Motorsport Composite Fundamentals: Demoulding & Finishing

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Demoulding & Finishing

04.40

00:00	After the part has cured fully, we're ready to remove it from the mould.
00:03	This cure will likely take a minimum of 12 to 24 hours, but it's often ideal to give it a few days if possible.
00:10	Depending on the mould design, we may start by splitting the mould sections if we have multi -piece moulds.
00:16	For this process and demoulding the part itself, we'll use demoulding wedges, compressed air and our hands.
00:23	We just need to be careful not to damage the mould surface, the surface of the part or our hands with any of the sharp or rough edges.
00:30	A light knock on the flanges with a mallet can help free up the part.
00:34	We just need to be careful not to hit too hard or hit the backside of the mould surface as this can lead to cracks in the part.
00:40	The geometry of the mould, the laminate and the release agents used will all dictate how easy the part releases, hopefully with as little effort as possible so we can reduce the risk of damaging the part.
00:52	With the part out of the mould, it's ready for the finishing steps.
00:55	This will depend on the application for the part and to some extent how good our work has been so far.
01:01	Finishing composite parts almost always requires the removal of material via cutting, sanding, drilling and polishing and this is generally a very messy process.
01:11	Throughout these steps we've assumed the use of PPE but it's worth reiterating here.
01:16	Glasses, respirators and hearing protection are all a must.
01:19	Gloves and coveralls are also recommended.
01:21	Straight out of the mould, almost every part is going to require a trimming and shaping of the edges.
01:27	The go-to tool for this is a cut-off disc on a die grinder although an angle grinder will work with some extra care.
01:33	If we don't have access to either of these tools then a hacksaw or rod saw is a good choice and will provide some more control.
01:40	What cut-off disc is ideally used depends on the reinforcement as we discussed throughout the course.
01:45	In any case, a finer grit or a higher tooth count on our cutting tools can help reduce the chance of the backside of the cut chipping.
01:52	Once the edges are roughly cut and the bulk of the excess material has been removed then we can use a die grinder with a burr wheel, a sanding disc as well as a good old-fashioned sandpaper on the sanding block to accurately shape the edges.
02:06	When it comes to drilling holes in our composite parts the primary concern is the backside of the laminate chipping.
02:12	The drill bit type and backing material can help prevent this.
02:15	We'll often use wood behind the material and drill bits like a tapered reamer, straight flute spade or dagger drill bit to achieve the best finish and most accurately size holes.
02:25	Also, like cut-off discs, general drill bits for cutting metal work well for fiberglass whereas solid carbide is ideal for cutting carbon fiber.
02:34	Once the edges of the part are shaped as desired and any holes are drilled we can start looking at the finer end of the material removal spectrum with surface finishing.
02:43	As always, the work here will depend on the application of the part and how we want it to look as well as its current state.
02:50	Any surface voids should be filled by using a coating or laminating resin.
02:54	The surface needs to be keyed with something like 400 grit sandpaper to prepare for this and then thoroughly cleaned.
03:00	A small piece of flash tape can be used as a dam to hold the resin in place while it cures.
03:06	Once cured, the excess material needs to be sanded back to match the surface of the part at which point the rest of the part can also be keyed with sandpaper cleaned and then coated with a spray on automotive style clear coat or coating resin.
03:18	Alternatively, we could have used a gel coat in the construction of the part but in either case, the steps from here will depend on the level of finish that we're after.
03:26	Typically, this will be a high gloss finish so we'll start by sanding the part up to about a 1200 grit wet and then move on to a cutting compound and then a finer polishing compound either by hand or with a polisher.
03:39	Other coatings like paints can be used but that's getting outside the scope of this course so before we get off track let's summarize the last step of our composite project.
03:48	Once our part has cured in the mold it's time to remove it.
03:51	This could involve splitting the mold sections and releasing the part with our hands, wedges or compressed air.
03:57	Just be careful not to damage the part or the mold.
04:00	With the part out of the mold the work remaining will vary for different projects however, in almost every case the edges will need to be trimmed and shaped which can be done with rotary power tools manual saws or sandpaper all the usual suspects for material removal.
04:15	We just need to consider what composite material we're working with and if this would benefit from a different tool material.
04:21	The same goes for drilling holes where a primary concern is around preventing chipping and delamination.
04:27	Finally, surface finishing will typically involve filling any surface voids then sanding, coating and more sanding followed by cutting and polishing for a high gloss finish.