Carbon Fibre layer shift in tool

[BrianGar]

So, Ive been working with this a lot lately. One thing I failed to notice, or ask about after walking the floors of a dozen composite factories in Shenzhen is this>

Once the operator has wrapped the pre-preg layers around form as per lay-up sheet/instructions in-front of him, the form then gets removed and bladder inserted before layup is placed in a steam heated two part mould tool for bladder expansion/confirmation to tool walls.

How do they control layer shift as bladder is inflated? Is there enough overlap on layers for them not to care?
From what I saw-Id imagine the shift rate could differ between parts, depending on how firm the operator pressed on said layer/layers to the others.

Perhaps they dont need to care if they have plenty of overlap dialled in. Maybe Im just being anal, but, it does seem uncontrollable, and could result in one part differing aesthetically from another to a keen eye.

Opinions/advice?

BG

 

[MikeHalloran]

All the prepreg I've worked with is sticky, or very sticky.
Shifting would not be a problem.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianGar]

I know Mike, but it still needs to expand slightly to conform to tool surface? Does it expand radially and the strands just get closer circumferentially, that way there would be no strand linear slide-if that makes sense?

 

[MikeHalloran]

If the layup puts the fibers at +/- 45 degrees to a laid-up cylinder's axis, then expansion of the cylinder just changes the fiber angles a little.

If the fibers are at 0/90 degrees to the axis, then there must be slip at the ends of the circumferential fibers.

A useful analogy might be made to tires.
Bias ply tires are, or were, laid up on a cylindrical form, straight between the bead wires, and a bladder was inflated to push the plies outward into a simple mold. The molds typically have just one parting line, at the midplane of the produced tire.

Whereas radial ply tires are laid up on a more nearly tire-shaped form, and the mold separates on many radial and circumferential lines.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianGar]

Mike, thanks, that makes sense. I guess they do shift a little bit 'depending'. One factory I visited made carbon bikes, the handlebars seemed to be laid up all over the place in respect to direction, not in a bad way, just following plans I guess. They did all seem to be +/-45 deg as you mentioned.
Another factory made F3 parts, there, the cloth seems to be at 0/90 to axis, as again you mentioned, so I guess a little conformation shift here made no odds.

Thanks Mike as always for your replies. Ive spent nearly 3yrs now reading the forum, I start at the end of each section and work my way to present day, your name comes up a lot, along with a good few other resident posters. Great to see it over such a period of time. I must support the forum again soon.

Brian,

 

[BrianGar]

Just to add, the F3 part in question was a straight aero wing about 4ft long.

BG