This guide explains how to use the resin infusion process tocreate a carbon fibre part with particular emphasis on the techniques andtimings necessary to result in a perfect surface finish straight from themould.
The guide is also accompanied by a video we have uploaded toYouTube. Whether you’re using out materials and equipment, we hope you enjoythe guide and unlock the potential of resin infusion for your parts.
If you need to buy any of the materials or pieces of equipment mentioned in this guide then please take a look at our Resin Infusion Starter Kit or the individual equipment and materials listed on the Easy Composites site.
For a more detailed guide to resin infusion, download the instructions that accompany the kit (no purchase neccessary!).
Resin infusion is a way of making composite parts where thereinforcement (and any core materials etc) are laid dry into the mould before baggingmaterials including peel-ply and infusion mesh are laid on top of thereinforcement and then enclosed in a vacuum bag. At this stage all the air isremoved before finally resin is drawn into the laminate under vacuum to ‘infuse’through the reinforcement.
The trick to a perfect surface finish in this process (whichthis guide is focussed on) is in ensuring that the infusion is undertaken atfull vacuum and that a small amount of surplus resin is allowed to remain inthe laminate; this is achieved by allowing the resin to infuse all the waythrough the part before clamping off the resin feed line and then finally thevacuum line.
The key to successful resin infusion really does lie inhaving the right equipment, the right materials and preparing in advance. Thisis not a process that rewards ‘make-do’ solutions or compromises and the vastmajority of failures or problems that we help people solve all stem from nothaving the right materials or equipment.
A mould with a sufficiently large flange around the edge toallow the positioning of some of the bagging materials. The quality of themould’s surface will determine the quality of your part’s surface.
If you’re using a composite mould ideally, your mould shouldhave a surface made from epoxy tooling gel coat. Surfaces such as glass sheet,stainless steel or aluminium will all also be fine.
Cut your reinforcement to the appropriate size for yourmoulding. Where possible, always try to make the part using a single piece offabric for each layer. A typical carbon fibre product will use anywhere between2 and 6 layers of carbon fibre. If you’re unsure how many layers to use, 3layers is often right for a small, light part.Ensure you cut the fabric large enough that it extendsbeyond the all the edges of where the trimmed part will come to. Position themultiple layers of fabric into the mould (you can position them all at once).
4. Tape reinforcement to hold it in place
On complicated shapes or moulds with steep sides it is oftennecessary or at least helpful to use some masking tape or similar to hold thereinforcement in place. As you add additional layers of reinforcement you wouldtape those to hold them in place too.
5. Cut and position a layer of peel-ply
Peel-ply is the first layer of the infusion ‘bagging stack’ and is a removable barrier that is peeled off the finished part, leaving a relatively consistent surface that is also ideal for bonding to.
Peel ply is usually applied in one single layer, positioned to completely cover all areas of the reinforcement. The peel-ply does not need to overlap the edges of the reinforcement but it does need to cover it all so it is usually cut to be just fractionally bigger than the reinforcement.
6. Cut and position infusion mesh
The infusion mesh (also known as ‘flow media’) is used to ensure that the resin can flow from the resin feed line (and spiral tube) freely through the laminate. The shape of the mesh means that even under total vacuum, there are still gaps through which the resin can flow.
The infusion mesh is also applied in a single layer (although it won’t affect anything if multiple pieces are overlapped where necessary). It should be cut to be the same size as the reinforcement/peel-ply apart from at each end where the mesh should extend sufficiently to allow for the vacuum connector at one end, and the resin feed line at the other. By positioning the vacuum connectors directly onto the infusion mesh we ensure good channels for both air and resin will be maintained once the vacuum is drawn.
7. Cut and position infusion spiral and silicone connector
The resin feed spiral is spiral wrapped plastic tube that is used to improve the flow of the resin from the feed tube into the laminate. Resin will be disbursed along the full length of the spiral therefore the standard configuration is to position the spiral all the way down one side (the side where the feed tube will be positioned). This means that the resin is quickly distributed along one side of the mould and then advances more evenly towards the other side.
It is essential that the resin feed spiral is positioned directly over the infusion mesh. This ensures that the resin can flow easily from the spiral into the mesh.
In larger or more complicated infusions, multiple resin feed lines and more considered positioning of the resin feed spiral is sometimes required. This is not likely to be necessary for most projects, however, if you find that some areas of your laminate wait an excessively long time for the resin to reach them you can improve resin flow to those areas with some additional feed spiral.
Secure the resin feed spiral in position using a couple of small pieces masking tape.
Resin infusion connectors (made out of silicone rubber) are used to aid the resinflow from the hose into the infusion spiral and again at the other side to ensure a good airflow from the mesh to the vacuum line hose.
Position the resin feed connector in the centre of the resin feed spiral. Press the connector down onto the spiral so that the spiral tube runs through the bottom of the connector.
8. Cut and position extra infusion mesh for flow balance
Doubling-up using an extra strip of infusion mesh at theopposite side of the mould to where the resin will be introduced ensures a goodflow of air from the mesh to the vacuum line. Cut a strip of mesh large enoughto run all the way down the opposite side in a strip and tape it in place usingmasking tape.
9. Position vacuum line silicone connector
The vacuum connector is another silicone infusion connector.
Position the vacuum connector on top of the infusion mesh at the opposite side of the mould to the resin feed spiral. The connector should sit on top of infusion mesh in an area beyond where the reinforcement ends.
10. Cut the bagging film oversize to allow for pleating
When doing the bagging it is absolutely essential to ensure that there is sufficient bagging film to get into all the shapes and contours of the mould. Any ‘bridging’ of the vacuum bag where it doesn’t get right into the corners of the mould will result in resin-rich areas, reducing the strength and quality of the finished part.
Cut a piece of bagging film (the green plastic film) that is plenty large enough to cover and area about 50% larger than your mould area. Starting in one corner, peel the backing paper off some of the bagging tape and press the corner of the bagging film down onto the exposed tape. Move around the edge of the mould, removing backing paper from the tape and sticking down the bagging film as you go. Don’t be tempted to remove all the backing paper from the tape; this is likely to result in the bag sticking to the tape before you’ve aligned in properly.
11. Stick the bagging film to the gum tape, adding pleats as you go
As you stick the film to the tape, be as careful as possible to do so without having any wrinkles or folds in the bag. Press down very firmly and use your fingers to ‘massage’ the film and tape together to create an airtight seal. If you end up with leaks in your finished bag (which we’ll test for later) then it is likely that wrinkles or folds in the bagging film where it contacts the tape will be the cause.
12. Cut PVC hose for resin feed line, adding gum tape seal
With all the bagging stack and reinforcement sealed within the vacuum bag, you’re now ready to ‘breach’ the bag to connect the resin feed hose. Using a pair of scissors or a knife, make a small incision in the vacuum band directly above the red silicone resin feed connector.
Cut a length of the clear PVC hose long enough to run comfortably from where you will position your resin feed pot to the resin feed connector on the vacuum bag. When you cut the hose, do so at an oblique angle (such as 45º) so that it is impossible for the tube to accidentally be sealed against the bottom of the mould.
Wrap some bagging tape around the PVC hose several times to make a 'donut' of tape about 15mm from the end of the hose.
13. Pierce bag above connector and firmly connect resin feed hose
Press firmly to ensure the tape has made an airtight seal.
14. Cut PVC hose for vacuum line and firmly connect to bag
Repeat the process from the previous step, this time usinganother length of PVC tube that will connect the catch-pot to the red siliconevacuum connector at the opposite end of the part to the resin feed connector.Cut the tube at an angle, cut a small hole in the bag, push the tube throughand seal the tube to the bag using some more tape.
15. Connect the vacuum pump and catch-pot
Connect the other end of the vacuum hose to one of the push fittings on the resin catch-pot. Push the hose on firmly to ensure an air-tight seal.
Next, cut a length of PVC tube sufficient to run from the vacuum pump to the other push connector on the catch-pot. This tube can be as long as you need and will not be spoiled by the infusion process (meaning it can be re-used indefinitely).
16. Use an infusion line clamp to close the resin feed line
Position the line clamp tube near to the start of the resin feed tube and turn the wing-nut to clamp the pipe shut. Ensure that you close the pipe properly to create an airtight seal.
17. Evacuate the bag and check for any leaks
Switch on the vacuum pump and open the valve (if it has one)
As the air is removed from the vacuum bag you will see the bag tighten around the mould surface. As this happens you should move the bag around and position it so that you move ‘spare’ bagging film into the areas of the mould which need it. This process is essential to all vacuum bagging processes (resin infusion, standard vacuum bagging and even pre-pregs) so give this step plenty of attention.
As the bag begins to become reasonably tight (certainly not full evacuated but not slack either) temporarily switch off the vacuum pump. This will allow you all the time you need to reposition the bag, working wrinkles towards where they’re needed and ensuring that no-where on the mould is the vacuum bag ‘bridging’ a gap.
During your first few infusion projects, it is possible that you will underestimate the amount of bagging film necessary for your mould. If this happens you will find out at this stage because the bag will be ‘bridging’ across certain points of the mould and there will be no amount of re-positioning that can fix it. In the unfortunate event that this happens, you should stop, remove the bag (and tape) and do the bag again. If you proceed with a bag that is too small, your finished part will suffer greatly.
Switch the pump back on and finish evacuating the bag. Youshould see the needle on the vacuum gauge begin to rise. Leave the pump on andwait as the needle approaches full vacuum. Keep adjusting the bag if necessaryto ensure there are no ‘bridges’.
After a few minutes the vacuum gauge should read somewherevery near to 100%. Because of variations in atmospheric pressure andcalibration of the gauges the needle might not point precisely to 100% vacuumeven when full vacuum is being drawn. The most practical way to know when youhave a perfect seal (100% vacuum) is to look at the vacuum pump and see whetherany oil vapour is being emitted by the pump. When the seal is total, the pump’ssound will change slightly and oil vapour will stop being emitted by the pump.
If the seal isn’t total, work your way around the bag,pressing the bag hard against the gum tape until it is.
Once you're confident that the bag is completely sealed close off the valve on the pump and swicth the pump off. Firmly close a line clamp between the catch-pot and the bag. Wait at least 15 minutes.
18. Check the sealed bag after 15 minutes
After 15 minutes return to the part. The vacuum guage on the catch-pot should still read -30 (or 100% vacuum depending on how it is calibrated). If the guage has changed then there is potentially a leak on the catch-pot. This isn't relevent at this point but it's something to look out for. If the gauage has droped at all, switch the pump on and open the pumps valve to retore the catch-pot pressure to -30 before preceeding with the test.
Now, looking at the guage, we open the line-clamp that sits between the bag and the catch-pot. As you do this keep looking at the guage; if the guage drops when you open the line-clamp then it indicates there is a leak in the bag. Check the bag thoroughly and repeat. If you can't find the leak you should scrap the bag and do it again - it's possible something has punctured the bag whilst you were working.
If the guage does not move then you're ready to proceed with the infusion!
19. Accurately mix the epoxy infusion resin with its hardener
It's now time to mix up the resin for the part. It's not possible to know exactly how much resin the part will require but you can work it out pretty closely. For information on how to do this, please see other guides in this section.
Once you have worked out approximately how much resin youwill need you next need to calculate the right ratio of resin to hardener andmix the resin according to the ratio shown on the pack.
Use a set of digital scales to mix the correct ratio ofresin to hardener. Mix the resin in a container other than the resin feed pot and then pour the mixed resin intothe resin feed pot. This will greatly reduce the risk of any unmixed resin(usually clinging to the sides of the mixing pot) from being drawn into the infusion.
20. Allow the resin to degass for 10 mins
Depending on the pot-life of your resin you might have time to allow the resin to de-gass. If possible 10 minutes would be ideal but if the resin only has a short pot-life then you will need to skip this step.
21. Clip the resin line to the resin pot using a spare line-clamp
To hold the resin feed line in the resin and prevent it fromaccidentally coming loose we advise clipping the hose to the side of the resinpot. Under no circumstances allow the hose to come out of the resin pot duringthe infusion.
22. Release the resin feed clamp and start the infusion!
With the vacuum pump still running, gently start to unscrewthe wingnut on the resin feed line clamp. As you loosen the screw you willimmediately see resin start to be drawn down the feed line and into theinfusion. Unscrew the clamp all the way to ensure there is no restriction tothe flow of resin into the infusion.
Depending on the size and shape of the part, the layout ofthe feed spiral and the amount of reinforcement used, the resin will takesomewhere between a few minutes and an hour to infuse fully through the part.
Because the resin feed pot is at atmospheric pressure, onlythe viscosity of the resin itself prevents the part of the mould around wherethe resin feed hose enters the infusion from being at normal atmosphericpressure. This means that around this area the vacuum bag will no longer feeltight and that excess resin will be accumulating. For this reason, it is normalto clamp the resin feed line closed again well before the resin has fullyinfused through the part. This gives chance for the excess resin at theatmospheric pressure side of the mould chance to carry on infusing through thepart. As it does, the bag will tighten again at this end of the mould.
Never allow the pot to run out of resin. If this isabout to happen, simply clamp off the feed line firmly (before the pot runsdry) and mix up some more resin before unclamping the feed line again. Disasteraverted!
Keep watching the infusion all the way until the resin reaches the vacuum line.
23. Clamp the resin feed line when the resin reaches the catch-pot
When the resin does reach the vacuum line on the other side it's time to clamp off the resin line.
24. Wait around 10 seconds then clamp off the vacuum line
Allow the resin to be drawn down the vacuum line for somewhere between 10 and 30 seconds, depending on the size of the project. This is an oppetunity for any airated resin to be removed from the system and also draws off some of the excess resin in the laminate. When you're ready, use another line-clamp to firmly close off the vacuum line.
25. Switch off the pump and wait for the part to cure
At this stage, the part is completely isolated from the feed line and vacuum line and so the vacuum pump can now be switched off whilst the part cures. Ensure you wait plenty of time for the resin to cure fully before attemting to demould the part. Infusion resins are designed to cure slowely meaning that at least 24hrs is often required.
Because excessive amounts of mixed resin in one place canexotherm dramatically, you should dispose of any resin in the feed pot andcontinue to keep an eye on the resin in the catch-pot if there is a lot inthere. Exotherming epoxy resin can set itself on fire - be warned.
26. Remove the bagging materials and de-mould the part
When the part has cured it's time to remove the bagging materials. Start with the bagging film, spiral and tape. Use short sharp tugs to remove these. All these materails are thrown away, although be careful not to throw away the silicone infuson connectors, they can be re-used indefinately.
27. Remove the peel-ply and infusion mesh in strips
Removing the peel-ply and infusion mesh can be hard work. We suggest cutting nicks at the side of the mesh and peel-ply so that you can remove it in thin strips.
The finished part!
Once you've removed all the bagging materials and de-moulded the part it should have a perfect surface finish, free from any air bubbles or voids. The fibre will be very well consolodated resulting in a very strong, lightweight part with a flawless surface finish. Take a look at our guides on trimming carbon fibre parts to make light work of the trimming.
If the finished part is likely to be subjected to lots of wear, sunlight, grit, or other abuse then we would suggest finishing it with a pk clear lacquer for maximum protection, alternatively just enjoy it as it is!
Matt StathamEasy Composites / Carbon Mods - Technical Sales