working with honeycomb first time questions

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#1

I’ve been working with composites for a little while now but this is actually my first time working with honeycomb. I did a search but didn’t quite find an answer. I’m making a splitter for a corvette so its relatively flat. Heres how I plan to do it, but if someone has any input please let me know.

This will be setup to vacuum bag the part in the mould.

  1. Apply first layers of carbon into the mould. Leave slightly wetted out to make a “bed” for the honey comb to sit on/in. The slight extra resin is to adhere to the honey comb.
  2. Lay in the honeycomb.
  3. Lay on the next layers of carbon and wet out. The resin should soak through the carbon to bond the subsequent layers to the honeycomb.
  4. Continue with the vacuum bagging steps just like normal.

Does this sound right? After my search I was more confused then when I started as people started talking about adhesive films, foam filled honeycomb, etc. but that seemed like it was for when you are using pre preg which I am not.

Also, last question, can you apply too much vacuum? I do plan to do test strips about 1" x a foot long to see the results but any input is appreciated.

Thanks.

#2

Yes you are on the right track with your process. The edge of the core will need to be tapered down to the mold side. Think of making a ramp from the pre core laminate up to the top of the core. This will minimize the distortion in your surface plys. Do not get carried away adding resin to bond the core. You are doing a wet lay up and odds are you are way resin rich anyways. You may even find that your surface where the honeycomb exist is better than the solid laminate areas.

#3

Cool. Thank you. And yes, I planned to chamfer the edges. Just wanted to make sure my layup process was on the right track.

#4

Wetting out the inner layers of carbon outside the mould(on a table or something) wil prevent you from oversaturating you layup (filled cells are heavy!)

Another way with somewhat more control over your Vf is to layup the outer skin alone, later bonding the honeycomb in place with some thickened resin( applied with a roller for example), and layup the inner skin.

#5

Yah with prepreg the honeycomb is very easy.

I haven’t used it in a wet layup. I would think that the cells would collect extra resin and then make the surface layer dry. It’d be worth doing a test panel before you make any parts. I’m thinking that a wetlayup with honeycomb might not work. Whenever I’ve done wet layup/infusion, I use a closed cell foam or balsa for core. Especially if you follow your order and try to wet out the fabric on top of the core. You’ll definitely want to wet out the cloth before you lay it up.

and you can apply full vacuum. I do with 2.5 PCF 1/8 cell core and have never had any issues. The core is strong in the z direction.

#6

Good tips. Thanks guys.

#7

be careful, Its difficult to get a good bond on the back layers. Typically, too much resin is pulled out during vacuum and you do not get the resin fillets you need to make a good bond. A side is no problem as the resin doesnt get pulled out. I would suggest making test panels first then ripping the b side laminate off to see how well your process is. You will probably find using a foam core to be much better in the end. Honeycomb is great, but in use with prepregs using a film adhesive to get a good bond. Good luck!

#8

I agree with hojo, foam is the way to go on a splitter or undertray. but if you still want to use honeycomb I suggest sucking the nomex into the first skin, curing, mask and fill any areas that are going to have bolts or pentrations -I tend to use a qcell/aerosol brew. once cured ,sand reinforced areas and secondary bond the next laminate. prime the nomex with a sticky resin slurry, use a roller with excess removed, prewet cloth. be sure to use multiple layers of breather film to minimise resin bleed. bag and cook under vaccum.

#9

I have seen others using honeycomb with wet laid resins do a tissue layer on the inside of the nomex first and I think this may have been done with a thickened resin to help the bond to the cell edges. Then when this is cured you can do a regular wet layup or vac bag the laminate too.

Though I also favour foams too. Cheaper, very light and sometimes lighter than honeycombs depending on your process and product. Also 100% surface bonding rather than relying on just cell edges and in the case of a boat no hollow sandwich that can fill with water or expand/shrink with temp change.

#10

Wet layup and honeycomb work fine.

The mold side laminate should have a little extra resin to help bond to the honeycomb. A good way to tell if you have enough resin is to take a plastic spreader and push with the edge vertically into your laminate. If you have enough resin you will see a small amount collect at the edge of the spreader.

For the bag side laminate the reinforcement is wet out on a piece of plastic film before you transfer it onto the honeycomb. The resin content is controlled by weighing the dry reinforcement and resin to verify you will have the correct ratio. Allow 10 to 20 percent more resin for bonding to the honeycomb.

Use a perforated release film in your vacuum bag to control resin removal.