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Old 11-15-2016, 01:19 PM   #61
Zebra

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Also, I'm not too worried about surface finish at all. This is more a proof of concept thing at this stage.


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If you are going to go through all the effort of making a cf part, you might as well do it right. There is no half measures with cf. I understand why you would want to dip your toe before getting serious but the most likely outcome is that you will waste all of your materials and end up with nothing you want to use.

If you are looking for an easier life and a quicker / more forgiving process, I would recommend working with fiberglass instead. It's 100x easier to work with and far cheaper.

If you end up making a fiberglass part you are happy with, you can then use that as a plug to make a mold for CF at a later date. Fiberglass adheres to corners so easily that it even works in a silicone mold...
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Old 11-15-2016, 04:42 PM   #62
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Default preventing voids in closed mold layup

When laminating over foam I think the main thing is to make sure your foam is strong enough to withstand the force of the vacuum. I have access to some sturdy enough foam. But I will def take your point about sharp corners and not design any harsh edges into the shape.
I'll likely be using braided sleeves and possibly MTI infusion hose as it can be laid straight onto the part.
Proof of concept, yes but more in the sense that I'll like the barrel to actually be useable. Anyways, I'm drifting thread this seriously now. But thanks for the pointers.


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Old 11-16-2016, 09:21 AM   #63
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Learning to make your own prepreg gives you a lot more control over the process. My prepreg is significantly higher quality than most of the overpriced commercial stuff. I pre-seal it with all the air bubbles removed before it gets anywhere near my mold.
Zebra,

I appreciate the feedback. I have looked into compression molding, but since our stocks are molded as one piece, it's just not possible. I would be interested in hearing about your technique and resin choices for the prepreg. Are you using a thermoset resin?
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Old 11-20-2016, 02:07 PM   #64
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Zebra,

I appreciate the feedback. I have looked into compression molding, but since our stocks are molded as one piece, it's just not possible. I would be interested in hearing about your technique and resin choices for the prepreg. Are you using a thermoset resin?

I have both heat cure and room temp resin on my shelf. I use both and find the process works well with either. Which one I choose has more to do with what the final product will be used for. If it will be exposed to high heat and needs to stay dimensionally stable then resin with high heat resistance is the way to go.

Choosing one over the other won't help a broken process though. I.e. If you have voids using room temp resin then heat cure resin won't be better. It might actually be worse as the cf fabric will slip away from the mold surface when the resin liquifies again in the oven.

I have made a good number of carbon fiber stocks now with 10 different patterns of varying complexity and I usually mold mine as one piece too. I reserve compression molding for parts with tight corners or small details.

I would consider the stock pattern in your photos to be relatively simple and straightforward. I wouldn't need compression molding to make it without voids. It just requires the right starting materials, good technique and the right mold.

I know a lot of people will not agree with me but I have never had good luck with fiberglass molds for stock making. I find certain epoxy blends to be superior - being both easier to lay up and producing a cleaner finish first time. Fiberglass always gives me more problems. It has poor rigidity which is a terrible quality for long thin parts like stocks. Fiberglass molds are worst off all for any process that relies on a vacuum or inflatable bladders. Hpa or a vacuum easily distorts fiberglass molds with long straight sides like that.


Remember, the difference between bladder molding and compression molding is only that a bladder can be easily removed from a closed mold. There are various solutions and work arounds to give you the benefits of both.

For one particularly difficult pattern I was working with, I made an effective bladder replacement inside the mold using expanding urethane foam. As the foam tries to expand to 20x it's original size, it had the effect of holding the CF against the mold surface like a bladder. I left it in there as a foam core when I was done as it was so light it made no sense to remove it.

I've had success using plastic bags full of sand or hot water too - they were also easy to remove from a closed mold after it was done curing.

One thing I will say though is that sometimes it is better to change a problematic design than it is to invest time and cash in figuring out how to make it work with cf. This is especially true if you are starting a business where you can't afford to be throwing away every other batch because of one tight corner that you could have sanded down.

For a business it is most important to have an efficiency process that works consistently.
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Old 11-20-2016, 02:18 PM   #65
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This is the stock pattern that has given me the most trouble. It's quite literally a nightmare:




This one is made out of carbon fiber sheet molding compound (which is what Steyr uses for their high end cf stocks). It works well for a painted piece. It's light and strong.

It is when I try to replicate it as a cosmetic piece that I have issues. It has tiny 90 degree angles, sharp corners / edges and long flat sides to cause bowing. Plus, the surface has a texture and I wanted to make it without ruining the original.

When I have finally figured out how to make this pattern with an exposed glossy twill weave, I will consider myself a cf master. I can't tell you how frustrating this pattern is to work with....
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Old 11-22-2016, 03:22 PM   #66
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I'm currently in the process of making new molds using epoxy resin with a extra slow gardener and DT 082 high density filler. The mold will have a heavy rigid outer body, epoxy/filler mix for interior detail. This mold design will allow much higher bladder pressures with minimal flexing, which is a problem with the first fiberglass molds. Due to the required demand of the part, mold manufacturing efficiency and life cycle is very important, as well as efficiency in laying up the parts.

I have researched DIY prepreg, but without the use of thermo set resins, I'm not sure how it would work or benefit me. What would be the process to prepreg the cf with standard resins, how would they be preped and stored?
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Old 11-29-2016, 08:31 PM   #67
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Hey Compositesman. Would you mind sharing, or showing pictures of how you attach an air line to your bladder? Thats the only bit I'm kind of confused about at the moment is how you cap the end or install a fitting to it.

Thanks for all the info so far!
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