Vacuum bagging

There are a variety of methods for bonding and laminating, one of which is called vacuum bagging. This is an old technique that originated during World 

War II. The majority of composite parts are made by vacuum bagging. The part being bonded is surrounded with an airtight membrane (vacuum bag) or diaphragm and utilizes the surrounding pressure to squeeze the vacuum bagged article, followed by curing in an autoclave (oven).l l 

A bleeder cloth, a nonstructural layer of material such as polyester felt, is used to allow the escape of excess gas and resin during cure. This material is removed after the curing process is completed and the excess resin taken with it. Next, a barrier film is 

Once the article is vacuum bagged (Fig. 6.67), it is allowed to cure for a specific amount of time. For articles comprising heat-activated (thermoset) or heat-formed (thermoplastic) resins and adhesives, the vacuum-bagged articles (Fig. 6.68) are cured in ovens or, when more pressure is required, in autoclaves 

A list of the steps taken in vacuum bagging is shown below  

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Bolted patch No surface treatment no refrigeration, heating blankets, or vacuum bag required Bolt holes weaken structure bolts can pull out Fast Low... 

Vacuum bag bonding is restricted by definition to less than 1 atm (<15 psi) which can be insufficient to achieve good part contact and prevent bondline voids. Hence vacuum bag bonding is rarely used outside of repair situations. 

Most bonded repairs are cured using electric heat blankets and vacuum bags, shot bags or clamps for applying pressure. Programmable heat blanket controllers... 

Variations on this basic process are (i) vacuum bag moulding and (ii) pressure bag moulding. In the former process a flexible bag (frequently rubber) is clamped over the lay-up in the mould and a vacuum is applied between the moulding and the bag. This sucks the bag on to the moulding to consolidate the layers of reinforcement and resin. It also squeezes out trapped air and excess resin. The latter process is similar in principle except that pressure is applied above the bag instead of a vacuum below it. The techniques are illustrated in Fig. 4.67(b) and (c). 

Class C applies to hand lay-up, vacuum bag, and other methods using molds made of RP/C material. It applies to parts that would be covered by Class B when they are not molded with a high degree of care. 

Filament Winding, Hand Layup. Compression Molding. Iniectior. Molding. Vacuum Bag. Stamping. Coming. Pultrusion... 

Hand Layup. Compression. Injection. Spray Jp. Vacuum Bag, Autoclave, RTM. RtM, Rotational. Stamping. Autocalve. Coining... 

Pressure bag molding This is a take-of to vacuum bag molding where the bag and mold is placed in a closed system and is subjected to pressure during the curing cycle. 

Figure 5.24 shows the principle of vacuum bag moulding after draping. 

This process (Figure 5.25) resembles vacuum bag moulding but the vacuum is replaced by pressure. After the composite has been manufactured onto its mould ... 

The curing of the adhesive bonding is carried out by heat and pressure specific device, vacuum bagging, autoclave, press... 

The transfer of autoclave pressure to the resin in the laminate does not occur hydrostatically because the resin is not enclosed in a constant-volume system. Flow can occur initially both vertically (thickness direction) and horizontally. Furthermore, the network of fibers can also eventually act as a network of springs to which the vacuum bag and bleeder assembly transfer the stress from the autoclave pressure. This stress can then be transferred... 

Figure 6.2 Curing cycle temperature-time profile for typical graphite-epoxy composite in a vacuum bag autoclave process. Autoclave pressure is applied during the 135°C (275°F) hold...

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

High pressures are commonly used during autoclave processing to provide ply compaction and suppress void formation. Autoclave gas pressure is transferred to the laminate due to the pressure differential between the autoclave environment and the vacuum bag interior. Translation of the autoclave pressure to the resin depends on several factors, including the fiber content, laminate configuration, and the amount of bleeder used. 

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