As a composite manufacturing process, vacuum bagging provides compaction pressure and consolidation of plies within the laminate. It is also known as an extended version of hand lay-up process and vacuum bag molding. In this process, the mold base is kept horizontally, and the prepreg composites are placed in equal distribution into the mold base. It is then horizontally layered and placed over the composites. Finally, all the composite laminates are covered by a vacuum bag and sealed properly using sealers.
The vacuum and autoclave pressure cycles are adjusted to permit maximum removal of air without incurring an excessive resin flow. Vacuum is usually applied only in the initial stages of the curing cycle, while autoclave pressure is maintained during the entire heating and cooling cycles. Curing pressures are normally in a range of 50–200 psi (3–12 MPa). Compared with vacuum bag moulding, this process yields laminates with closer control of thickness and lower void content.
The heat transfer design of autoclaves is not straightforward. Both convective and radiative heat transfer mechanisms occur and thermal resistance is a function of both the mould and the layup itself. Cycle times, certainly in the heating phase of the process, can be dominated by this latter effect. An advantage of autoclave type techniques is that components which may require secondary bonding can be co-cured in a single operation.
