Mold Material For CFRP Prepregs for oven curing max(120 degree C)


Mold Material For CFRP Prepregs for oven curing max(120 degree C)
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Gaurav Kumar Thakur
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Hi, can we use  POP as mold material for CFRP prepreg component??
maximum temperature for curing-120 degree

Hanaldo
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Plaster of paris? No. It is highly porous, so it would need to be sealed. You could maybe use plaster of paris and then wrap it in Teflon tape/glass, but it wouldn't leave a nice surface finish. Possibly an option for non-aesthetic parts, but not a great one. It doesn't have a fantastic CTE either, so probably a few issues there.
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Hanaldo - 10/28/2020 11:02:16 AM
Plaster of paris? No. It is highly porous, so it would need to be sealed. You could maybe use plaster of paris and then wrap it in Teflon tape/glass, but it wouldn't leave a nice surface finish. Possibly an option for non-aesthetic parts, but not a great one. It doesn't have a fantastic CTE either, so probably a few issues there.

What if we will use some filler paste or putty to fill the small holes and paint it,or is there any other mold material which is cost effective and i am looking for one time use only.?

torsten Ker
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HI
I did use plaster of Paris in 2012 to create a prototype like other do with modelling clay and found plaster easier to sculpture
once completely dry I coated it with wood hardener/cellulouse  to consolidate the surface, sprayed it with 2k epoxy high-build filler and then 2k car paint
But I doubt that plaster would work as mould material

From that with using wax and PVA i created  final mould still in use today :-)



Edited Last Year by torsten Ker
Hanaldo
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Yes for general pattern work for use at ambient temperature, use anything you like, at the end of the day its about having a hard shiny surface and doesn't matter too much what is underneath it.

Unfortunately pre-preg makes that quite a lot more complicated, because your surface also needs to be hard wearing and temperature resistant/stable and compatible with epoxies at high temperature - which regular fillers and paints are not.

The one way you could potentially do it is if you were milling the plaster of paris on a CNC. Then you could mill the plaster slightly undersized, coat it with a high temperature epoxy gelcoat or resin, and then mill it back to true size. 

Works in theory a little bit better than it works in practise, but you can get there. Unfortunately epoxies aren't going to polish up super nicely though, atleast not compared to other coatings, so it is still a compromise. Plus if you are using it as a mould rather than the pattern, you have to worry about the durability of the material and how stable it is going to be. It is less than ideal for sure. 


For pre-preg, unfortunately you're either choosing between cheap or effective. Adding heat to the equation really makes the process quite unforgiving, and personally I feel it is cheaper to do it once and do it right than to do it 2 or 3 times the 'cheap' way.
torsten Ker
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in addition to what hanaldo said,

You can do a plaster mould and finish the surface at is finest but I doubt it would survive more the 1, max 2 remoulding of cured epoxy and pull parts off the mould surface every time.
This majority has to do with density and adhesion of the mould sealed surface to the plaster itself which is very limited.

Best to demonstrate, use your fingernail to scratch plaster, then try that on epoxy, Plaster is just to soft and porous to be a stable surface for that kind of stuff.

Why creating a plaster mould? for a one off use silicone and hand lay-up if teh resulting part is small enough





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Hanaldo - 10/29/2020 12:26:25 AM
Yes for general pattern work for use at ambient temperature, use anything you like, at the end of the day its about having a hard shiny surface and doesn't matter too much what is underneath it.

Unfortunately pre-preg makes that quite a lot more complicated, because your surface also needs to be hard wearing and temperature resistant/stable and compatible with epoxies at high temperature - which regular fillers and paints are not.

The one way you could potentially do it is if you were milling the plaster of paris on a CNC. Then you could mill the plaster slightly undersized, coat it with a high temperature epoxy gelcoat or resin, and then mill it back to true size. 

Works in theory a little bit better than it works in practise, but you can get there. Unfortunately epoxies aren't going to polish up super nicely though, atleast not compared to other coatings, so it is still a compromise. Plus if you are using it as a mould rather than the pattern, you have to worry about the durability of the material and how stable it is going to be. It is less than ideal for sure. 


For pre-preg, unfortunately you're either choosing between cheap or effective. Adding heat to the equation really makes the process quite unforgiving, and personally I feel it is cheaper to do it once and do it right than to do it 2 or 3 times the 'cheap' way.

Thanks for the suggestion...i will go with the effective one ...but which material Aluminium or some other material are there for high temperature ??? 

Hanaldo
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A composite mould is probably going to be the cheapest. Vinyl ester or epoxy, whatever system you can get that can handle 120° cure cycles. 

Alternatively, epoxy tooling board or aluminium can be affordable if you are getting a small mould milled. Depends where you are and what you can get within your budget really. 
Rosta Spicl
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Hanaldo - 10/29/2020 6:15:10 AM
Hanaldo, please, tell something about your experience and skilful of epoxy tooling board making to top mirror finish. I just testing that proposal, I have a several brands of sealers (Marbocote, Acmos, Axel, Frekote), but all of them, that's a little bit nightmare work to finish the surface in top mirror look. I'm still unsuccesful. I have tested a several processing methods just like brush, roller, spray gun, sand it 400/600/800/1000/1500/2000, linth free cloth, apply another several coats, but still not top class....marks, dust. I tested polishing that too, but that's not effective way to do.
I just working on an high accuracy autoclave mould, that's the reason why the sprayable topcoats are not possible to use...I have tested that way as well...

Hanaldo
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Yeh no, my experience is very much in line with yours. Tool sealers do a good job, but I haven't ever managed to get anything close to the surface finish I can get with traditional mould making. For me the only way to do it is to make splash moulds and then new patterns that can be polished to a higher standard and then remake the final moulds. Its tedious and not an ideal way to do things, especially if accuracy is critically important. Making copies of copies always results in some degree of dimensional change.

This is really why I dont use much epoxy tooling board. When I mill things, I mill it from polyurethane tooling board and pattern coat them (the thickness of which is taken into account when doing the CAD model), then make moulds the old fashioned way.
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