How to make a silicone mold
Mold is a kind of container with a hollow cavity. In most cases, a liquid material can be poured or forced into the container and then hardened (by cooling or another method), making a solid object in the shape of the mold cavity.
Molds can be made of different materials like tool steel or aluminum. They can also be made from silicones, a group of polymers made up of siloxane that is sometimes used to make products like flexible protective casings, gaskets and contact lenses.
Silicone molds are not as durable as metal ones, but they are affordable, easy to make and highly flexible. This flexibility, coupled with the fact that few materials adhere to silicone, makes it easy to remove molded parts from within the silicone mold.
How to make a silicone mold
Making a silicone mold
is surprisingly simple and requires only a handful of components. And while professional equipment gives you more options, there are also plenty of at-home uses for silicone molds.
The components needed to make a silicone mold are:
Liquid silicone: Silicone for mold making is widely available and usually comes in two parts that must be mixed together immediately before use.
A container: The liquid silicone is poured into a container, which should be larger (but not much larger) than the master pattern. In many cases, a new and suitably sized box can be made on demand using e.g. wood or cardboard.
A master pattern: The master pattern is the original object that you will duplicate using the silicone mold. A master pattern can be an existing object like a plastic toy, or a newly made item fabricated using e.g. a 3D printer.
Mold release: Mold release is a spray-on liquid used to prevent the mold from sticking to the watertight container and also to prevent casting materials from sticking to the inside of the mold. (It should not be used for applications like making food products.)
Casting material: The material poured into a silicone mold can be anything from polyurethane to melted chocolate.
Clay (optional): Clay is only required when making a two-part mold.
Making Silicone Mold
The silicone mold
making process as follows:
Obtain or make the master pattern: The master is a positive original of the parts you will make with the silicone mold. This can be an existing solid object or a new item made with manufacturing equipment. (See next section.) For best results, the master should not contain complex cavities or overhangs.
Lay the pattern(s) in the container: In many cases, a container is made specifically for the pattern. The box container can be made from e.g. wood or cardboard. After applying mold release to the inside of the container, place the patterns flat side down in the container or suspend them within the newly made container. If you have multiple patterns (for making a popsicle tray, for example), spread them out evenly. Spray them with mold release. If you are making a two-part mold, half of the container should be filled with clay and the patterns inserted half-way into the clay.
Mix and pour the silicone: Mix the two silicone components according to the instructions on the bottle, then pour it slowly into the container. The surface level should rise half an in inch above the top of the master pattern to prevent the mold from tearing. Curing can take several hours (specific times may be specified on the silicone bottle). For professional applications at Tinheo, we remove air bubbles, then cure the silicone mold
in an oven at a medium temperature.
Remove the cured mold: Once it has fully cured, the silicone mold can be gently removed from the container. If you are making a two-part mold, you should remove the clay, leaving just the mold with the pattern still half sticking out. Return the mold to the container the other way up, so the pattern is protruding upwards. Apply mold release to the mold and pattern, then fill the other half of the container with silicone like in Step 3, wait for curing, then remove.
Remove the master pattern from the mold: Gently remove the master pattern(s) from the silicone mold. If you are making a two-part mold, you will first have to separate the two halves of the mold.
Cast the parts: Depending on your casting material, casting your parts may be as simple as applying for mold release then pouring liquid into the mold. Professional processes like vacuum casting involve inserting the silicone mold into a machine that removes air bubbles from the casting material.