Folding the composite panels

1 Aug

The chassis of the African Solar Taxi is formed by folding and joining composite panels consisting of polypropylene honeycomb cores with fibreglass skins.

Folding a panel first requires that a shallow groove be routed through the fiberglass skin, along the joint. A heat gun is then used to heat and soften the polypropylene honeycomb, and the panel is then folded to the required angle. Ultimately, the joints are fiberglassed, making a very strong yet lightweight structure.

The first video below shows a joint with the skin removed, prior to heating and bending. The second video, taken by a thermal camera, shows the joint being heated and bent.

 

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5 Responses to “Folding the composite panels”

  1. Stan Koprowski August 2, 2014 at 1:29 am #

    The cutting video was OK but the thermal imaging, while cute, is not very informative although it points out that you should use flame resistant fiberglass.

    • africansolartaxi August 2, 2014 at 7:41 pm #

      Fair enough Stan – we were just mucking around with a thermal camera & thought we’d share it

  2. Tony November 21, 2014 at 12:56 pm #

    Very hmmm. Does the heat affect the integrity of the material ?
    U could try cutting slots along the fold line,using a disk grinder,leaving tabs at each end and some in the centre, acting as hinges. i.e. I ——— ——— ——— I
    The advantages are ——
    U only have to heat the tabs,(Saves heat source,easier and quicker to bend)
    Insert resin into the slots,strengthening the fold and anchoring any gussets U may use.
    I am a boilermaker,and this is how I fold steel plate, when I am working in the bush.
    If U had an attachment facility, I could send some pics.
    Just trying to help,but I don,t know much about polypropylene honeycomb cores with fibreglass skins. —– cheers —-Tony

    • africansolartaxi November 21, 2014 at 1:31 pm #

      Hi Tony, thanks for your interest.

      Cutting slots as you suggest is often used with core materials such as foam or balsa wood. With other cores, such as aluminium foil honeycomb, you can simply crush the core to form the bend. With the polypropylene honeycomb, heating and bending as we have done does not degrade the material. Polyproplyene honeycomb sheets are designed to be formed in heated moulds. Heating and folding gives a stronger joint than cutting; rebonding cut core is difficult because the cells will no longer align properly, and bonding polypropylene is difficult.

      The other important consideration is that the main job of the core is to hold the two skins apart. Most of the stresses are carried by the skins. (Our structural skins bond onto a nonwoven tissue that is thermo-bonded on the surfaces of the honeycomb boards.)

      • Tony November 21, 2014 at 4:05 pm #

        Thanks for the info.I like to learn something new every day.
        . —– cheers —-Tony

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