oCarbon.com - 981 carbon fiber project thread
01-18-2015, 11:00 AM
#16
We just started molding full carbon replacement door sills and I figured I'd do a little write up on the process for those who are interested.
Most low end molded parts are a single cosmetic layer of carbon fiber backed with a couple layers of fiberglass for thickness. They'll be laid up in a mold, completely drenched in a polyester resin, and then the mold gets placed in a vacuum bag and the air is sucked out with a vacuum pump. Some of the excess polyester resin will be pulled away but what you're left with is a part that is resin rich and mostly fiberglass. Having too much resin in a part actually makes it heavier, weaker, and much more brittle, since now you've essentially just got a plastic part that looks like carbon fiber.
They do it this way because its the cheapest manufacturing method and most consumers wouldn't know the difference between a full carbon part and a mostly fiberglass part, as fiberglass goes clear when its saturated with resin. These methods are how Honda Civic owners can have carbon fiber hoods for $465. If you've ever seen one of those hoods on a vehicle in person, even if its only a few months old, they're almost always yellowing and the clearcoat is chipping away on them. Using the cheapest possible materials just wont hold up.
Instead of vacuum bagging our parts, we vacuum infuse them. We never use cheap polyester resins and only use epoxy resins that have been treated with UV inhibitors to combat yellowing. Making parts this way takes longer and costs more, but the end result is totally worth it, as it yields a perfect part every time.
First we lay up several layers of carbon in the mold. We don't use any fiberglass, so our parts are full carbon. Then we put a release film on top of the carbon fiber followed by a flow media. These will help us remove the consumable material from the carbon part and allow the resin to flow freely through the part. Next we seal everything up and run the vacuum pump. The pump removes all the air and compacts the carbon very tightly against the mold. Now the magic happens. We then inject the epoxy resin into mold. Since the part is already very compact and under vacuum, there isn't much room for excess epoxy. Only the exact amount of epoxy needed flows into the carbon where it can and the carbon doesn't become oversaturated. Once the epoxy hardens, what you're left with is a part that is mostly carbon and has the perfect carbon/resin ratio, so it is very strong and very light.
Here is a picture of the sills in our mold under vacuum before they've been infused with epoxy. As you can see, everything is extremely compacted against the mold, even though there are several layers of carbon and a couple more layers of release film, flow media and breather material, as well as some hoses to allow the flow of air out of the part and epoxy into the part. The needle on the gauge reads -29.9 Hg so we know its at full vacuum with no leaks:
After everything is at full vacuum and we're certain there are no air leaks, its time to infuse the part with epoxy. Unfortunately I didn't have a chance to snap pictures of the sills being infused, but here is a picture of a flat carbon plate being infused. You can see the epoxy flowing from the left side to the right side. The white stuff is the dry release film, which goes clear and appears black from the carbon under it once it gets wet with epoxy. The textured mesh on top over everything is flow media, which helps the epoxy move across the carbon. The spiral tubing at the top is connected to the vacuum pump and drawing air all along it, so that the resin is pulled somewhat evenly across the part (notice how its a little slower in the middle where the tape is?):
When the epoxy gets from one side of the mold to the other, we're all done. Then we just allow everything to cure and pop it out.
Here are the sills right out of the mold. A little ugly and a lot of excess carbon around the edges. I wiped them down with a solvent to clean them off so they appear to be a little sticky here, but other than that, the weave looks straight and the part looks good:
Next we trim them down a bit and clean them up:
A quick rinse under the water will give us a pretty good idea of how these will look after they've been clearcoated:
On the back of the part, you can see we've got a different, thicker type of carbon fiber that is stronger (but not very pretty) to give this part more rigidity and strength:
That's all for now. We'll get them finish trimmed and prepped for clearcoat in the next few days and I'll follow up with more pictures as well as pictures of the completed parts.
Most low end molded parts are a single cosmetic layer of carbon fiber backed with a couple layers of fiberglass for thickness. They'll be laid up in a mold, completely drenched in a polyester resin, and then the mold gets placed in a vacuum bag and the air is sucked out with a vacuum pump. Some of the excess polyester resin will be pulled away but what you're left with is a part that is resin rich and mostly fiberglass. Having too much resin in a part actually makes it heavier, weaker, and much more brittle, since now you've essentially just got a plastic part that looks like carbon fiber.
They do it this way because its the cheapest manufacturing method and most consumers wouldn't know the difference between a full carbon part and a mostly fiberglass part, as fiberglass goes clear when its saturated with resin. These methods are how Honda Civic owners can have carbon fiber hoods for $465. If you've ever seen one of those hoods on a vehicle in person, even if its only a few months old, they're almost always yellowing and the clearcoat is chipping away on them. Using the cheapest possible materials just wont hold up.
Instead of vacuum bagging our parts, we vacuum infuse them. We never use cheap polyester resins and only use epoxy resins that have been treated with UV inhibitors to combat yellowing. Making parts this way takes longer and costs more, but the end result is totally worth it, as it yields a perfect part every time.
First we lay up several layers of carbon in the mold. We don't use any fiberglass, so our parts are full carbon. Then we put a release film on top of the carbon fiber followed by a flow media. These will help us remove the consumable material from the carbon part and allow the resin to flow freely through the part. Next we seal everything up and run the vacuum pump. The pump removes all the air and compacts the carbon very tightly against the mold. Now the magic happens. We then inject the epoxy resin into mold. Since the part is already very compact and under vacuum, there isn't much room for excess epoxy. Only the exact amount of epoxy needed flows into the carbon where it can and the carbon doesn't become oversaturated. Once the epoxy hardens, what you're left with is a part that is mostly carbon and has the perfect carbon/resin ratio, so it is very strong and very light.
Here is a picture of the sills in our mold under vacuum before they've been infused with epoxy. As you can see, everything is extremely compacted against the mold, even though there are several layers of carbon and a couple more layers of release film, flow media and breather material, as well as some hoses to allow the flow of air out of the part and epoxy into the part. The needle on the gauge reads -29.9 Hg so we know its at full vacuum with no leaks:
After everything is at full vacuum and we're certain there are no air leaks, its time to infuse the part with epoxy. Unfortunately I didn't have a chance to snap pictures of the sills being infused, but here is a picture of a flat carbon plate being infused. You can see the epoxy flowing from the left side to the right side. The white stuff is the dry release film, which goes clear and appears black from the carbon under it once it gets wet with epoxy. The textured mesh on top over everything is flow media, which helps the epoxy move across the carbon. The spiral tubing at the top is connected to the vacuum pump and drawing air all along it, so that the resin is pulled somewhat evenly across the part (notice how its a little slower in the middle where the tape is?):
When the epoxy gets from one side of the mold to the other, we're all done. Then we just allow everything to cure and pop it out.
Here are the sills right out of the mold. A little ugly and a lot of excess carbon around the edges. I wiped them down with a solvent to clean them off so they appear to be a little sticky here, but other than that, the weave looks straight and the part looks good:
Next we trim them down a bit and clean them up:
A quick rinse under the water will give us a pretty good idea of how these will look after they've been clearcoated:
On the back of the part, you can see we've got a different, thicker type of carbon fiber that is stronger (but not very pretty) to give this part more rigidity and strength:
That's all for now. We'll get them finish trimmed and prepped for clearcoat in the next few days and I'll follow up with more pictures as well as pictures of the completed parts.
02-09-2015, 11:51 AM
#19
First set of full carbon replacement door sills is done. I can make these in any fabric or finish. Email me at matt@ocarbon.com if you're interested.
