Motorsport Composite Fundamentals: Demoulding

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Demoulding

04.38

00:00	After leaving our layup to cure overnight in a heated room, we're ready to release it from the mould.
00:04	A quick check by touching the backside of the parts will confirm that the surface is nice and hard.
00:10	If there's any tackiness or softness to the surface, we need to leave them to cure for at least another few hours.
00:17	Trying to demould a part that isn't fully cured is almost always going to result in ruining it.
00:22	We'll start by undoing all the M8 hardware holding the mould sections together, and then using a rubber mallet to knock the edges of the flanges to help free up the parts.
00:31	We should never knock the backside of the mould surface as this can cause star cracks in the surface of the part.
00:37	From here we can start to pull the mould sections apart from the flanges.
00:41	If this isn't possible by hand, then we can carefully drive some plastic wedges down the parting gap.
00:47	Always be careful when using demoulding tools not to damage the mould surface or the part.
00:52	One slip of a tool can cause damage that might undo a lot of work.
00:56	For this mould design we want to pull off the mould section for the fender mounting flanges first.
01:02	To be honest, this would have been a lot easier if we'd made it a three piece mould, because with only two pieces, we have to flex and rotate the mould section slightly to get it out of the way of the door jamb mounting flange.
01:15	It's still very achievable though, and with that part out of the way, we can start releasing the part from the main mould section.
01:21	We often need to slide our hand between the parts and the to help apply an even amount of pressure and leverage to release the part without risking damage.
01:31	This can be tricky to do with gloves, so if we forego using them, we need to be extra careful of splinters.
01:37	Depending on the specific part and mould design, more tools and compressed air can also be useful for this step.
01:44	In some cases we can also flex the mould slightly if it's not too stiff.
01:48	With the part released, we can finally see our hard work come to life and get a chance to review its condition and our work.
01:55	In the case of our fenders, we have some flashing which is to be expected along the mould split lines which is easily removed with some sanding.
02:03	Overall the surface finish is very smooth and consistent.
02:07	Any rough areas are those that'll be trimmed off.
02:10	The clear gel coat allows us to see through the laminate and spot a few very small and insignificant air bubbles under the surface.
02:16	The stiffness of the part feels suitable.
02:19	Not too thin and flimsy but certainly not overkill and bulky.
02:23	Like we mentioned in the preparation module, the first articles are often a trial to determine the suitable layers of reinforcement but we made some educated choices to get us in the ballpark.
02:33	The orange colour on the surface of one of the fenders is some transfer of the tooling gel coat from the mould.
02:39	It won't cause any issues but it indicates that the gel coat could have been left to cure for longer.
02:44	The main point is we have practically no surface voids which is great as it saves us a lot of finishing work.
02:51	This mostly comes down to the use of the gel coat and the resin bulk for subsurface voids.
02:56	The realities of a wet layup and open cure like this, particularly on a part with any detailed areas, is that it's very difficult to get a result free of any voids even for pros doing this every day.
03:08	As we mentioned before, the use of resin bulk and a small bit of extra weight or a reduction in some strength around the very edges is much better than voids.
03:17	Vacuum bagging, resin infusion and especially the use of prepregs will reduce and often eliminate the chance of voids but at the compromise for more expense and a more involved process.
03:28	Again, these are covered in the advanced composite course.
03:31	All this said, if we have these surface voids, that doesn't mean we need to live with them and we'll cover how they can be repaired in a coming module.
03:39	For now, let's recap the main points before moving on to finishing our fiberglass fenders.
03:44	Depending on our part, mold design and release agents used, the demolding or release process can be very different but all the preparation work we've done previously was with the aim of making it as easy as possible.
03:57	For our CRX fenders, we removed the hardware securing the two mold sections and then used a rubber mallet to carefully knock the mold flanges before prying them apart with the help of some plastic wedges.
04:08	With the mounting flange section removed, we carefully pulled the part from the main mold section, primarily using our hands.
04:16	The surface finish of the part, while needing some finishing touches as we'd expect, was completely free of surface voids.
04:23	This is something that's relatively hard to achieve for parts with sharp edges and details using hand lamination and an open cure, and was mostly achieved by using a gel coat and a resin bog.