Vacuum Bagging Body Molds - male / female ?!?

[johnnySV]

I am curious what percentage of teams are using male vs. female body molds, and what some nuiances might be working with either. I imagine that the female molds require more work initially (usually made from a male plug mold) but result in a cleaner product with less finishing required.

Are there tricks to using female molds when vacuum bagging fibreglas ?? My experiance has been restricted to male molds, and quite limited at that, but I imagine that it may be more tricky to get the release film / bag materials to conform to the contours of, say, a nose cone. What kind of large polyethelene material (and what kind of sealing technique)can be used to create the 'bag'?

thanks,

[johnnySV]

I am curious what percentage of teams are using male vs. female body molds, and what some nuiances might be working with either. I imagine that the female molds require more work initially (usually made from a male plug mold) but result in a cleaner product with less finishing required.

Are there tricks to using female molds when vacuum bagging fibreglas ?? My experiance has been restricted to male molds, and quite limited at that, but I imagine that it may be more tricky to get the release film / bag materials to conform to the contours of, say, a nose cone. What kind of large polyethelene material (and what kind of sealing technique)can be used to create the 'bag'?

thanks,

[Didier Beaudoin]

We're using the male plug/female mold technique this year. Of course it's longer but when well done, it gives the best finish. No bondo is needed on the body itself if the female mold is well finished.

As for vacuum bagging, there's no real difficulty in making one for a female mold. You just have to make sure you use enough bagging film for it to go in every corner of your mold when you turn on the vacuum. Also, I don,t recommend release film for complex forms, it kinda messes up with the finish as it is almost impossible to position without any wrinkle. Just use many layers of wax or some freekote. You can also use PVA, but be aware you finish won't be as glossy. You should use vacuum bagging sold by composites company, although I'm not aware of the exact material. Maybe some cheaper bagging could do the trick, but you have to ake sure it won,t react with the resin.

As for sealing technique, hi-tack sealer is the only option. Put some masking tape strips on the edges of your mold to make sure you get non-contaminated areas for your sealer to adhere. Try not to drop any resin on the sealer, I can tell you it won't stick anymore afterwards, and it will be a mess to seal the bagging.

I hope everything's clear.

[Mike Cook]

Male pieces are easy to sand. Female pieces are tough. It's best to make the male plug perfect, then take a mold off of that. Then when you lay up your part, your finish will be perfect. Experiment with laying parts up by hand, it isn't that hard and requires a lot less tooling than vacuum bagging.

[Big D]

I agree with the above. A male plug, then a female mold, is the way to go, and make it as perfect as you can at each step. Vaccum bagging shouldn't be needed for wet layup glass or carbon.
I used the PVA (actually I was not up to applying it myself, but another guy was more of a PVA ninja than me, and got it working, the stuff is water based, and you are applying it over mold release wax.... go figure that it's a tad difficult to apply) ANYWAYS... it's true that the PVA will give you a bit of a pebbly texture on the part, but nothing a coat of primer can't fix.
I am interested, for the teams who used no PVA, how much, and what kind of wax did you use, and were there any problems with it letting go from the mold?

[James Waltman]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Big D:
Vaccum bagging shouldn't be needed for wet layup glass or carbon. </div></BLOCKQUOTE>

What makes you say that? I don't agree with it at all.

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by James Waltman:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Big D:
Vaccum bagging shouldn't be needed for wet layup glass or carbon. </div></BLOCKQUOTE>

What makes you say that? I don't agree with it at all. </div></BLOCKQUOTE>

I don't agree either... Vacuum bagging gets the extra resin out of the part, and thus lowers the part's weight without changing its mechanical properties. It's also useful to make sure the layers of composite stay in place and that there are no space between them.

[gug]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Didier Beaudoin:
Vacuum bagging gets the extra resin out of the part, and thus lowers the part's weight without changing its mechanical properties. </div></BLOCKQUOTE>

doesnt a higher fibre/matrix ratio also give greater strength? depending on the fibre/matrix type, i think there is an optimal value of fibre/matrix ratio that gives maximum mechanical properties?

if thats right (im 90% sure it is), then a part that has been vacuum bagged (or had some sort of compression) will not only be lighter but will also be stronger than a part that uses the same amount of carbon fibre but just a wet lay-up technique.

of course, i could be getting mixed up with strength to fibre weight figures and strength to final composite weight figures...

anyways, you can get away with not vacuum bagging a body mold (we have, and got voted the best looking car there!). i would say its worth it if you could find the time though.

oh yeah, if you are getting your resin from a boat manufacturer (or anywhere else for that manner, but boaties always have this problem), check the data sheet on it. a lot of resins will have a glass transition temperature (Tg) or a heat distortion temperature (HDT) (not the same thing, but similar) of about 40 degrees C. while its not too noticable when they are mounted to the car, if you plan on getting the parts painted and then getting the paint baked on in an oven, 40 degrees C HDT isnt good enough and the part will seriously distort. thats what happened to ours and they had to have the paint baked on at a lower temperature.

btw., what sort of paint do you guys use on your shells? we had 2-pack automotive paint, but i think it actually weighed a fair bit and there might have been lighter options.

[Big D]

Vaccuum bagging is NICE, but is not strictly needed. It does, however, provide some advantage, although in a non structural body application, you'll most likely be fine without said advantage.
So, if you don't have the wherewithall/equipment/facilities, or if this is your first time, don't worry about it. Squeegee as much resin out of the cloth as you can, and be happy. I had never done a body before, and that's how I managed. If you have more experience/resources, by all means, bag it, if not, it is a step that you can survive without.
Another great way to reduce weight is to use 'micro-balloons' in your resin. These are TINY hollow spheres, and you pour a bunch into your resin, so your resin goes further, with less weight.

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by gug:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Didier Beaudoin:
Vacuum bagging gets the extra resin out of the part, and thus lowers the part's weight without changing its mechanical properties. </div></BLOCKQUOTE>

doesnt a higher fibre/matrix ratio also give greater strength? depending on the fibre/matrix type, i think there is an optimal value of fibre/matrix ratio that gives maximum mechanical properties? </div></BLOCKQUOTE>

Yeah, you're right.

[Dr Claw]

Again, Vacume Infusion is the way to go. no wet layup at all, no fumes, best quality parts short of an autoclave. its a crapshoot the first few times, unless its a flat dashboard panel, but it is nice. thats how this was made (http://fsae.com/eve/forums/a/tpc/f/412600868/m/66710672411) and its also how i do our dashboards, body panels and other composites. carbon, fiberglass, carbon/kevlar, it all works pretty well.

[gug]

hey Dr. Claw, ive been looking at vacuum infusion, but im pretty inexperienced and thought that it would be too hard to learn (get over the "crapshoot" time u were talking about).

how long did it take you/how much did it cost you to learn?

[Dr Claw]

wow, i thought i was like a cement anchor to any composites thread....they always seem to sink to the bottom after i post in them.


well, like i said, flat parts are fairly easy. you have your vacume source (make sure it runs the width of your layup), and then accross your part you have your resin source (also running the width of your layup) and draw resin accross your dry fibers. it is really pretty idiot proof, as long as you seal. the through-bag connections are sorta tricky, as is just sealing to the flange of your part in general...but its not that bad; just dont pull resin until you have a definate seal and you wont waste any materials.


in doing something like a seat, or the body though, you need to gauge how well your resin will flow arround the curves. its all about the pressure differences as you pull resin farther away from a resin line. its sorta tricky..but doable.

start off on a flat part though, you'll have a kick ass dashboard panel, or maybe a headrest mount if you core your laminate with some 1/8 inch foam or something. try with fiberglass first too, so you dont waste expensive carbon.

now go make some parts http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Travis Garrison]

It might be worth mentioning a few of the basics to the total newbs...

The obvious stuff...no bleader/breather! the bag sequence should be something like fabric, core (obviously no honeycombs, unless foam filled), fabric, release fabric, transfer medium, bag.

Fiberlay.com sells everything you'd need...I've also used screen door screens that you can buy at the hardware store for the transfer medium...so like Dr. Claw said, its not rocket science.

Also, you need VARTM specific resins...for fiberglass you can thin out polyester with styrene, but epoxy is a different story so make sure you get the right resin...

Along with this, different resins have different viscosities (obviously) so just becuase one laminate worked with polyester is no garuntee that it will work for a given epoxy. You'll find that you can only flow a given resin so far...if you're good you'll know that point and use additional inlet ports that you can turn on once your flow line stalls out..the point being do a test run with the materials you intend to use before you risk a valuable part.

Also, for the sake of your vacuum pump make sure you have a LARGE catch pot between your laminate and your pump...

I guess the one other warning I have is that like Dr. Claw said leaks are murder on this type of layup...especially if they are located around the resin inlet side...so be methodical when laying down the bag.

Travis Garrison

[Dr Claw]

i guess i didnt put the link in this post...i must have posted it in the OTHER carbon fiber post that sank right after i posted it.

anyways, here is a good how-to guide for vacume infusion. or VARTM.

http://www.fibreglast.com/contentpages-Vacuum%20Infusion-316.html


by the way, i use breather cloth under my vacume source. it delays the resin from entering hte vacume source before the entire part has wetted out...which is good because i usually need the extra time http://fsae.com/groupee_common/emoticons/icon_smile.gif

[da boos]

hey dr claw
making 4 seats of poor quality does not count as 4 parts on 4 cars, nor does designing an unaerodynamic body for a race car count as engineering. thats more like decorative design.

Inspecta Gadget

[Dr Claw]

ya know what, i think i know you. i probably see you every day, but if you care to hide behind your alias, go right ahead. i have no problem with what you have to say if thats how you go about saying it.

[da boos]

hey freshman
you couldnt have seen me everyday you haven't been in the lab more than 4 times this year. plus last time i checked schoolcraft does not have a formula team. i'm sorry about the aerodynamics comment i wouldn't expect someone who didn't pass calculus to understand it anyway.

Penny

[Dr Claw]

so is any of this necessary at all? i admire your cowardly attempts at attacking me, keep hiding if you dont mind. keep spouting off too, its no reflection on me; you just wont see any more responses as this forum isn't where you take care of this kind of stuff.

[nathan s]

Another thing to remember with your fiberglass molds is to make sure you use dense foam with a high melting point (like the blue and pink house insulation foam). We made the mistake of using polystyrene (styrofoam) last summer and the heat from the resin made the mold shrink about an 8th of an inch. Thus making the body really wavy and ruining about 3-4 weeks worth of work (1st time using fiberglass).

Styrofoam can work, it is just very difficult keeping the compound that you use to smooth everything out thick enough to keep the mold from melting. The insulation foam is also better because it gives you a color that shows through your compound when the compound starts getting thin.

[James Waltman]

Nathan,
Are you suggesting that the pink home insulation foam is better than Styrofoam? What do you think that stuff is made from? (Hint) (http://secure.owenscorning.net/Portal/uploads/document/20050208/21528_01_D_1.pdf)
http://www.owenscorning.com/around/insulation/products/images/oc13364-large.jpg

[nathan s]

If I am not mistaken, the pink and blue stuff has different properties than the white stuff used for packing. I am pretty sure that the pink and blue stuff can't be cut with a hotwire because everyone that I know who has used it cut it with various forms of knives and saws.

[James Waltman]

I suspect that the properties are largely the same. The home insulation stuff is very easy to cut with a hot wire cutter – we have done a lot of it here. It starts to melt around 220?F.

We use High-Density Polyurethane foam (http://www.generalplastics.com/products/product_detail.php?pid=19&) from General Plastics for a great deal of our tooling. It's good stuff – easy to machine, sand, finish, and paint.

[Travis Garrison]

A word of warning on that insulation foam...if you can crush it with your fingers its probably not suitable for vacuum bagging...your part won't be the shape you intended...

And I've seen lots, and lots of the blue and pink polystyrene foam get cut with a hot wire...definetely possible...just a little on the nasty side of mold making...

The other thing to keep in mind is that you can't really sand that insulation foam...what I'm getting at is use proper tooling foam if you can...

-Travis

[Denny Trimble]

Where did they get that picture of our new car?
http://www.generalplastics.com/uploads/product/FR-7100.jpg