Question on Tooling

General Composites Discussions Composites Talk
#1

Hey everyone I am planning on making a Carbon Fiber Diffuser cover for a bumper like this. One issue in making a piece like this is that when I take a mold straight off this bumper and then make a part I will have issues with the thickness where it wont fit up against the original bumper because the size of both exteriors of the CF part itself and bumper will be the same exact size. I plan on making the CF cover with 15mils of clear gelcoat and 4 plies of .009’’ material say, 1 ply of 3k plain weave, and 3 plies of 8 oz. which will make a thickness of around .060’’. One thing that I don’t want to use is sheet wax because of the complex geometry of a part like this it would be almost impossible to lay sheet wax down properly. Do you guys have any other techniques that you would use to build up thickness on the actual bumper before pulling a mold off from it.

The fitment would be crucial and need to match up perfectly!

By the way this is my very first post/thread here but not my first time in composites. I have been doing this religiously for 6 years now. Just to let people know that I will understand most terms thrown at me.

#2

I don’t understand why the thickness needs to change when you build the mold. Don’t you want the molded part to be the exact final dimensions of the existing part? If the molded part is thinner than the existing part then you can shim the back in the mounting positions so it sits in the exact same position.

I can understand why you would want to build up the thickness of the existing part to make the mold.

I must be missing something…

#3

It’s going to be a cosmetic part which will just lay over the stock bumper therefore it needs to be a little bit bigger to fit over the original shape of the bumper. the part is already going to be made .060’’ from the surface back. So i will run into fitment issues. I need to make the bumper like .070’’ thicker before I splash my mold.

I hope you can understand that better.

Thnks

#4

What I do in these circumstances and where sheet wax is not an option is wrap the original part in CF and clearcoat it. This gives the even additional thickness required.

#5

Ahhhhhh…now I understand. It sounds like the above is a good alternative.

#6

I am going to assume that bumper part is fixed to the car, which is why you want to make a mould to basically produce an “over-lay” - is this correct? If it is possible, I would lean more to producing the complete part. I am sur eyou have your reasons, but can I ask why not just make a replacement?

#7

Yes its all molded together nothing is separate on that bumper except the back light of course.

For this particular vehicle, market, these guys don’t like adding on fiberglass or bumper replacements. It would be more ideal for them to buy something that would cover the black area in CF so that a new bumper wont have to be installed or painted yada yada. I am also planning on making a functional diffuser to tie in together with that overlay piece that I will make. But for right now we are just talking the overlay piece. The crucial part of this part is the trim line where it will meet the boundary of the black section on the bumper. I already mfg. another part that is similar to this but I didn’t make the tooling and the person that did make the tooling used sheetwax and had dents and scratches on the tool from copy of his plug/master.

I wish there was a vinyl that would be like several mils thick that can mimic the thickness of the laminate. And it being vinyl will allow it to drape over the shape better than sheetwax. But I may just overlay the part then with the proper thickness I will probably just used fiberglass because its cheaper.

#8

Would it be possible to spray with a Duratec high build type product to build up the required thickness then flat back, buff and polish?

#9

The only way to achieve an even thickness is with the wax sheets. It takes a little time and skill, but is duable.
I’ve encountered and made much more complex shapes.
Any other method will not guarantee the right corner radiuses.
And if your radiuses are not adaquate, all your job is gone. Unless you provide for more clearance, backing the surface with a thickness much bigger than the actual carbon part thickness.
Of corse you have to be able to make the carbon part with an even thickness, without any bridge or resin buildup on the inner corners.

#10

Maybe there is another option, if you like it: make a copy of the car body parte or use the actual part, and cover it with some layers of dry fibers to achieve the desired thickness plus tolerances. Vacuum bag it and make a splash over the bag.