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Bladder Molding Parts (Need Advise)

Bladder Molding Parts (Need Advise)

Bladder Molding Parts (Need Advise)

I have designed a platform for a personal project. I am needing to know if I am on the right track. I plan on using Latex bladder molding with clam shell molds. I have never attempted to do a project like this but I am ready for the challenge. I have attached a picture on how I have broken up the parts for bladder molding. I would love constructive advise or tip on helping me achieve the best results. I have other pics I can up load for better observation. Thanks you all so much.

RE: Bladder Molding Parts (Need Advise)

Hi Ducks,

I'm not a professional, or an expert in composites by any means, but i do have a couple of years experience with composites, and have tried to make some tricky stuff using a variety of methods including bladed molding technique you are proposing.

At first glance, I can offer the following feed-back:

- The parts you are proposing to manufacture are very complex. The process can get very expensive very quickly if you (and you probably will) keep scrapping parts. Consider simplifying geometry as much as possible. and make things as large as possible to give yourself the best possible access.

- your 'W' section piece with 5 spigots in the lower left of your image doesn't look like it will assemble to the first 'rung' (with 3 spigots). All three spigots need to be co-linear to assemble, the inward angled spigots won't line-up until fully in-gauged (if that makes sense).

- The 4 lugs you have extending from the top surface of the tubes should be separate components bonded in place as they would be impossible to include as a feature integral to the part.

- Don't underestimate how stiff & strong the mold tools will have to be to withstand even modest pressures (do some calcs to get a feel for the resultant forces). At the very least you're mold tools would need to be machined from Alu and bolted together at regular intervals. If you intend on making you're own molds from male patterns, then i would look at an alternative process as its unlikely you would be able to make you're tools robust enough.

- Radii should be as large as possible, I would say a minimum should be R3.0mm + laminate thickness as a rough guide, but bigger will always be much better!

- Don't attempt to create you spigot shoulders by draping material across the stepped geometry. Shoulders like this should be created by the edges of the ply stack, and the spigot created by further plies (like a kind of lap-joint).

- Never assume the the bladder pressure will chase material into corners etc. - it won't. material needs to be conforming to the mold tool during lay-up, and i would de-bulk at every odd numbered ply layer (1, 3, 5 etc..).

- Tool heating? (I'm assuming prepreg here)

- finally, make sure you understand all the COSH, HAZ-MAT & Material data sheets before you start. Health and safety all the way!

All of the above assumes you are using prepreg material, based on you're proposed manufacturing process. I definitely wouldn't rule out a wet layup, which could still be consolidated under vacuum, or even vacuum infusion. I've not seen a wet lay-up with inflated bladder before, but I'm sure it has been done!

If you decide to go ahead with this then good luck!

Best wishes,


RE: Bladder Molding Parts (Need Advise)

Hey guys,

First post! Although, not a composites engineer, like CarbonDog I have a couple of years experience working with them and echo how hard this will be as a first project!!

CarbonDog has covered most of it, my suggestion would be to avoid bladder molding with parts this complex and instead use solid dissolvable mandrels like those used by many bicycle manufacturers (start from about 1:20 - http://www.youtube.com/watch?v=LJ46J3NQIVg). Developing a bladder this complex may not be effective and will likely be very costly. You can create your own primitive dissolvable mandrels by using wax or a water soluble ceramic.

Also, it should be possible to bladder mold, using wet layup, some good threads can be found here: http://www.rcgroups.com/forums/showthread.php?s=a3.... This will however make it much harder to achieve a good surface finish,though it will allow you to use a moulding material with lower thermal requirements (epoxy-carbon fiber-sand moulds might be a good fit).

Good luck!


RE: Bladder Molding Parts (Need Advise)

Thanks Carbon Dog & Jeremy! Carbon Dog, The W part that you are calling! Great Point, it wont' fit together. I know this is a complicated part however, everything I do is outside the box and isn't easy! I want to make things(no matter how hard they are) that haven't been done by others before. Love challenges and I have nothing to loose(except money)! Thanks for the post, I really have a different options after your posts! Thanks a million! DUCKS2525

RE: Bladder Molding Parts (Need Advise)

Your production methods here depend on the number you are making: Make the part in one piece, or put joint lines where you know you can plug parts together
One part, hand carved or machined tooling wax core, Hand lay, wet lay up on male mold, sand and putty for final paint, melt out core.
More than 10, Fiberglass female mold, insert tooling sheet wax for core dimensions, make water soluble ceramic core inside mold with wax stand off. Remove wax, fab with low temp pre-preg or wet layup. Use spring loaded clamps to drive mold closure as pre-preg softens.
More than 50 Machined aluminum mold, Water soluble ceramic core from separate mold, low temp pre-preg.
More than 200 Machined Metal mold, Hot salt preform from machined mold. Hi temp pre-preg, dissolve salt with boiling water after cure.
While salt is more trouble to make and cast with its attendant high temperatures, production rates are faster, it is also easier to get out with boiling water than water soluble ceramic.

You are judged not by what you know, but by what you can do.

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