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Thread: BodyWork thickness

  1. #1

    Question Bodywork issues

    Hi everyone.
    I have searched and couldn't find the answer to these questions. I'd appreciate it if you would help me.

    What is the proper thickness for fiberglass bodywork and undertray?

    How can we split the CAD model of mold so that it can be milled by CNC?, provided that we use polystyrene foam
    Last edited by Farzaneh; 08-06-2014 at 05:31 AM.
    FUM Racing Team
    Ferdowsi University of Mashhad -Iran (2012-2016)
    www.caspianFSAE.ir

  2. #2
    What thickness is required to meet the rules? What thickness is required to meet the functional requirements of those parts?

    How did you create the CAD model in the first place? What software are you using? Surely if you know how to design a part to be laid up in a CNC mould you know how to design the mould for it. If you don't know how the mould design will work then I would suggest that your part design is incomplete/incorrect. If you haven't designed for manufacture you haven't designed properly/ Maybe you should contemplate 3D printing your entire car, that way you don't have to worry about any of these things.
    Dunk
    --------------------------------------------------------
    Brunel Racing
    2010-11 - Drivetrain Development Engineer
    2011-12 - Consultant and Long Distance Dogsbody
    2012-13 - Chassis, Bodywork & Aerodynamics manager

    2014-present - Engineer at Jaguar Land Rover

  3. #3
    Hi Dunk.

    Actually there are no specific rules for body thickness.
    I've worked months on modeling this body. I certainly understand some of ways to make the body and mold. my problem is that i think if i put several
    surfaces in one mold and glued them together ,the body wouldn't be smooth and wouldn't look good.
    I used Solidworks surfaces. and to be honest our finance won't run into 3D printing.
    Last edited by Farzaneh; 08-06-2014 at 04:18 PM.
    FUM Racing Team
    Ferdowsi University of Mashhad -Iran (2012-2016)
    www.caspianFSAE.ir

  4. #4
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    I would say that in general you make your bodywork as thin as possible, because all it is doing is providing sticker space. As for the undertray, I guess you'd have to know how much force it will see and work out some kind of deflection level based on its mounting points with material thickness as your variable.
    I don't really know much about the manufacture of bodywork so I can't say anything about your process there but I'd suggest that most of the common bodywork shapes can be formed with a hot wire on the foam (or some wooden profile cut bits stuck together).
    Jay

    UoW FSAE '07-'09

  5. #5
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    You can make some very simple (and reasonably decent looking) molds by using sheet aluminium formed over wood. Fillet the corners and you ahve bypassed the whole plug manufacture alltogether.

    Do a few numbers for what your plug and mould manufacture will cost you. The required materials are reasonably cheap, but you need a lot of it. Make sure you cost sandpaper, paint / surface finish, plenty of bog, safety gear etc. as well. For some of the bodywork if you can eliminate some steps (i.e. straight to part, or straight to mold) then you can save a lot of time, money, and probably keep everyone a little healthier. For straight to part look at folded aluminium. The ECU guys use thin folded aluminium honeycomb sheet for sidepods (a move away direct mold manufacture). A folded tub means no need for other bodywork, except the nose. The nosecone mold is made directly (i.e. no plug).

    Also do a points analysis of what fancy bodywork gains you in the comp, when compared to much simpler bodywork. Make your car use angled surfaces as a feature (like KTM x-bow) and you can make a good case for it being aesthetically pleasing. Quality of vehicle finish (i.e. every single component) has a larger impact on the aesthetics of the car rather than the lines of the bodywork. All FSAE vehicles are pretty ugly when it comes to body-shapes. Short-squat little snot boxes with high roll-hoops. No amount of swooping styled lines will save that. But they look good (or at least purposeful) overall when finished well.

    Kev

  6. #6
    Quote Originally Posted by Farzaneh View Post
    Actually there are no specific rules for body thickness.
    I've worked months on modeling this body. I certainly understand some of ways to make the body and mold. my problem is that i think if i put several
    surfaces in one mold and glued them together ,the body wouldn't be smooth and wouldn't look good.
    I used Solidworks surfaces. and to be honest our finance won't run into 3D printing.
    So, if there are no thickness requirements, surely "as thin and light as you can possibly make it" is how thick you should be making it. No? or do you want to add in some functionality, like "not falling apart under vibration", "resist puncture by track debris". Again that's for you to decide.

    I'll be nice and add to Kev's advice. Bent ali sheet for molds is great, lookup Brunel Racing BR14 photos to see side panels on the cockpit made this way, combined with a nosecone from a fully machined tooling block mould.

    For these side panels we used 0.5mm bent ali sheet molds (thicker wouldn't bend easily enough), and 2 ply of 205g/sqm prepreg carbon. The carbon side panels were half the weight of the aluminium sheet, but less rigid. For us, the extra work and time involved was probably worth it, especially for aesthetics. But that actually only equated to a few hundred grams weight savings. If we'd have done all aluminium bodywork, it would probably have only been an extra 3 to 4kg, much less if we'd have done it with wet lay, fibre-glass or just heavier pre-preg. Which if you're struggling for funds, time and know-how isn't that big a sacrifice. You can always make them as body panels and then clean them up and use them as moulds down the line if you've still got time and resources available.
    Dunk
    --------------------------------------------------------
    Brunel Racing
    2010-11 - Drivetrain Development Engineer
    2011-12 - Consultant and Long Distance Dogsbody
    2012-13 - Chassis, Bodywork & Aerodynamics manager

    2014-present - Engineer at Jaguar Land Rover

  7. #7
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    Farzaneh: It is impossible to give any specific answer to your question as it contains almost no information at all. You didn't even tell which material you plan to make your bodywork from. As you already correctly said, there is nothing specific about the wall thickness of the bodywork in the rules. That means, it is one of your design choices. If you have done any sort of aerodynamic design, you want to parts to be stiff enough to be able to work as planned. On the other hand you want them to be as light as possible. You also want the surface to look nice. And so on, and so on.

    In general it is much easier to get a good surface quality if the wall thickness is not too thin. It depends very much on the geometry which wall thickness will give you a proper stiffness. If you have a lot of small radii in your shape, the part will be quite stiff with only a very small wall thickness, large plane or nearly plane areas will need more wall thickness to be stiff.

    The question about how to cut your CAD model, I do not really understand. You have to decide yourself how many parts your bodywork consists of. Again a traidoff between how quick can it be removed vs. how smooth does it overall look.

    How many moulds you need for the parts again depends on your design. If it is very complex you might need multiple moulds to be able to get it out of the mould after curing.

    If your task is to design a bodywork it is not only about designing a nice shape. As with every system of the car you have to analyze what the requirements are and how you priorize different design goals BEFORE even start your CAD program as this will influence you result.
    Rennteam Uni Stuttgart
    2008: Seat and Bodywork
    2009: Team captain

    GreenTeam Uni Stuttgart
    2010: Seat and Bodywork / Lamination whore

    Formula Student Austria
    2012: Operative Team

  8. #8
    0.012" thick (0.3 mm) sheet steel is REALLY easy to form and you'll learn a lot about the flanges and bends needed to make thin sheet metal parts work (as in a production car). You can weld it to your steel tube frame if you're good at TIG.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  9. #9
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    You can also use 0.25mm toughened aluminium sheet. It is used on aircraft wing skins. Great stuff, we used it on the early UWA spaceframe cars. Can cut it with scissors, very easy to fold. We found it much better for flat panels than making fibreglass or carbon sheets.

    Kev

  10. #10
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    We also used the plastic heat shrink plastic used on model planes for some panels. Repairable is sliced, pretty resistant to anything but sharp edges. I would say I haven't heard of anything thinner or lighter than that.

    The aircraft fabric with dope was reasonably common at one point, but I haven't seen it for a while.

    Kev

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