Vacuum Bagging

What is Vacuum bagging ?

This is basically an extension of the wet lay-up process described above where pressure is applied to the laminate once laid up in order to improve its consolidation. This is achieved by sealing a plastic film over the wet laid-up laminate and onto the tool. The air under the bag is extracted by a vacuum pump and thus up to one atmosphere of pressure can be applied to the laminate to consolidate it.

Vacuum bagging is widely used in the composites industry. It is a technique in which you create uniform pressure to the surfaces of the object inside of a bag, holding parts together while the adhesive cures. Pressurizing a composite lamination serves several functions. It removes any trapped air between layers and provides pressure that prevents shifting of fiber orientation during cure. It also reduces humidity and improves the fiber-to-resin ratio in the composite part. The mechanical properties of open-mold 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. 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 mold and used to compact the laminate and remove air voids. 

Process

In the basic simplest form of vacuum bagging, a flexible film (PVA, Nylon, Mylar, or Polyethylene) is placed over the wet lay-up, the edges sealed, and a vacuum drawn. 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. A breather ply of a non-woven fabric is placed over the bleeder ply, and the vacuum bag is mounted over the entire assembly. Pulling a vacuum from within the bag uses atmospheric pressure to eliminate voids and force excess resin from the laminate. The addition of pressure further results in high fiber concentration and provides better adhesion between layers of sandwich construction. When laying non-contoured sheets of PVC foam or balsa into a female mold, vacuum bagging is the technique of choice to ensure proper secondary bonding of the core to the outer laminate.
The mechanical properties of open-mold 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, and excess resin. 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 mold and used to compact the laminate and remove air voids.

Materials Options

  • Resins: Primarily epoxy and phenolic. Polyesters and vinyl esters may have problems due to excessive extraction of styrene from the resin by the vacuum pump.
  • Fiber : The consolidation pressures mean that a variety of heavy fabrics can be wet out.
  • Cores: Any.
Our extensive experience with vacuum bagging molding enables us to produce innovative and cost-effective parts for our OEM customers. The process is best suited for low production volumes where a one-sided finish is required..

Advantages

  • Higher fiber content laminates can usually be achieved than with standard wet lay-up techniques.
  • Lower void contents are achieved than with wet lay-up.
  • Better fiber wet-out due to pressure and resin flow throughout structural fibres, with excess into bagging materials.
  • Health and safety: The vacuum bag reduces the number of volatiles emitted during cure.
  • Laminates with a uniform degree of consolidation.
  • Minimum void content.
  • Complete fiber wet-out can be accomplished
  • Improved core-bonding
Our extensive experience with vacuum bagging molding enables us to produce innovative and cost-effective parts for our OEM customers. The process is best suited for low production volumes where a one-sided finish is required..