Newbie questions. Complicated part fabricating.


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svedberg
svedberg
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Hi!

I'm a racing motorcycle nut from Sweden. I have a lot of questions regarding my very first prepreg project, a tank/seat combination for a race bike I've been working on forever, it seems.

The mould is 5-piece design made from the Uni-mould system. The part to be made is a quite complicated shape, fully enclosed by the mould, featuring a LOT of curves, sharp edges/corners and also some mounting points that must be very strong.

At first I wasn't even considering using prepreg, but after having thought long and hard about this layup, I came to the conclusion that no other method is possible. A wet layup would inevitably cause a total mess because of the limited space inside the mould, and infusion would be very tricky as well.

Using prepreg will allow me the time to lay up the fabric very carefully and free of messy resin, and I can prepare and test the vacuum bag until all is perfect.

Now some questions:

The part will be painted, as I'm not a big fan of the glossy carbon look. Therefore, the surface layer weave direction doesn't matter a lot to me, appearance-wise. Since the part is very complicated, I am thinking about cutting smaller pieces of the surface layer prepreg to increase  my chances of getting the fabric perfectly tight into all the sharp edges/corners of the mould, in order to avoid bridging problems.  After that, I'll be cutting the bigger pieces and continue normally with the layup. Thoughts on this approach?

The mounting points will need to be very strong. I am thinking of bonding aluminium/titanium inserts in these areas. Even so, the laminate needs to be considerably heavier/thicker around these areas. I am thinking of making these areas in two steps: At first, just laminate the whole part using 1  215g surface layer, and 2 450g layers. Then, after curing the part continue to build up additional strength around the mounting points, adding maybe 5 more layers of 415g and curing again.  Am I thinking straight here?

Hoping for opinions from those more experienced!

Thanks/

Lasse Svedberg

Racing motorcycles!
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morepower
morepower
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Hanaldo is right.. Laying up with larger sections will be the best for strength. I have to use 2 sections on each side of the surface layer but it is also joined where I add extra strength too. I would say you need to debulk at least twice once with the surface layer then after every 2 or 3 backing layers. As for inserts you can bury them into the pre-preg during lay up and this is a good way to get them deep inside the part and build outwards spreading the load better and not needing to bond them later. 




Not got experience with the material you are planning to use so cannot say how good or bad it would be. But as it seems to be a 245 gram material I would say you will need some areas with quite a few layers to get the strength you need but it is a good thing as you can make many changes in the material orientation to give it strength in as many directions as possible. Mine is also a fuel cell so the tank has a base and carries fuel. The tank base adds a lot of strength too. 
GO

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