Figure 7-34.  A mold of an inlet duct. Figure 7-33.  Five-axis CNC equipment for tool and mold making. Bleeder Ply Peel Ply Layup Tapes Solid Release Film Perforated Release Film Release Agents Breather Material Vacuum Bag Materials  Repairs of composite aircraft components are often performed  with a technique known as vacuum bagging. A plastic bag is  sealed around the repair area. Air is then removed from the  bag, which allows repair plies to be drawn together with no  air trapped in between. Atmospheric pressure bears on the  repair and a strong, secure bond is created. Several processing materials are used for vacuum bagging  a part. These materials do not become part of the repair and  are discarded after the repair process. Release agents, also called mold release agents, are used so  that the part comes off the tool or caul plate easily after curing.  The bleeder ply creates a path for the air and volatiles to  escape from the repair. Excess resin is collected in the  bleeder. Bleeder material could be made of a layer of  fiberglass, nonwoven polyester, or it could be a perforated  Teflon$^{®}$ coated material. The structural repair manual  (SRM) indicates what type and how many plies of bleeder  are required. As a general rule, the thicker the laminate, the  more bleeder plies are required. Peel plies are often used to create a clean surface for bonding  purposes. A thin layer of fiberglass is cured with the repair  part. Just before the part is bonded to another structure, the  peel ply is removed. The peel ply is easy to remove and leaves  a clean surface for bonding. Peel plies are manufactured  from polyester, nylon, flouronated ethylene propylene (FEP),  or coated fiberglass. They can be difficult to remove if  overheated. Some coated peel plies can leave an undesirable  contamination on the surface. The preferred peel ply material  is polyester that has been heat-set to eliminate shrinkage. Vacuum bag sealing tape, also called sticky tape, is used to  seal the vacuum bag to the part or tool. Always check the  temperature rating of the tape before use to ensure that you  use appropriately rated tape. Perforated parting film is used to allow air and volatiles out  of the repair, and it prevents the bleeder ply from sticking to  the part or repair. It is available with different size holes and  hole spacing depending on the amount of bleeding required. Solid release films are used so that the prepreg or wet layup  plies do not stick to the working surface or caul plate. Solid  release film is also used to prevent the resins from bleeding  through and damaging the heat blanket or caul plate if they  are used. The breather material is used to provide a path for air to  get out of the vacuum bag. The breather must contact the  bleeder. Typically, polyester is used in either 4-ounce or  10-ounce weights. Four ounces is used for applications below  50 pounds per square inch (psi) and 10 ounces is used for  50–100 psi. 7-21