Original Post:

From: Art Sandoval <sando@lunar.com>
To: design-alumni@lists.Stanford.EDU
Sent: Tue, January 25, 2011 9:21:44 AM
Subject: [design] Carbon Fiber, High Volume

In search of resources/experts/vendors to quickly get up to speed on the ins and outs of using carbon fiber on a high volume consumer electronics product. 

Design guidelines, limitations, tolerances, etc. 

RESPONSES

I'd call Tencate. They're in Morgan Hill (408) 776-0700 and Benicia (the Benicia facility used to be named Bryte). They do some medium volume production of precision carbon fiber parts, but mainly I'd say to call them because they're the most important prepregger around our region. Anyone around here who's an expert in composites will likely have gotten prepreg from them at some point, so Tencate might be able to point you the other direction, toward a good consultant.

Joe Silber

How big are the parts? Are they structural?

I am currently working on a process that uses a high temperature membrane press to form and cure pre-preg sheet material for relatively large auto body panels. The process is already several times faster than the traditional autoclave method and we are working with a partner on new chemistry to further improve.

Give me a ring if you are interested: +1 206 240 1046

Drew Bamford, PD '96

Hi Art
I used to do a lot of work in the bike industry which fostered much of the innovation in molded carbon fiber parts.  I suggest contacting Josh Deetz ( josh@deetz.com or joshdeetz@gmail.com ).  Josh is an ex-pat who lives in Taiwan and makes a living as a liaison for all kinds of bike and electronics manufacturing including carbon fab.  He is very knowledgeable which usually makes up for the occasional confusing comuinication.

I also suggest contacting Pete Dreissigacker from Concept 2 which makes carbon rowing oars etc.  He is a Stanford alum (maybe a PD alum?)  They used to do it all in VT.  Not sure if they still do.

I've done a lot of carbon prototyping for both bike parts and electronics and I'm happy to talk with you about how to get prototyping done quickly.  I can show you some sample parts if you have interest.

Jamie

Art,

I am presuming you are looking to use woven or unidirectional carbon fiber in this product, rather than fiber-filled resins.  I admit to not having brought any part to production volume using CF, but I did meet with a vendor in Taiwan recently who was showing off their new high-volume capabilities.

The gist of their process was to layer thin sheets of CF and a structural thermoplastic and then heat the layers in a mold until the TP reflowed into the CF, creating your composite part.  In practice this means the CF and TP layers are hand laid into a mold that looks very much like a typical high-volume injection tool, but features something like RHCM (rapid heating/cooling molding) technology that allows the tool to make fast and significant temperature changes between safe-to-handle temperatures and the thermoplastic's glass transition point.

(Note that RHCM tools tend to be about 2x the cost of a standard injection tool, but their cycle time is fast enough to ensure the process remains commercially viable.  While I suppose it's not required to use RHCM to reach the proper temperatures for thermoplastic reflow, a typical tool architecture will probably be too slow to be used in a production environment.  But I digress...)

Once the tool halves are then brought together, they are heated above the glass-transition temperature and clamped while the TP flows into the carbon fiber sheets and forms any internal structures you want to create on your part.  This means any bosses, ribs, thickness changes, etc, all need to be prepared for by adding extra raw material in those areas before they are placed into the machine.  The parts I saw had small squares of ~%30 fiber-filled TP taped onto the outermost layer of plastic being set into the machine, roughly in the location of the bosses to be formed.  Tedious, yes, but the vendor did not know of a version where plastic could be externally injected; all the material that eventually ends up in the part needs to be manually introduced into the tool before it is clamped together.  This may not be a universal truth, I could conceive of a process that injects the plastic into the carbon fiber sheets, but I have not seen this myself.

Clearly such an allotment of material is imprecise and the process needs to accommodate some variation in the material volume that is introduced to the tool.  This was achieved with substantial venting on the tool and regularly using oversize sheets to ensure complete "fill" of the part and features.  This has the effect of making the as-molded parts look like they are covered in "flash" and excess material.  The part edges are necessarily trimmed after the fact, either by a shear built into the tool itself, or with post-processing.  The edges thus have a very different surface quality from the molded surface; the fibers are cut and exposed and the plastic edge lacks the glossiness that the tooled surface can achieve.

Cosmetically it seemed like the flow of material in this process is difficult to control, and the part finish is somewhat affected: unidirectional fibers looked a bit wavy and weaves seemed non-uniform where the plastic flow shifted the "dry" CF around.  Note that the fiber is not only shifted around in "XY" but also within the part thickness itself, in some areas the cosmetic faces were thick with plastic and in others the fiber was nice and close to the surface.  Do note that I'm extremely picky when it comes to surface finish, so your mileage may vary with your expectations.  The as-molded surfaces you can achieve with RHCM processes are phenomenal, though, so the worry is only relevant when molding CF with a clear TP.

So, the process works but it comes with tradeoffs.  On the one hand you can produce durable, true carbon-fiber composite parts with a design that is familiar to anyone who has injection-molded parts in volume.  On the other hand they were cosmetically inconsistent, exceptionally glossy but lacking the perfectly uniform appearance that traditionally laid-up carbon fiber parts can achieve.

All in all: good, but not great.

In any case, this is only one process for producing carbon fiber composites en-masse and I'll be curious to hear what else is out there.  Good luck with your search!

Regards,

Dave Evans  MSPD '09(.5)

Art,

You could talk to Joe Luttwak of Blackbird Guitar. His company makes a really cool carbon-fiber guitar.

Joe Luttwak

joe@blackbirdguitar.com

http://blackbirdguitar.com/

I’m not sure how much time he has, but he’s a nice guy and definitely has lots of knowledge about carbon fiber in low- to mid-volume production.

Best wishes,

Sascha

forensic fibres experts

Hi Art,
I've never used/designed w/ CF, but Ploom has been taking me to Taiwan a bunch, and one of the biggest players in the CF bike market (http://www.topkey.com.tw/tech-material.htm) is in the same industrial park as our CM.   Actually, almost all CF bikes come from Taiwan (and subsidiary Chinese factories) now.  Topkey may be able to quote the part, they have a big operation in Taichung, and they have satellite factories in China (Xiamen) I believe.  Also, Alibaba might give you some leads on other vendors (http://www.alibaba.com/products/carbon_fiber/TW--121399------------_1-TW,.html).  I don't know much about domestic CF mfg.
good luck
Patrick