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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
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svedberg
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Here's a picture of the (nt really finished) plug for the part I'm making, by the way. It's the seat/tank part.
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Hanaldo
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Regarding the layup technique, cutting small pieces is fine, but you will be reducing the strength of the part. On a cosmetic item this normally isn't an issue, but your piece does have a structural element which you are aware of. You can make up for this loss of strength by overlapping the cuts with additional reinforcement. This obviously results in a slightly heavier part. So I think decide on what is going to give you the best result. Laying up in one piece isn't always as difficult as you might expect; and by the same token, laying up in multiple pieces may not necessarily be easier either. As for your mounting points, again what you have suggested would work, provided you key the area you are laying additional carbon to allow for good bond strength. That said, I think you can do it in one go, without the initial cure. If the whole part needed to be 6 or 7 layers thick then I would say you couldn't do it without debulking, but when only the mounting points are that thick I think you would get away with it, especially if you use a roller to consolidate it a bit between layers. You might get some pinholes from this, but if you're painting it anyway then you can just fill these.
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svedberg
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Thanks for the reply! Regarding the mounting points: They are some of the most difficult areas of the part to properly get the prepreg well seated into, which makes me think a cured "shell" would be easier to succeed with. If I decide to go this route, do you think covering these areas (which are to be further reinforced later on) with regular peel ply before/inside of the non perforated release film would create a nicely keyed area to get the additional layers to bond to? /Lasse
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svedberg
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I have been offered a great deal from a composites supplier close to where I live to buy an OOA 245gsm twill prepreg called DeltaPreg GG245, using the DT806 resin system. From the product data sheet, it seems to me it woukd be a nice prepreg for my purpose, but I would love to hear from anyone experienced with this particular product. Anyone? /Lasse
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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.
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svedberg
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Thanks Morepower! Very nice units you've got there for the RS250! And very similar to the parts I'm making right now. My "tank" area will house only the airboxand a lot of electronic stuff, no gas there,so basically just a shell, but with a flat flange to join the airbox lower half sitting deep inside the frame spars. Regarding my query about using smaller prepreg pieces for the lay up scheme, I meant for the first/second layers only, not the rest of the reinforcement. Your opinion on my thought of first making a 2-3 layer complete "shell" to be later on strengthened by more layers where needed? About the debulking sequence: please describe the stack of materials you use on top of the prepreg to be compressed into the mould. Do you use perf film or unperf? breather/no breather? Is a very long debulk time to be prefered(overnight)? Do you debulk each part of the mould separately? Any heat at all involved? A lot of Q:s, I know, but yours are easily the closest in design I've seen to the part I'm making, so I guess the moulds and techniques would are also need to be very similar between the two. Thanks! Lasse
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morepower
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Ok I will try and answer what I can below directly..... svedberg (13/03/2016)
Thanks Morepower! Very nice units you've got there for the RS250! And very similar to the parts I'm making right now. My "tank" area will house only the airboxand a lot of electronic stuff, no gas there,so basically just a shell, but with a flat flange to join the airbox lower half sitting deep inside the frame spars. Regarding my query about using smaller prepreg pieces for the lay up scheme, I meant for the first/second layers only, not the rest of the reinforcement. If you mean for the surface and second layer I would still try and use the largest sections of material possible,. Backing can be smaller sections overlapping but for the first couple of layers try and do them in one or two sections. Your opinion on my thought of first making a 2-3 layer complete "shell" to be later on strengthened by more layers where needed? I would say use at least 4 layers over the tank cover section and onto the seat unit where you would sit. Then the seat pad area make at least 7 layers thick and run those layers down to the any possible inserts that would be structural. You may only need to run strips about 50mm wide from the seat pad area but stronger is better and I would run " a rib" of carbon over the widest point of the tank shell which is 30 to 40mm wide and is at least 7 or 8 layers are a strengthener as when i made my upper section and test fitted it before I made the tank base it would try and splay open and would have needed strengthening to make it usable. But the base added a lot of strength so I left it as it was. You risk delamination by adding strength afterwards so make it strong straight away unless you plan on making more of them. About the debulking sequence: please describe the stack of materials you use on top of the prepreg to be compressed into the mould. Do you use perf film or unperf? breather/no breather? Is a very long debulk time to be prefered(overnight)? Do you debulk each part of the mould separately? Any heat at all involved? Debulking. You have two options. One is to debulk exactly like you are bagging for a cure with the breather and release film you plan to use. if you are using a perforated release it can be good as it will allow some trapped air through the perforations. If you are using non perf then use some old release film that has been crumpled up and the creases will do a similar thing allowing air out. I have debulked both with breather on the material face and without using breather. It makes very little difference to be honest apart from on tight areas like a filler cap shoulder where you struggle to push the material hard into the 90 degree corner so in that case I do not use breather on the material face. BUT always use breather cloth on the back of the mould.
Time and heat? I will always allow it to debulk for a few hours but prefer to allow an overnight debulk. Usually if it is overnight I just leave it in the workshop with no heat. If it is for a few hours it can be in the oven at 25 degrees C until you are ready to finish the lay up. I do each section individually so each section is being debulked while I lay up the next section etc. Once the mould has been assembled I will do another debulk with the first couple joining sections getting a few hours to really pull down over the joins. I would say my monocoque would have at least 3 debulking sessions as I do not rush to finish it over one day. I did when I first started out but the results were not consistent and would always have some issues somewhere. Now if it is two or three days from start to finish I dont worry and it makes a better part in the end.
 This is a fuel tank untrimmed and straight out of the mould. They all come out like this now I have slowed down and take my time. Multiple debulks and just loads of care are the key.
 You can see the backing layer does have some small sections placed all over the backing. it all overlaps and may look untidy but the tank is strong.
 A lot of Q:s, I know, but yours are easily the closest in design I've seen to the part I'm making, so I guess the moulds and techniques would are also need to be very similar between the two.
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VVS
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Hi Lasse be great to see the bike finished, I follow your build on 400gb. @ moorespeed, do you need to use those many layers in the seat area? could Lasse make use of a core, nomex etc to add rigidity while keep the cloth count down.
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svedberg
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Morepower: Again, thank you, and thumbs up to you for sharing your hard earned experience, I really appreciate it! I can see a LOT of bagging film in a near future... Just to clarify; So you debulk each mould piece separately, while working on the lay up of other parts? Seems like a good plan really taking your time doing the lay up work. How about the overlapping 40-50mm of prepreg? Do you just let this "excess" material debulk onto the not yet assembled flange of the mould piece? VVS: Yes, it's about time to get this project going, don't you think? I got kind of fed up with the whole thing, so I've been working on other race bike projects for a couple of years now. Even done some racing, actually! /Lasse
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