Molding and Casting

My mom is fascinated by 3D printing but, due to the current pandemic she hasn't been able to visit me and see it in action. So as I planned to go home for Diwali, I get a request from her if I can print some planters and figurines for the garden.

Now printing articles is not challenging, but the PLA filaments , the one's most commonly used for 3D printing are not suitable for outdoor use. PLA when exposed to sun, experiences pigment loss, becomes brittle and tends to breakdown. And secondly, the time taken to print each of the articles is huge. On an average it can take ~10-12 hours to print each article, and if I have to take 3-4 items of each article, there simply isn't enough time (yes I did calculate hours before flight and time needed for each print :))

Keeping these two things in mind, I get an idea why not to print molds itself? The molds once printed, can be used to cast multiple planters, thus saving time. And the casting can be done with Plaster of Paris/Cement which are more suitable for garden use.

Though it may be a novel idea for me, but as always, internet is full of things you think to be novel :). Asif suggested the below video from Alex Chapman, which explains this in detail. I ended up using his design for the planters, and casting is super easy and fun to do!, below are few pics I clicked during the entire process.

3D printed molds are great way to make casts which are durable and fit for outdoor use. On similar lines I tried to create molds for the garden figurines, but it's not simple as it looks, separating the cast from the mold is a work in itself, which I realized while trying to build my own mold for a duck.

Methodwise, it is simple, you take a model, and intersect it with a cuboid and split it into multiple blocks. But 3D printed section may or may not align always, it is an iterative process and some tweak is needed. In the case of the mold, on the left. I could not separate the mold from the cast as the plaster stuck so well to the mold! Using clingwrap in the mold to avoid the sticking problem resulted in inconsistent cast with lots of creases.

As I had to depart soon, which meant my access to 3D printer was coming to an end for a few weeks. I had to find another way of making molds. And guess what, there is one, it's called brush molding!

In brush molding one creates the mold by using the model itself. It can be done by using Silicone rubber. There are lot of silicone rubber mixing kits available on amazon. It essentially is a 2 part mixing kit. Once both parts are mixed, the mixture begins to set and becomes silicone rubber in a few hours. Silicone molds are widely used for jewelry making. I used the Chemzest silicone for mold making.

In brush molding one needs to make the silicone mix and coat it onto the model. The level of duplication is really nice. Be sure to apply mold release compound to the model before applying rubber on it. The video below shows how to do brush molding. It does not need to be followed exactly, but just to give a little idea.

I used the mentioned technique to make molds for figurines ( I had already printed a few beforehand). I did not used any thickening agents for the rubber, By increasing the amount of catalyst one can make the rubber very sticky, and it can set in 5-10 minutes.

I made a mold for a bunny, as seen below.

In the first coat it is important to ensure that all the features are captured fully. The second coat of rubber is more to give strength to the rubber.

For casts it is important to make a thick creamy plaster of paris mixture, a more fluid mixture tends to trap more air bubbles, and the structure is weak. I had to make multiple attempts to get the bunny cast right, as a weak plaster was causing the ears to break off, you can notice a little damage to the ear in the below pics.

Once the casts are ready it's time for them to be painted. Honestly, thats not my strong suite, so I will not make any recommendations, or give any tips here :P, I just used simple acrylic colors from Camlin.

Done with all of this, it was time to put them in the garden, I put them in a bonsai pot, and that;s how they looked:

And ofcourse, the pot pics once more on a parting note :)

Overall this has been a fun project, with lots of learnings and insights.

There are still few designs which I am yet to finish. But they need a bit of more time. Stay tuned for the next round of mold making :)

Thanks for reading! Please do leave your comments.