Motorsport Composite Fundamentals: Pattern Making Materials

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Pattern Making Materials

06.38

00:00	As you're well aware by now, the focus of this course is around the construction of composite parts, and this naturally covers the moulds, as they're usually constructed from composites as well.
00:10	Patterns are a different story though, as they're very rarely composite based, unless we're pulling a mould off an old part that's no longer available and we want to recreate it.
00:19	We haven't discussed patterns much so far, so to clarify, a pattern or a plug is a replica of the shape of the object we're trying to create, and we use the pattern to create the mould.
00:30	The pattern should be rigid, dimensionally accurate, and representative of what we're trying to achieve with the final part.
00:37	The materials and construction method for the pattern are very wide ranging.
00:41	Many composite projects aren't original designs, they're often based on an existing part that we want to make in a composite material.
00:48	For example, making a carbon fibre version of a bonnet or a hood from a factory piece.
00:53	If we're trying to replicate the factory hood, then the hood alone is the pattern or the plug, which might be made of steel or aluminium.
01:01	In this case, the pattern making process isn't necessary, but if we're trying to modify the hood and add a radiator duct, then we need to modify the pattern, cutting out a hole in the hood and building a pattern for the duct ourselves, perhaps out of sheet metal.
01:16	In other cases we'll be producing an original design, so for the pattern we'll be starting from scratch, with the aim of creating the design surface accurately and sturdy enough for mould construction.
01:28	Again,, maybe we use sheet metal, maybe wood, foam, or a 3D printed pattern.
01:33	As you can see, the scope here starts to open up quickly.
01:37	So, in the interest of keeping things brief and digestible to round this module out, we'll just run through a few typical approaches taken and the materials and tools used with them.
01:47	As we discussed, sheet metal fabrication is a common route, using aluminium or steel in similar thickness to our vehicle panels, along with general cutting and forming tools as well as welding.
01:58	We can then follow this with the use of body filler and plenty of flatting and sanding for a smooth finish.
02:04	As we've mentioned previously, the surface of the pattern will be transferred onto the mould and then this onto the surface of our part.
02:12	So, we want the best results at each stage.
02:14	Other very common materials are MDF board and low density polyurethane or PU foam.
02:20	MDF is great for geometric shapes, it can be cut and glued together as well as sanded easily to efficiently create the bulk of large patterns.
02:29	Clearly we can't round internal edges with sanding, so we'll press modelling or filleting clay or wax or plasticine into these areas and use a filleting ball or in some cases our finger to create a rounded transition.
02:42	For flat surfaces or those with gentle curves that don't need to be bent sharply, plastic board like fluted signboard or polypropylene sheet is an alternative to MDF.
02:52	Polyurethane or PU foam, which is also often called model board, is the choice for pattern making over other foams as it's very easy to shape with sandpaper and not dissolved or compromised by solvents, resins or body fillers.
03:05	After the foam is shaped to the desired forms of the pattern, a polyester based body filler can be used to fill in the surface roughness.
03:13	Of course, many of these boards and foams are porous, so they'll absorb any liquids that are applied to them.
03:19	Because of this, we need to use something like a specific pattern coat primer, which can be followed by a pattern coat gloss.
03:26	Again, the surface finish of the pattern is important due to how it transfers to our mould.
03:32	Alternatively, we have board and model sealer, and the name is fairly self explanatory.
03:37	It helps to seal up the board while also providing a high gloss finish.
03:41	All of these materials we've discussed can be designed and shaped by hand, but it shouldn't be ignored that with modern accessibility, many of us are now utilising the power of computer aided design, more commonly known as CAD.
03:55	The trickiest parts of this process is going to be transferring our design from the virtual world to a physical pattern.
04:01	If what I'm about to discuss goes right over your head, I highly suggest checking out our next free CAD and 3D modelling lesson, and you'll find a link to this at the bottom of this module.
04:10	A commonly used approach with CAD designs is creating section profiles of the parts that fit together with slots.
04:17	We can print templates out on paper and transfer them onto a sheet material to build a 3D reference frame of the pattern.
04:25	The volumes between the frame can be filled with low density foam, either cut and glued in place, or alternatively, an expanding foam that's sprayed into place.
04:34	PVC foam or wood is commonly used for the frame as it's higher density than PU foam.
04:40	So, when we're sanding the lower density foam to match the frame, the frame material itself will better preserve its shape for reference.
04:48	The alternative is to use CNC machines to do the heavy lifting for us and create the bulk of the pattern.
04:54	Some typical options are 3D printing for smaller parts, machining foam or wood on the router to create the frame pieces that we just discussed, or even routing the entire 3D pattern from foam.
05:06	You might be asking yourself, if we have a CAD model and we're using CNC machines, why not just skip the pattern making step altogether and just create the mould? And this is completely possible for some projects, but it's really going to depend on other variables, like what we want to make our mould from.
05:24	For example, if we're aiming for a large part that will be constructed using prepregs, then we need a mould suitable for a high temperature curing process.
05:33	Machining the mould from a metal for a big part is extremely expensive, so instead we could route it from foam and then work towards making a carbon fibre mould.
05:43	Side note here, we'll typically use high temperature epoxy foam, also called tooling board, rather than polyurethane for a step up in surface finish, stability and service temperature.
05:54	Before we get too far in the weeds, let's wrap up this module with a summary, as again, we'll be getting into the practical skills of pattern making later in the course.
06:03	The key takeaways here are that we might not need to make a pattern at all, or it could be a very involved job to craft a pattern from scratch.
06:11	Alternatively, if we're using CAD to model our design, we could leverage the power of CNC machines to create our patterns for us.
06:18	Some typically used materials are sheet metals, foams and low density woods, although anything that provides an accurate and sturdy pattern is suitable, we just need to be aware that the surface of the pattern will be transferred to the mould.
06:31	So, ideally we'll get it as good as possible at this stage.