Motorsport Composite Fundamentals: Lamination

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Lamination

15.35

00:00	Our tooling gelcoat is now cured to a tacky surface, and now we're finally ready for our first look at practical lamination.
00:07	We'll be doing this lamination in two steps for the main section of the mould.
00:11	The first will be a thin skin, using a lighter weight CSM reinforcement that contours to the details of the part easily, and ensures that we have reinforcement right up to the mould surface.
00:23	A lighter weight reinforcement closer to the mould surface also helps reducing print through, which is where the texture of the reinforcement is present on the mould surface, and therefore will be transferred to the surface of our parts.
00:36	The next step after this is mostly cured is a heavier backing layer that will provide the bulk of the stiffness and structure of the mould.
00:42	After this is cured, the flute sideboard flanges will be removed, and we'll be applying release agents and gelcoat, as well as laminating the backside of the flanges.
00:52	So the first step is to prepare the reinforcement.
00:54	For the thin skin, we'll be using 225 GSM emulsion bound chopstrand mat, with some 35 GSM surface tissue on hand for the extra fine details, while the backing layers will be done with 450 GSM.
01:10	It's typical to aim for about three to five times thicker than the part we're going to pull from the mould, to ensure that the mould is nice and stiff.
01:18	The composite parts we'll make will be around the thickness of the original panel, to ensure that they fit the car well.
01:24	We'll discuss this more later in the course, but this is around 1 to 1.5 millimetres, or six hundredths of an inch, or 16 gauge.
01:33	225 GSM mat is around 0.4 millimetres thick, and 450 GSM is around 0.7 millimetres thick.
01:42	So we'll be aiming for about two layers of the 225 GSM on the thin skin, and four to five layers of 450 GSM on the backing layers.
01:50	We need to make sure we have enough of each mat on hand to cover the area of our parts.
01:56	It's fair to say that each of the fenders is less than half a square metre in area, so two metres square of 225 GSM mat and four metres square of 450 GSM should be more than enough.
02:09	We can cut and tear the reinforcement to size as we go, but it's worth having some sections ready, with straight cut edges that will lay up into the internal corners, and then torn edges for overlapping.
02:20	This will make more sense as we get started.
02:23	Before we prepare our resin, we're first going to prepare what's called a resin filler or bog.
02:28	Essentially this is just a thickened resin, which we'll use to fill irregularities and find details that our reinforcement won't be able to get into, to help to prevent voids.
02:39	This is somewhat of a controversial step, as some will argue that using resin bog or filler is detrimental to the strength of the laminate, and if your laminating is good enough, then you shouldn't need it.
02:50	This is a fair point, but we also need to be practical here.
02:54	This is a fundamentals course, and many of us won't have much practical experience.
02:59	Understandably, we won't get the laminate perfect, and a bit of resin bog is much better than voids.
03:04	We're going to use an unwaxed vinyl ester laminating resin for our moulds, so we can work in stages like we just discussed, and ensure that our backing layers bond to our initial thin skin.
03:15	An unwaxed polyester resin would typically be our choice here, but to be honest, we just didn't have any on hand, and the process won't be any different with vinyl ester, and we'll likely get a slightly stronger mould, so no harm done, other than a bit more expense.
03:30	Anyway, back on track, we'll use this same resin for our resin bog, thickening it with fumed silica filler powder, also known as colloidal silica, silica thickener, or commonly by brand names aerosil, and more recently cabosil.
03:45	This filler powder not only thickens the resin, but also increases its thixotropy, meaning it'll help it fill voids, while also clinging to the vertical sides of the mould and not running.
03:56	There's no need to focus on the specific mixture quantities here, just keep in mind the initial amount of resin used when it comes time to catalyse.
04:04	We'll start by adding 200mm of resin to our mixing container, and then continuously add cabosil, while mixing thoroughly until we achieve the consistency of smooth peanut butter.
04:15	Keeping in mind the pot life, we don't want to catalyse this yet, so let's prepare our laminating resin.
04:21	Again, we'll be using unwaxed vinyl ester laminating resin, so we can work in stages without having to worry about the wax rising to the surface, and creating a hard, fully cured layer, that will prevent a good bond between our thin skin and backing layers.
04:34	This also means if we run into any difficulties, we can simply stop, allow the layout to cure, regather and continue where we left off.
04:43	With two separate containers, each containing 400mm of our laminating resin, let's shift our focus back to our resin bulb, and catalyse this with MEKP.
04:53	Recalling from before, this mixture contains 200mm of resin, and it's important we catalyse it at 2% based on this volume, not the total volume including the cabosil.
05:03	In practice, cabosil is such a fine powder that it doesn't change the volume much, but this is still important to keep in mind if we're ever using other fillers or additives.
05:13	So we add 4ml of MEKP to the bulb, and then mix thoroughly.
05:18	We should be able to see it change from the blue original colour, to a greener tinge in this case as it becomes fully mixed.
05:25	Mix vigorously for 1-2 minutes, continuously scraping down the sides.
05:29	Then we can get straight into the work, with a brush applying the filler bulb to all the fine detailed areas, edges and corners of the mould.
05:37	We want a generous amount to fill the details so the filler can do its work, but not excessive.
05:42	This only takes a minute or so, so the pot life of 20-30 minutes isn't an issue.
05:48	We still want to complete our lamination within the gel time of the resin, which is about 45 minutes, so we'll move straight on to catalyse our laminating resin.
05:56	To be clear, gel time is the point where the resin stops flowing and becomes a solid but gel -like state, like the back of our gel coat.
06:04	It's the same story for catalysing our resin.
06:07	2% for our 400ml containers, so 8ml into the first one, and then mix thoroughly.
06:13	We'll catalyse the second one as we need it if we're working alone, or we can do both at once if we have a helper.
06:20	Once it's fully mixed we can begin.
06:21	Having a bucket of acetone on hand is also helpful for any brushes or mixing sticks to help clean them off.
06:29	We don't want to transfer the bog into our resin pots, or we can ideally just start with a new brush.
06:34	The first step is to apply a good coat of resin to the back of the gel coat, and then start to lay up the 225gsm reinforcement for the thin skin, with the cut edges into the corner, and wet them out with the paintbrush.
06:47	Again, we've got 20-30 minutes of working time, so we should start at one end and work systematically.
06:53	Don't be shy with the resin here, we aren't trying to achieve the lightest laminate possible for our mould.
06:59	At the same time we don't want to be too excessive and have too much thickness or uneven thickness.
07:05	Remember the resin cures through an exothermic reaction.
07:08	An overly thick area of resin will result in a hot spot and local shrinkage in this area, which will become a weak spot in the laminate and could ruin the whole thing.
07:18	Brushing it on helps with efficiency, but it can move the reinforcement out of place, so we use the brush to dab the resin through the reinforcement.
07:26	It's fairly easy to see when the reinforcement is wet out, as it changes from the original white to a darker shade.
07:33	Laying the cut edges of the CSM up into the corners helps ensure we get reinforcement right up to the edges of the mould, and we don't get a void just under the surface on that edge where the mould would be the weakest.
07:45	The next layer of 225 GSM on the thin skin overlaps the corners and helps to tie it all together.
07:52	You'll notice that the mat often won't wrap around external corners initially, however if we apply some resin to the mat and leave it for a minute or so, it'll start to dissolve the emulsion binder, making the mat much more flexible and easy to fold.
08:06	In some cases though we'll be fighting a losing battle, and there's often no need to get too hung up on it, as once cured we'll denib the surface and trim these back.
08:16	Once the mat is fully wet out, we can turn to our rollers to consolidate the layup into the internal corners and drive out any air bubbles trapped in the laminate that'll cause voids.
08:26	Different sized rollers, like brushes, are used for different parts of the mould, depending on how tight the details are.
08:33	Rolling and more generally hand lamination is somewhat of a learned skill from experience.
08:37	It's easy to pull the reinforcement out of place, so it takes some time to get it right.
08:43	Don't be too hard on yourself if your first attempt feels a bit messy and frustrating.
08:48	We'll often be able to see the air bubbles coming out of the resin as we roll, and hear the change in the rolling noise as all the air is removed.
08:56	We want to aim for a consistent number of layers and thickness, however what's important about the thin skin is getting into all the tight details and tying the first layer together.
09:06	The bulk of the structure will be achieved with the following backing layers.
09:10	After two layers of the 225 gsm mat are fully wet out and consolidated with the roller, we can leave the layup to cure.
09:18	Remember to dispose of the remaining resin safely, and clean your brushes and rollers in acetone for reuse.
09:24	Curing should take around four hours, but what we're looking for is a solid feel to the outer surface, so we can't easily push dents into it with our hands.
09:33	Because we've used an unwaxed resin, we should be able to form small dents if we push hard, and the surface will be slightly tacky, but this is what we're after to ensure that the backing layers bond well to the existing surface.
09:47	At this point we'll use sandpaper to denib the surface, and remove any raised sections that will prevent the next layers from consolidating nicely against the surface.
09:56	The next lamination process is very much the same as we just covered, just with more layers of a heavier mat.
10:03	Catalyze and mix the resin, wet the surface, laminate and wet out the 450 gsm mat, use the sharp edges into the corners and then overlap with torn pieces.
10:14	Consolidate with the rollers and then allow to cure.
10:17	After an hour or so when the lap has cured to about the consistency of cheese, we can complete what's called a green trim.
10:24	This is where we use a sharp blade to trim the overhanging edges up to the edge of the flanges.
10:30	The benefit of this is eliminating or reducing the amount of cutting and grinding we need to do to the cured fiberglass, since it's such a messy, dusty and itchy process.
10:41	Just be careful as the mold isn't fully cured, if we're too rough we can damage the mold and in the worst case have to start from scratch.
10:48	I'd recommend foregoing a green trim if it's your first time laminating.
10:52	Now it's time to leave the first section of the mold to fully cure.
10:56	Ideally we'll leave it overnight or for 24 hours, at least to ensure the mold is nice and strong before completing the next steps.
11:04	Another quick denib of the surface can help prevent the risk of cutting our hands or splinters, and then it's time to remove the flute board flanges.
11:13	Care needs to be taken here to avoid releasing the mold from the pattern.
11:18	We want to keep the mold on the pattern in its current location.
11:21	The aim is only to release the flute board flanges from the pattern, where they've been hot glued on.
11:28	At this point we should be able to see the divots for the locating keys in the mold side of the flange.
11:33	The flanges needed a little bit of tidying up, as some gel coat and resin had found its way into the small cavities, and created some raised sections around the flanges.
11:43	We want them to be as nice and flat as possible, so they don't form locking features that could prevent release.
11:49	We'll use a soft fibre disc on a die grinder to smooth the flanges, and then clean the dust and PVA off the existing mold flanges.
11:57	Since the PVA is soluble in water, we simply use a wet rag for this.
12:02	We'll also scrape away the plaster seam with a plastic blade, and use wax and grease remover to get rid of the remaining residue.
12:09	Following this we'll apply some new plaster seam to fill any small unwanted gaps and details, and use tape to cover the backside of the holes needed for mounting the fender to the car.
12:19	From here we essentially repeat the entire process again.
12:23	Mold release wax was originally applied to all the surfaces of the patterns, but not the flanges of the first section of the mold.
12:30	So we'll start by completing a few coats of wax here, and also on the surfaces of the pattern for good measure.
12:36	Wiping the wax on, allowing it to haze, and then wiping it off, allowing it to cure, and then re -coating.
12:42	We can also apply our PVA parting film as before to ensure we get a good release.
12:48	If you need a refresher, pop back to the Application of Release Agents module.
12:52	After this is fully dried, we're back to our gel coat, catalyzing and mixing thoroughly, and then brushing it onto the surfaces of the part and the existing mold flanges, before leaving it to cure to a gel state for a few hours.
13:05	Again, pop back to the gel coat module if you're hazy on the process.
13:09	At this point we're back to the lamination stage, and we can take a bit of a faster route here, laminating in a single stage.
13:16	Although we still want good results, the backing sides of the flanges aren't visible and are a much smaller area.
13:23	First we catalyze another mixture of resin bog, and then apply it around the internal corners and the sharp details to prevent voids.
13:30	Then we catalyze and mix our laminating resin and start the layout.
13:34	The idea here is the same, wetting the backside of the gel coat surface, then laying the reinforcement into the corners and details, to ensure we have reinforcement as close to the mold surface as possible.
13:45	And then overlapping with backing layers for more structure.
13:49	After this is fully consolidated with the rollers, and we're happy with our laminate, we should leave it to cure fully.
13:55	This should be at a minimum overnight, but ideally if we have the time, it can be worth leaving it for a few days to ensure a full cure, and good strength before we demold it.
14:05	The last thing to do is dispose of our leftover resin safely and clean our rollers.
14:11	We've covered a fairly lengthy lamination process in this module, so let's recap what we've done before we move on to release the mold from the pattern and apply the finishing touches.
14:21	The first step in the process was preparing our materials.
14:25	We also prepared a resin bog or filler, made from laminating resin and fume silica aka cabosil, mixed to a peanut butter consistency.
14:33	This was applied to the corners and edges of the part and areas of detail to help prevent voids that would cause weak spots.
14:40	It's important to keep in mind the pot life and gel time for the resins once catalyzed and mixed.
14:46	An unwaxed resin was used so we could work in stages while still achieving a good bond between layers.
14:52	225 gsm chopstrain mat was used to wet lay a thin skin that conformed to all the details and ensured we had reinforcement as close to the mold surface as possible.
15:02	After this thin skin cured and was denibbed, it was backed up by wet laying heavier 450 gsm mat and multiple layers to achieve the bulk of the structure.
15:12	This was allowed to cure overnight to ensure the laminate was strong before we removed the temporary flute board flanges.
15:19	With these removed and the mold sides of the flanges tidied up, it was rinse and repeat, applying release agents, then gel coat and then finally laminating again before allowing the entire laminate to fully cure.