Roman

Fibreglass, Carbon Fibre, Paper Mache - The composites chat thread

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I've been meaning to have a play with zinc stearate - there is so little practical information about this sort of thing past around industry (in nz) looser consultants wanting to keep baby powder a sellable secret.

are you familiar with tim scott/mr handley (Plexinate)? -he's good for a yarn about this stuff, we are currently using polyurethane/polyester mix to try and improve surface finish in closed mold lrtm process, multi-year battle. It's 2018 I just want to buy working solutions not know about these things!

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He is our supplier of PU. He's supposedly been working on a mix of P100/P200 (for a couple of years now) all in one barrel but we haven't heard anything recently

Mixing PU and PE doesn't really seem to end too well as getting the cure rates balanced between the two can be a nightmare.

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Haha yeah - although probably easier at room temp with all the time in the world than squishing through a hole

if we could get v0 + decent uv from unpigmented unfilled resin we would change to literally anything else in a heartbeat - I'm keen to learn about liquid caprolactam inmold polymerisation to nylon 6, there is a guy in Rotorua who apparently does it - he hung up on me immediately hahaha 

The future sure doesn't feel bright in high tech nz manufacturing, just lots of losers wanking themselves about 3D printing and a handfull of actual g.c's who are getting old.

(I'm sitting in a hotel with nothing to do hence the rambling) 

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I've been playing around some more with mold making. 

A little sparse on pictures right now but I'll add some later. 

Here's what I've learned lately. 

Making Male and female molds for a big bellmouth. 

3d printed some big molds and filled them with plaster.

First attempt at this was no sanding of the molds, so they had layer lines from printing. Which hasnt previously been an issue.
Not much wax on molds. A pretty shitty layup as I mixed epoxy then was trying to cut the cloth as I felt needed to patch on some bits. 
This sucked from start to finish haha. 
Was in too much of a panic of trying to get things done before epoxy pot life ran out.
And then in a rush to try and cut and arrange the pieces, so not very good layer coverage. (thin in some areas and thick in others)
Using big clamps to hold the 2 halves together, squeezes out a massive amount of epoxy and compresses them together awesomely.
To get the two mold halves apart I had to use some big screwdrivers and chisels to hammer in around the edges to split it. 
I ended up having to cut the bellmouth off the mold because there is no way it would budge on the part where there is no draft angle and the layer lines holding it in place.

Attempt 2:
Still trying to be lazy and not sand the molds, I thought I'd try cover the pipe part that had no draft angle with brown packing tape.
This time I arranged the cuts of fabric BEFORE mixing the epoxy. Then instead of laying them up on the part then brushing on epoxy. Much better.
Laid the sheets out flat and brushed epoxy onto them all before laying any of them up. 
This worked better for 2 reasons - Getting all of the epoxy out of the pot means it doesnt cure so fast. and it gave it some time to get rid of some bubbles.
Then it was actually way easier to drape these onto the mold as well. 
So this all worked reasonably well, except for that where there were crinkles in the tape made for a shitty surface finish on the part. But it came off the mold in one piece at least.

Attempt 3: 
So this time, finally spent a few hours sanding the molds to a smooth surface finish up to 800 grit.
Then a bit too much wax as I was still paranoid about having it all stick when its such a big part. 
But then same as above, doing an off-part epoxy layup and improved shape of my cuts again and more layers.
This time, it all came out great!
I broke the lower mold in the process of separating them, but draft angle wasnt an issue and the surface finish on the actual part was nice. 
Only problem is the white appearance in the epoxy from the wax, so I think its time to retire the car wax as a mold release agent haha.
Overall this 3rd attempt is a good strong usable part though, so surface appearance aside I'm not to bothered about having broken the mold as I've got the part I wanted. 
Could probably repair it if I wanted to make same part again. Or keep it as 3 piece haha.

Next thing

For the next thing I want to make molds for, its basically an L shaped pipe with a big radius. so there's no way I can have a reusable core because you cant get it out.
Also I want to try further reduce the amount of 3d print time and plastic used for the molds too. 
So I've borrowed some vacuum bagging stuff from a friend.
I am going to make a dissolvable core from HIPS filament, and then have thin outer mold halves from PLA that are just say 5mm thick solid with no infill or plaster. 
Then chuck this whole lot inside a vacuum bag. By not having to make a mold solid enough to clamp the halves together, material usage can be a lot lower. hopefully. 
I'm nearly ready to print PLA outer mold halves, then presumably go through a bit of a learning curve with HIPS filament.
Hopefully my learnings from above mean I get the layup right first time, as I only really get one chance per core that I print.
This time I've got some PVA release agent for the PLA so should be a nicer surface finish. 
I've tried vaccum bagging some small test parts with bagging material and butyl tape. Its been infuriating to try and chase the vacuum leaks haha. 
So I'm going to buy a food bag sealer thing so I can just make a big envelope of bagging material and melt the perimeter together.
Rather than trying to form a perimeter with butyl tape which is fiddly/expensive.
Hopefully this method will be quicker and more reliable as any overlap will just get melted together for no leaks. So long as its strong enough to withstand the vacuum.

fake edit: Will add some pics to this post later


 

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Have you tried putting some air ports in your moulds so you can just hook up an air compressor to separate the parts from the mould?

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That's a good idea! 

I'm not sure if it will blow PLA to smithereens but I'm willing to try haha.

Would probably serve as paths to help the epoxy to run out as well. 
 

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What do you need one for, and do you have 3 phase power? 

I've got a few big 3 phase ones here, but probably akin to swatting a fly with a missile if you're doing something small.
 

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3 hours ago, Roman said:

That's a good idea! 

I'm not sure if it will blow PLA to smithereens but I'm willing to try haha.

Would probably serve as paths to help the epoxy to run out as well. 
 

You'd probably be fine.

Good thing with 3D printing is you can design it to route the air to wherever you want, allowing you to focus on the super sticky bits. But if the ports get filled with epoxy then they essentially become useless so you could possibly try something like a 3D printed plug that you can pull out and put the air supply on to after making the part.

I'd recommend keeping the pressure low though, 1 bar (15 psi) will give you 1 kg/cm^2, so a 200 mm x 200 mm part would have 400 kg pushing it apart for example.

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hi David.

What is the point in using an inner and outer mold if you are vac bagging? 

EG, you could just make an outer mold and then create a vac bag that is sortof this shape (a tube inside a tube) to suck the CF out into the mold.

31kNjmC-WdL.jpg.7b100c4f0af892acdce4a4d4f8bf34b2.jpg

or, you could hold the mold outer together with large hose clamps and blow up some sort of bellow/bladder inside the mold to hold the CF out in place (like a piece of inner tube or something)

 

http://forums.mtbr.com/frame-building/show-tell-monday-milestone-carbon-lugs-909417.html

 

 

 

 

 

 

 

 

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I tried vacuum bagging to just half of one of my molds and it produced the worst parts I've made so far, by far.

Areas get sealed off by the vacuum bag pressure and it pools resin and air bubbles. So it squashed out almost none of the resin. Which is exact opposite of what i was hoping for.

I think I need some of the breather material as outer layer for it to work better that way.

The point of vacuum with inner and outer inside the bag is to uniformly put pressure on the part rather than needing a mold solid enough to take the point loads of clamping only a few areas on the perimeter. And so I don't get bag wrinkles etc on the surface which was another issue.

And I can lay up all of the cloth and have it in place without it moving around while fucking around trying to find vacuum leaks haha.

Obviously the one half method works but I've found it to be super fiddly by comparison.

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8 hours ago, flyingbrick said:

 

or, you could hold the mold outer together with large hose clamps and blow up some sort of bellow/bladder inside the mold to hold the CF out in place (like a piece of inner tube or something)

 

 

 

 

 

 

 

 

I have a mate that makes things using this method. Aluminium moulds that are polished to death. Lay up the cf on both halves, chuck a bladder inside, bolt together, pump up and chuck in hot box for a time.

Impressive results on a 1m long part

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On 4/10/2018 at 21:52, Roman said:

I tried vacuum bagging to just half of one of my molds and it produced the worst parts I've made so far, by far.

Areas get sealed off by the vacuum bag pressure and it pools resin and air bubbles. So it squashed out almost none of the resin. Which is exact opposite of what i was hoping for.

I think I need some of the breather material as outer layer for it to work better that way.

The point of vacuum with inner and outer inside the bag is to uniformly put pressure on the part rather than needing a mold solid enough to take the point loads of clamping only a few areas on the perimeter. And so I don't get bag wrinkles etc on the surface which was another issue.

And I can lay up all of the cloth and have it in place without it moving around while fucking around trying to find vacuum leaks haha.

Obviously the one half method works but I've found it to be super fiddly by comparison.

There is another method.

See if you can find info on latex vacuum bags. The hamilton fg shop told me about it. You paint multiple layera of latex onto your mold, peel it off then lay your material/ resin then lay your latex back on top. The latex becomes your bag material, is precisely the right shape etc 

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Gave it a bit of a scrub with 600 > 1000 grit and came up a bit nicer

With some clear coat or another layer of epoxy it'll be looking pretty sharp! 

ylhiih5e.kyx.jpg

Will try make it prettier once I've finished making the whole intake. 

Printing the molds for the second part of the pipe now (on of the outers pictured)
 

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Please also make one with golfball spec dimples and see if you get any improvements. Include graphs for bonus points.

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Been having trouble with 3d printer but some flow mesh stuff turned up so i could try some resin infusion. Holy shit this is so cool hahaha.

Once you get the bagging right (thanks ned for bag sealer)

It works really well.

(I assume so at least, find out tomorrow!)

sepf0lxg.h51.jpg
 

 

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