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Steve Broad
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+xI use infusion for the big parts, as the material get's quite expensive. I don't know how stiff you want your part to be, but 3mm sandwich is usually enough for body panels. I followed your project on lotuselan.net (I am a elan fan). you are planning a flip front? No offense, but I think that this might be a little beyond your current skill level. To get this looking nicely and working good, you will need to do some serious rework on the bonnet and the car (an inward edge around the back of the bonnet for example). I would recommend to redo the front in cf sandwich, cut of the original section out and glue both parts together. Personally, I would do it with resin infusion, with soric lrc 3mm as a core. But split mould infusion is a difficult task. Prepreg will be a lot easier for people with less experience. I would make a three or four piece mould (front, sides and maybe top, depending on the original bonnet cut off) No doubt it is beyond my current skill level but that hasn't stopped me before, as you have obviously noticed :-) However, even with my limited experience and skill level I realise that there is a little more work to do on the body :-) I have a stock of fabric and I bought all the gear to infuse some time ago so the additional cost compared to prepreg is minimal. If I make the mould to cope with prepreg heats I have options. How well does the fabric adhesive stick the cloth to the mould, as the trickiest part seems to be the nose section?
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Steve Broad
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+xI would agree that by the time you have added flanges and stiffened the mould sufficiently then you would need a multi-part mould to get a release. You will struggle to make a dimensionally accurate or a part that easily lines up if you keep the mould or part too thin.. Cheers Warren.. Nice to put a face to a name :-)
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oekmont
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Two things:
1st: I really want to help you. If the parts you have done so far are like 20% skill level, this would be like 90%. It is even harder than you can imagine. At least in infusion. I just want to save you from using 400£ worth of material to get a part you are not satisfied with. Be live me, I went that path. Better make slow progress with your part complexity. Said so, prepreg is definitely the easier way for a part like this.
2nd: As you realised yourself, the double wishbone chassis is not nearly as smart as everybody says it is. When it comes to torsional stiffness, the elan has to rely on the additional resistance from the body. By converting it to a flip front, you pretty much cutting away all of its moment of inertia.
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oekmont
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I rewatched the photos. My point about the moment if inertia might not be that important, as the front will be entirely ahead of the front axle.
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Steve Broad
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+xTwo things: 1st: I really want to help you. If the parts you have done so far are like 20% skill level, this would be like 90%. It is even harder than you can imagine. At least in infusion. I just want to save you from using 400£ worth of material to get a part you are not satisfied with. Be live me, I went that path. Better make slow progress with your part complexity. Said so, prepreg is definitely the easier way for a part like this. 2nd: As you realised yourself, the double wishbone chassis is not nearly as smart as everybody says it is. When it comes to torsional stiffness, the elan has to rely on the additional resistance from the body. By converting it to a flip front, you pretty much cutting away all of its moment of inertia. I am always happy to listen to others, so thanks for the advice.. If the infusion attempt goes wrong it is a few hundred pounds, with the prepreg it is over a grand! However, the jury is still out on the way forward as there is no rush. The body of the DHC adds almost no torsional stiffness to the chassis, which is why I fitted a full roll cage, from suspension uprights to suspension uprights. It is pretty stiff now :-)
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oekmont
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If prepreg goes wrong, you could likely fix it with a fair amount of 2k filler (If you are still planning to paint it). At least if you get the bagging right, for wich you have several tries for a few pounds.
Infusion can result in parts, wich are half unimpregnated.
It could be infused, no question. But it is a complicated part. Prepreg scales more user friendly when it comes to bigger and more complex parts.
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+x+xTwo things: 1st: I really want to help you. If the parts you have done so far are like 20% skill level, this would be like 90%. It is even harder than you can imagine. At least in infusion. I just want to save you from using 400£ worth of material to get a part you are not satisfied with. Be live me, I went that path. Better make slow progress with your part complexity. Said so, prepreg is definitely the easier way for a part like this. 2nd: As you realised yourself, the double wishbone chassis is not nearly as smart as everybody says it is. When it comes to torsional stiffness, the elan has to rely on the additional resistance from the body. By converting it to a flip front, you pretty much cutting away all of its moment of inertia. I am always happy to listen to others, so thanks for the advice.. If the infusion attempt goes wrong it is a few hundred pounds, with the prepreg it is over a grand! However, the jury is still out on the way forward as there is no rush. The body of the DHC adds almost no torsional stiffness to the chassis, which is why I fitted a full roll cage, from suspension uprights to suspension uprights. It is pretty stiff now :-) Yeah, the more I look at it, especially the nose area, prepreg seems the less hard (rather than easier) option. And, yes, I still plan to hide the carbon :-)
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MarkMK
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Have you the facilities to cure the pre-preg...either a temperature controlled oven or access to an autoclave? If so and you are planning to paint the panels afterwards, then this feels like the right way to go as you'll have the advantage of having a fabric that can be applied to the mould relatively easily and the final surface finish might not be a big deal. You'd also have the in-built heat tolerance ideally required for a bonnet. If going down this route, then look to build in as many splits in the mould as you need to gain a stress-free release, as any visible signs of the mould can be flatted back afterwards However, infusing that mould is indeed possible and using a good spray tack will allow you to lay in cut sections easily also. I use Cytec's Aerofix 3 all the time and, used sparingly, it tends not to leave any residue when used with EC's infusion resin (although I use an in-mould coating on most parts). Infusion will also offer you a greater choice of fabrics and also allow you to build in various core materials if added stiffness is needed (although at the cost of a little additional weight). Be aware, though, that an elevated post-cure would likely be needed to help cope with the under-bonnet heat and this will, most likely, lead to some shrinkage which will show up as unevenness on the surface. This would likely be even more apparent if using a product like Soric, where the matrix tends to show through on all but the thickest laminates. This can be addressed by flatting the panel down afterwards and clear-coating/painting, however. An infusion would also likely need the mould to be envelope bagged if it's a multi-part one, which can make controlling the flow of resin to the outer section of the mould tricky. If the part's a one-off, then not so much of a concern. Conventional bagging is possible, but sealing such a large mould would take some skill and thought in the mould design.
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Steve Broad
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+x
Have you the facilities to cure the pre-preg...either a temperature controlled oven or access to an autoclave?
If so and you are planning to paint the panels afterwards, then this feels like the right way to go as you'll have the advantage of having a fabric that can be applied to the mould relatively easily and the final surface finish might not be a big deal. You'd also have the in-built heat tolerance ideally required for a bonnet. If going down this route, then look to build in as many splits in the mould as you need to gain a stress-free release, as any visible signs of the mould can be flatted back afterwards
However, infusing that mould is indeed possible and using a good spray tack will allow you to lay in cut sections easily also. I use Cytec's Aerofix 3 all the time and, used sparingly, it tends not to leave any residue when used with EC's infusion resin (although I use an in-mould coating on most parts).
Infusion will also offer you a greater choice of fabrics and also allow you to build in various core materials if added stiffness is needed (although at the cost of a little additional weight). Be aware, though, that an elevated post-cure would likely be needed to help cope with the under-bonnet heat and this will, most likely, lead to some shrinkage which will show up as unevenness on the surface. This would likely be even more apparent if using a product like Soric, where the matrix tends to show through on all but the thickest laminates. This can be addressed by flatting the panel down afterwards and clear-coating/painting, however.
An infusion would also likely need the mould to be envelope bagged if it's a multi-part one, which can make controlling the flow of resin to the outer section of the mould tricky. If the part's a one-off, then not so much of a concern. Conventional bagging is possible, but sealing such a large mould would take some skill and thought in the mould design.
Cheers, Mark. I have just built an oven big enough to take the bonnet -1.8m x 1.8m x 0.9m, with thermostacially controlled temperature so cooking isn't a problem :-) The car is away being wired so I have plenty of time to come to a decision on whether to infuse or prepreg. Even when I start I will build the mould in materials that are suitable for both methods. The final result will probably end up crap as, as oekmont points out, I lack the necessary 90% skill level but I will give it my best shot :-)
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oekmont
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The problems with difficult infusions are:
It is much harder to get a frayless finish in places where you need to cut the cloth. With painting, this isn't a problem for you.
The flow media is much harder to get into complex shapes, than everything used in a prepreg process.
on complex 3d shapes the resin front easily flows around some higher or lower shapes, trapping some voids, resulting in pinholes or (In worst case) unimpregnated areas.
Split mold infusion is a different topic on its own.
If you are careful during the layup, get the bag tight into the corners, and follow the heating instructions, prepreg parts always come out nicely. I never had a failed part.
Infusion is in comparison an art. The process allways has to be adapted to the shape of the part. To get it right on first try, you need experience.
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