Making Silicone mold is one critical step in the Urethane Casting process which is used for rapid prototyping and low-volume manufacturing, but do you know how to make the silicone mold? and why use silicone to make mold? today, in this ariticle, we will share the steps of how to make a silicone mold to help you manage this process.
What is silicone mold?
A silicone mold is a tooling made from silicone rubber. it is use to pour resin into it and create exactly the part shape you need. Liquid silicone rubber is poured over an master pattern and cure to form the mold.
advantages of Silicone Mold
Silicone mold can be made in less than 24 hours which is faster than any metal mold. With silicone mold, you can get your protoypes in less than 10days or even faster. this will save time for your product devolopment.
Silicone materials used for mold is very cheap compare with Steel, and the process of making silicone mold is easy, this can help reduce the total cost of the prototypes.
Fine Detail Reproduction
Silicone mold can get a exactly same cavity shape with the master pattern with all the details. so, after Urethane Casting, the prototypes can have the same surface finish and dimension accuracy with the master pattern.
Silicone mold is soft and flexible, it can be bent or twisted. So it will be easy to take out the prototype from silicone mold. no draft needed in the design even some small undercut is still ok. this will let you have a flexible design.
Silicone Rubber hardness
The hardness of silicone mold will impact the parts flexibility. A soft silicone mold is able to make more complex shape prototpye, but the quality of the prototpye will be worse if you use too soft mold. So, you need balance between the complex shape and parts quality. here are some tips for you:
- Silicone with A Shore less than 20 means a very soft silicone used for very complex shapes.
- Silicone with A Shore from 20 to 40 is a proper level to balance flexibility and dimensional stability
- A Shore from 40 to 80 is hard silicone. it can resist high pressure but with simple structure parts.
Making silicon mold Step by step
Prepare Tools and Materials
- silicone rubber (including curing agent)
- Master pattern (commonly made from 3D printing or CNC plastic machining)
- Modeling clay
- Mold release agent
- Cutting blades
Step 1: Master pattern Preparation, clean the master pattern to have smooth surface.
Step 2: Create a two-part mold to complete the silicone rubber mold. Embed the master model partially into modeling clay.
Step 3: Establish Alignment Holes, Gently press small wooden sticks along the edge of the master model to create alignment holes. Also, position pour spouts and vents in appropriate locations.
Step 4: Construct Mold Frame, You can use smooth materials like wooden boards, acrylic sheets or building blocks as a mold frame. Apply mold release agent to the frame’s surface to prevent adhesion. Surround the lubricated master model with sidewalls, leaving a gap of 2-4cm in between. For larger products, additional support with steel bars may be required.
Step 5: Create two parts of the Mold, Pour the prepared liquid silicone rubber into the Mold Frame space until the master pattern is entirely covered. then repeat the process to make the other part.
Step 6: Put the mold in a vacuum machine and remove air from the liquid silicone rubber to avoid any bubbles.
Step 8: After the mold is cured, remove the frames, Technicians will carefully split the silicone mold and remove the master pattern. then, the mold making is finished.
Tips for making silicon mold
- Use Proper amount of curing agents, because too much curing agents can make the mold hard and brittle, while too little will extend the working time.
- To prevent changes in the properties of the silicone rubber, it is recommended not to add silicone oil.
- For best mold performance, store the mold for at least 24 hours before use.
- Due to the limited lifespan of silicone rubber, the ideal number of uses for a silicone mold is 10-20 times.
Silicone overmolding follows the hard tooling inejction overmolding, are used for bi-color prototypes. here are some tips for making a silicone mold for overmolding.
- Adhesion: Ensure proper adhesion between the silicone and the surface to be over molded.
- Curing Temperature: best curing temperature is around 160 degrees Celsius.
With a good silicone mold making skills, you can make prototypes with high quality and accuracy. use the right slicone hardness is the key. KSULA specialize in High quality rapid prototyping and low-volume manufacturing services.