Motorsport Composite Fundamentals: Pattern Making - Sheet Metal

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Pattern Making - Sheet Metal

07.10

00:00	The remaining sections of this course will be focused on the practical skills needed to successfully create composite parts for your vehicle.
00:06	First we'll be looking at work involving patterns and then the construction of composite moulds before finally using these moulds to produce composite parts.
00:15	We'll also cover post processing work on cured parts like cutting, finishing and performing repairs.
00:21	Our discussions for this course will be limited to wet layup techniques and open cures without vacuum bagging.
00:27	As we've covered this along with resin infusion and pre pregs in a separate advanced course.
00:32	Before we start I need to mention that we are using the word pattern throughout this course to keep things consistent.
00:39	In reality you'll find a range of alternative terms used such as plug, buck or original.
00:44	While it could be argued that there are slight technical differences, these terms essentially refer to the same thing.
00:50	A version of the part we're trying to recreate as a composite.
00:53	As we discussed in the pattern making materials module, the options are vast and therefore the processes of making the patterns are also wide ranging.
01:03	So to avoid getting away from the focus of this course, that being composite construction.
01:08	We'll keep our discussions in the section to the typical approaches and only a surface level view using some examples from real projects as we go.
01:17	At the end of the day the aim is to create a rigid and accurate representation of our part that's dimensionally stable with the desired surface finish that we'll be able to use to construct a mould.
01:28	So we'll begin by looking at sheet metal work.
01:31	Replacing sheet metal body panels with lighter composite parts is one of the primary uses for our new skills when looking for performance gains.
01:39	In this module we'll look at an example of the front fenders on our Honda CRX race car.
01:44	Modifying the factory arches and using them as a pattern to make a fiberglass mould.
01:49	However the sheet metal work involved here is fairly representative of most pattern making projects so we'll use it to illustrate the idea.
01:57	We'll also be continuing with this example through the rest of the course to produce some composite fenders so it'll give you a chance to see a project from start to finish.
02:06	So let's get into the practical work and this starts by widening the arch of the fender significantly to allow for a larger wheel and tyre package.
02:15	It's not always necessary but it's a fairly common project in motorsport builds.
02:20	This isn't a panel beating course so again we'll gloss over the basics here but the process looks like this.
02:26	First we use some card to make a template and plan the desired shape and then transfer this onto some 1.2mm sheet metal, cutting it out with an angle grinder.
02:35	The paint is removed from the OEM fender.
02:38	There's various methods for this, either using a chemical paint stripper or some form of abrasive like a flap disc on an angle grinder or a sanding machine.
02:46	It's likely we'll use some form of abrasive so what's important is that we don't remove too much of the original material thickness, leaving ourselves with a very thin area of sheet metal that's not very stiff or easy to weld to.
02:59	With a MIG welder we can then tack the new flared arch in place.
03:02	This allows us to mark out the area under the flare and cut off the excess area, again using an angle grinder.
03:09	The flare is then MIG welded onto the panel and we can reuse the flange from the original arch to make a nice finish edge that also adds some stiffness to the new arch.
03:19	I'd recommend checking out the HPA fabrication and welding courses if you're interested in picking up these skills.
03:24	However one of the key considerations when welding relatively long distances on thin sheet metal panels is heat management.
03:31	That means avoiding putting excess heat into the panel as this will cause it to warp.
03:36	The general approach to avoiding this is by welding short stitches, moving around the panel as much as possible.
03:43	This means welding a stitch on one side and then the other and then in the middle and then back to the original area and so on.
03:49	We're also going to cut off the lower section of the fender behind the wheel and add a flange here for stiffness.
03:55	This area is going to be replaced by an aero part to evacuate air from the wheel well, although we'll be keeping our focus on just the upper fender for this example.
04:04	Any irregularities in the panel can be removed with panel beading and of course body filler.
04:09	Panel beading is a skill that takes time and experience to learn so we won't be taking a deep dive into sheet metal forming using the myriad of tools available.
04:18	As with any panel beading work, the closer we can get the metal to the desired shape and the less body filler the better.
04:24	But with that said, these parts aren't going to remain on the car, they'll be replaced with our composite versions.
04:30	So the use of some extra body filler and the additional weight and strength penalty to speed up the process isn't going to be a problem.
04:37	Most typical automotive body fillers will do the trick here.
04:40	Most of these body fillers are polyester based and mixed with a BPO hardener aka Benz oil peroxide to initiate the curing process.
04:49	Reviewing the technical data sheet we can see the different surfaces this can be applied to.
04:54	Which includes bare steel, the original paint and also GRP so that means we can also use it on our composite part.
05:01	This also lets us know that we should clean the surface with a wax and grease remover and then key the surface with 80 grit for bare steel or 180 grit for anything else.
05:10	At our 20 degree Celsius ambient temperature the recommended mixing ratio is 2% hardener.
05:16	We'll typically mix this on a scrap piece of metal using the body filler applicator or scraper.
05:21	We want the filler to be fully mixed and nice and smooth with no air bubbles when we apply it to the irregular parts of the surface in a thin even layer.
05:29	The gel time is only 5 minutes so we need to do all this relatively quickly.
05:33	Then we can let it cure and it'll be hard enough to sand in about 20 minutes.
05:37	The initial sanding can be done with 80 to 120 grit to remove the bulk of the material and then we can finish up with 180 to 240 grit for a better finish.
05:46	At this point we have a smooth and sturdy widened fender that we want to replicate as a composite.
05:52	Everything we do here is repeated on both sides of course.
05:55	They're not quite ready for pulling a mould yet so we'll be completing more work on these fenders in the section of the course to prepare them for pulling a mould in the following section.
06:04	Of course the specific process here for this project won't look exactly the same but the ideas are those typically applied when working with sheet metal for pattern making.
06:14	So let's summarise the key takeaways.
06:16	Most sheet metal projects are based around general fabrication techniques such as cutting, grinding, forming and welding.
06:23	Using flanges, bends and forms will help to stiffen the structure which is often necessary to ensure we have a sturdy pattern when it comes time to pull a mould.
06:32	There's a lot that goes into panel bending which we can't cover in this course.
06:36	But during any welding of sheet metal we need to consider heat management to avoid warping the panels.
06:42	Finally when pattern making we're not overly worried about the weight of the pattern itself so we'll turn to body filler to fill any irregularities.
06:50	It's important to consider its compatibility with other products that we'll be using and it should be mixed with hardener and applied to the surface as per the supplier's recommendations.
06:59	Once cured we can sand it to the desired shape and for a smooth finish.