Hi I'm Paul from Easy Composites and in this video I am going to show you how to use our XT135 Tooling Prepreg
to produce highly accurate mould tools suitable for high temperature use.
To produce the mould I will be using this CNC machined epoxy pattern that we made in the previous tutorial.
Unlike traditional mould making methods that use a wet gelcoat and then multiple layers of reinforcement wetted out with wet resin;
a prepreg mould is made using layers of a special tooling prepreg which is already impregnated with the optimum amount of resin.
The tooling prepreg is cut as needed into appropriate panels.
Once all the reinforcement has been added, the mould is vacuum bagged and loaded into an oven to reach initial cure, under vacuum for several hours.
The new mould is then removed from the pattern and then returned to the oven for its final full cure.
In many ways handling prepregs can be much easier than working with wet resins,
especially on complex forms.
The process has no smell, it is very clean
and in most cases it is quicker due to the fact that the material is laid up all in one go.
But the main advantage of prepreg moulds is the ease with which you can reliably produce accurate moulds that are stable at high temperature.
Especially if you choose carbon fibre as a reinforcement.
This is the reason why prepreg moulds have become the industry standard in both aerospace and F1.
To achieve a good surface finish and low void content most tooling prepregs require an autoclave to cure,
which unfortunately puts it out of the scope of most users.
However the XT135 system from XPREG is different.
It is designed from start to finish to work under vacuum only in an oven.
The system is made up of a surfacing ply and a backing ply.
We have got to allow these to fully thaw to room temperature before we can use them.
So whilst that is happening we will prepare the pattern.
For a new pattern like this we need to apply a minimum of 6 applications of release agent before we can go on to make the mould.
For further information on the best methods and practises to applying Easy-Lease refer the technical datasheet.
We now need to make templates that will allow us to accurately cut the prepreg
and make sure that we get a good fit on the shape of the pattern.
A very simple method of doing this is using masking tape over the surface of the pattern,
marking out where the cut lines are and then using that to make your templates.
When templating for a mould tool you can often do the component in a lot more pieces.
So wherever you have any angles, corners or features put a cut there
and it will make the laminating process that bit easier.
With the tooling prepreg now fully defrosted it can be removed from the sealed packaging and the templates can be used to cut the material itself.
You can see here I am laying the templates down at 45° onto the material.
That will make the drapeability of the material and therefore the layup that bit easier.
A knife tends to be the easiest way of cutting it
as scissors or shears can easily clog with the heavy resin used in tooling prepregs.
The backing material is cut in much the same way as the surface ply.
Again, just going around the same templates using a knife.
Rather than kitting for some of the smaller features like around the flange
I am actually just going to cut some small strips at 45° and use them as and where necessary.
With the kit of tooling prepreg prepared, the release agent applied and fully cured on the pattern we are now ready to start the actual layup.
So the first ply down is the surface ply which has a glass scrim on side and this is the side that should be placed down onto the pattern.
The other side is the carbon fibre reinforcement.
Laminating with the tooling prepregs is much the same as working with any other prepreg.
So accurate placement of the components on to the pattern and then firmly pressing them against the surface ensuring that is follows any contours.
Here we are using a laminating tool just to ensure that we have got all of the detail consolidated against the surface of the pattern.
It is important when applying adjoining plies of laminate to ensure that
a slight overlap is maintained so that the entire surface of the pattern is covered with the surface ply.
Where necessary if you do get some gaps it is perfectly acceptable to use off cuts of material to fill them in.
Pay extra attention to small negative features such as this one as it is very easy to get voiding or bridging in these areas.
Ensure that is properly consolidated down against the surface.
The perimeter flange of this mould is being laid up using a series of strips cut at 45°.
Laminating in this tiling method makes both the layup procedure and the templating that bit quicker and easier.
After the mould has cured the join between these plies will become completely invisible.
With the first ply down we could now continue to laminate with the backing plies.
However to reduce any chances of voids or pinholes it is best practise to do a debulk,
which is what we are going to do now.
Debulking uses a Perforated P3 Release Film pressed firmly against the surface
and then it is bagged using a conventional vacuum bag and a layer of breather over the top.
The bag should be properly manipulated into position into all of the contours and then a full vacuum should be held.
After 10 minutes our debulk is complete so we can now remove this from the bag and continue with the backing layers.
The backing plies are substantially thicker than the surface plies
and can be identified by having a very resin rich side.
This should be laminated face down onto your layup.
The same care should be taken as with the surfacing ply to ensure that is it fully consolidated against the surface
and that no bridging of the material occurs.
Again overlaps wherever you have adjoining pieces should be maintained and wherever necessary should be filled in.
So we have got the surface ply down, the first layer of the backing and for a small mould
like this we are just going to do 2 layers of backing so that is the next layer that goes down now.
When making a mould it is quite different to making a component as you only actually need a very small overlap.
So although we have got lots of pieces here you can see we just retain adequate strength in the mould
by just having a very, very slight lap of the join.
That is the layup of the mould complete.
All that is left to do now is to vacuum bag it and cure.
The stack that is used for the tooling prepreg is exactly the same as we used in the debulking earlier on.
So we have a perforated release film, a breather layer and then the vacuum bag.
As the reverse side of the backing ply is dry we can actually take advantage of that
and use the vacuum to slide the film into position allowing it to fully conform to the back of the part.
In some instances it may be advantageous to use some spray tack or some flash release tape to aid in more accurate positioning of the film.
As with all vacuum bagging processes it is of paramount importance that the bag fully conforms with the surface of the laminate.
With the bagging complete this is now ready for its initial cure.
One of the great advantages of the XT135 tooling system is that it has a very low initial cure of 65℃
which is great for maintaining dimensional accuracy between your pattern and your mould.
So we are going to load that into the oven now.
Full vacuum should be maintained throughout the cure and it is important that your oven
is capable of accurate and stable control.
With the mould now cured we are going to release it from the pattern.
With the combination of the S120 Board Sealer and several applications of the Easy-Lease Release Agent
you can expect the mould to pretty much fall straight off the pattern.
With the initial cure completed and the moul d removed from the pattern we are now ready to go on to the post cure.
This is essential to achieve the full surface temperature of the mould tool.
This is done free standing off the pattern and it is essentially the process
of very gradually raising the temperature in a controlled manner up to the final surface temperature.
Then it is held there to allow the resin matrix to fully cure.
So here we have the finished mould.
We actually produced this mould in a little under 1 hour excluding the curing time using just 3 plies of material.
Although this is quite a small mould the XT135 system can be used to produce a mould of any size.
And because it is made using carbon fibre reinforcement it has incredibly low thermal expansion
meaning it will maintain its accuracy right up to its full surface temperature of 135℃.
In the last video in this series we will be using this mould to produce a carbon fibre part using the XC110 pregreg system.
So if you want to find out how that is done, stay tuned.