A Comprehensive Guide to Making Silicone Molds
Silicone molds (negative copies of parts that can be filled with material) are an integral part of the manufacturing industry. In fact, most of the world’s plastic parts are made through injection molding.
But while metal injection molds are expensive and only professionals can make, flexible silicone molds are very affordable and can be made at home or in the office.
Their uses are many, from vacuum casting for professional-grade prototypes to small-batch wax casting for jewelry making to home applications such as baking and candy making.
This article describes the relatively simple process of making silicone molds, discusses its applications and advantages for professional and personal use, and provides tips for making silicone molds at home.
1.What are silicone molds?
A mold is a container with a hollow cavity into which a liquid material is poured or pressed and then hardened (by cooling or other methods) to form a solid object in the shape of the cavity. Molds can be made of different materials, such as tool steel or aluminum. They can also be made of silicone, a class of polymers composed of siloxanes that are sometimes used to make products such as flexible protective cases, gaskets, and contact lenses. Silicone molds are not as durable as metal molds, but they are affordable, easy to make, and very flexible. This flexibility, coupled with the fact that few materials adhere to silicone, makes it easy to remove molded parts from silicone molds.
2.How to Make Silicone Molds
Making silicone molds is very simple and only requires a few components. While professional equipment gives you more options, silicone molds also have many home uses. The components needed to make silicone molds include:
① Liquid Silicone
Silicone used to make molds is widely available and usually comes in two parts that must be mixed together immediately before use.
② Container
Pour the liquid silicone into a container that should be larger than the master model (but not too much larger). In many cases, a new box of the right size can be made using materials such as wood or cardboard as needed.
③ Master Model
The master model is the original object that you will replicate using the silicone mold. The master model can be an existing object, such as a plastic toy, or a new item made using, for example, a 3D printer.
④ Release Agent
A release agent is a spray liquid used to prevent the mold from sticking to a waterproof container and also to prevent the casting material from sticking to the inside of the mold. (It should not be used for applications such as making food.)
⑤ Casting Material
The material poured into the silicone mold can be anything from polyurethane to melted chocolate.
Clay (optional): Clay is only needed if you are making a two-part mold.
3.The silicone mold making process is as follows:
① Get or make a master model
The master model is the positive original of the part you will make with the silicone mold. This can be an existing solid object or a new item made with manufacturing equipment. (See the next section.) For best results, the master model should not contain complex cavities or overhanging parts.
② Place the model in a container
In many cases, the container is made specifically for the model. Box-type containers can be made of wood or cardboard, etc. After applying mold release agent to the inside of the container, place the model flat side down in the container or hang it in a newly made container. If you have multiple models (such as for making popsicle trays), spread them evenly. Spray them with mold release agent. If you are making a two-part mold, half of the container should be filled with clay, and the model should be inserted into half of the clay.
③ Mix and pour silicone
Mix the two silicone components according to the instructions on the bottle and slowly pour them into the container. The surface level should be half an inch higher than the top of the master model to prevent the mold from tearing. Curing may take several hours (the specific time may be specified on the silicone bottle). For professional applications at Xavier, we remove air bubbles and then cure the silicone mold in a medium-temperature oven.
④ Remove the Cured Mold
Once fully cured, you can gently remove the silicone mold from the container. If you are making a two-part mold, you should remove the clay and leave only the mold with half of the pattern still sticking out. Place the mold back into the container upside down so that the pattern sticks out upward. Apply mold release to the mold and pattern, then fill the other half of the container with silicone as in step 3, wait to cure, and then remove.
⑤ Remove the Master Model from the Mold
Gently remove the master model from the silicone mold. If you are making a two-part mold, you must first separate the two halves of the mold.
⑥ Casting Parts
Depending on the casting material, casting parts may be as simple as applying mold release and then pouring liquid into the mold. Specialized processes such as vacuum casting involve inserting the silicone mold into a machine to remove air bubbles from the casting material.
4.3 Ways to Make a Master Pattern
The master pattern determines the outcome of silicone molding, so it is important to obtain or make a high-quality, detailed master pattern that is easy to mold. It is also important to make a master pattern that has a long life if multiple silicone molds are needed (for example, for small batch production using vacuum casting). If you are making a pattern from scratch, there are three different methods you can use.
Method I: Manual
People have been making patterns for thousands of years using non-digital techniques. For this method, we can carve patterns by hand using soft materials such as clay and manual cutting tools. Experts can also carve patterns from wood or other materials.
Advantages:
- No expensive machines are required
- Great for replicating artwork and handicrafts
Disadvantages:
- May be inaccurate
- Requires professional manual skills
Method II: 3D Printing
Digital technology and CAD software have made pattern making much more efficient and easy for non-professionals to use. 3D printers, especially high-resolution stereolithography machines that can print smooth surfaces, are now widely used to make masters.
Advantages:
- Uses digital files (downloadable from the internet)
- Accurate and repeatable
- Printers can be used in non-industrial settings
- Minimal post-processing required if using SLA
Disadvantages:
- Expensive machinery
- Cannot meet the tightest tolerances
- Very short model life due to the use of brittle resin
Method III: CNC machining
CNC machining is another digital manufacturing technique used to make master models. With CNC machining, high-durability materials can be used, resulting in stronger, more durable models. CNC machines can also meet tighter tolerances, although they are less accessible to non-professional users and cannot be used in home or office settings.
Advantages:
- Most accurate and precise
- Very long pattern life
- Compatible with heat-resistant materials
Disadvantages:
- Expensive and difficult to obtain machines
- Some post-processing required
5.Professional Uses of Silicone Molds
Small-volume manufacturers such as Xavier use silicone molds for a variety of purposes. With the help of silicone molding process, we can make molds of plaster statues and other handmade artworks, so that we can easily replicate them.
Making silicone molds can also help us complete other manufacturing processes. One of them is vacuum casting, which fills silicone molds with polyurethane in a vacuum environment to create high-quality plastic parts and prototypes. Vacuum casting is suitable for small-volume part production and is cheaper than small-volume injection molding. The life of silicone molds in vacuum casting is about 20 castings, and for high-resolution parts, we use CNC-machined master molds.
Another use for silicone molds is wax casting, which is an ancient technique used to make metal parts such as jewelry and industrial parts. In lost wax casting (or investment casting), silicone molds are filled with molten wax to make wax copies of the master model. These wax models can then be coated with ceramic and then burned in a kiln. The remaining ceramic structure can be used as a new mold, into which liquid metal is poured to create a new object.
Making professional silicone molds in a manufacturing environment usually requires the use of specialized machinery, such as vacuum casting machines and silicone curing ovens.
6.Advantages of Silicone Molds
① Durable
Silicone molds can be used multiple times before they degrade, especially when they are thicker and used in less demanding applications.
② Flexible
Since silicone molds are similar to rubber, it is easy to remove the casting without damaging the part or the mold itself.
③ Heat-resistant
Silicone molds can be used at high or low temperatures without degradation or deformation, making them suitable for applications such as cooking.