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 be the first to hear about our videos as we
release them subscribe to our youtube channel.