Hi everyone!
So after we got our first injection machine built and running, we started experimenting by making plaster molds and here are some of the results…
The beauty of using plaster (called “yeso” in México) is that molds are very cheap and easy to make, and the model being molded can basically be anything that can be submerged in the plaster mix. So you can either place any existing object in the plaster or make your own models with modeling clay! Just make sure to cover the model in vaseline or another lubricant before submerging in plaster 
Creating models with modeling clay (a.k.a., Playdough) is great because it’s easy, fun and kid-friendly! So it becomes a perfect learning opportunity to take recycled plastic and convert it into something completely new.
The down-side of this technique is that plaster is kind of brittle, so the molds don’t last very long. But they’re so cheap, it’s not a huge issue for small projects.
What molding techniques have worked for you?
Hope this helps!
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Here’s an example of an existing product replicated with recycled plastic!
Amazing idea. If I was trying to make a pen casing out of plastic would this method create a hollow replica that i could put an ink cartridge in perhaps?
@xxxolivierxxx Thanks for the suggestion. We’re also experimenting with concrete and grout, and have found that even combining materials (e.g., concrete for the outer structure of the mold and plaster for the part touching the model) yield to better results! We’re documenting some of that process and will post more details soon 
@andresornelas using plaster is a great idea 
There is a proyect on Instructables that show how to make a mould with Epoxy Resin. This resin is pretty cheap and much harder than plaster, I bet it would make a perfect and more durable mould
http://www.instructables.com/id/Home-Plastic-Injection-Molding-with-an-Epoxy-Mold/?ALLSTEPS
Concrete (cemento) could probably make great moulds as well
@andresornelas thanks for the answer, i will try with dentrific plaster and test T° and resistance, also I will try with “masilla mágica” (dont know how its called in english) its also a good molding material.
@andresornelas, hey I’m also came to this thought in a while, what a wonderful thing a collective mind C: But I want to give a try with gypsum, and without injection, only with shredder and oven. Maybe do some tiny press for hot molds with molten plastic on it. Time will tell
@davehakkens Thanks! Glad you liked it and found it inspiring!
Yeah, working with clay is awesome; the kids are loving it!
Regarding durability, we’re seeing it varies quite a bit, anywhere from 1 to 5 uses. Seems the main issue is you need the mold to resist the pressure form the plastic being pushed into all its grooves. Thus, how easily it cracks seems to be due to several factors, such as:
* The shape of the model: a sphere is going to last longer than the crocodile above
* The temperature of the plastic: higher temp means softer plastic means less pressure
* How long you let the mold dry: this may be obvious, but when you’re excited to try it, it’s easy to use it as soon as it feels dry!
We’re experimenting with different materials to see if we find a better molding technique, so we’ll report back when we have something!
@ismaelgonzalez it’s just regular plaster, but you might as well experiment with different materials to compare results!
Wow nice post @andresornelas!! Never tried making plaster molds before, very inspirational seeing your images. Any idea on how often you can use a mold, 1-2 times? I really like the fact that you can work more freely by using clay to make molds. Again thanks for sharing this well documented story!
great work, so plaster (yeso) Works fine, is it a regular plaster or dentist plaster? (i have worked with dentist plaster when i was studying because its better with fine details) im asking myself if some epoxic will work to.
here in chile there is a product called “masilla mágica”.
CONGRATS on your work.
And here’s our first attempt at making something functional
The overall molding process we’re doing here is:
1. Create model with clay (or use existing product)
2. Fill container halfway with plaster
3. Place lubricated model in plaster
4. When plaster somewhat sets, create alignment groves with a coin
5. Once it’s fully dried, lubricate plaster
6. Place drill bit for injection hole
7. Fill rest of container with plaster
8. Remove model once mold fully dries
9. Clamp model halves and place mold firmly against injection machine (This can get tricky; we used a car jack to press the mold upwards)
10. Inject, wait a bit, and admire your new creation!
Let us know how this works for you!
