Hi I'm Paul from Easy Composites and in this video I hope to give you a complete introduction to working with out of autoclave prepreg carbon fibre.
Specifically the XPREG XC110 system which can be used to produce both structural and cosmetic components.
In this video we will be producing this fairly complex engine cover.
I will briefly explain what prepregs are, how they are shipped and handled and the equipment that you would need to process them.
And then I will demonstrate in more detail the process of templating out, cutting the prepreg,
laminating the surface and then the backing plies and then the correct way to vacuum bag the component.
Finally, we will oven cure the component under vacuum.
In this video I will be using the mould that we made in a previous tutorial.
So if you are interested in how we made this prepreg mould, check that video out.
I will also cover the alternative moulds that are appropriate for use with prepreg processing.
Simply put, prepregs are just conventional dry reinforcements like this carbon fibre,
that have been pre-impregnated with a resin that already has the hardener in.
So here we have the plain dry reinforcement, and then here we have the prepreg equivalent with the resin already impregnated into it.
And because the resin is already combined with the reinforcement like this
to make parts using prepregs you only need to laminate the prepreg material itself into the mould,
so there is no handling wet resins like there would be in a hand laminating process or resin infusion process.
And, within reason, it won't start to cure until it is heated.
There are two main methods of processing prepregs.
The most common is to use a heavy piece of industrial equipment known as an autoclave.
This is essentially a pressurised oven.
However, gaining in popularity with the advancement of prepreg technology are out of autoclave prepregs.
These are laminated and vacuum bagged in exactly the same way as an autoclave system.
However they only need an oven to cure.
If you are working without an autoclave, so just in an oven,
one of the biggest challenges you will face is to reduce the surface pinholes and the void content.
However the XPREG XC110 system has been painstakingly developed to deliver results
that are comparable to the results you would get when processing with an autoclave.
I have got a couple of examples here which clearly illustrate the difference between the XPREG XC110 and a conventional prepreg.
You will notice that the XC110 is void free whereas the conventional prepreg here has surface imperfections all over.
This is typical of any attempt to process a conventional autoclave prepreg in an oven.
So these are the rolls straight from our freezer.
If you have not worked with prepreg before you might be put off by being unsure about the storage, handling and shipping of the material
but actually it is all pretty straight forward.
Essentially, when not in use, prepreg should be kept frozen in a sealed bag.
There is no special type of freezer, anything from a small domestic freezer to a large walk in cold store can be used.
For many individuals and small businesses a chest freezer is ideal as it is easily big enough to accommodate a few rolls.
In the case of this XC110 system it has a working time or out life of 4 weeks.
Which means that is the period of time it can spend out of the freezer before the resin system starts to deteriorate.
So if you are planning on using the material within that period of time you may never have to freeze it.
If you were wondering what would happen if it were left out longer we have got an example here.
Which you can see has gone really crispy.
This has been out for about 6 months but it just shows the resin is always curing even at room temperature.
The rolls that we got out of the freezer earlier are still defrosting and you can see the condensation forming on the surface.
This the reason they must be kept in sealed packaging while defrosting.
Otherwise that condensation could form on the roll itself and potentially contaminate the material.
So while these are defrosting we are going to crack on and start out with the templating.
We are doing this because we want to know the accurate shape of the various pieces of material that we are going to laminate into the mould.
We are just going to use a very simple method of masking tape over the surface
and mark the various joins and shapes that we have.
There are many ways to create templates.
From a trial and error approach using cut pieces of paper to CAD flattening methods.
In all cases the important part is choosing where to put the cut lines.
The reason why I am putting cuts down in the negative features in the corners is it actually makes these laminating procedure that much easier
and reduces the chances of bridging so you are less likely to get voids on the corners of your parts.
I can show you in more detail here.
I have set up this small example which hopefully should illustrate how putting cuts in corners and negative features can really help in the laminating stage.
So here we have it done in just one piece of material with an overly exaggerated bridge in the corner,
but you will notice it is very, very difficult to press the material down
as it has got to pull it down from these faces to get the material in the corner.
If these were long expanses it could be virtually impossible to press the material down into the corner.
If we look to the other side where we have done it in two pieces
we have one piece that has been butted down into the corner and then another one with a small overlap.
It is now very easy to consolidate that material into the corner as we only have to slide this small section against the piece.
And as I mentioned earlier on larger sections this is particularly important.
I am making these markings to show the angle that I want the fibre to line up to.
That way, the final cut pieces will have the weave aligned.
This masking tape guide can now be carefully removed from the mould, cut in to sections and applied to a backing.
I am using fluted signboard as it is inexpensive and easy to cut.
The sections should then be flattened out as neatly as possible and extensions added for any overlaps required between the pieces.
After cutting mark the templates as required for identification and orientation.
Now the prepreg has fully defrosted it can be removed from its sealed packaging.
The templates can then be nested on to the material and marked out.
One of the great advantages to working with prepreg is how tightly and efficiently the material can be tessellated together
meaning that generally there is very little waste.
When doing this remember to pay attention to the fibre orientation and ensure that the components are aligned as needed.
These strips cut at 45° will be used around the rim of this component and will be used on the job.
You will notice here that I am using a knife for the cutting.
Generally this is the quickest way however high quality shears will also cut the material very effectively.
The backing ply can now be removed from its packaging and templated and cut in just the same way as we did with the surface ply.
This is a heavier 450gsm carbon as opposed to the 210gsm we used in the surface ply.
This builds the thickness more quickly and cost effectively than using 210g throughout.
Before moving on to the laminating I want to take the opportunity to go through the compatibility of various mould materials with the XPREG system.
So we have some that are highly suitable and recommended for the processing
and then we have some that aren't recommended but could be used
and then we have some materials that should be completely avoided.
The mould that we are using in this video is the prepreg mould that we made in the previous video in this series.
It has got a maximum surface temperature of 135°C and is fully compatible with the XPREG.
Another very common mould material is high temperature epoxy which is hand laminated.
So this is made using a wet gelcoat and then this has been backed up with a high temperature laminating paste.
But equally that could be done with a high temperature epoxy resin and glass fibre or carbon fibre.
Then for short production runs or prototypes you can work directly from epoxy model board,
so this has been sealed with the S120 sealer and this can be used directly as a mould.
Other highly compatible tooling surfaces can be metals, so that can be aluminium, stainless steel
which can be either folded into a mould tool like this or machined into a full mould.
Or for producing flat plates glass is absolutely ideal.
This mould has been made using a standard epoxy tooling system which means that it doesn't have a
particularly high surface temperature so you will be limited on the cure cycles that are available.
So whilst it could be used, we don't recommend it.
Another material which isn't ideal are vinylester tooling systems such as our Uni-Mould system.
The reason for this if twofold.
Firstly, again it doesn't have a particularly high surface temperature so you are limited on your cure cycles
and you can encounter a compatibility issue between the mould surface and the prepreg, leading to minor surface imperfections.
There are some types of materials that absolutely cannot be used with epoxy prepregs.
So we have here a polyester mould tool so that is conventional fibreglass mould.
This cannot take the temperature and you are likely to get severe release issues.
The other material we have here is polyurethane model board.
This is widely known to cause cure inhibition with epoxy prepregs so this also cannot be used.
So we are not going to have any of those problems today as we are using the epoxy prepreg mould.
Before laminating Easy-Lease Release Agent should be applied to the mould.
Please refer to the product datasheet for application guidelines.
Laminating with prepreg is actually very easy, in fact the hardest part is probably removing the backing plastic.
A thorough methodical approach is required to ensure that the material is laminated correctly.
The aim is to ensure that the material is in intimate contact with the entire mould surface.
To achieve this you should systematically work the material down starting from a centre point and working outward.
Depending on the job in hand there are a number of different laminating tools that can be used, ranging from rollers to the back of shears.
On this job I am using a tool that I shaped from a piece of carbon fibre sheet.
To maintain strength the second piece of prepreg has been made to have an overlap with the first
Due to the geometry in this area of the mould it would be difficult to laminate without creases,
so I am using some composite snips to cut the material and allow it to lap.
9 times out of 10 laminating faults are due to not properly pressing the material into negative corners and features in the mould.
Although as I discussed earlier placing joins in these areas help reduce the risk of bridging, you still need to pay these features extra attention.
You will notice that some of the smaller details on the moulding I didn't template for.
In this case it is easier to cut the pieces by eye as they are needed.
If you can remember these strips for the rim of the part were cut at 45°.
Cutting them at this angle allows them to follow curves very easily, meaning that they only need to be cut and joined on the sharper bends.
This 45° cut also helps the material drape more easily into the mould, making the laminating quicker and reducing the likelihood of creases.
So snipping is not normally needed.
With the first ply down I am now going to do a debulk.
Now on a component like this it probably isn't necessary,
but a debulk can help to reduce pinholes and reduce bridging in larger or more complex structures
and certainly on laminates with multiple plies, they are a necessity.
Debulking is done using a perforated release film and then a conventional breather and vacuum bag.
As with any vacuum bagging process the bagging should be moved and positioned to ensure that it is properly following the form right into any corners.
Using a blunt tool wrapped into breather can help to firmly press it into position.
A full vacuum should be pulled on the part and held for at least 10 minutes to ensure all trapped air is evacuated.
Once completed the part can then be removed from the bag ready for the subsequent plies to be laminated.
You can clearly see how well consolidated the laminate is after the process.
We are now moving on to laminating the heavier 450g backing ply.
As this material is much thicker than the 215g surface,
it is slightly more difficult to laminate as it doesn't conform quite as easily
but it all other respects the process is exactly a repeat of the surface ply laminating procedure
and so the same care should be taken to press the material into all of the sharp features and details.
Although I am not using one for this job in certain circumstances a hairdryer or a low temperature heat gun can help soften the resin which helps with drapability.
If used this should be done sparingly so as not to overheat the material.
With the laminating completed we can now vacuum bag the part before curing.
An unperforated release film should be applied to the laminate.
It is actually just as important that this follows every detail and feature as it is with the prepreg itself.
Allow for extra film by creasing it in the corners or before firmly rubbing it down using a cloth.
If needed the film can be secured in place using flash release tape.
As this is a small component I am going to put it into an envelope bag.
In fact it is very common to put multiple smaller parts into one large bag.
For thin intricate laminates like this, best results are achieved by using the breather only on the reverse of the mould.
This provides the air path needed to the edge of the release film but means that the film can get into all of the details without the breather getting in the way.
As the vacuum is pulling down the bagging film should be manoeuvred and manipulated so that it conforms to the laminate without having to stretch.
You will normally need to disconnect the vacuum supply a few times to allow for repositioning before a full vacuum is pulled.
Once you are happy that the bag is properly positioned full vacuum should be applied and seal checked for leaks.
Once you think you have the bag well down and perfectly sealed it is recommend that a 10 minute drop test is conducted to ensure a perfect seal.
With this component now vacuum bagged properly all that is left to do is to cure the part.
To get the incredible results that this prepreg system is capable of,
it is absolutely essential that you follow exactly one of the XC110 cure cycles,
which use a 2 step cure to ensue optimal flow of the resin.
There are some alternative cure cycles that be used depending on your oven control and mould material.
So please check the datasheet to find the cure cycle that best suits your need.
Because this mould is made using the XT135 tooling prepreg and our oven has full ramp and soak control we will be using the XC110 standard cure cycle.
The standard cure cycle consists of 2 stages.
Firstly, we control the heating rate to an initial lower temperature and hold it there for optimum resin flow.
And as you can see from the graph we then increase the temperature to fully cure the resin and realise the materials full mechanical properties.
With the part now fully cured we can remove all the vacuum bagging materials and demould it.
The edges on a freshly demoulded part can be very sharp so I am just going to trim those to make them safe to handle.
If you want further information on how we have trimmed and finished this component take a look at our how to cut carbon fibre video.
So it is clear to see the excellent results that be achieved using the XPREG XC110 system.
We have a pinhole free finish across the surface of the part and there is no evidence of voiding or imperfections on these difficult 90° corners.
Which was no doubt helped by cutting and joining of the material in these areas, careful laminating and proper vacuum bagging technique.
Although in this tutorial we have used the XC110 system to produce this relatively small engine cover component,
the excellent mechanical properties of the prepreg system allow it to be used to make fully structural components of any size.
In fact we have manufacturers using it to produce everything from bike frames through to air frames.
I hope you have enjoyed this tutorial.
We believe that the XPREG prepregs offer an unrivalled combination of performance and value
and together with our complete range of vacuum bagging materials and equipment
it has never been easier to manufacture components using prepreg technology.
So if you are interested in this material or you have any questions please get in touch.