Hi to all, Greetings from Tijuana Mexico
First of all excuse mi grammar, I working in a company who made BOWS, musical bows to play Violin , Cello and Bass, we use fiberglass from axiom and carbon fiber from Newport, and a kind of aluminum sandwich as mold, we use a silicon bladder and high pressure air to inflate (90 to 100psi) in a press with temperatures (250 to 255[FONT=Calibri]°F).[/FONT]
I been reading the topics and I don’t find any similar to mi problem that’s why I prefer write down:
My major problem is the alignment of the bow, I mean one end is not align to the other end (some pictures is attached), y check my rolling process and now we rolling straight, y do some test with the air pressure and temps and curing time but nothing , I´m still have the same problem.
The mold have 15 cavities, every cycle I have 8 to 10 parts NG, so you can figure at the size of the problem.
We use a jig with camera to check if are ok or not
So any idea of how can be control the alignment problem?
Thanks in advance.
So basicly what you mean is that there is torsion in the bows? (twist).
If so, this is due to the fibers still not aligning up. Another cause can be temperature distribution. From every batch you get 5 or so good ones. Do these always come from the same cavities in the mould?
One more thing to look at is the cooling down process. Do not cool too quickly. (or open the mould too early)
Thank you Herman,
Yes I mean the parts have torsion, let me see the temp distribution in the plate of the press and see again the alignment of the fibers, let see if we wait some 5 to 10 min, of cooling out of the press with the mold closed can help, and no the parts no good, not came from the same cavities
again thanks.
You should wait until the parts cool down to 60°C.
Maybe 10 minutes could not be enough.
It depends also by the Tg of the resin.
Alexbows,
We run some aluminum tools as well, at present we can cycle the moulds as follows:
4 to 6 minute infusion
30 minute heat ramp from 72 F to 275 F
At the 30 minute mark the moulds are cooled back down within a 5 to 10 minute cycle to 90 F, parts are de-bagged and pulled from the mould by hand, no wedge or forced popping from the mould.
Please answer the following:
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What is your cycle time after the infusion -or- how long till it can be removed from the mould?
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Are you pulling the parts by hand or using wedges and force to pop the bows?
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Do you have an IR or laser temperature gun to verify part temperature.
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Please explain the silicone bag for me? You mentioned a press? So I understand, the silicone bag is inflated to 90 to 100 PSI to create the “B” side pressure to the “A” side of the mould. Then there is a press cycle?
Is it possible the silicone bag under pressure is not uniformed and causing the alignment issue? How are you pressing it? Is the press equal size to the mould dimension, meaning uniformed?
The parts should not twist (torsion) on you, there is something wrong in your process from when the lay-up is created and resin is shot and cured. I would guess it has something to do with how your parts are “pressed”
Took a better look at first pic, I see the “B” side to the left, the silicone you refer to are the tube strips between the bows?
PS…you should polish that tool to a mirror, makes for nice parts…
Thanks for you answer SLS,
we dont do a “infusion” it is a bladder molding process, the silicon bladder receive the air and get inflate and make the shape of the cavity. the total cycle is 20 min since the mold is in the plate thru the part is removed, and yes we use a tool to remove the part from the mold.
yes i have a laser to check the temps, actually the part when we open the mold had 230 +/- degrees.
the silicon bladder dont sound to me as a somethig that may cause the problem due we remove inmediatly after we take out the air valves.
You can’t pull the parts off the mould so hot and hope they stay straight. They have to cool down way more.
Another problem is the aluminium mold: it has different CTE and temperature inertia than carbon and this doesn’t help.
Plus, you wrote that you use also fiberglass. Once again, different CTE when used toghether with carbon.
Another problem is rolling the fibers on a bow: it’s impossible to get straight fibers along the bow lenght: this leads to not simmetric fiber placement through the laminate thickness along the bow. The use of a braid helps a lot.
I would have used full carbon bows in a carbon tool (it’s faster to warm up an to cool down too).
Are the bows made only with uni-directional materials?
If they are made with a constant section, the use of pultrusion could be interesting.
Thank everybody, for you prompt response i been busy checking your recomendations in process, but still i´m not an expert in the tecnical language
it has different CTE and temperature inertia than carbon and this doesn’t help.
what is the CTE Roberto?
Are the bows made only with uni-directional materials?
it is a prepeg…like a cross of fibers in zig zag
CTE is ‘Co-efficient of Thermal Expansion’ which means the rate at which the material expands when heated. Aluminium has a much higher CTE than carbon fibre, for example Aluminium could be 20E-6 mm/mm/degree C where carbon could be 3E-6 mm/mm/degree C.
To prevent warping you want the fibers going in 0*, 90*, and 45* to the length of the part. If you are only putting the fibers on 0/90 then its very likely that the part will develop a twist. If you are putting the fibers in both 0, 90, +45, and -45 and getting torsion/twist then move the +/-45 fibers to the outside of the structure to increase the torsional stability.
Ideally you want the orientation of the fibers mirrored from the inside of the stack to the outside. Like: +/-45, 0/90, 0/90, 0/90, +/-45 for example.