What is Vacuum Bagging?

Vacuum bagging employs atmospheric pressure as a clamping method to hold epoxy-coated parts of a laminate in their intended position throughout the curing process, facilitating the best possible shape and longevity for the epoxy coating. The composite parts are set into an open-face mold and then sealed into a vacuum bag, after which air is removed and the parts start to set.

Vacuum bagging is also commonly used in prepregs. Rather than using a press, technicians place the workpiece in a bag, include peel ply and bleeder cloth, and vacuum bag the part to apply heat and pressure that sets the final product. This blog post will discuss the materials used in vacuum bagging, the process itself, and the advantages vacuum bagging offers.

Vacuum Bagging Materials

Vacuum bagging requires the following materials to fully control and optimize the process:

• Bagging films. Bagging films are made from nylon and various other materials that can handle high temperature levels. This film seals the open side of the composite so operators can evacuate all of the air between the composite and the film.
• Release films. Release films come in colored, clear, perforated, and non-perforated options. These films assist in keeping the epoxy in the laminate.
• Breathers and bleeders. Breathers and bleeders help air throughout the envelope travel to the vacuum port by creating a breathable layer between the laminate (or composite) and the vacuum bagging film to keep air from getting trapped in laminates.
• Sealant tapes. These tapes help create an airtight seal around the space where the manifold enters the bag, so air can’t re-enter the system.
• Peel plies and release fabrics. Mold release fabrics and associated materials help ensure the laminate will release from the mold without damage.
• Pressure-sensitive tapes. Tapes are essential for holding films, breathers, peel lies, and other components in place during the vacuum bagging process.
• PTFE-coated release fabrics. These fabrics are similar to other release fabrics, but they have a polytetrafluoroethylene coating for higher temperature resistance.
• Valves and hoses. Vacuum valves are typically made from aluminum, steel, or stainless steel and assist in removing air from around a laminate.
• Impression film. Honeycomb refits may require impression films, but they are otherwise not required.
• Miscellaneous. Vacuum bagging materials may also include bondable and non-bondable shrink tapes, and non-silicone tooling rubber.

The Vacuum Bagging Process

Vacuum bagging follows specific steps to enclose a laminate and evacuate the surrounding air in a controlled process during the curing process:

1. The prepreg, laminate, or composite is set inside a one-sided mold.
2. Operators layer bleeder material (to capture excess epoxy during the process) and breather material that will allow the vacuum to evacuate the air through the ventilated fabric without it getting trapped between the vacuum fabric and the composite.
3. Operators insert the valve base or vacuum hose onto the fabric and enclose the entire open side in vacuum fabric or a vacuum bag. The assembly should have at least two vacuum valves.
4. The vacuum pump is activated, which evacuates the air in a slow, consistent process to remove wrinkles and excess air.
5. Once the air has been removed, technicians turn off the vacuum and check for potential air leaks. If the air is removed and doesn’t leak back into the bag, technicians may allow the composite to cure naturally or in an oven.

The Advantages of Vacuum Bagging

Vacuum bagging offers several benefits, including:

• Even, consistent pressure across the laminate surface
• Reduced instances of voids and glue lines in the final product
• Produces laminates with higher fiber content and a better fiber wet-out process

Vacuum Bagging From APCM

At APCM, along with vacuum bagging, we offer expert advice in every aspect of prepreg manufacturing and forming. Contact us today to see how we can help with your next project.