Body Work Molds

[jonesy112]

I have a question regarding what teams are using to build the molds for their bodywork. I have heard of many people using some type of foam, but i dont know what specific type of foam could be used. Please reply with any knowledge that you may have. Thanks in advance.

Michael Jones
michaej@clemson.edu
www.michaeltjones.com (http://www.michaeltjones.com)

[Lyn Labahn UW-Madison]

We usually use a skeleton out of plywood to make up the main structure, and then fill the voids with a two part expanding foam, cover it with bondo, sand to the desired shape, and then prepare the surface for pulling a mold off of it. Word to ya mutha,

2002/2003 Team Leader

[Dominic Venieri]

In the past we've used 2" pink insulation foam boards that we buy at Home Depot. The stuff is sold in 2' x 8' sheets and we hot-wire-cut out cross sections of the body. You can't use Bondo or anything like that on it... you have to fill it with joint compound. There are other, better, closed cell foams that can withstand bondo. Take a look at Aircraft Spruce or Wicks Aircraft Supply. They sell a variety of foams for composite purposes. This year we are using Corecell foam - can't wire cut it, but you can use bondo.

www.formularpi.com (http://www.formularpi.com)

[Michael Jones]

...another Michael Jones doing body work? Guess it's in the genes.

We too use insulation foam, although the two-part foam model works fine as well. I find that the two-part foam is a bit harder to sculpt (tends to break off easier) but with ample supplies of bondo, it's OK.

As for bondo eating insulation foam, we've found it really doesn't - at least not in any appreciable manner. Does cause a bit of a soft spot that might sink the foam core by a millimeter or so, but body work carries with it a surprisingly large margin for error, so I've found it more efficient just to slap more on and go with it.

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Cornell Racing
http://fsae.mae.cornell.edu

[Dominic Venieri]

Another reason we are using the closed cell foam is so we can vaccum bag and oven cure pre-preg, instead of wet-lay. (the pink foam tends to crush under vaccum)

www.formularpi.com (http://www.formularpi.com)

[Ben Beacock]

What do you use for a 'hot wire'. Can this be rigged up or does it require specialty stuff. I checked the Wicks Aircraft place and they had a voltage regulator, but no wires or anything.

Ben Beacock
Chassis Design and Technical Coordinator
Gryphon Racing - University of Guelph

[Dominic Venieri]

to make a hot wire cutter, you build a frame (a flat base with 2 uprights), string a wire (we use Ni-chrome) between the uprights. keep tension on it with some sort of spring (the wire will stretch as it heats up, and want to sag, so you need to take that slack out somehow). you then hook up power to both ends from the regulator.

You can do a Google search for "foam hot wire cutter" and get lots of guides to building one.

www.formularpi.com (http://www.formularpi.com)

[EliseS2]

I have not noticed bondo eating into the pink high density insulation foam. Our body moulds from two years ago had about two inches of bondo layed up on it (the members that did it are no longer with us, thank god). They were still the same shape.

We have also vacuum bagged panels with the pink foam and there was no appreciable shrinkage.

[Scot Costello]

I've seen a few teams using Owens Corning "Foamular" Insulation.
Sandwiched together and then "shaped".

[Scott Wordley]

We have our body plug CNC machined from polystyrene foam (the white stuff used for packaging), then we get it sprayed with a polyurethane coating and finish it by hand. If you want to use foam for your plug the best type would be urethane foam (usually green). This stuff is really easy to shape (but very messy) and you can use body filler on it.

What the hell is bondo?

Regards,

http://www-personal.monash.edu.au/~fsae/sig.jpg
Scott Wordley & Roan Lyddy Meaney
Monash FSAE Wingmen
http://www-personal.monash.edu.au/~fsae

[Brent Howard]

Bondo is the same stuff that you use I think (green goop). It's just a filler material....lots of very bad auto body shops use it to fill in any dents you get.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Nigel Lavers]

We use a high density (density of 80... not sure what the units are) polyethylene foam in 3" thick flats that are 2" x 8" long. We mill out all of the shapes and then glue them together. Milling out after you glue causes problems and creates a lot more sanding...

We get all of our foam donated from DOW Chemical... they are extremely great to us giving us twice as much as we need.

Nigel Lavers
FSAE, UofAlberta

[Michael Jones]

Our is incredibly sketchy but homemade and thus cheap. Two planks of wood with a crossbeam; one wire with a couple of screw hooks to regulate tension, the other is a hotwire (I assume Ni-Chrome as mentioned; it's sold as hotwire at aircraft spruce and other composites joints...) We used to have a dedicated power supply but it fried. We now use the battery charger at mid-range setting, works just fine.

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Cornell Racing
http://fsae.mae.cornell.edu

[Angry Joe]

http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wNTAwMTE2czQxM2RmZDMxeTU0MQ%3D% 3D

Insulation Foam

http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wNTAwMTI2czQxM2RmZDMxeTU0MQ%3D% 3D

Spackle

http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wNTAwMTM2czQxM2RmZDMxeTU0MQ%3D% 3D

Latex paint (seals the spackle but is a pain to sand)

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Michael Jones]

...to build molds around the frame like that. Our car usually is driving naked during the time body construction goes on. A bit harder to do, but doable with some attention to key dimension in sculpting. We more or less eyeballed it last year, and was only off by 1/4" or so. Measure elaborately with templates in 2001, and were off by light years. Way fat. Nice aesthetic, but a waste and a pain to mount.

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Cornell Racing
http://fsae.mae.cornell.edu

[Angry Joe]

I don't see us having much of a problem with mounting the body, we have it sectioned and test-fitted already.

As far as being a waste, you can engineer your car to perfection but it will still be judged by most people on appearance. The best way to convince people to support and/or give money to a car built by a bunch of students is to make sure it doesn't look like it was made by a bunch of students...

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Angry Joe]

On second reading Mike, were you talking about your body or ours being a waste? Sorry if I misread what you were saying.

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Michael Jones]

the 2001 one at least...The 2002 was pimpy.

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Cornell Racing
http://fsae.mae.cornell.edu

[MikeWaggoner at UW]

If you just build a monocoque, you don't really need much of a body...

Western Washington University FSAE
dot.etec.wwu.edu/fsae

[Ben Beacock]

Which type of 'foamular' did you use? there is
foamular 150/250 and foamular CW 15/25 on their website.

Luckily enough, there is an owens corning plant in town and they're willing to supply materials if we let them know what we need.

Also, their resins engineer suggested we use a spray on 'gel coat' after laying the fibreglass/resin so that it fills the dips and makes sanding alot easier. Anyone tried something like that?

Ben Beacock
Chassis Design and Technical Coordinator
Gryphon Racing - University of Guelph

[Andy K]

We're going with the 2x8 sheets to make our plug and a hardening layer so that there are fewer imperfections, hopefully resulting in a smoother finish. To those that glued their sheets together before milling, what sort of problems did you experience?

McGill Racing Team - Body Design

[Howard]

Do you guys have any issues with toxic gasses from the hotwire and home depot type foam?

[Michael Jones]

...I have no issues with toxicity of various composite materials, but I´m so resilient to such things I´m thinking I may be part-cockroach. Others complain. Good ventilation and masks are a good idea.

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Cornell Racing
http://fsae.mae.cornell.edu

[Richard Lewis]

Michael, more than likely you've allready killed off anything in your body that might be annoyed by such things. http://fsae.com/groupee_common/emoticons/icon_wink.gif No mask... "You've got a get a FEEL for the resin" http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

-------------------------
UVIC Formula SAE Team
http://members.shaw.ca/drax77/UVICFSAEcar.jpg
http://uvic.fsae.ca

[Nigel Lavers]

Andy,

By glueing the foam together after it's milled (we use 3" thick foam rather than 2") you'll just save some sanding time.

Sanding a glue line is quite tedious and often results in more after work (bondo-ing etc). We just use some alignment pins from 3" sheet to 3" sheet and then glue it all together after milling.

however, we have to finalize our body design before any of that can happen... http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Nigel
FSAE, U of Alberta

[Andy K]

In that case, gluing our sheets shouldn't be a problem for us. We are planning skim our plug with some sort of material to make a more consistent and harder surface.

Andris Kanins
McGill Racing Team - Body Design

[HB]

Here at Akron, when it comes to body work and molds, you name it, we've tried it. We used to use sheet aluminum. This was faily easy to work with but hard to get rounded surfaces. We also tried thermoforming plastic over male plugs. In theory, it worked, but it was very labor intensive and was hard to get the panels to fit. We started with chicken wire and dryway mud over the frame then layed fiber glass over that. Then we filled the cavities with 2-part epoxy based foam but inorder to get the molds looking somewhat respectable, we had to use 11 gallons of bondo. The heat involed with thermoforming caused the foam and bondo to deform. Next we had a very large log of oak donated to us and Goodyear was nice enough to CNC our molds. That worked very well except that the oak wasn't quite dry so it cracked and warped, so more bondo. This year, we with the help of Trickflow Cylinder Heads, are laying up several layers of 3/4" thick m.d.f. and are cnc'ng the molds again. Instead of plastic we are using fiberglass.

We use the pick foam for our molds for the radiator ducks and then cover them with yet more bondo. The thing you have to watch out for is exothermic reaction of the bondo drying. Bondo won't attact the foam, but the heat melts it.

Just remember, bondo is your friend http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Andy K]

Bondo is not your friend if weight is an issue! http://fsae.com/groupee_common/emoticons/icon_wink.gif

Andris Kanins
McGill Racing Team - Body Design

[HB]

Bondo or any kind of filler is used only to straighten the molds. We do not use it on the body work.

[Angry Joe]

We glue our foam sheets together with expandable foam, which is also good for filling in gaps. It's more of a pain to sand than the insulation foam, but it's managable.

You guys mill your molds? That's pretty hardcore. Our tolerance check is a guy standing on a chair six feet away telling us the left sidepod is still a little bigger than the right.

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Joseph Coady]

Last year we glued our sheets of styrofoam together into roughly a 2X6X3 foot block, and had that chunk milled into a female body mould. Then sanded it down. Then put in the fibre glass. We never used a proper releasing agent so getting it out was a complete bitch. What everyon's saying about sanding glue is correct. Glue is usually much more resistant to sanding than foam, so you end up getting a high ridge where the glue is and a valley on either side of it. Very hard to repair.

Drive It Like You stole It