air, excess resin and compacts the laminate. A higher percentage of fiber reinforcement is the result. Additionally, vacuum bagging reduces styrene emissions. Vacuum bagging can be used with wet-lay laminates and prepreg advanced composites. In wet lay-up bagging the reinforcement is saturated using hand lay-up, then the vacuum bag is mounted on the mould and used to compact the laminate and remove air voids. 

Process

1. In the simplest form of vacuum bagging, a flexible film (PVA, nylon, polyethylene) is placed over the wet lay-up, the edges sealed, and a vacuum drawn. 

2. A more advanced form of vacuum bagging places a release film over the laminate, followed by a bleeder ply of fiberglass cloth, non-woven nylon, polyester cloth or other material that absorbs excess resin from the laminate. 

3. A breather ply of a non-woven fabric is placed over the bleeder ply, and the vacuum bag is mounted over the entire assembly. 

4. Pulling a vacuum from within the bag uses atmospheric pressure to eliminate voids and force excess resin from the laminate. 

5.The addition of pressure further results in high fiber concentration and provides better adhesion between layers of sandwich construction. 

6. When laying non-contoured sheets of PVC foam or balsa into a female mould, vacuum bagging is the technique of choice to ensure proper secondary bonding of the core to the outer laminate. 

Advantages

1. Vacuum bag processing can produce laminates with a uniform degree of consolidation

2. Remove entrapped air, thus reducing the finished void content 

3. Complete fiber wet-out can be accomplished if the process is done correctly. 

4. Improved core-bonding. 

5. Higher percentage of fiber reinforcement

6. Reduces styrene emissions.

Disadvantages

1. Wall thickness is depend on operator skill