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Oliveros

3D Printing Molds

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Posted · 3D Printing Molds

Hey guys,

 

So, I'm onto another avenue which is injection molding, unfortunately it costs about 5-10K just for the mold so that's off the table already.

 

Next thought was a pour-able compound into a 3D printed mold, it seems there are some pour-able materials which might work but will need testing.

 

To do the testing, I'll need to make a mold and I'm wondering if anyone has any experience with designing 3D printed molds? from what I saw on Cura, when I clicked the "mold" button it just made it so I could pour something into it but gave me no way to release the part once finished, no air holes or anything either.

 

I have absolutely no experience with plastic molding so any advice or ideas you guys have is welcomed. The guy I spoke to from the company who makes the compound said I could do a 2 part mold and just bolt it together or whatever, then just squeeze the material into the mold and bobs your uncle, once it's finished, open the mold and voila.

 

Here's the material I'm thinking of using. https://www.smooth-on.com/products/sorta-clear-40/

 

I also attached the file of the part to be made in the mold.

Original Peg O.G.obj

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Posted · 3D Printing Molds

There are a couple of techniques to mould printing. I've made both one-part and two-part moulds for use with epoxy resin (ArtResin).

 

One approach is you can design a two-part mould in CAD, creating a shaft through which you pour the medium, such as resin. Check out my model on Thingiverse for an example: https://www.thingiverse.com/thing:3945872.

 

The other approach is to print the actual object you want to model and then embed it in something like moulding silicone. I've used https://www.barnes.com.au/addition-cured/pinkysil-silicone-2209 with good results.

 

Layer lines and porous surfaces are an issue with 3d printing moulds. From an aesthetic perspective, without smoothing the part/mould before pouring, the layer lines and micro holes will be replicated in the final object. Even if you sand the part/mould first, you'll at best, end up with a rough or matte appearance, which isn't ideal if you're going for a smooth injection-moulded look. An unsmoothed mould will also tend to stick to whatever medium you cast in it, making removal a pain.

 

To smooth your part/mould, you can print in ABS and give it the acetone treatment, or use something like Polymaker's Polysmooth filament. I've tried both and the Polysmooth filament produced some excellent molds, with good surface detail and smooth appearance. See the attached pic for an example. The surface bubbles are from the resin, not the mould itself. ABS was harder to get an evenly smoothed surface and detail was lost in the process due to running/melting of the plastic. Also, printing a complex ABS object with supports can be tricky as PVA is basically a no-go due to the bed temp.

 

Surprisingly, I haven't been able to find much about 3d printing moulds online. My guess is the setup cost is fairly high and for a casual hobbyist, it's probably easier to find an existing mould on eBay or similar, instead of working through the trial-and-error and learning curve associated with 3d printing and casting.

 

Hope this helps!

IMG_20191217_225901.jpg

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Posted · 3D Printing Molds

Excellent info from p-kimberley above. What is said, is absolutely true: any layer lines, blobs or irregularities will show up in the cast, and they will make it *much* more difficult to remove the cast from the mould.

 

I have made silicone moulds from 3D-printed models. It goes as follows: first 3D-print a model, including what will become the filling canals and venting holes. Print in multiple parts and assemble as required. Carefully remove all blobs and irregularities, and smooth the model, as any defects will show up. Stick the model to a plastic base plate, or provide some form of support or hanging it stable, so it does not go swimming away when you pour silicone in later on. Using plasticine, wood, or plastic plates, build a container around the model. Make sure the container is absolutely watertight at the bottom and sides. Make sure it has pouring and venting openings (or leave the top open). And then pour silicone in the container around the model, and let cure. Then cut the model out of the silicone by cutting zig-zag lines, so both mould parts align themself correctly later on. Now you have an empty silicone mould, in which you can pour resin. Spray the silicone with silicone oil as release spray, prior to casting. Silicone is watertight because it repells water, but it is *not* oil-tight and not solvent-tight. So the solvents of resins creep into the silicone and destroy it soon, after a few times of use. Therefore you really need to saturate the silicone with release spray, prior to casting. As with any moulding and casting, keep aware of undercuts, use slanted side-walls, and avoid enclosed features and stuff that could make removal of the cast difficult.

 

I have also done the opposite: cast silicone models in a 3D-printed mould. Thus: 3D-print a mould in PLA, carefully remove defects, smooth it. Then carefully seal all openings in the seams in side-walls and bottom. Pour silicone in and let cure. If you do not smooth the layer lines, and close tiny gaps in the model from the 3D-printing process, it will be almost impossible to get the model out of the mould. Don't ask how I know.  :-)

 

You can tap or shake the silicone to remove bubbles, or gently (!) blow on bubbles. Gently pouring from a high distance in a thin stream also helps. Vacuum degassing is best, but only works for slow-curing silicones, not the fast ones I have, and you need professional vacuum equipment.

 

On Youtube there are tons of excellent tutorial videos, showing the techniques. Search for: moulding and casting. You find info on really anything: thick silicone paste (like for body masks), thin liquid silicone, slow and fast curing, epoxy and PU-resins, coloring, info about avoiding bubbles, and so on. Be sure to study a lot of these, even if it takes a few days: you won't regret it, and you will very soon recuperate that invested time. Preferably download good videos and store them locally, so they won't be affected by "linkrot" and error-404.

 

For smoothing PLA-prints, you can use the "cloadfiend method", optimised by user cloakfiend. See his topic on this forum.

 

A few photos (I have them, so I can as well show them):

 

1. Silicone moulds, with a hard shell for more stability. The original models are not shown here, and were made from plexiglass (right), and very hard wax (left), but you could use a 3D-printed original as well. This was before we had 3D-printers. Notice the zig-zag cuts, so both parts align well. Also notice the notches in the shell, for alignment. And see the pouring and venting openings. The blue model has a base-plate in the shell, so it stays upright.

DSCN5784b.thumb.jpg.01a44dd724a596732d34f50108979af2.jpg

 

2. Orange 3D-printed models, and green silicone impressions of them. Top one is as-printed, bottom one is smoothed with acetone (using the "cloadfiend-procedure"). The difference in the silicone impressions is obvious.

before_after_acetoning.thumb.jpg.1f1e418e4ae0e6a41dbda0378546a7a7.jpg

 

3. Same model 3D-printed, but with different post-processing. Left = smoothed with acetone. Center = smoothed with heat-gun: don't do this: it causes craters due to internal bubbles exploding when heating the plastic. Right = as-printed, untreated.

DSCN5944.thumb.JPG.ff6c801482333201e233f7ca2872ae44.JPG

 

4. Idem, different camera angle.

DSCN5950.thumb.JPG.c7d33bc4c5ffe03fb4f3a2e16c50288e.JPG

 

 

 

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Posted · 3D Printing Molds

Thank you for all the feed back guys, I appreciate it.

 

I designed and printed one half of the mold yesterday. The idea is to just put the 2 together, tape them or whatever, then pour or inject in the liquid silicone/plastic. Due to me planning on using Silicone as the material, at least the first test, the mold can't be silicone, so I printed it out of PLA since silicone also doesn't heat up when poured so it should work out.

 

I'll post a picture of it later ,it looks pretty nice, the surfaces or at least the flat surfaces were ironed so I think most of it will look pretty nice, I don't particularly care for supremely clean surface finish in this particular application so I'm not too worried about the lines transferring over, as long as it doesn't make a groove for food or bacteria to collect in.

 

I'll be printing the second half today and hopefully I can do some sort of sample with some sort of material, to see how it'll look.

 

In terms of releasing the print, I was thinking of just putting oil on the surfaces of the mold, that way it won't stick, is that a bad idea?

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Posted · 3D Printing Molds
2 hours ago, Oliveros said:

In terms of releasing the print, I was thinking of just putting oil on the surfaces of the mold, that way it won't stick, is that a bad idea?

 

It's not needed IMHO, silicone does not stick to PLA (or any other plastic) - no need for any release agent.

 

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Posted · 3D Printing Molds

Okay great.

 

That's some advantage. With a shore hardness of A40 it's supposedly as hard as an eraser on a pencil. 

 

I'm wondering if it will have any rigidness to it at all or just flex all over the place.

 

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Posted (edited) · 3D Printing Molds

Oil *could* be a bad idea, depending on the oil and silicone combination. Some chemicals inhibit curing of silicone, such as sulphur, mint, some oils,... Try compatibility with a little bit of silicone beforehand, or otherwise you might end up with a half-cured mess that is very hard to clean from the mould.

 

Further, make a small test piece first with the same angles of side-walls as the real model, to see if you need smoothing of the walls. Silicone flows into the tiniest pores, so it gets a very strong mechanical grip, even the non-stick mould-making silicones. For complexer models smoothing will be required, just to be able to get the model out of the mould, unless it is very simple and flat like coins.

 

Also preferable use platinum-cured silicone (additive cured). No tin-cured, as that tends to decompose over time, and is only good for short term use.

 

Edited by geert_2
corrected typos

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Posted · 3D Printing Molds

Well, as an update.

 

I brought the mold to a co-worker who has done molding in the past and he helped me make a sample peg to see what it looked like when it comes out of the mold.

 

It came out surprisingly well, used some sort of 2 part silicone and poured it in with the mold clamped shut and it came out really good, stuff was oozing out of the holes I designed into it so it was pretty successful.

 

I'll have to post some pictures later.

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Posted · 3D Printing Molds

Sorry for the long wait,

 

Here's some pictures.

 

One half of the mold.

 

DSC01687.thumb.JPG.a92126f23be83220f3ed0f45e671f495.JPG

 

Second half of the mold.

 

DSC01688.thumb.JPG.18628aeda90b6a5ea12f19085f95bdb2.JPG

 

Side by side.

 

DSC01689.thumb.JPG.48a28bd1503401188608a7e09a20289a.JPG

 

Put together. I added a little chamber up top to help keep it full.

 

DSC01693.thumb.JPG.d224e99fdc283879c0788a469067d00c.JPG

 

The results.

 

DSC01690.thumb.JPG.9d2815360ea27e2e95a65ab981eb5aea.JPG

DSC01691.thumb.JPG.893499299847ec85eea7d850a4fa9759.JPG

 

Very nice surface finish, this was my one and only pour with silicone, WAY to flexible and soft but I have some material coming to test out and see if that works, it COULD work if only I could get the right material for it.

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