Class A finish on very thin laminate - what's the best way?

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#1

Hey guys,
So I’m trying to figure out how to get a class A finish on both sides of a laminate. The laminate needs to be very thin (2x plies of 3k 200gsm or one ply of 6k 300-400gsm), and the actual thickness is important (needs to be thin…) so I can’t infuse the layers against a caul plate while using soric as a flow medium between the two. the application is solely cosmetic.

Right now my theories are:

Infusing with Compoflex RF and just finding a way to really flood out the B side (does anyone have any photos of a compoflex RF surface finish? I emailed fibertex but haven’t heard back and can’t find any good ones online)

Infusing two separate laminates and gluing them together (way too resource intensive!)

Try and infuse OOA prepreg against a caul plate (guessing this would still lead to pinholes and voids as OOA prepregs needs some sort of air evacuation? Would ultra-resin rich systems, or maybe one side coated systems like easy composites version, work? I could lay 1 ply onto each source [1 on the mold and 1 on the caul/b side close mold surface] and then just bond them together and hope for the best??

Only other option I can think of is to get a manufacture to try and pultrude them for us but I’m not sure what the cosmetics of that would look like.

Let me know if you have any ideas! Thanks!

#2

What size is the panel? Do you think you could infuse through the thickness without a flow medium so you could use the upper caul plate? Perhaps put the inlet completely around the periphery and have the suction port in the middle even through a slot in the caul plate to minimise distance for the resin to travel? Not sure if the whole panel has to be perfect? Alternatively, have a few suction ports around the periphery beyond the OML

OOA pre-preg with caul plates: This works with a good pre-preg and edge breathing such as glass tows or breather fabric. It would be even better if you could debulk 1 ply against the tool, 1 ply against the caul plate and then combine for final cure.

#3

How about 2 plys of a single sided hot melt prepreg with a low level of resin integration so the layup could be edge bled.

#4

The infused-across distance isn’t massive, so this is something we’re considering. We’d have to go about 15 inches without any through-thickness infusion medium to make it work, so it’s doable, but it’s just a question of can we infuse across something like that without getting pinholes from the resin degasing. Debulking both layers against the mold surfaces wouldn’t work for us because that’s just too time intensive. we’re trying to do this as cheaply as possible! Thanks for the suggestions.

AVT, I was considering this. Something like easy composites’ surface side prepreg is what I had in mind. Two layers, with the edges of the layers seamed with breather. I wouldn’t even be opposed to having some sort of dry vacuum carrier within the laminate, like a very thin breather that gets wet out and becomes part of the laminate. Not sure if there is enough resin in to support that but it’s definitely a possibility. Has anyone tried something like this before?

#5

What’s the absolute thinnest resin system that’s out there? Mechanical properties don’t really matter to me. I’m just looking for something that I can infuse as easily as possible and keep the velocity high since I don’t want it to degas as it’s moving across this surface. VE and PE suggestions are welcome

#6

Vectorply sells a material called Micromesh, its basically a 17gsm veil. It increases permeability of the laminate. you can place a layer of micromesh between each layer of carbon. I was able to successfully infuse about 15" between a glass panel, and aluminum caul plate on a 6mm thick panel. Works pretty good, however its a bit pricey

#7

How many are you making? I’m planning to do a similiar type of project. From what I’ve seen using a heated press is probably the easiest way to do it. I don’t have one at home but, that’s why I"ve been working toward making a home version. The prepreg I use gives an excellent surface on the molds at work, and these aren’t super polished out aluminum. So I figured if I can use polished plates, the panels should come out pristine.

#8

I was thinking of a hot press application as well but I too don’t have one and I don’t think it’s worth the capital investment to do. What type of prepreg do you use, if you don’t mind me asking? I have Gurit SC110 and I’ve never tried hot pressing it, but by looking at the surface finish I have the distinct feeling that it won’t work. Not going to rule it out off the bat (it’s supposed to work great as an OOA), but it just has too many voids on both surface sides that make me think it needs a reasonable amount of flow time for air evacuation through a breather.

Hojo, thanks for the info on the VectorPly stuff. That company makes some really interesting products. I had one of their sales reps come out and meet me a few months ago and I was impressed. I’m guessing the micromesh is the same A-glass stuff that they bond to some of their stitched fabrics to improve resin flow? I’ll give my rep a call and ask him how much it is.

#9

I’m using a cytec OOA prepreg. I have to say it’s quite nice. In our metal molds the parts come out beautiful… We’ve made pressed plates, some with foam core, some just carbon, they come out fantastic. And these are with surfaced aluminum plates that aren’t mirror polished. I’d imagine with a polished plate, they would be completely perfect. Not too much issue with pinholes, especially in the press.

I just made a two ply panel yesterday and it looked great. There was no edge damn used and it squeezed out just a tiny amount of resin. I believe its a 42% resin content.

This is why I’m thinking of making a plate type heated thing for home, with bolts that I can torque down for compaction. I’m not looking for structural panels, though I’d bet they’d be great for that. Mostly I want that sexy gloss without having to paint clear or fix any surface blemishes.

I’m curious about the vectorply stuff you’re talking about. I’ve used their biaxial glass for infusion, strong stuff; difficult to cut.

#10

Yes, that is correct, they use the micromesh in their stitched fabric. I would of also suggested pressing, however I didnt know if you have that kind of budget. If you want, send me a PM, I have a good connection for presses, I might be able to help you with that.

#11

Thanks hojo, I’ll send you a PM.

Sammy, could you recommend a specific prepreg with good surface characteristics from Cytec? I’m on their prepreg selector page (http://www.cytec.com/selector-guide/ Aerospace>Prepregs and Resin Systems>Aircraft Interiors) but there seems to be a really wide selection. I want to have some talking points before I call them up. Looking for something that can cure at low temperatures (250-300F)

Thanks!

#12

It’s MTM 46 that we have. Not sure if it’s UV stable though?

It has a variety of cure temps. I do think it can be cured at like 180F for 5 hours or soemthing along that lines. NOt sure what the service temp is at a lower cure, we usually post cure everything.

let me know if they have a UV stable resin. From what I’ve seen, the aluminum molds will give a great surface finish.

#13

Thanks Sammy. I called in and left a message with their sales department, so I’m waiting for one of their reps to get in touch with me.

Quick question: why are the cycle times of press cured prepregs so short compared to autoclave or OOA prepregs, even though the cure temperatures are about the same (~250F)? I’m looking through the press cure prepreg TDSs on Cytec’s website and many of them list sub 10 minute cure times. Is it solely because of the better heat conduction straight from the metallic mold into the part?

#14

That’s a good question… I think it’s mostly as temp increases, the cross linking hapens faster.

In the press we’ve cured parts and usually they can be run at a higher temp, thus a faster cure. I remember one time they cured a panel at a really high temp, and it cured super fast… easily less than 10 minutes. This was with the OOA pre preg.

If the laminate is thin, it will heat up quickly because the platens are heating from both top and bottom. Also the press must have pretty high power and thus the ability to heat quickly.

So wait, to clarify, you’ve found some products that are listed as specifically for press use? If so, this could be very handy indeed.