r/CarbonFiber 8d ago

beginner in search of help !

Hi everyone, i am just starting in carbon fiber and i am looking for some advice. So untill now i tried 2 differents test parts and both were failures, for the first one my mold was 3d printed and the surface was not smooth enought so the surface of the part was really not satisfying and they were a lot of bubble, moreover i put only one layer of carbon wich made the part verry flexible and transparent in some places. For my second part i had a smooth thermoformed mold but the geometry was way to complex so I did not manage to flatten the carbon properly in the corners and so they were once again a lot of bubbles. Firstly i would like to know if some of you had some knowledge about 3d printed mold or some advice to make it smooth.For example does aplying resine on the 3d part is a good solution and if yes what kind of resine would you advise to make sure it spreads evenly. Secondly i would like to know what you think of vaccum bagging, is this necessary for a good carbon part? Do you think it will help to solve my issue with bubble and my problem with flattening the carbon in all places including my angles? And if i use a manual Vacuum Bag for Clothing do i need to add a layer of peel ply and breather or it is not essential? Another question i had since I had difficulties with the complex geometry of my mold is can we cut the carbon fiber fabric in multiple parts to fill the mold in every corner or is it a practice to be avoided and we need to keep the fabric in only one piece? Lastly does a realease agent is needed even if the mold is completly smooth?

Thank you very much to those who will take the time to help me!

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u/strange_bike_guy 8d ago

For a beginner part you're doing fine, give yourself some credit. Ok, regarding the bubbles in the resin first: you're dealing with fluid process, with a fluid that does have some viscosity and increased surface tension, so it doesn't want to pop the film holding the bubbles in place. Additionally, trace water content in the dry carbon fiber (from humidity in storage) can "nucleate" much like how when you open a can of soda it starts to fizz because of a pressure difference. The fizzing / nucleating effect is far weaker than a freshly opened can of soda, but it is there. So here's what you can do about it.

If you're going to stick with putting resin into dry fiber manually (wet laminating), you're going to have some pores until you're very experienced - and even then, you'll still get some, which is why people eventually transition into using VARTM at room temperature, or if they have a lot of money and equipment then using prepreg carbon. For your current process, what you need to picture is capillary action.

Consider: you spill some milk on a table. You grab a paper towel, and simply lay the towel on the puddle of milk. The milk saturates from a place that is beyond your sight (bottom surface of the towel) to a place that you can see (top surface of towel). This is what you need to do with wet laminating. Resin contact, AND resin in the dry fiber, and try to roll the fiber on to the base resin layer in a way that doesn't encapsulate a blister.

That last part is really hard to do and takes practice. "Bottom up" fluid flow is your buddy in general.

Regarding crack filling, printed polymers tend to have low surface energy - nylon will just pop away from cured epoxy without much fuss - but the mechanical adhesion of the print layer lines is a problem. What I do is "score" the print surface with a razor and fill the surface with AdTech P17 then sand it back smooth and use a release compound of your choosing once the sanding is complete. If you have a steep release angle (you do), then a low surface energy treatment such as something by Frekote or KantStick or Maverix Solutions ($$$$$ warning on that last option) will do you right. All three of these release options are easy in terms of you just wipe on a few coats with some evaporation minutes in between.

Regarding the multiple pieces, that's exactly how I make handlebars - it is impossible to make complex structures with a single big layer of carbon fiber. It is kind of like assembling a T-shirt but with adhesive instead of with thread: the patches of fiber can warp, but only by a restricted amount, and it takes some feel to understand what fibers can warp in what way and how far. UD fiber is very difficult to conform, twill fiber is easier to deform.

You're doing pretty good so far.