Fabrication of forged carbon cases - and why the rep manufacturers won't do it

[chefcook]

Hello guys,

one of my dream watches is the Audemars Piguet ROO Bumble Bee. I think it is the perfect mix of the best materials AP has ever used: Carbon and Ceramic.

Unfortunately the rep factories only offer a crappy version with a PVD coated steel case instead of the wonderful looking forged carbon case. When thinking of steel prices carbon rovings (the stuff AP makes the cases from) are very cheap, so why won't rep factories be able to get it right?

I've gained the knowledge of resin transfer molding (RTM - the correct term for the process used to create "forged carbon") during my former work for the Porsche's Motorsport department and the BMW M department and want to share it with you.

RTM is used for parts with small surface in relation to their volume. You won't get the nice woven carbon pattern on the surface, but as you can see from AP's forged carbon cases it looks nice, too.

Body parts for cars for example would not be made by RTM. To produce them multiple layers of woven carbon mats are laminated with epoxy resin. All you need is a negative to form you body part.

For RTM carbon parts the setup is very different. Instead of a simple negative one needs a mold that is able to withstand pressure and heat.

After filling the mold with carbon wires (rovings)it is evacuated to ensure that the mold will be filled completely. Bubbles would destroy the surface and / or the later strenght of the manufactured part. After evacuating the mold it is filled with an epoxy resin under high pressure and then baked to harden.

This for example is the mold Audemars Piguet uses for their cases (look what kind of watch AP employees wear ):

The mold is filled with the cutten rovings:

Then evacuated and filled with epoxy resin:

In the oven:

The finished case and the rovings it is made from:

As you can imagine after seing these pics it is not the the material costs that make such a case very expensive, it is the labour and the know how. I estimate that AP needs several hours to create one case and as far as I know it took them years of experimenting how to produce a carbon case that really works. Too long for rep factories, that simply stamp, forge and finish the cases.

But now to the most interesting part: With the pictures above they reveal so much information that it could be possible to replicate the case.

A mold is not cheap but the possibility to rep my dream watch, the bumble bee, is very tempting . Maybe an aluminium mold is enough for a home made project.

The mold has to be designed slightly different to work under home made conditions and the finished product won't have the same stability as the genuine case. The look should be replicateable.

I'm about to order an Offshore and will make a CAD file of the case. It will be a long term project and I don't know if it will be successfull in the end but I think it's worth a try.

Let's see if it works...

[jkarpas]

thank you for this amazing info and pics. I envy this carbon watch case but as a pistonhead i envy more your career at porsche and bmw motorsport

good luck with the project

[rkdk]

Would it be possible to emulate the carbon case with plastic maybe? It would probably be an easier material to work with.

[MADRED7]

Thanks for the information....saw it on one of the AP forums.

My question for the factories/dealers was allways : Why not use and produce a plastic case, with 2-3 different plastic colors to gain the effect of the carbon....that solution should be cheap, light and kind of easy to do as we see 1000s of CASIOs and other plastic-case watches.

I don

[StormTooper4]

I agree plastic looking CF is the way to go and should be easy to do , maybe someone on RWG works on a plastic factory and could knock one up

http://www.youtube.com/watch?v=NDq3yZlsxS4&feature=related

[chefcook]

After some years in Motorsport and go-faster-departments I am now in a position were I have a lot to do with plastics.

Actually I doubt that it will be possible to create a good looking plastic case to replicate the look of carbon fiber and epoxy resin.

The epoxy resin is clear like water and creates a unique look as the light is not reflected by the epoxy resin but by the CF. That makes CF part sparkle like nothing else. CF parts and the AP cases are not black as well: The actually are clear and filled with CF to about 95%.

With injection molded plastic parts the structure of CF is not reproducable and the effect created by the clear epoxy resin is so too.

The mold for injection molding of a watch case like the AP case should be in the $5k range for mass producing but injection molding of plastic parts has one major down side that does not allow producing a case like the AP case: The wall thickness must be constant (or in a certain proportion to each other) and beneath a certain thickness to avoid shrink marks. The AP case is definetly to thick. They would not be able to create something with correct measurements and even surfaces if they made a case completely from plastic in the same dimension as the steel case.

Only solution to this is a metal core underneath the plastic, but we all know the difficulties with that from other reps.

I have massive doubts that a plastic case will be an accurate replication. It won't have the weight nor the surface appearance of the genuine CF case.

BTW: The genuine CF cases are not very durable, too. After some use and wear the usually get "fuzzy" edges.

[Bike Mike]

A production injection mold (IM) for a AP case, would be well above $5K due to the mechanics involved. You would need retractable slide pins for the lug holes. Depending on how you split the core and cavity, they might need to be actuated by hydraulics, adding more costs. Not just that, but due to the sharp lines, multiple EDM burns would be required. You could get around the sink with material like Dylark, but you would never get the CF look like AP. Even with the additional of CF fill

[chefcook]

A production injection mold (IM) for a AP case, would be well above $5K due to the mechanics involved...

IMO not in China and without lugholes out of the mold. Slide pins are not neccessary when drilling the holes afterwards. I've purchased molds of similar complexity before in the $5k range...

But more important: You are completely right when saying that even with CF fill the look of the gen case could not be replicated with a plastic part.

Your C5 door trim looks very well made Normally I did not pay that much attention to the surface of the parts. It does not matter in racecars

[Bike Mike]

IMO not in China and without lugholes out of the mold. Slide pins are not neccessary when drilling the holes afterwards. I've purchased molds of similar complexity before in the $5k range...

Agree, but really depends on the mold...lower qaulity steel, hand loaded, yes you could do $5K. Anything production intent (volume dependent) is going to be multi cavity, at least 2, with a degree of automation. 85% of my IM suppliers have tooling facilities in China and cost saves are about %50 saving compared to having tooling done State Side or Europe.

Few race car (C6R) parts for you...they had to look pretty...so they had to be post cured to fight UV effects. Do a web search on the Chrysler ME412...Did all the CF work on 2 functional prototypes.

[sander]

I did some homework.

I think a can sell them for arround $700,-

The problem is that my minimum order is 10 pieces

I'm not sure how many people want them?

[FxrAndy]

Are you going to machine it from the solid block?

This is interesting

[sander]

Are you going to machine it from the solid block?

This is interesting

yep!

[redwatch]

I just love this place! The mad scientists that collaborate here are just amazing!

@Sander - that is definitely intriguing! Will they allow for a one off prototype to be made before you have to commit to ordering 10 pieces? It would be good to make sure they can deliver what they promise before gathering $7k for 10 cases.

[sander]

I just love this place! The mad scientists that collaborate here are just amazing!

@Sander - that is definitely intriguing! Will they allow for a one off prototype to be made before you have to commit to ordering 10 pieces? It would be good to make sure they can deliver what they promise before gathering $7k for 10 cases.

Once the program is written and the cutting machine installed, it almost doesn't matter if you cut 1 or 10 pieces.

Why do you think I don't have one yet

So the cost is not really the cutting itself.

If we order 20 the price would be arround $ 350,-

[redwatch]

Once the program is written and the cutting machine installed, it almost doesn't matter if you cut 1 or 10 pieces.

Why do you think I don't have one yet

So the cost is not really the cutting itself.

If we order 20 the price would be arround $ 350,-

Gotcha! Well $350 is way more manageable. There must be 20 people on this forum and RG that would be interested in going in on it.

[sander]

One of the big issues I have with the bumble bee is the wrong tachyring and the PVD coated bezel.

[chefcook]

The wrong tachy ring is something I could live with. A dlc coated steel bezel could look nice enough I think...

For 350 I'd be definetly interested!

[redwatch]

What is the bezel made of on the gen? Is there no rep with a ceramic bezel out yet? (forgive my AP noob question )

[aanival]

wow.. nice possible project here... I am all ears

[Chronus]

yes there is an ap with a ceramic bezel but that's the rb2 and the survivor which are different from the bumblebee.

[eunomians]

I'd purchase a custom CF bumble bee case by Sander. Just like I'd also purchase a custom movement plate for RB2!

[AstroAvia]

I never cease to be amazed by how talented and curious people are! Amazing thread!

Are you going to machine it from the solid block?

This is interesting

Very interesting indeed. Is it possible at all?

If we order 20 the price would be arround $ 350,-

I don't think it would be difficult to garner interested buyers. Maybe more than 20 people would pay for a CF case.

[Jakob]

@ 350 I'd be interested too, but we still need the ceramic bezel.

[chefcook]

Only thing I am concerned of when machining a case from a CF block is fiber ends sticking out of the surface. That's a main problem with such parts and a huge advantage of RTM where it is very unlikely.

[apollo22]

I would be keen to buy two cases if this could be done!