Manufacturing technologies for composite materials: Prepreg with autoclave

December 20, 2021

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Manufacturing technologies for composite materials: Prepreg with autoclave


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The different manufacturing technologies for composite materials have certain characteristics depending on the production requirements of the part.

Historically, the shaping of this type of materials has been a manual and limited task. However, these processes have given way to others in search of automation and repeatability in manufacturing, finding today various manufacturing processes. Each of them is recommended for a specific situation, taking into account parameters such as: 

· Geometric complexity of the piece 

· Dimensions of the piece 

· Properties and final physical requirements sought 

· Visual properties of the final product 

· Types of materials 

· Output 

· Production costs 

In our Technologies section you will be able to learn in more detail about the main manufacturing processes with composite materials and which one is most suitable based on these mentioned parameters.

Autoclaved prepreg

In this case, we are going to focus on this manufacturing technology that is intended for short/medium series with high requirements in terms of properties of the final product . 

Likewise, it accepts a high level of geometric complexity and a medium or low part size. However, the production cost is high, since in addition to being a manual process, the raw materials are expensive.

Although it is a process suitable for any type of material, carbon and other high-property reinforcements are the most common to find. Likewise, thermosetting epoxy or phenolic resin are the norm, although all types of resins, both thermosetting and thermoplastic, can be used. 

The prepreg material used in FRP, commonly known as “prepreg”, is the reinforcing fiber in the form of fabric or unidirectional fibers that has been previously prepreg with the resin . In this way, it is possible to provide the right and necessary amount of resin, maximizing the mechanical properties of the materials and the weight of the pieces. 

The polymerization process of the polymer resin begins from the moment of initial impregnation during the production phase of the material. Due to this, it is necessary to store the prepreg at temperatures of approximately -18ºC in order to stop this process. The work rooms, on the other hand, must have a constant temperature of around 25ºC since these materials are very sensitive to temperature. Additionally, the areas where you work must be free of dust and contaminants, any agent will disturb the final properties of the piece. 

The process of manufacturing parts using prepreg begins with cutting the material into the necessary shapes. After this, a specialized operator will laminate the material, that is, he will take the cuts made previously on the mold into place following its geometry . This process is of vital importance, since the uniformity of the thickness, the overlaps of the material and the perfect copying of the surfaces must be controlled. 

This is where the prepreg shows one of its greatest advantages, since it makes it possible to create complicated shapes in a relatively simple and clean way. 

Finally, the piece will be processed by curing the polymer matrix in different ways. The most common techniques are vaccum bagging curing and autoclave curing. 

The differences between these processes are the curing temperature and especially the pressure. The higher the latter, the better the mechanical properties are obtained, since the compaction of the material increases and the appearance of air bubbles is avoided to a greater extent. However, there is a limit where the material is choked and the resin is not able to flow. 

On the other hand, with temperature we will be able to control curing times, another parameter of vital importance. 

It is important to know and have control of the temperature and pressure slopes and curing times of the materials to carry out the process satisfactorily. In autoclave curing, temperatures range from 90 to 200ºC with pressures up to 10 bar. These installations have a high cost, so other processes that do not exceed 0.8 bars are often used. 

The future of prepreg focuses on the development and research of process automation, as well as the application in products of complex shapes and scalability for large structures in diverse markets.

New approaches have been the focus of research to produce materials that are faster to lay, easier to use and produce higher quality laminates.

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