Bladder Mold

General Composites Discussions Composites Talk
#1

Newby to composites but I want to learn. I have done tons of research and I have come to this point when I need advise before I start cutting a aluminum mold. I hope to use the bagging method that (wyowindworks) uses instead of latex bladder. I’m not sure exactly if my mold is proper. I am going to use UD Zoltek 50k 3 layers, 0,90,45.

  1. Do I need to seal the mold all around (as shown in groove between the mold)?
  2. Can I weld a poly bag to the shape as shown in picture?
  3. With the shape I am trying to do, can I layer it as
    wyowindworks shows for his seams?
  4. Do I need to insert grooves around mold for the resin to flow into?

wyowindworks (you have been a blessing understanding bladder molding!) Thanks a million.

#2

You aredoing a pre-preg part I assume?

You can make a vaccum bag tube using a ‘welded’ bag piece if you don’t have a tube bag. Even a tube bag would have to be sealed on the end.

If you are going to go with vacuum instead of a bladder, then you will have to either seal the tool for vacuum integrity or envelope bag it.

For the seams, you can do it as pictured, you can do it differently… it depends on your design but, yes that is how we are doing it pretty much that way on some aerospace spars with a bladder mold at my work.

#3

Yes it is a pre-preg uni part. The recommended temp for pre-preg is 250F. Will it melt the poly tube? Also where can I get the poly tube at? I recently called Piercan USA about a latex bladder. However, I have to make the mandrel to send to them and it is $75 per bladder up to 10 pcs with a minimum order of $250.

I’ve been trying to contact this company for days and I get nothing, no call back no anything! SMP Smart Tooling. http://www.smarttooling.com/ It looks like it would be a perfect fit but can’t get a hold of them. Anyway, I did tons of research on bladders trying to find out what the bike community was using. I found a neat bike company looks like they used this product (not sure). http://argonautcycles.com/about_argonaut.php Tried to contact the owner but no response. http://www.bikerumor.com/2013/01/28/inside-look-at-argonaut-cycles-unique-full-custom-carbon-monocoque-road-bikes/

Sorry for the rambling. Just really excited about working with this stuff!:slight_smile:

#4

Yes, this is a pre-preg uni part. I have experimented with welding poly sheets. I’m not sure what Mil thickness of poly would be the best for bladder molding. Last night I made a 6 mil (.006") thick bag and it was very stiff. Also I’m not sure how hot it can get before it gets damaged. The pre-preg carbon recommended temp for curing is 250F.

Would this work? http://www.uline.com/Grp_43/Poly-Tubing?keywords=poly+tubing

Not sure what you mean by vacuum bag for the tube? Not sure how that works?

Other ideas I’ve had were SMP Bladders. http://www.smarttooling.com/ anyone heard of them?
It is a polymer that has memory when it is cooled and flexible when it is heated. I was doing tons of research on bladders and found this company. Not sure but I think a small bike company(very cool by the way) Argonaut Cycles http://argonautcycles.com/about_argonaut.php

I was reading an article on bike rumor http://www.bikerumor.com/2013/01/28/inside-look-at-argonaut-cycles-unique-full-custom-carbon-monocoque-road-bikes/
and he had a picture that looked like the SMP Bladder molding that Spinetech has.

#5

Yes, this is a pre-preg uni part. I have experimented with welding poly sheets. I’m not sure what Mil thickness of poly would be the best for bladder molding. Last night I made a 6 mil (.006") thick bag and it was very stiff. Also I’m not sure how hot it can get before it gets damaged. The pre-preg carbon recommended temp for curing is 250F.

Would this work? http://www.uline.com/Grp_43/Poly-Tub…ds=poly+tubing

Not sure what you mean by vacuum bag for the tube? Not sure how that works?

Other ideas I’ve had were SMP Bladders. http://www.smarttooling.com/ anyone heard of them?
It is a polymer that has memory when it is cooled and flexible when it is heated. I was doing tons of research on bladders and found this company. Not sure but I think a small bike company(very cool by the way) Argonaut Cycles http://argonautcycles.com/about_argonaut.php

I was reading an article on bike rumor http://www.bikerumor.com/2013/01/28/…ue-road-bikes/
and he had a picture that looked like the SMP Bladder molding that Spinetech has.

#6

Sounds exciting.

we just demoolded a part this morning using a bladder… came out fantastic. Had an aluminum piece that was bonded to the end. I have to say it’s a great method of producing parts.

Our bladder was made by a company out of rubber. I know they’re not that cheap but, the results speak for themselves.

As for the poly, I would use nylon actually. Vacuum bag material. Though it doesn’t elongate very much so probably something like stretchalon would be better.

Oh man that mandrel/bladder stuff by smart tooling is probably the way to go. Looks much more durable than a rubber piece. I’ll bet it’s very expensive, though great for production. It does look like those bike builders use it… i’ll bet many do now. A metal tool, with bladder, 150psi, and a heated press is a great workflow. Not cheap but excellent quality parts.

Also you had asked about resin flow grooves. The part we made had them, though I believe the engineers were saying that in retrospect we probably don’t need them. I personally don’t think they’re necessary unless resin bleed is something required for the part. That bike company you linked to didn’t have them on their tooling. Really with the pre-preg it shouldn’t be needed if the resin content is optimal to begin with. With the large compression from the bladder the compaction should be high enough to avoid any areas where resin can pool. Like anything it’s case by case.

So where are you at now with the project?

Also, it’s not rambling, it’s stream of consciousness :smiley:

#7

sammymatik

Thanks for the reply. I am crossing my I’s and dotting my tee’s! The mold is going to be expensive and I don’t wont to rework it if I can keep from it. You said something about vacuum. Can I use vacuum if I had open ends? That may be cheaper than a bladder?

#8

Yup that’s exactly it. If you vacuum it like that it would be the same concept. Of course you’re only going to get 14.7 PSI of compaction from vacuum but, this suffices for most parts. Vacuum bag and sealant tape are pretty cheap. You’ll just bag as usual, with pleats, breather, etc. Nice thing about doing an envelope bag is you don’t have to worry about vacuum sealing the mold. But you will have to be conscious of any resin bleed that may occur due to the vacuum but, that’s probably a minor issue.

What is this part for, if you don’t mind my asking?

#9

Sammymatik, I sent you a pm!

On the 14.7 psi, that’s it? I always thought pressure was pressure? If you have 25 inches of mercury, that’s the pressure you get with the vacuum bag?

#10

No vacuum is not pressure. Pressure is from the weight of the atmosphere pushing down on the bag. At seal level it’s about 14.7 pound per square inch. The measurement of inches in mercury is derived from the pressure of the atmosphere which depends upon altitude. So if you’re at 5000ft altitude you lose about 17% of your vacuum (if this chart is very accurate) which is 12 psi.

vacuum is an odd thing… it’s not really something we see in nature on earth so it’s a little bit odd to understand. I’ve had some strange conversations with engineers about vacuum. And then there’s the old double bagging will give you more pressure arguments…

For what it’s worth though, vacuum is good stuff. You can make some great parts. Obviously a bladder or silicone mandrel would be better but, logistically is much more difficult.

#11

Thanks Sam! Something I didn’t know. Thanks for the info and your help!!!

#12

=D so much to know! Makes my headspin!

Anytime, glad to help

#13

You mold should not be airtight or sealed. You need the mold it to leak (not the bladder)! The purpose of that little grove is to catch the excess resin that comes out of the part. It also creates a short pathway of escape. The bladder must be supported everywhere though.

I prefer to use a juicy layup and evacuate the excess resin with bladder pressure. Air trapped within the laminate will only move if the resin moves. If the excess resin can’t move out of the part then neither will any trapped air. I don’t close my molds completely during the evacuation phase. I leave it about .005" open. The evacuation phase is when the excess resin is leaving the part as the laminate is compacted to a thinner state. Again, if the excess resin can’t get out the laminate will not get compacted. I’ve found it takes around 10-20 minutes to reach a full debulk. You want to slowly raise the bladder pressure. I pressurize the bladder too high and too quickly the area closest to the cavity/seaming edge will quickly and tightly compact. This tightly compacted area will prevent resin and air from areas farther away from passing through the area closest to the edge. A dam is essentially created that prevent a full debulk. Once the evacuation phase is complete the mold fully closed tight with the clamps. I like really glossy flanges so the mold cleans up quickly and stays clean. My mold when fully clamped shut will significantly restrict the resin flow. I control the Vf of the laminate by controlling the bladder pressure, evacuation phase durations, and mold opening.

The above process gets really challenging with prepregs. They need to be heated up before the resin can flow. Adjusting the closure is difficult if the mold is in a heating press of oven. Pregregs often need little bleeding ports between the mold cavity and the resin channe, that allow resin into the vented collection channels. This allows the mold to be firmly closed but still allows resin out of the system. These little ports can be prone to clogging with resin with use and difficult to keep clean and releasing well. It is possible to vent from the inside of the part by using some perf-ply and bleeder. The bleeder needs to vented to the outside atmosphere. Under high pressures it is prone to compacting so tightly that the excess stuff can’t pass through it.

About the seams: They are difficult to assemble if the bladder is in the way. This is why is use a bladder material that can be tightly compacted with vacuum while the seams are “shifted” together when the mold is closed. When possible I like to insert the bladder after the molds are closed. Bulky bladders make this seaming process impossible. My parts in testing always fail in other places before the seams fail. The fabric stagger at the seam is important as it better distributes the forces when under stress.

#14

I have been kicking this idea around. Would the need for bleed ports be negated by adding peel ply and bleeder cloth between the layup and the bladder? Also I am thinking of a bladder composed of spliced inner tubes within an enclosed 2 part chamber, think bike rim. With a setup like this is there such a thing as too much pressure, or only too fast a ramp up?

#15

I think wyowindworks, correct me if I’m wrong, You’re saying that the ‘bleed’ ports are for the air to escape and to avoid void entrapment?

If so then would this bleeder do the same? If I’m using prepreg and I have bleed ports this means my part is losing some resin and thus creating a higher fiber ratio. Which may be good if intended but, what if my resin ratio is already low and I don’t want to lose any more resin.

I’ve had the same idea as Trackdawson in using a bleeder instead of vents. I could see some issues with keeping everything in place and even… overlaps might cause an imprint but, maybe it doesn’t matter since it’s on the inside.

As for too much pressure!!!? Bring it on! Though the issue I run into is having a mold that can take it. The more compaction the merrier right?

#16

If you do a laminate debulk and no resin is absorbed or evacuated then your laminate is almost guaranteed to be porous. If you are trying to control the Vf by how much resin is the prepreg then you have have insure that you are getting a compaction level that can guaranteee little to no porosity. It’s more reliable and consistent to use a juicier layup and control the Vf through the proces with excess resin porting… At least that is my experience.

The compaction pressure is part of the process that dictates the Vf. Vf can only be increased by pressing the fibers closer together. If the mold isn’t vented then compaction cannot occur regardless of the pressure. For the fibers to get closer together then air or resin must leave. If you use less resin but don’t get adequate compaction then the laminate will have a higher degree of porosity. The impact strength of carbon fiber can decrease dramatically in laminates with Vf greater than 60 percent or laminates that are porous.

I discussed the issue with breeders and high pressure in my previous post. The bleeder must be vented which has it’s own issues.

#17

Not sure what Vf is? Could someone explain. Thanks

#18

Fiber volume fraction. This tells you how much of the total volume of the laminate is fiber and how much of the volume is resin.

#19

I have an idea. Not sure if this is something that can be done but it looks like it would be plausible. This other part I am making is a Tee shaped part. If this would work it could be done on all my parts. What do you all think of using a solid silicone mandrel. The Silicone mandrel will be smaller by the thickness of my carbon fiber layers. Lay my pre-preg on top of the Silicone mandrel then close up the mold and cure it. Haven’t seen anything like this (not to say it hasn’t been done) but it looks like it could make a nice looking part. Would love input from everyone! Thanks a million!!!

#20

good thinking

It’s definitely not a new technique. We just made a part here at my work using this technique, came out awesome. I also made a bridge for a student competition using this technique. The compaction is ridiculous… I had Boeing engineers asking how i made it and whether it was autocalaved.

This is one of my favorite techniques. It gives such good compaction. You do need a very strong mold to contain all the force of the silicone expanding. I know a good silicone that is easy to work with and has a hight CTE for this application if you need a recommendation. Also it’s good to imbed a piece of rope to help in removing the mandrel after curing.

I’m not sure exactly how to calculate the compaction in PSI, maybe some one else can give some equation for it?

You can also pour the silicone and use something to displace some of the volume if you want to control the compaction. What I mean is if you have a part with varying shape, the thicker bits will get more expansion and thus more compaction than the thinner bits.

Nice drawing by the way. Though I don’t thik you’ll need locators for the silicone mandrel. You could also cast the longer piece so it has a small recess for the longer T piece to fit in. The metal alignment stuff you show could pose more difficulty than a purely silicone piece. If you did want to use location pins, just cast the recesses into the silicone pieces, no need for sleeves or screws.

Of course this technique require making a mold for the silicone piece. You could either machine something, or 3d print the pieces, pour a mold, then cast the silicone pieces. You can also make the silicone with an an inner and outer piece, if necessary to help with it’s removal after curing.

You’re planning on doing a metal mold? You can do a two piece mold and then either layup right on the silicone, or you can lay up on the mold and then join them together. I’d just go right on the silicone. It’s pretty high durometer and would be easy to work with.

There’s a lot of considerations to make things fit, but very doable.