How to Make Prepreg/Dry Carbon Fibre Parts (Carbon Fiber Airbox Pt. 3)


Hi, welcome to the third and final part in
this video tutorial series. In this video we’ll be showing you how to make this professionally finished prepreg carbon fibre airbox, using the complex three piece split mould that we made in the previous video. If you are new to prepreg check out our complete introduction to prepreg carbon fibre video. In that video you’ll find lots of information on the handling, processing and curing of this material. For what we’re doing today we can keep things really simple because almost everything that we’re using to produce this part comes in
our prepreg carbon fibre kit starter kit. In the kit you’ve got all of the consumables
that you need. You have five metres of vacuum bagging film, unperforated release film and breather cloth. You also get high temperature silicone vacuum hose, through bag connector, two rolls of vacuum bagging gum tape and optionally if you don’t already have a pump, a composites vacuum pump. Then of course the prepreg itself. We have over 1.2 square metres of both the Easy-Preg surfacing layer and the Vari-Preg backing layer This is dispatched straight from our freezers in sealed packets and stored on roll. One of the great things about working with prepreg is how accurately and efficiently you can cut the material. So the first thing we’re going to do here is just lay masking tape on to these moulds to give us some accurate cutting templates. This one is a very simple part to template for because we’re going to laminate this is one component. When it comes to the lower section we actually want to laminate these two while they are fastened together. So I’m going to bolt these together now and then create the masking tape template inside there. When deciding where to put cuts in
the material you should consider both the cosmetic appearance of the join will be and
also the ease of which the part can be laminated. In many cases this will mean locating the
join in a corner on the mould. Corners visually hide the join and also make it easier to lay up without bridging. You can transfer these templates that you’ve made onto any material
that you like. We’re going to be using fluted signboard as it’s very to cut and fairly durable.
With templates from compound shapes you will find that they often will not easily lay flat.
In these cases you should flatten them and interpret the true shape as best as you can.
With the rough templates down we’ve got to consider before we cut these out whether any
of them need extending or how they’re going to sit into the mould. This will be our first
component into the mould. So we want this piece of material to be precisely cut to this line
so this won’t get changed. It will be cut out at that size. However where the join is
it’s much better to have overlap of material rather than a butt join. So we will extend
the side panels here out by around a bout 10mm to give us that overlap. When we’re looking
at the top section we will be cutting this one slightly oversize. Just to give us an
extra bit of tolerance and margin for error when we’re laying it up. Before precisely
cutting it down to the seam on the mould. So these are the basic templates now and you
can see roughly how they’ll fit into the mould itself. Now the other thing that we want to
consider is where ever these parts of are joining. so where that part meets that part.
We’d like the weave to align. There’s a simple trick to doing that and that is to mark up
the orientation of the weave on the respective components. So again with the top section
there to be in that position. We can do the same thing and ensure that the weave along
that join will line up. Before we go on to cutting out the prepreg material itself we’re
going to take the opportunity to apply release agent to the mould. Now as you may have already
gathered we’ve produced a part from this so its already had several applications of release
agent. But it is always a good idea between every release to apply one more application.
Normal release agent, conventional release agent such as wax and PVA don’t work for prepregs
due to the high temperatures that are involve. So you really have to use chemical release
agent such as Easy-Lease. Now when this part is actually vacuum bagged some of the resin
will get driven between the parting lines. So it’s equally important to get release agent
on to the flanges of the mould as it is the surface of the moulding. So we’ll be applying
release agent right over the surface over here and also these areas here and here. If
you’ve been storing your prepreg in a freezer make sure it’s fully defrosted before you
unpackaged it. We need a piece of the surfacing and a piece of the backing ply of the prepreg.
The special Easy-Preg surfacing ply you can identify because it’s dry on one side. This
prepreg really is the secret behind getting a pinhole free surface finish. The backing
ply is much heavier material made from 450g cloth and that can be identified by the fact
that it’s got plastic covering on both sides. You’re looking to get these templates nested
as tightly as you can thus avoiding waste material. Cutting the prepreg is very straightforward
as long as you’ve got a substantial pair of shears. The surfacing layer being much
thinner than the backing can be cut quite easily using a pair of shears or a knife.
Now we can see here how we’re looking to get the weave alignment. This is the first layer
into the mould so this is the piece of material that you see. So we’re looking to ensure that
our weave alignment is absolutely perfect on these parts. With the twill fabric you
get quite a distinct line running in the diagonal across at forty five degrees to the weave.
These lines here we’re looking to align those with the lines that we can see on the surface
of the material. So we’ll be taking the templates and making sure at every stage that line carries
through from the lines that we have marked. The excess material that we have got here,
if it’s not going to be used immediately that can be rolled back up put into a sealed bag
and re-frozen. With out kit of prepreg ready and our moulds prepared we are now ready to
start the lay up. First loosely place the material into the mould ensuring that it is
accurately in position before firmly pressing it against the surface. It is goods practise
to work the material from the centre outwards. This ensures that the material is in intimate
contact with the entire mould surface. Any air pocket or bridging of the fabric in corners
must be driven out. In a cooler working environment for intricate shapes it’s sometimes advantageous
to slightly warm the prepreg using a hair dryer or a heat gun to make it tackier and
more pliable. In the case of this part however it won’t be needed. The backing ply is laminated
in much the same way as the surface but extra care must be taken when placing it into the
mould as repositioning can often disturb and lift the surface ply beneath. You will also
find that this heavyweight material is less pliable and can take a little more force to
manipulate. Prepreg laminating tools are often used to aid the laminating process. These
normally consist of a range of blunt instruments, often hand shaped by the laminator from plastic
or even carbon fibre. These are then used to push, manipulate and burnish the material
firmly against the mould surface. If ever there is a fault in a final component. 9 times
out of 10 it will be small pin holes in a corner this is as a result of the material
bridging. You must pay extra attention to corners ensuring that there are no voids between
the mould surface and the prepreg. With the two plys properly laminated into the mould
the excess is trimmed off with a sharp knife blade. Ensure that the blade is kept flat
and does not scratch and damage the mould flange. You should make sure that the cut
line is neat and level with the flange. This will ensure a neat join in the part is provided.
With the opposite section complete we will now move on to the slightly more complex lay
up of the lower mould tool. Starting with the base piece of material this is laid precisely
into the mould. The edges of this piece will be the visible join on the part so accurate
placement ensures a neat final finish. To make handling easier the hole for the aperture
is not cut until the piece is in place. The hole is then simply cut with a knife. The
sides pieces are then placed into the mould. If you remember these are cut slightly larger
to allow for overlap onto the first piece. In the case of this part the overlap of around
10mm will provide a strong joint. When curing the resin will flow around this joint making
a seamless finish at the point of overlap. To make the lay up easier in the corners I’m
snipping small nicks into the material. I’m only doing this where the material is overlapping
so that it won’t excessively weaken the part or be visible on the surface. Again here I’m
using the same prepreg laminating tool mentioned earlier to ensure that this special surfacing
prepreg is pressed down firmly against the mould surface. Small snips are used again
in the corners to allow the main material to be folded into the mould with minimal distortion.
A real benefit of working with prepregs is the way the intricate layups like this can
be carefully assembled step by step with the prepreg tacking itself into place on the mould
surface and staying in position. Again the backing layer we’re laying down here is tacky
enough to stick nicely to the surface layer. We position it carefully and then apply pressure
to stick it down firmly. Excess reinforcement is easy to trim away using scissors or a knife.
That’s the prepreg carbon laid into both these two parts. You can see on this one we’ve put
the carbon completely level with the flange there. Whereas on the other half we’ve left
about 15mm on the top. That 15mm flap will be folded in, but then we’ll join the two
together when we come to the vacuum bagging stage. I’m going to put a few small snips
into the carbon around the corner here to allow the flaps to be folded in without creasing.
We’ll fold these over and give them a quick press so that they align in to the mould and
get the lid section on before they have chance to straighten up. Now we’ve got these two
moulds parts bolted together you can see the extension that we left on the lower part of
the section will overlap over the upper part making a very strong bond between the two.
With the layup complete we’re now going to move on to the vacuum bagging. it uses a completely
conventional vacuum bagging stack so we’re using the materials that come in the kit.
Starting with the unperforated release film follow by breather layer and then We’ll put that
into an envelop release bag. The purpose of this release film is to provide a non stick
impervious barrier between the prepreg material and the breather layer which we will be adding
next. Prepregs have perfectly measured resin to fibre ratios and so we don’t want the breather
to absorb any resin from the laminate. Which is why always use unperforated release film
with these prepregs. Ensure the film covers the whole surface of the part without any
tight spots of bridging using some tape to hold it in place. Don’t worry about overlaps
and creases as these will not have an adverse effect on the part. Check again carefully
for any bridging particularly in the corners. So now we’re onto the breather layer. Which
again we’re going to put in to the mould in the same way we did the release film. The
breather cloth is there to maintain air paths through the bag. it should be positioned across
the whole surface of the mould and then held in place with some tape. To eliminate the
chances of any of these sharp mould edges or the bolts themselves puncturing the bag
we’re also going wrap the back of the mould in some breather. This will offer a reasonable
degree of protection. Now we’re going to use the vacuum bagging film from the kit to make
an envelope bag. So a bag that all of this goes inside and then seal it. To seal the
bag you want to go slightly beyond the fold in the film. Then lay your sealant tape flat
onto the bag. Then that fold, once the backing tape has been removed, can be doubled back
on itself and will provide a perfect seal. It makes life a lot easier at this point if
you also apply the seal to the other side, but obviously don’t seal the bag up completely.
Lift the whole mould and the extra breather surrounding it into the vacuum bag. Through
bag connector is the next thing, easily forgotten. So we put one insert on the inside there.
Then pinch a small amount of the bag, snip it, place that side of the insert through
the bag and then firmly tighten the two together. Now that both the part and the through bag
connector are where they should be inside the bag peel off and seal the tape that we
positioned earlier. We’re now ready to pull a vacuum. So all we need to do is take the
composites vacuum pump. Connector our high temperature silicone hose to it and then to
the through bag connector. Switch the pump on and we’ll gradually pull down the bag whilst
positioning it. Being such a complicated shape it is perhaps a little difficult to see what’s
happening here as we first begin to pull down the vacuum. Essentially what I’m doing
is feeding all of the surplus bag inside the mould through the aperture in the base and
then pushing this surplus of bag up into the neck of the airbox. Whilst at the same time
pushing more surplus bag into the neck through the other side As the bulk of the air is removed
from the bag you’ll want to periodically close the vacuum valve to provide sufficient time
to reposition the bag. It is essential that by the time the bag starts to tighten up it
has been carefully positioned and jostled in to place so that it’s properly in to all
of the corners of the mould. Without any bridging or tighter areas. You can see here where the
vacuum bag that’s been pushed into the neck from the inside meets the bag that’s been
pushed in from the outside. We need to make sure that there is no bridging around the
outside of this area too. With the bag fully pulled down all that’s left to do now is fully
cure this part. To do that we’re going to be curing this at 80 degrees Celsius which
is 176 Fahrenheit for eight hours. Here we are using our own specialist composites curing
oven which gives us plenty of space for loading parts like this. It also has vacuum lines
ready available inside the oven. It is however perfectly possible to cure prepregs in a range of different
types of oven, from small domestic ovens through to large industrial ones. The key thing is
that you need a vacuum line into the oven to maintain vacuum throughout the cure. For
more information on prepreg cure cycles including ramp breaks and cure times at different temperatures,
please download the companion PDF guide that accompanies this tutorial. Now that we’ve
left the part to cure for eight hours all that’s left to do is remove it from the oven,
allow it to cool and demould it. We’re back down to room temperature now o we can look
at removing the bag. Like most vacuum bagging processes we generally regard the vacuum bag
as disposable but don’t forget to remove the through bag connector first. The breather
cloth can if you like be saved and used repeatedly. But like the bagging film the release film
is normally discarded. Once the consumables have been removed we can unbolt the various
sections of the mould to release the part. The Easy-Lease that we used earlier ensures
that the part release incredibly easily. We can see what we’re left with here is just
some flash lines that can b cleaned up and then the trim around the lower section to
make the final part. A quick way of cleaning up the flash lines is just taking a Stanley
blade and scraping it across the surface until the flash has been brought down to a minimum.
To trim the part we’ll be using a Dremel Fortiflex which in our daily production environment
has proven itself to be incredibly reliable. Fitted into the Dremel is a perma-grit tungsten
carbide wheel which is absolutely perfect for cutting carbon fibre. The fortiflex is
great because its remote motor keeps the electric part of the tool away from the conductive
carbon fibre dust which would quickly damage the smaller hand held models. And it’s foot
pedal operation leaves hands free to concentrate on the trim. Perma grit sanding blocks and
round files are ideal for shaping and correcting the cut edge before taking it to a smooth
finish with abrasive paper. For lots more information on trimming check out our video tutorial on
cutting and shaping carbon fibre. Once all the edges have been nicely smoothed off our
brand new top spec carbon fibre part is finished and ready to use. I hope you’ve enjoyed this
video series, we’ve finally got there. We started from an original design idea. We made
a pattern carving it out of foam, gone on to make a split mould and finally prepreg
carbon fibre part. I hope this gives you the confidence and inspiration to take on your
own project no matter how complex. If you do take on your own project we’d love to hear
from you. Get in touch with us on our facebook, twitter or forum. of course if you want to
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