Two-Piece Silicone Mold Making step by step Tutorial

Two-piece silicone mold is better for reproducing your 3D master without a flat side or has deep undercuts. The mold splits into two pieces that join back together, forming a fillable 3D cavity.

Making molds from rtv silicone rubber is not as difficult as it may sound. With our step-by-step instructions you can make a great silicone mold, even if you are a beginner. The following pictorial step-by-step tutorial records in detail the process of making a two-part mold:

Step 1: Lay out the masters in clay

Before making the actual two-part mold, we need to lay out its dividing plane. We will cut the pouring channel and air vents into the mold later before the casting itself. The dividing plane will be created as follows: push the master model into the modeling clay up to the intended dividing plane level. To be able to properly align both mold halves later, create so-called Positioning hole.

lay out the masters in clay

Step 2: Mixing the Silicone

First weigh the required amount of silicone, and then mix the two components in the correct ratio. Be careful not to waste too much silicone. You can determine the amount required either by calculating the volume or roughly by using a measuring stick.

rtv-2 liquid silicone rubber

Step 3: Stir the silicone

Stir the mixture for a while to make sure the mixture is completely mixed.

stir the silicone

Step 4: Pour silicone

Pour the rtv liquid silicone slowly into the clay and the mold shell on top of the master mold. Note: This layer of silicone will be one half of your two-piece mold.

pour liquid silicone

Step 5: Waiting to cure

Depending on what type of silicone you are using it can take anywhere from 1 hour to 24 hours to cure. Temperature and humidity will affect curing times, so we recommend this process be done in a room temperature environment.

waiting to cure

Step 6: Prepare mold part two

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. Coat the top of the master mold and the existing silicone mold with a thin layer of release agent so that the two halves of the mold can be easily separated later.

mold part two

Step 7: Prepare and pour the silicone for your second mold

Next, repeat steps 2-5 and create the second half of your mold using the methods mentioned above.

Step 8: Wait for your second mold to cure

Allow plenty of time for your second mold to cure before attempting to remove it from the mold housing. Once both halves of your mold have cured you are ready to remove them from the mold box and begin using them to recreate parts.

wait for your second mold to cure

Step 9: De-mold your parts

When the silicone mold is finished depends on its size and the silicone used. Some silicone molds take only one hour to harden, some up to 24 hours. To check if the process is complete, gently press into the mold with a finger. After confirming that it is completely cured, Remove both silicone molds from the mold housing and gently pull them apart.

two-piece silicone mold

Step 10: Reassemble mold

Gently remove the master pattern(s) from the silicone mold. Tape both mold halves tightly together.

You also have to cut at least one air vent to let the air escape the mold quicker. Such vents should be always placed above the point where the pouring channel meets the model cavity, and also in every place where any air pockets could form. It is characteristic of a correct casting procedure, that all air vents are also completely cast.

reassemble mold

Step 11: Measure Resin

Just as with silicone you will need to measure each part of the mixture taking into account the volume needed to create a part. Note: Resins typically have a shorter “pot-life” than silicone meaning they will cure faster.

polyurethane resin

Step 12: Poure Resin

Once mixed, immediately pour it from the opening of the mold. Note:pour slowly as not to overfill and spill resin.

poure resin

Step 13: Cure

Once poured, allow the resin to cure for the appropriate amount of time.

cured mold

Step 14: Take out the casting

Once your resin has cured, you can open the mold and remove your cast part.

comparison of casting model and prototype

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