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Courtesy of Mendel Autosport, Composites product manufacturers, Croughton, Northants

Stage 1 Material Preparation

When cutting out to ensure accuracy templates must be made for all but the simplest and regular of shapes.

The economical use of all consumables is vital to produce cost effective end products. Where more than on layer of reinforcement is to be used the material is cut such that alternate layers are at 90degrees to each other so that the weave runs in different directions in the product. There are two ways of achieving this:
1- Cut at alternate angles from the roll.
2- Cut in the same direction but place in the mould alternate top side up and top side down.

The decision on which method is most suitable lies with the most economical method of cutting out from the roll of reinforcement material.

Stage 2 Mould Preparation

This flat sheet product does not require a special mould, but does require a flat smooth surface which can withstand the temperature and pressure of the Autoclave. With any mould the surface preparation is vital so that the product releases after curing. If this stage is not carried out effectively both the mould (often called the tool) and the product could be scrapped.

The release agent is a polish that will prevent the resin from coming into contact with the tool surface. In non-autoclave cures a wax-based polish can be used. For all high temperature cures a synthetic release agent is required. This is applied in several coats at 90 degrees to each other allowing to ‘flash off’ between coats.

Stage 3 Materials Assembly

The first layer of pre-preg is placed onto the mould surface with all subsequent ones having the weave at 90 degrees to the last. When all reinforcement layers are in place the resin film is placed on top. This is a loose weave mesh that carries extra resin to bond the honeycomb reinforcement onto the adjacent carbon fibre. The mesh itself adds no strength in terms of reinforcement.

The honeycomb core is added to give much greater rigidity through its cell structure being sandwiched by the carbon fibre shell. This is placed on top of the resin film.

Prior to completing the top of the sandwich any insets or strengthening to avoid the honeycomb collapsing are added.

The trim line is marked and any key points where bolts etc. will pass through. These areas are filled with resin to give a solid point for edge trimming and hole drilling during product assembly.

The top layers are applied in the reverse order to the bottom layers to produce a symmetrical sandwich.

Layers
1. Carbon Fibre
2. Resin Film
3. Honeycomb


Resin to give solid edges when trimmed	Release film in place over the completed carbon fibre and honeycomb sandwich

Stages 4 to 8

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