Carbon Fiber

First off, I’m by no means an expert in working with composites; I’ve had some experience working with both carbon and fiberglass in a few projects (a chair and formula sae car) and just wanted to share a few things I’ve learned that are specifically relevant to an ID student considering working with them. Please consider this a guideline to use once you’ve already begun researching the general materials. Composites:

Overview
*Carbon fiber and fiberglass come in different weights and weaves, each one will behave a little different in your mold (ie 2x2 twill weaves will be more flexible with curved surfaces than a 1x1) *The heavier the fabric the more it will cost (ie 8oz vs 11oz) *Twill weaves generally cost more (this is usually what you see on automotive parts) *On average of $50-$80 per yard depending on weave (2008) *You can use filler materials to get additional strength. For example if you want the look of carbon fiber, you can always make a part out of several fiberglass layers and then layup carbon fiber on the two outer layers for a carbon appearance. *For structure, take time to consider the form. If you add a lip (ie Eames molded chairs) you’re going to add a lot of strength to the piece, which will prevent flexing. It’s cheaper (and lighter) to build these features into your design rather than add many additional layers for the same rigidity.

Pros:
*Lightweight *Extreme strength *Unique material *Large surfaces *Flexibility in design (creating the mold to find the form then doing the layup once your design is finalized)

Cons:
*Extremely expensive compared to other materials *A challenging and time consuming process *You may be limited as to which shops you’re allowed to work in and what you’re allowed to do	*It’s harder to repair an imperfect epoxy surface compared to other modeling materials because you cant simply repair it by adding fillers and painting over, in many ways what comes out of the mold is what you’re stuck with (at least from my limited experience)

Tips:
*Your finish is going to be very dependant on the quality of your mold, how well pieces of carbon overlap/meet, and if the epoxy is evenly distributed (no air bubbles). *Vacuum bagging or a positive/negative mold will help ensure even epoxy distribution *Different epoxies have different properties, be sure you’ve chosen one that best suits your application (pot life, flexibility, uv stabilization, etc)

Health and safety
*Tape the edges of the fabric and cut on the tape, you don’t want to get hundreds of tiny shards in your skin, it’ll irritate your skin and it gets everywhere like foam dust (including your throat and lungs so wear a mask); wear gloves as well. *You’ll need to work in a paintbooth/room when working with epoxy

Mold Making Techniques
Overview *You’ll need to create a mold to give form to the fabric. There’s a large variety of different ways you can go about this, each with their own ups and downs. Tradeoffs include cost, size limitations, one time use, ease of construction, workability, surface finishing, etc. Be sure to understand these tradeoffs well, your time is going to spent with this part of the process, the actual layup doesn’t take long at all. You’re already familiar with most of the materials required to make a mold, so the newest factors to consider for this particular application might be making a durable mold for several uses, something strong enough to be vacuum bagged (just like vacuum bagging wood veneer), and something that will give you an extremely polished surface. *Do practice tests with the materials before attempting to do anything, its easy to destroy days of work and hundreds in materials by rushing the process. ***for all molds** Take the time to make sure your release agent is properly applied so you don’t end up having to destroy your mold to remove the layup (this also includes making sure your surface has fully cured/dried if you used bondo or woodfiller). *The surface finish of your mold is exactly the same finish your layup will have, so if you want that glossy automotive look your mold better be extremely well buffed and polished *Consider which side of the composite part you want to have the nice finish. Unless you’re doing a two piece (male/female) mold, the smooth side is going to be the side your layup is against. A layup with nothing on the other side will have a texture similar to the weave and a vacuum bagged piece will have the texture of the breather fabric. *You can do the layup over your form and leave the backside open or you can vacuum bag or use a male/female mold to ensure the fabric is pushed against the mold to properly follow the curves and contours – this might be necessary for more complex shapes *As mentioned before, there are many different mold making techniques, some of them include: *Foam molds covered with a bondo or woodfiller to close pores *Benefits: *Relatively low cost, large scale molds are very feasible, the foam itself is easy to shape and explore forms in before committing to a finalized design and coating *Cons: *Be prepared to spend a lot of time coating and sanding the surface to get a nice finish *Tips: *Make sure the woodfiller/coating has fully cured otherwise its likely to come off and stick to your layup resulting in a lot more time spent trying to remove it as well as possibly messing up the carbon’s finish. *Clay *Wax *this can later be melted out of your part *Plaster *a good option for making male/female molds *non porous and can be sanded to a sheen *Vacuum formed *Benefits: *Smooth gloss surface perfect for laying up against *Easily accessible and fast *Cons: *You still need to have something else to form the plastic over *you can’t use pink foam as it will melt when the hot plastic comes into contact with it	*Tips: *If you use a yellow foam, you can vacuum form a thick sheet of plastic over it and skip dealing with fillers all together *Thick plastic will help remove any small surface imperfections *CNCed metal,plastic, foam, etc