carbon/kevlar mustang please help.

[robinairtechsupport]

hi, i am building a car, been working on it for several years, and this is my problem... i made a frame and cage, and i am planning on droping the body over it, as a nonstressed member, so i cut EVERYTHING out of the car, all that is left is literally the skin, meaning the outside layer of sheet metal, and the fender and door supports, as well as the cowl, but no floor, firewall, etc. the chasis will contain everything needed for the car, and could probably be driven like that, however i want it to look like a car, not a dune buggy. its a mustang II, and i was wondering about carbon/kevlar body panels, and mold making. my plan is to use the actual body as a model, as the body work is done, complete w fender flares, body mods, sheet metal etc... could i use a brush or spray on rubber mold making substance on a waxed primer body, with a release agent then lay fiberglass sheet or mat over it with resin to add stiffness to make a set of negatives so i could lay carbon/kevlar inside the molds with resin and vac bag them to make body panels, wich i could then attatch to an aluminum frame so my whole shell would be extreemely light and strong. impact/weather/uv resistance is not a factor, as i have uv resin and a garage available, and its strictly a race car. could i re use the molds to make more than one body? would it work?

 

[patprimmer]

Rubber moulds will not hold their shape in such large parts.

You can make fibreglass moulds of original parts, but you need to allow for undercuts so as to be able to separate the mould and the part or pattern.

You will get mould shrinkage, so the mould ends up smaller than the pattern and the part will end up smaller than the mould.

Normal practice is to cut the mould in appropriate areas and stretch it then insert material in the gap created by the stretching. Also of course reinforce behind the joins. Hand blending is required to smooth out the joint.

The accuracy of the reproduction and final appearance and size will depend on how many cuts, where they are located and how well you match and align the pieces, and how well you blend in after joining.

It can be reused many times if you do it right AND if you are careful when you prepare the mould and when you eject the parts.

Regards

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[robinairtechsupport]

PATPRIMMER: You will get mould shrinkage, so the mould ends up smaller than the pattern and the part will end up smaller than the mould.

how much smaller? is this uniform shrinkage, or does it have to do with the orientation of the materials? if the shrinkage is uniform enough, shrinkage may be acceptable, as i am basically building a car from scratch. how much will it shrink? i always did want to build something like smokey yunick's 7/8 scale chevelle. would it be a lot? would the shrinkage be uniform? i want to make the whole body, and i can change dimension as much as i want, as this will only be my toy. thanx for the response, and the rubber would be sprayed on the body before i lay the fiberglass for the mold, just to cach the finer details like body lines, then cover the rubber w fiberglass and resin to keep the shape. anyways, i guess thats not a good idea, but shrinkage, to an extent, may be a good thing. thanx, A.D.I
]

 

[patprimmer]

It varies with resin and fillers and curing conditions.

Ask the resin supplier as he should have lots of data. If not get another supplier.

Not knowing the resin or system I think about 2% is typical but this is NOT a reliable number for all systems. If in doubt make test strips and measure.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.