08 Mar

Mould Making

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Last Wednesday I ran a small ‘Messy Workshop’, where I introduced several students to the processes of moulding and casting. I only had a short amount of time – around 3 hours. Within this I had to squeeze quite a bit in, so I  put on my best motor mouth for the occasion!

I brainstormed what I could include, and got some guidance from the tech in the casting room – I’ll create some basic moulds using the vac former, a silicone mould of the same shape in order to do a comparison of the two processes, and a couple of different resin types;  polyester (clear cast in this case) and Polyurethane (Fast cast).

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After half an hour of me waffling on about the contents of each canister, types of facilities available, and associated H&S we created some basic alginate moulds and created a plaster cast of our hands / fingers.

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This was pretty decent and took us to around 11am, when we took a short break – this allowed for us to give the plaster some time to cure. We were all rather hasty in our de-moulding, and lost a few fingers, most people thought this was the most distressing thing they had ever seen, whilst others found the whole thing rather hilarious!

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Typical art college fayre!

After all that, we continued on to the resin room where we created the reproductions using the vac form moulds. I prepared several, but gave the option for students to create their own if they wanted to make more than one. I also showed the silicone mould off and we poured that one as well. Over the remaining hour, resin was mixed and moulds were poured.

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Well, onto one of the real reason I made this a forum post, was to show off some nifty mould making processes I had a go at. Not only is the nature of these mid week workshops a way to get some cool stuff (mostly hard skills) introduced to students, but is also a way for me to indulge my nerd and try and create / explore new ways of doing the stuff we do already, which can all be summed up as making.

Tuesday was spent mostly drafting in Rhino 3D some nifty tile pieces, the kind of thing we might look at 3D printing one offs, and then going off to reproduces using a variety of casting mediums. (or maybe in the future, we will simply 3d print the lot?), anyway – I made a bunch of tiles.

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a typical process would be to create a plastic / wooden / Lego box to place them in to enable us to pour silicone over.

Well, now we’re in CAD and can 3D print the form, why not add a mould box into the mix, print it all out, and pour strait away.

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The next thing I went on to illustrate was the process of creating a shape from a two part mould.

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The parts for a two piece mould

All the components we went on to make on the Wednesday were simple one piece moulds, with an open back – this enabled us to quickly make some shapes. I created both side A and side B, in Rhino, as if they were made from silicone. The components also included the pour hole and the bleed lines already in place. This is something that you would usually create by submerging the parts 50% on clay and sculpting out the pour and bleed lines.

The next cool thing you add are the ball bearings / marbles, as these create locator pins for both side A and B, ensuring that you don’t miss align the mould and create a miss cast.

In the real world, that’s a days work (sort of ) and is also rather messy, you have to take precautions that you don’t get clay all over your original work. Once you have one side in silicone, you dismantle everything, take it all out – and then re construct the box; this time with the silicone and the part in the bottom, and now you can pour a new batch of silicone on the top (silicone wont stick to silicone) and your on your way to having a two piece mould. Sounds tricky? It is until you do it yourself!

Well – that will all take 2 days what with the cure time, if I’m lucky – and I only have 3 hours. I do have the benefit at this point to a couple of hours to prep for the session however. I think to myself, what if I were to take the workflow of creating the walls for my simple shape and turning it into its own mould box, and creating the mould box for side A and side B of a two piece mould?! Well – here goes. Mouldception.

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This is what the mould will look like, rendered blue to represent the silicone material! note the pour holes, bleeder lines and the positive and negative locators.

Everything went as planned! I created the mould boxes for side A and side B, poured in the silicone, and 12 hrs later, had the silicone in my hands.

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The silicone parts visualised next to their respective mould boxes.

A quick pour of the parts and we can see how things turned out. the pour hole could have done with being a little larger – perhaps we can use a syringe to force in the material as the working time is around 1 or 2 minuets.

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The two parts of the mould taped up and ready to pour

The bleed holes worked really well…. except for perhaps my positioning of them , I was still left with a hole in the first reproduction.

I was able to position the two together, make the pour, and 15 / 20 mins later I got the parts out. The striking thing here was how much they resembled the 3d printed parts!

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The parts that I printed were done so on the ‘fast print’ setting so contain all the features of a fast 3d print – its really amazing how much detail is carried through the mould / casting process – and how many comments we got thinking the resin part was made by a 3d printer, as it had a similar weight, finish, and surface quality.

I’ll return back with some HQ images of the printed + resin parts later, so into the process I guess I forgot to document the later (more interesting?) steps!

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Collection of moulds, in both PLA and silicone.

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Plaster cast finger mountain

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The two part moulds.

The principle is that you cannot cast material that goes hard (plaster / resin) into a rigid mould. So here you can see we played around and injected silicone into the PLA moulds.

In the silicone moulds of the same shape, you can see we have poured / cast the resin. the reproduction (minus the air bubble) is great! All details captured.

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The two types of mould for the larger tile piece. The ‘Vacform’ moulds and the silicone mould. The silicone moulds (condition cure) are only good for the Polyurethane resins (fast casts) and the vac forms for the polyester resin (clear cast).

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Clear cast with pigments – and loosely mixed inside the vac form!