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quinn
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So far having bad luck with high temp tooling. Mostly issues with post curing off the plug causing surgace issues. Anyway, out of fruatration im ready to just machine some solid molds. The price isn't all that bad considering what I've spent so far on high temp surface coat and epoxy.
So I watched the video on this tooling board and it says it's great for master patterns and can be used directly as a mold for "small" production runs and prototyping. What exactly does this mean? I'd like to mill a mold directly into this stuff and get some decent use out of it. Will it not last long with repetitive use? How many pulls will I get and what happens when I get beyond that point? Will it be ok for maybe 50 parts or so? Maybe recondition with more s120 at that point?
I'm also finding it very difficult to get a pinhole free surface in prepreg with vacuum bagging. Also not really happy with the wrinkles on the inside of the part. Needs to have a not so horrible surface in there. I'd like to solve both these problems with either a custom bladder or expanding silicone, but I'm not sure what this tooling board will hold up to. It will be a 2 peice mold, similar shape to football, each half milled out of solid block of tooling board with minimum wall thickness around 25mm. Will the mold hold up to some decent pressure? Nothing crazy, maybe 25 psi, just need a bit more than what you get with vacuum.
I realize my other option is to mill a plug from the tooling board and that would solve my problem of post curing mold off the plug since the tooling board can handle the post cure, but I would still prefer to skip all that mess and mill a mold directly since I know nothing can really go wrong. Less work and no dealing with surface coat and lay up.
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Lester Populaire
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+xSo far having bad luck with high temp tooling. Mostly issues with post curing off the plug causing surgace issues. Anyway, out of fruatration im ready to just machine some solid molds. The price isn't all that bad considering what I've spent so far on high temp surface coat and epoxy. So I watched the video on this tooling board and it says it's great for master patterns and can be used directly as a mold for "small" production runs and prototyping. What exactly does this mean? I'd like to mill a mold directly into this stuff and get some decent use out of it. Will it not last long with repetitive use? How many pulls will I get and what happens when I get beyond that point? Will it be ok for maybe 50 parts or so? Maybe recondition with more s120 at that point? I'm also finding it very difficult to get a pinhole free surface in prepreg with vacuum bagging. Also not really happy with the wrinkles on the inside of the part. Needs to have a not so horrible surface in there. I'd like to solve both these problems with either a custom bladder or expanding silicone, but I'm not sure what this tooling board will hold up to. It will be a 2 peice mold, similar shape to football, each half milled out of solid block of tooling board with minimum wall thickness around 25mm. Will the mold hold up to some decent pressure? Nothing crazy, maybe 25 psi, just need a bit more than what you get with vacuum. I realize my other option is to mill a plug from the tooling board and that would solve my problem of post curing mold off the plug since the tooling board can handle the post cure, but I would still prefer to skip all that mess and mill a mold directly since I know nothing can really go wrong. Less work and no dealing with surface coat and lay up. I found that the surface quality start to deteriorate already after 5 pulls with the tooling board moulds. reapplying sealer is not really an option once you started applying domoulding agent (I think, would be nice to get some input on that from someone...). I would never try to pressurize a mold made from tooling board. it is not a structural material. I think the best way for you would probably to mill a plug from high temp. tooling board and then make moulds from tooling prepreg. However, i wonder if you are expecting a little too much from a moulded surface. even if you have a mirror like surface, 2 weeks after demoulding you will get surface imperfections due to relaxation of internal stresses in the composite. this is just the very nature of bringing two so vastly different materials together that absorb humidity differently and have very different thermal properties. If i need a perfect finish i would always varnish the part. especially with a two part mould. I know this is additional weight you do not want to have, but i think it is either this, or a satin finish that hides defects better.
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quinn
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Group: Forum Members
Posts: 155,
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+x+xSo far having bad luck with high temp tooling. Mostly issues with post curing off the plug causing surgace issues. Anyway, out of fruatration im ready to just machine some solid molds. The price isn't all that bad considering what I've spent so far on high temp surface coat and epoxy. So I watched the video on this tooling board and it says it's great for master patterns and can be used directly as a mold for "small" production runs and prototyping. What exactly does this mean? I'd like to mill a mold directly into this stuff and get some decent use out of it. Will it not last long with repetitive use? How many pulls will I get and what happens when I get beyond that point? Will it be ok for maybe 50 parts or so? Maybe recondition with more s120 at that point? I'm also finding it very difficult to get a pinhole free surface in prepreg with vacuum bagging. Also not really happy with the wrinkles on the inside of the part. Needs to have a not so horrible surface in there. I'd like to solve both these problems with either a custom bladder or expanding silicone, but I'm not sure what this tooling board will hold up to. It will be a 2 peice mold, similar shape to football, each half milled out of solid block of tooling board with minimum wall thickness around 25mm. Will the mold hold up to some decent pressure? Nothing crazy, maybe 25 psi, just need a bit more than what you get with vacuum. I realize my other option is to mill a plug from the tooling board and that would solve my problem of post curing mold off the plug since the tooling board can handle the post cure, but I would still prefer to skip all that mess and mill a mold directly since I know nothing can really go wrong. Less work and no dealing with surface coat and lay up. I found that the surface quality start to deteriorate already after 5 pulls with the tooling board moulds. reapplying sealer is not really an option once you started applying domoulding agent (I think, would be nice to get some input on that from someone...). I would never try to pressurize a mold made from tooling board. it is not a structural material. I think the best way for you would probably to mill a plug from high temp. tooling board and then make moulds from tooling prepreg. However, i wonder if you are expecting a little too much from a moulded surface. even if you have a mirror like surface, 2 weeks after demoulding you will get surface imperfections due to relaxation of internal stresses in the composite. this is just the very nature of bringing two so vastly different materials together that absorb humidity differently and have very different thermal properties. If i need a perfect finish i would always varnish the part. especially with a two part mould. I know this is additional weight you do not want to have, but i think it is either this, or a satin finish that hides defects better. Ah yes, didn't think of that. Not gonna be applying more sealer on top of frekote. As for the finish im looking for, it doesn't need to be perfect, but so far my results have been far from acceptable. I did some sanding in the second mold, got it polished up and looking pretty decent, then tried laying up a prepreg part. The mold behaved as though it was never post cured. It lost its gloss completely and the weave pattern of the prepreg actually printed into the mold surface. I post cured my mold to 130c before hand, holding at that temp for 3 hours. The prepreg part was cured to 120c. Not really understanding why my surface coat is behaving this way. Sounds like the machining molds straight into tooling board isn't gonna be an option. like you said, I'll have to mill a plug from it and I guess try again with laying up a mold. Being able to post cure on the plug will surely help, but I guess I'm just traumatized by the repeated failures so far. Already many hours and dollars into this with no good results. Basically statting completely over now. Just wish it was as simple as milling a mold and being done. My aluminum boom molds came out beautiful and give a perfect finish, but that method isn't an option for this. Probably would be over a thousand dollars worth of aluminum and just way too much mass to heat in the oven. Oh wait, hmm, didn't think about the tooling prepreg option. I would very much love to never have to deal with high temp surface coat ever again, literally having nightmares lol. I think it would be pretty hard to screw up a mold using tooling board plug and tooling prepreg mold. Maybe I'll go that route
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Lester Populaire
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yeah i know the frustration and wish i could give better advice to others, but there are just a milllion little things to think of and little differences between products. What you describe sounds like the glass transition temperature of your resin was not high enough. This can be because the post curing was not sufficient, the resin system cannot get a glass transition temp which is high enough, or the part got hotter than the oven temperature during curing due to thermal runaway.
With the thin walled canopy you are making the last one is certainly a non issue. I don't know the system you are using to make your moulds, but it is very well possible that 3h post curing is not enough. i am using a mould resin that needs 10h at 120°C to get the maximum glass transition temp. with ramps this takes more than 24h, which is rather annoying...
So double check that.
Furthermore i would stay at least 20°C away from the Tg while curing. But I'm sure you could bake your prepregs at lower temp. than 120°C?
cheers, Lester
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quinn
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Group: Forum Members
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+xyeah i know the frustration and wish i could give better advice to others, but there are just a milllion little things to think of and little differences between products. What you describe sounds like the glass transition temperature of your resin was not high enough. This can be because the post curing was not sufficient, the resin system cannot get a glass transition temp which is high enough, or the part got hotter than the oven temperature during curing due to thermal runaway. With the thin walled canopy you are making the last one is certainly a non issue. I don't know the system you are using to make your moulds, but it is very well possible that 3h post curing is not enough. i am using a mould resin that needs 10h at 120°C to get the maximum glass transition temp. with ramps this takes more than 24h, which is rather annoying... So double check that. Furthermore i would stay at least 20°C away from the Tg while curing. But I'm sure you could bake your prepregs at lower temp. than 120°C? cheers, Lester Ok, maybe my post cure wasn't long enough or hot enough. My prepreg is specd at 120c cure So I don't think I can go lower, however I could go higher with the post cure on the mold. I didn't really know how much higher the post cure needed to be so I stopped at 130c assumining it was enough. Sounds like not the case. All that being said, tooling prepreg mold on tooling board plug sounds like a pretty attractive process so I might go that route for the next attempt. I need to order the tooling board from easy composites anyway so I can get some of their tooling preg. Would you say the prepreg mold is an easier process and less likely to go wrong? Aside from my post curing issues, I still had a hard time avoiding tiny air bubbles in the surface coat. It was better on the second try but not completely void free. I would rather avoid surface coat completely and do a prepreg mold if you think it's a more reliable process with less chances for things going wrong.
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Matthieu Libeert
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why not CNC mill it out of Aluminium then? would solve all the possible problems for multiple pulls compared to the tooling block. An other way you could try is use the tooling block and use the Hight temp gelcoat and high temp epoxy resin to make the mould. About the wrinkles on the back. You could try it with peelply on the back of the prepreg but it's not recommended as it will take some of the resin in the prepreg, that is needed for a pinhole finish.
Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com  
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quinn
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Group: Forum Members
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+xwhy not CNC mill it out of Aluminium then? would solve all the possible problems for multiple pulls compared to the tooling block. An other way you could try is use the tooling block and use the Hight temp gelcoat and high temp epoxy resin to make the mould. About the wrinkles on the back. You could try it with peelply on the back of the prepreg but it's not recommended as it will take some of the resin in the prepreg, that is needed for a pinhole finish. At this point I'm seriously considering aluminum. I was about to order the tooling board and tooling prepreg, plus other needed things, board adhesive, s120 sealer, etc. I was up to almost 800 dollars shipped so put a hold on that. Originally I thought it was gonna be over a thousand dollars to do aluminum but I must have calculated wrong, it's only about 650 shipped, so at this point I'm leaning toward the nice aluminum molds. My only concern is the weight. Need to model the molds to see what it is, but the rough stock is almost 100kg. Most of that will turn into chips. I think I can get the molds down to 30kg or so but that's still a ton of mass to be heating up in the oven. Still would be so sweet to just mill these molds out of aluminum. My boom molds came out so perfect and I'm sure they will last forever. Aluminum molds will also open up possibility for bladder or expanding silicone Yeah after thinking about it aluminum is really gonna make the most sense with the machining capability I have. Also after thinking about it, because of the roundish shape of the mold, 10 or 15mm wall will make a very strong mpld capable of pressure do more like 15kg final mold weight. My machine will get a serious work out removing 85kg of aluminum, but just comes down to time and insane chop management. About 20 hours just for roughing and probably have many trash bags worth of chips. Sucks to buy 650 bucks worth of aluminum and turn 85% of it into chips, but it's gonna yeild the best results and actually still be cheaper than a prepreg mold on tooling board plug
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oekmont
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Have you considered infusing the molds? When I read about using jelly resin, it was unavoidable that the air pockets would ruin the mould during post cure. At least the first layer has to be absolutely perfect. And that means using a fine cloth and using thin resin. Anything much more viscous than fresh standard laminating epoxy will not wet out the cloth air free. With a fine glass cloth and black gelcoat you can see how it is getting harder to get the bubbles out as the resin starts increasing it's viscosity.
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quinn
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Group: Forum Members
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+xHave you considered infusing the molds? When I read about using jelly resin, it was unavoidable that the air pockets would ruin the mould during post cure. At least the first layer has to be absolutely perfect. And that means using a fine cloth and using thin resin. Anything much more viscous than fresh standard laminating epoxy will not wet out the cloth air free. With a fine glass cloth and black gelcoat you can see how it is getting harder to get the bubbles out as the resin starts increasing it's viscosity. On my last try I vacuum bagged the mold after wet lay which seemed successful at removing all air, but the problem still remains that post curing off the tool (my plug was mdf and duratec) seems incredibly finicky. I didn't have positive dimples in the surface of the second mold like i did the first try, but the surface still didn't stay perfect through post cure, just kind of a wiggly surface. With another attempt of doing it on a proper tooling board plug and post cure on the plug, I could probably get the results I'm looking for, but by the time i order tooling board, more surface coat, etc., it'll cost just as much as milling these out of aluminum which is a process Im familiar with and will work perfect at making an excellent mold. Nothing can really go wrong.
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