Quick question: Vacuum forming with mold making

General Composites Discussions Composites Talk
#1

Curious question, have been researching carbon fiber projects and mold making and know there is a huge market in the automotive aftermarket field. I see folks doing halfassed C.F. overlays on their door panels and little window switch panels etc, but I know those panels have little mounting nubs and crap to fit/secure that make doing an entire panel difficult.

So my question to the great collective group, could I use a window switch panel(for example) and use it as a base to place a fiberglass mold and subsequently C.F. while using a vacuum forming machine to make sure the fiberglass/C.F. get in all the base panel’s nooks and crannies?

If y’all think it may work then I’ll do a write up!

Thanks!!!

#2

Anyone??? Help?

#3

vacuum forming machine? You would probably use a vacuum and vacuum bag. A vacuum forming machine is made to heat a plastic sheet then suck down over a plug to make a shape.

Not sure exactly what you’re asking about.

Yes you can make a mold of the original part. Then you would use vacuum bag to make the part in the mold.

#4

I’m meaning the vacuum forming machine with the plastic to make the fiberglass conform to every nook and cranny to make a mold. Will just a vacuum and bag be enough to form the fiberglass exactly the shape of the mold?

#5

I doubt it would work with a regular woven fiberglass / wet layup because the fabric is not even close to being capable of an air tight seal before it has cured. You could breath through uncured woven fiberglass or carbon fiber.

If you use a vacuum bag over the back of the cf, that would work (in a female mold). It can’t go over the front of the part, as it would in a vacuum forming process that uses a male mold because the bagging film would leave a rippled imprint on the part’s surface.

There are companies that sell thermoforming composites but nothing that would result in a cosmetic 2x2 twill cf part.

At one point I considered using a vacuum forming machine to make quick molds with the intention of reinforcing them (from the back) with a stronger material. It didn’t work very well for me.

I would suggest using the original part you want to copy to make a regular rigid mold (out of carbon fiber or fiberglass). You can then use the vacuum pump from your vacuum forming set-up for a regular vacuum bagging process (assuming it uses a proper vacuum pump and not a diy vacuum cleaner job).

If you plan to experiment with the vacuum forming machine for this, remember the crucial point that carbon fiber and fiberglass have zero stretch. They behave nothing like semi melted vacuum forming plastic that stretches easily over complex shapes when it’s hot.

What is the problem with making a regular female mold?

#6

It sounds like you want to just use vacuum to get the material to conform to the mold surface, filling all the voids and leaving a “perfect” finish. That won’t work for various reasons. Vacuum will not make the material “conform to every nook and cranny”. Vacuum alone does an excellent job of pressing the fiber against outside corners but not so much on inside corners. It won’t pull the fiber down into the inside corners, you need to put it there before applying vacuum.

#7

Also, for more complex shapes, most of us need to either cut the cf fabric into the right shape (using s template) or make strategic cuts over the corners and curves during the layup to enable the cf to conform to the mold shape and stay in place. If this process is forced without the cuts, you’ll just disturb the weave and that costmetic part won’t look so pretty.

Similarly, most people don’t use one piece of cf for each layer if the mold has corners and curves. They would do the lay up with a bunch of smaller pieces for the same reasons.

I have one complex part where I like to use a single layer of 2x2 twill for the surface. To make it work without destroying the weave, I have been using the weblock fabric from Composite Envisions with a compression molding process. My vacuum pump alone is not sufficient to hold the cf firmly into the tightest corners so the cf is sandwhiched between the female mold and a rigid (size reduced) male mold which is weighed down with 200lb of weights before it is placed in the vacuum bag.

This doesn’t mean that vacuum forming has no place in composites though. The cf and fiberglass materials that are designed for vacuum forming typically use chopped strands of cf empregnated with a thermoform resin and then pressed into a flat sheet.

#8

Most people use hand layup to make molds with no vacuum involved. I think the OP is suggesting using vacuum during the mold making process to eliminate voids, etc., but the reality is it would probably result in more voids than hand layup. I think you need to educate yourself more so you understand why molds are made the way they’re made. Or just try it. If you don’t have any experience, that’s one way of getting some.