Journal of Powder Metallurgy & Mining
Open Access

Autoclave moulding is a thermoplastic composite manufacturing process in which the fibre reinforcement and thermoplastic matrix are placed down on a tool in the proper sequence and spot welded to prevent the stacked plies from moving relative to each other. After that, the entire assembly is vacuum bagged and placed into an autoclave. With a few exceptions, the autoclave moulding procedure is fairly similar to vacuum bagging. The autoclave machine provides the heat and pressure required by the bio composites during the curing cycle. This method entails tightly stacking prepregs in a mould in a specified order. To prevent sticking between the polymer and the mould surface, a release gel is added to the surface of the mould. Furthermore, this method enables for the usage of cores and inserts. Following that, vacuum bagging is used to remove any entrapped air between the layers. Following that, the entire assembly is transferred to the autoclave machine, where both heat and pressure are used to aid in uniform and effective matrix distribution, as well as good fibre-matrix interfacial adhesion or bonding over a specific time interval. The autoclave moulding technique is a cutting-edge composite manufacturing technique. It’s commonly utilised in the aerospace sector to make high strength/weight ratio parts out of pre-impregnated high strength fibres. During curing, an autoclave is used to give heat and pressure to the composite material (prepregs). Prepregs are placed in a mould in a certain order in this procedure, and the entire assembly is vacuum bagged to remove any air trapped between the layers. Based on the material parameters, rated heat and pressure are delivered for a set period of time.

The autoclave moulding technique has the following benefits:

1. Applied to both thermosetting and thermoplastic polymer composites with fibre reinforcement.

2. Improved inter-layer adhesion.

3. Control of both the fibre and the resin is excellent.

4. Wetting the fibres properly and in appropriate quantities.

5. Component solidification has a high degree of homogeneity.

6. Supports a large volume fraction of fibre in the composite component.

7. Because of the vacuum bagging system, there is no void content in the finished component.

8. A better interfacial connection with inserts and cores is frequently produced as one of the benefits of the vacuum bagging process.

9. Used to make items with a high strength-to-weight ratio.

The autoclave moulding process of making fiber-reinforced polymer composites has been widely employed to create different engineering parts, mostly by aerospace, marine, and military businesses, in order to benefit from the aforementioned advantages. Aircraft components, military, marine, and spacecraft, as well as missiles, are examples of these items. Autoclave moulding is similar to vacuum bag moulding in that the layup is subjected to higher pressures, resulting in denser pieces. Component dimensions may be reduced due to the usage of an autoclave when compared to the vacuum bag technique. The bagged layup is cured in an autoclave by applying heat and pressure at the same time. The vacuum and autoclave pressure cycles are set to allow for maximal air removal while avoiding excessive resin flow. Vacuum is often used only in the early stages of the curing cycle, whereas autoclave pressure is maintained throughout the heating and cooling cycles. In the aerospace sector, autoclave moulding is commonly utilised to produce high-quality prepreg-based parts. The preimpregnated laminae are placed on the tool surface, followed by a peel ply, bleeder ply, and vacuum bag. Once sealed, the entire assembly is placed in an autoclave.

The behaviour of the bag during the consolidation and curing processes is an important component in autoclave moulding. Although the external pressure on the bag is constant, the pressure exerted to the component can change. There are several reasons for this, but the two most important are insufficient elongation to let the bag to conform to the mould shape and difficulties with the breather ply, which could prevent the entire pressure from developing onto the component’s surface. Auxiliary materials are essential in composite material component moulding, particularly vacuum bag moulding and autoclave moulding, and play a key role in achieving strong interfacial adhesion, homogeneous resin distribution, minimal void content, and exact geometrical size, among other things.