Guidelines for Epoxy Mixing and Vacuum Bagging Process in Carbon Fiber Composite Panel Fabrication

[oelarwadi]

I am working on creating a 4-layer 3K plane weave carbon fiber panel (30 cm x 30 cm) using vacuum bagging and hand layup (applying epoxy per layer). I have Epoxy 105 and Hardener 206 (From West Systems) available. Could you provide guidance on the following:

1. How much epoxy and hardener should I mix (in ml) for this panel?
2. How much epoxy mixture should I apply per layer?
3. Should I use a breather fabric, and if so, what type and how much?
4. What is the recommended curing time and temperature for this resin system?
5. How much weight or pressure should be applied above the composite during the vacuum bagging process?
6. How long should the vacuum be applied to ensure proper lamination and cure?
7. Should I add any surface agent and how do I do so? 
8. Do I have to degass the epoxy?

Thank you for your assistance!

[lo_0l]

On 7/26/2024 at 5:13 AM, oelarwadi said:

I am working on creating a 4-layer 3K plane weave carbon fiber panel (30 cm x 30 cm) using vacuum bagging and hand layup (applying epoxy per layer). I have Epoxy 105 and Hardener 206 (From West Systems) available. Could you provide guidance on the following:

1. How much epoxy and hardener should I mix (in ml) for this panel?
2. How much epoxy mixture should I apply per layer?
3. Should I use a breather fabric, and if so, what type and how much?
4. What is the recommended curing time and temperature for this resin system?
5. How much weight or pressure should be applied above the composite during the vacuum bagging process?
6. How long should the vacuum be applied to ensure proper lamination and cure?
7. Should I add any surface agent and how do I do so? 
8. Do I have to degass the epoxy?

Thank you for your assistance!

@Jeremy Senne might have some good input.

[Jeremy Senne]

Great questions!  A few inputs here:

1. How much epoxy and hardener should I mix (in ml) for this panel?
   1. First I'd suggest deciding your target fiber volume/resin volume, for wet layup this typically lives around 40% fiber volume/60% resin volume.
   2. Next figure out the dry ply thickness of your material.  3K plain weave is probably around 0.010" but you can measure with a caliper.
   3. Next calculate the total dry volume you expect the part to be.  Slightly imperfect science to not go into heavy levels of detail but you could conservatively approximate it as (Dry Volume) = (Dry Ply Thickness)*(Ply Count)*(Length)*(Width) or (0.010")*(4)*(15")*(15") = 9in^3.  Please forgive the english units... I'll convert back to metric later
   4. Next calculate the wet volume based on the ratio of fiber volume to resin volume (Wet Volume) = (Dry Volume)*(Resin Volume Fraction)/(Fiber Volume Fraction) = (9in^3)*(0.6)/(0.4) = 13.4 in^3.
   5. Finally add ~25% for spillage (Total Resin) = (Wet Volume)*(1+Spillage) = (13.4in^3)*(1+0.25) = 16.8in^3
   6. Finally convert back to metric units = 275ml
   7. NOTE: This method makes some assumptions about dry volume vs wet volume and assumes that the weave has no open area to take in resin which isn't the case.  It should be slightly conservative for how much you'd need to mix so you may end up with a fair amount left but can adjust from there.
2. How much epoxy mixture should I apply per layer?
   1. Generally you'd want to divide by the number of plies + 1 and evenly distribute (some below the first ply, some between each ply, some after the last ply)
   2. I'd suggest a wet coat of on the tool, possibly with a thickener like cabosil or a surfectant to avoid trapped air below the first ply
   3. Evenly distribute between each ply afterward and some after the last ply
3. Should I use a breather fabric, and if so, what type and how much?
   1. I'd recommend a release film directly on the wetted top surface then a breather like N10 or even dry fiberglass afterward to distribute your vacuum and encourage air out of the laminate.  Make sure that your laminate has a dry path for air to come out.  A trick I use is to put a few fiberglass tow bundles from the wetted laminate to the breather layer wrapping around the release film layer.
4. What is the recommended curing time and temperature for this resin system?
   1. Checking the datasheet it looks like it's 10-15 hours for working strength (you can pick it up and move) and 1-4 days for full cure.  This would be at room temp.  Without a viscosity profile through a range of temperatures it's tough to tell but if you went to 150°F it would probably cut it to a 4-8 hour cure.
5. How much weight or pressure should be applied above the composite during the vacuum bagging process?
   1. For a wet layup like this the key is just as much vacuum as you can pull after your complete the layup.
6. How long should the vacuum be applied to ensure proper lamination and cure?
   1. I'd recommend from lamination completion to cure completion.
7. Should I add any surface agent and how do I do so? 
   1. Pick your favorite, I haven't used many for a while.  Generally this is just an additive at a relatively small percentage directly to the already mixed resin.  It really does make a difference though.
   2. You can also improve your chances of minimal porosity if you degas the resin after you mix it.  A relatively cheap degas chamber for 5-10 minutes after mixing is all you need.  It will look like it's boiling as the air escapes.
   3. https://www.vevor.com/vacuum-pump-c_11109/vevor-2-gallon-vacuum-chamber-upgraded-multipurpose-acrylic-vacuum-degassing-chamber-transparent-vacuum-chamber-for-resin-degassing-silica-gel-degassing-gypsum-degassing-and-vacuum-extraction-p_010700464784?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=20851263822&ad_group=160381533727&ad_id=684421397984&utm_term=&gad_source=1&gclid=Cj0KCQjwwae1BhC_ARIsAK4Jfryf7aZmWPXlDzYcZIgPD9RHZIcwm-u2IbitqHsX56oo6ElgLIloSREaAvK9EALw_wcB
8. Do I have to degass the epoxy?
   1. Yup as above I do recommend it.

Thank you for your assistance!