Ok I have a question about epoxy surface/tooling/gel coats. Well actually a few questions, because I am new at this I hope that I can find some one who has had experience with this. I’ve played around with epoxy a little and wet lay up stuff but I’d like to make a mold and from that mold produce a carbon fiber part of decent quality. In the past I’ve never used a tooling or surface coat and I’ve always noticed print through and bubbles and imperfections in the surface (wet lay up). From here http://www.westsystem.com/ss/assets/HowTo-Publications/Vacuum-Bagging-Techniques.pdf I read that high density filler and aluminum powder should be used in the first coat of mold making to prevent fish eyeing and make the coat tough and in the first coat of the part from the mold colloidal silca should be used to prevent print through. My question is if those things work so great then why wouldn’t you use them every time in every surface coat and if these will cloud the clear of a carbon fiber part and lastly what have you guys actually used with success? Thanks for the help.
No advice? Well I went ahead and purchased filler and silca. I will post my results. Guess I gotta just learn through trial and error.
I didn’t read the article but surface coats with fillers, regardless of the filler, can still print-thru. The print-thru happens because of the shrinkage of resin in the backing of the mold. The key to eliminating the print-thru is allowing the resins to adequately cure. Pulling the mold off the plug to soon is the primary reason for the print-thru.
I like to use MGS L285 epoxy resin to make my surface coats. I add 29% by weight of West System 404 High Density filler and 11% graphite powder (West System 423). This has proved to be tough and easy to work with. I brush it on the plug. I don’t like using aluminum powder in the mold because I see a sheen change in the mold surface if I scrape it with a Popsicle stick. This doesn’t happen with the 404 and 423.
You also want to use light fabrics (1 ounce and 2 ounce) for the first several layers of your mold. I often use very fine fabrics like 6 ounce Style 6580 after the light glass as an insurance against print-thru. If you jump to 10 ounce coarse weave right off the bat you will have problems if you have to heat cure the mold without the plug in it.
I often let my epoxy based molds cure at room temp for 4 days. Then I begin a very controlled heat treatment where I raise the temp 2*F per hour. Slow curing is the way to go in my experience. I’ll take the heat as high as I feel is safe for plug. Then I’ll demold the plug and continue to heat cure the mold very slowly if higher temps are needed.
Some resins are prone to print-thru more than others. I’ve been using Adtech tooling resin (EL-301 and 302-PC) for low temp tools and been very happy and have had zero print-thru issues.
Here is a link to recent post I make about print-thru: http://www.compositescentral.com/showpost.php?p=42106&postcount=2
I also attached a picture of what a mold can look like. This mold had no sanding or polishing.
Where are you buying your MGS L285 Resin?
I’ve been getting it from Aircraft Spruce. MGS L285 is a phenomenal epoxy resin for high end and demanding structural parts. I don’t use it for “bling” parts because it’s pretty expensive.
Here is the part i am making a mold from, im very proud of it. It is a cooling panel for a 07-08 350z that i made from scratch. I wasnt happy with the ones that were available because they were designed for the 03-06 Z which has only one intake scoop, hence the 2 intake scoops or “humps” on this panel.
Ok so i completed the mold. ill explain the process and include any tips that i thought was helpful. I placed the cooling panel on some hard wood backing (stuff clipboards are made of) so i could make my lip/edge for my excess to hang off of and vacuum bagging to go. i filled in the cracks with modeling clay and after lots of waxing and a few coats of pva release. i layed down 2 coats of gel coat. From previous experience i noticed that my “gel coat” always came out with bubbles and all kinds of wierd imperfections (fish eye, ect). So after some research i decided to add West High Density filler to thicken the “gel coat”. After the gel coat i layed down diffrent weights of woven glass (starting from lightest to heaviest) and then waited for 24 hours for the epoxy to harden. I should have waited longer but dont have the patience. Anyways the piece came out fairly good. I do have a few areas in the mold i need to fix before i can produce a part. First the PVA mold release left a streaky surface that i have to buff out. I put it on by rubbing it on with a cloth which caused some streaks. The second thing that i need to fix is the area between the part and the mold edges where the clay was. becase the clay surface was not perfectly smooth, this are was not smooth on the mold. I think next time i do this i will use filleting wax which might give me a smoother surface. If anyones knows a better solution please share. The third thing is the hole in the middle of the cooling panel is too steep on the mold. I should of made it shorter so the transition is not so drastic and causes the weave of the part i make to appear distorted. I meant for there only to be just barely a line so i knew where to cut but instead i created a kind of “ledge” that will force the fabric to bend around a corner which i am trying to avoid. I can fix this by simply sanding the ledge down. And lastly some of the clear from the plug stuck to the mold, but this was a easy fix as it just chipped right off with my fingernail. This just means ill have to repaint/reclear my plug if i plan on using it again. The next step is to strengthen the back of the mold so that it lays perfectly flat and does not flex when i am making a part in it. If it flexes then there will not bea good seal on the edges of the cooling panel. So im going to work on perfecting my mold while i am waiting for my vacuum pump parts to arrive.
Hey Simon, just on the subject of the clay leaving an irregular edge on your mould - on all the videos I have seen, the clay or filleting wax has been scraped down using a paddle pop stick or similar, or if there’s a straight edge I have also seen a razor blade used to cut the clay into a straight edge.
Maybe give that a try? I think if you just pressed in the clay with your finger and left it, that would be the reason for the irregular edge (which would most likely still happen if you use that method with filleting wax).
Thanks Mugget, this mold turned out ok. Next time I would definitely make my flanges bigger and instead of using clay I think I will permanently bond my plug to the backboard with bonds and make it all one piece. Now if I can just get the air bubbles out of my laminate ill be good!