Composite stuck to mdf mold

Question

Composite stuck to mdf mold

muffinator_777 (Mechanical)

(OP)

10 Oct 23 20:34

Hi,

I have been trying to make a reasonably large composite piece and each time I have attempted it. The composite has gotten stuck to the mold. For reference, the first time I made it, I used spray adhesive and that was the main issue. This time, I didn't use it but the part still seems to be very well adhered to the mold.

I was wondering if anyone has any idea why this might be occurring or would be able to offer any assistance with regards to its removal.

Thanks

SWComposites (Aerospace) · Answer 1 · 2023-10-11 02:27:18

Are you (properly) applying mold release to the molds?
What is the composite material? Prepreg or wet layup?
Cure temperature?

muffinator_777 (Mechanical) · Answer 2 · 2023-10-11 02:33:03

I believe I properly applied mold release on the mold. Gelcoat on the MDF and then 2 layers of release wax and 3 layers of PV. I have also used the mold before.

Fiberglass. Wet-layup and then vacuum bagged. Cured at room temperature.

SWComposites (Aerospace) · Answer 3 · 2023-10-11 03:01:48

Do you mean PVA release agent?
Are you reapplying wax and PVA before each layup / cure?
Are you sure you cleaned off any residual resin before reapplying release?
Can you pop up a corner of the part with a wedge?

muffinator_777 (Mechanical) · Answer 4 · 2023-10-11 03:03:29

Yes to the first three questions. And the shape of the item makes it super hard to but i'm able to pop up a section. I am attempting to make a cone shape. It's pretty deep like two feet with a 'draft' angle of 11 degs

SWComposites (Aerospace) · Answer 5 · 2023-10-11 03:17:49

Ok, sounds like mold release application is not the issue.
Perhaps the resin is shrinking during cure locking it to the mold?
Have you made this cone part on this tool successfully before?

Is the top of the cone open so maybe you can rig up a tool to hold the part and press out the mold from the top?

muffinator_777 (Mechanical) · Answer 6 · 2023-10-11 03:35:37

Yeah I think so potentially.

I tried to at first and had to use an adhesive that held it at the top but it was hard to remove from there but the bottom came out perfectly. I had to angle grind it out though, the upper region I mean.

I'm going to attempt drilling holes in the bottom and pushing it out with rods similar to what you mentioned. I think if I need to, I'll also remove the top of the cone mold too.

I think this would have been mitigated if I made a two part mold but I didn't anticipate this level of difficulty.

muffinator_777 (Mechanical) · Answer 7 · 2023-10-11 03:38:26

Something a friend brought up was the possibility that the mdf absorbed some moisture from the air and expanded a bit against the laminate. I'm not too sure how that would interact with laminate but it should somewhat have helped with removing the laminate but that depends on the actual amount of expansion.

SWComposites (Aerospace) · Answer 8 · 2023-10-11 04:05:14

You could also try heating the part and see if it pops off the mold.

Wait, is the mold inside or outside of the cone (part)?

muffinator_777 (Mechanical) · Answer 9 · 2023-10-11 04:14:07

I'll try heating the part.

It's on the inside of the mold.

SWComposites (Aerospace) · Answer 10 · 2023-10-11 15:41:17

So if the mold is on the outside of the part, why not split the mold into two halves that you disconnect after cure. Seems like it would be much easier to demold that.

muffinator_777 (Mechanical) · Answer 11 · 2023-10-11 15:57:07

Yeah, I might do that.

The thing is the mold is huge and extremely heavy. I'm going to attempt that though somehow.

btrueblood (Mechanical) · Answer 12 · 2023-10-12 15:03:35

"the mold is huge and extremely heavy"

Why? If you have a part (or even just a mockup form) that works, make a fiberglass mold from it (put release agent on the part, then lay up fiberglass over it).

moon161 (Mechanical) · Answer 13 · 2023-10-20 11:39:25

Maybe if you vent extreme points of the cavity or blow with low pressure air?

moon161 (Mechanical) · Answer 14 · 2023-10-20 11:43:30

Depending on the coefficient of friction, is your 11° draft self-locking if you have a residual force between the mold and the part?

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Composite stuck to mdf mold