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I need convincing

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I need convincing

Postby 3InletsWindsports » Sun Apr 22, 2018 1:00 am

When the advantages of Carbon fibre and its stiffness versus weight is inherent in the continuity of its fibres and the ability to direct the fibre direction to best effect.
And in doing so minimise the resin content.

So how does chopping up the fibres into small enough pieces to then mix with enough resin to make it an injectable paste come close to the above.

Or is it not close?

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Re: I need convincing

Postby zfennell » Sun Apr 22, 2018 1:27 am

Not close.
But generally homogeneous or isotopic material properties.
Still has potentially low resin content with strength and modulus that exceeds “neat” resin.
I’m sure it’s good for use in fillets or thickened fillers/adhesives in areas with loose fitting parts.

Pultrusion / extrusion techniques can regain some of the fiber alignment benefits.
But the proof is always found in material properties data sheet ( actual test data results)
If the vendor cannot or will not offer that data look elsewhere.
Some folks are only selling light weight or thermal conductivity or perhaps electrical conductivity
With strength or modulus as a secondary property.
Regardless, they all are well defined material properties that should be measured before you use them as a design consideration.


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Re: I need convincing

Postby tomtom » Sun Apr 22, 2018 9:06 am

With chopped fibres there is actualy resin ratio where it start to be too dry and mechanical properties start to worsening. You need resin to hold part together /there are no continuous fibres to take strain/ . Im not sure but i think as small as 10% fibre ratio is max which actually do something positive in tensile strength. But its holly grail of composite manufacturing productivity so there is and will be new development

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Re: I need convincing

Postby TomW » Sun Apr 22, 2018 9:35 am

I haven't done any research, but Audi is showing a large injected CF part as part of a dashboard on a concept vehicle. It's mostly an aesthetic experiment.
This " new" CF injection molding is just further development of the fiber reinforced thermoplastic injection molding done for over 40 years.

In Hf manufacturing, The benefits of the method would be almost zero manual labour, and super low part cost on a high priced product. And let's say the performance tradeoff is not noticeable by the vast majority, and volume, of the market. Sounds good, right?
The other thing might be availability of manufacturing using certain methods. Might be a shortage of good CF suppliers as there's a lot of products now being made in CF.

But don't forget that people care about aesthetics, craftsmanship and the feeling that someone put time and effort into the product. This is particularly true when the user is passionate and engaged in the activity / product. I'm not buying a toaster ( no offence toaster lovers).

My guess is that as the design development curve flattens, the market segmentation stabilises, and volume increases as Hf becomes (?) more mainstream, there will be advances made in wing and fuselage production methods that allow more " pop out" manufacturing.

Further down the road, we will see wings and fuselages 3D printed in one piece, separately or together. And you will have 100% customisable to your style, size. Methods for this exist today but the printers are too small.
They won't be cheap though.

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Re: I need convincing

Postby revhed » Sun Apr 22, 2018 12:22 pm

I have "sliced" carbon and mixed with quality epoxy MANY times and has always done what I asked!
I use 2 new blades in razor knifes and cross them together pull apart on clean glass to get good clean 1-2 cm lengths.
Wear gloves, goggles, tyvek full body suit, and GOOD MASK as air will "sparkle", fuckin NASTY shit! :angryfire:
I feel the key is how much resin to mix in, I do it by feel and because SO many times have got it wired!
Filling holes, adding filites, even structral elements, ect..
Has always worked knowing roughing up surfaces and acetone clean is key to adhesion and vac sac for pressure!
I am willing to bet that the pros who know way more than me could pull off a lot with said technique!

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