Motorsport Composite Fundamentals: Remoulding & Finishing

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Remoulding & Finishing

07.07

00:00	24 hours has passed and we're ready to remove our carbon fenders from the moulds.
00:04	Depending on the ambient conditions, 12 to 24 hours is generally about the minimum time and it's often ideal to give it a few days if possible.
00:13	The demoulding process is much like we covered in the course for our fiberglass fenders, starting by removing the hardware and splitting the mould sections.
00:21	For this mould we need to carefully drive some plastic wedges down the parting gap.
00:26	Always be careful when using demoulding tools not to damage the mould surface or the part.
00:31	One slip of a tool can cause damage that might undo a lot of work.
00:35	From here we can tear off the peel ply which presents the issue we discussed in the last module.
00:40	Since our peel ply was laid down with a few creases, we can clearly see where the peel ply hasn't been touching the back of the laminate.
00:47	There's disturbances in the otherwise consistent surface texture left by the peel ply.
00:52	From here we can pry up the edges of the part using our wedges and since we've done a good job prepping the mould with release agents, the part pops free relatively easily.
01:01	With the part released, we get our first look at the mould surface and a good feel for the structure of the part.
01:07	The stiffness of the part feels suitable, not too thin and flimsy, but certainly not overkill and bulky, measuring at about one millimetre thick as we intended.
01:16	In the case of our carbon fenders, we have some flashing, which is to be expected, along the mould split lines, which will be easy to remove with some sanding.
01:25	The surface finish on the main body of the fenders is reasonably good with only a few small surface voids and some pin holes.
01:32	The realities of a wet layup in an 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 when we're not using a gel coat or resin bulk.
01:44	Vacuum bagging, resin infusion and especially the use of prepregs will reduce and often eliminate the chance of voids, but at the compromise of more expense and the more involved process.
01:55	But it doesn't mean that we have to live with these voids, so we'll come back in a moment and fix them.
02:00	Some of the details around the rest of the part have some larger surface voids.
02:05	For example, on the top of the main mounting flange, where there's a raised section on the original part and therefore a channel in the mould.
02:12	While laying up this area, it was near impossible to get the carbon fabric to consolidate into this detail and stay put.
02:19	Again, this is the realities of a process like this, using these materials.
02:24	A vacuum bag would be able to hold the section against the mould, but we didn't have that luxury in this case.
02:30	Luckily, these areas aren't visible with the fender mounted to the car, so this part is still very usable.
02:35	So, let's move on to the finishing touches, which will remove involving excess material and finding our desired outline, drilling mounting holes, filling voids and applying a clear coat.
02:45	Before we cut anything, PPE such as glasses, respirators and hearing protection are a must.
02:50	Gloves and coveralls are also recommended.
02:53	Carbon fibre is abrasive, so we'd recommend using carbide cutting tools if you have access to them.
02:58	Otherwise, you're likely to quickly dull whatever you're using.
03:02	We'll start by marking out the areas of excess material we want to remove, to avoid cutting off anything we need.
03:08	Then with a cut off disc on a die grinder, we can make some rough cuts to remove the bulk of the excess material.
03:14	We'll then come back in with a sanding disc to work up to the target edge of the part.
03:18	A round of hand sanding with our permagrip block can finish the sharp edges and make the part safe to handle.
03:24	At the same time, we can also sand off any flashing.
03:27	Don't worry about any scuffs this leaves on the surface, as we'll be sanding the entire surface of the part to prepare for the clear coating stage, which we'll get to in just a moment.
03:36	Before clear coating, we'll finish the major cuts and drilling the mounting holes.
03:40	Again, I'd recommend marking out the exact locations to drill these, and double checking against the original panel on the car to make sure we've got this right.
03:49	Generally, these mounting holes don't need to be a perfect diameter.
03:53	Some clearance is usually a good thing, so we can align our body panels.
03:56	We're using a drill reamer bit here, so we can cut a clean hole for M6 hardware.
04:01	But there's always a chance that we'll open these up depending on the fit of the panel.
04:05	Some wood clamped to the part can provide some backing material, which helps preventing chips and delamination of the backside of the hole.
04:12	Now, that the edges of the part are shaped as desired, and any holes are drilled, we can start looking at surface finishing.
04:19	We didn't use a gel coat for this project to show the alternative of applying a clear coat, but there's a few steps to prepare for this.
04:26	First, we need to fix our surface voids.
04:28	The surface around the voids needs to be keyed with something like 400 grit sandpaper to prepare for this, and then thoroughly cleaned, either with soapy water or a wax and grease remover.
04:39	The voids should be filled using a coating resin or laminating resin.
04:43	We'll use our polyester laminating resin in this case, catalysing at 2% with MEKP.
04:48	We then use a small piece of flash tape under the void as a dam to keep the resin in place while it cures.
04:55	The resin can be teased into place with a popsicle stick.
04:58	Once cured, we sand back the excess material to match the surface of the part.
05:02	400 grit can be used again for this on a DA sanding machine to speed up the process, at which point the rest of the part can also be keyed with sandpaper and cleaned again.
05:12	We're now ready for our clear coat.
05:13	For this, we're using a General Automotive 2K clear coat.
05:17	More specifically, we're using Diamond Chrysler Clear 7900.
05:21	We'll mix this as per the supplier's instructions at 4 to 1 before transferring it into our spray gun pot.
05:27	So, for 100 millilitres of part A, we'd add 25 millilitres of part B.
05:32	Again, we can follow the supplier's instructions for the spray application process, applying two coats with about 10 minutes of flash time between the coats.
05:40	We then allow it to dry for at least four hours.
05:43	The surface finish at this stage is relatively good, but there's always room for improvement.
05:48	Although these fenders will likely be wrapped or painted in the future, it'll be nice to get them looking as good as possible for the time being.
05:55	So, we'll start by sanding with 800 grit and then working up to 2000 grit wet.
06:00	And then we'll move to a cutting compound with our polishing machine and a foam pad, wiping off the leftover with a microfiber cloth.
06:07	We'll then move to a finer polishing compound and a wool pad, taking the part to a glossy finish.
06:13	For those curious, the final part weighs 440 grams compared to the 900 grams for the fiberglass fenders and 2.3 kgs for the original, albeit modified, fender.
06:24	To summarize the work we did in this module, we started by splitting the mold and releasing the part.
06:29	This gave us our first look at the condition of the part and an idea of the work required to finish it.
06:34	We then trimmed off the excess material, starting off with rough cuts to remove the bulk of it, and then gradually working up to the edge.
06:41	Remember to wear the correct PPE for this, work in a space that you can get messy and use appropriate tools for cutting carbon fiber.
06:48	Next, we drilled the mounting holes, filled the surface voids with our laminating resin before sanding the repairs back to match the part, keying the entire outer surface and cleaning thoroughly.
06:58	We then sprayed on an automotive clear coat, which we then wet sanded, cut and polished to a high gloss finish.