Vacuum Infusion – A Composite Process

Composite Processes

A vacuum infusion process makes use of vacuum pressure to drive resin into a laminate. It also applies pressure to impregnate the reinforcement with resin while using negative pressure to extract air.

It is a sophisticated system for manufacturing high-performance composites, and is often better suited to the production of carbon fibre parts for the marine and automotive industries. If completed correctly, infusion parts provide incredible strength, appearance and consistency across multiple components.

It’s important when infusing resin, to have a part based on the resin being used. For example, trying to create a piece with epoxy resin on a polyester based mold will likely result in the destruction of the part and the mould.

Our technical sales team are always striving to not just get you the best product, but help you get the most out of your mould processing, using multiple techniques saving you not just on time, but also on costs and wastage where necessary.

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Beginning the Vacuum Infusion Process

The process begins by preparing the mould with your preferred release agent, ensuring an even coverage. A gel coat can be added at this point if required, ensure it is fully cured before moving on to the next step.

To begin the infusion, vacuum tape gets placed on the perimeter of the mould. The operator will cut the fabric, usually carbon fibre, Kevlar or fibreglass, to ensure full coverage. Multiple layers can get added at this point.

Confident that the reinforcement layers are in place, the mould is ready for the peel-ply layer. This is a single layer and unlike the reinforcement, will not need to overlap the edges of the reinforcement, but instead cover it. As a rule, we recommend that it is cut just fractionally larger than the reinforcement.

Applying the Infusion Mesh

Once the operator is comfortable that the peel-ply is fitted properly they can move on to the infusion mesh. Like peel-ply, this mesh is applied in a single layer, but multiple layers can be overlapped if necessary, such as in corners or divots in the mould. It should be cut to the same size as the peel-ply layer with excess on two ends into which the vacuum and resin line gets fed.

Fit the resin feed to the edge of the infusion mesh to ensure a consistent flow across the mould. Most undertakings will only require one feed, but complex parts may require more. Give an additional check that all pieces are as they should be; the feed connector is attached to the feed tube (usually in the middle), this can be secured with some vacuum tape. Connect the vacuum to the feed connector on the opposite side of the mould, above the infusion mesh and secure with tape.

Adding the Vacuum Bag to the Vacuum Infusion Process

The vacuum bag is now ready to be added. Usually, 50-70% larger than the part itself, the bag is pressed down firmly into the tape, carefully going around the mould, stick the bag down as you go. Take care not to create any wrinkles or folds in the bag as this cause air leaks.

At this point, the operator can make a small incision into the bag to connect the resin pipe to the feed connector. Push the hose through the small incision and into the top of the feed connector, take care to ensure that it is pushed in fully. Seal the hose and incision with tape, press firmly to create an airtight seal. Recreate on the opposite side for the vacuum and resin catch pot.

On the other end of the carefully placed tubes, connect the resin feed to a resin feed pot, which is in a secured position. Connect one of the vacuum tubes to the resin catch pot, ensuring it cannot fall out, if necessary secure the pipe to the cup.

The second tube is to be fixed to the vacuum pump – push on firmly to ensure an airtight connection before testing the connection. Ensure you have clamped your resin feed. 

When turning on the pump, the operator will begin to see the vacuum bag tighten over the surface of the mould. Ensure that no area of the bag has any tightness, (as this can cause wrinkles). The operator can temporarily switch off the machine and gently move the bag around in order to offer an even coverage.

Once the mould is void of air, the vacuum gauge will read 100% (or as close as). If this cannot be  reached, turn it off and go around the mould, pressing the bag into the tape and checking all incision areas to create an airtight seal.

Adding Resin to the Mould

It is now time to add in resin. With infusion projects, the norm is to aim for a 60/40 fibre/resin ratio. Ensure that when mixing resin and catalyst that mixtures are as accurate as possible and the pot is thoroughly mixed, taking care around the edges and bottom.

Once the resin is ready, and the tube is in place, ensuring that the vacuum is on the operator can unclamp the resin feed and begin to see resin travelling through this line and into the mould.

Depending on the size of the mould, this can take up to one hour. The part should be observed; once the resin has impregnated the reinforcement, the resin feed can be clamped and curing can begin.

The vacuum should remain on during the curing process. The temperature will affect cure time. If planning to cure at a higher temperature, ensure that all products can withstand this temperature elevation.

Finishing the Process

Checking the mould is fully cured, the vacuum can be turned off. At this point, the operator will remove the bag, tape, mesh and peel ply. Peel ply can be challenging to remove and may require force. We don’t recommend using tools to remove peel ply.

The part is now ready to be trimmed and finished!

If you are looking to introduce Infusion processes into your business, why not take advantage of our Technical Support and book in for a free audit of your procedures.