Silicone rubber molds are a favored choice for creating flexible, durable, and highly detailed casts, especially in rapid prototyping and small to medium batch productions. However, several factors such as cost, lifespan, and dimensional accuracy play critical roles in the mold-making process. Understanding these aspects can significantly improve the efficiency and outcome of silicone rubber mold productions. Here’s a deeper look into the critical considerations for manufacturing silicone rubber molds.

1. Mold Frame Size

The size of the mold frame is crucial for managing costs and maintaining the quality of the mold:

• Smaller Frame Sizes: Opting for a smaller mold frame can reduce the amount of silicone rubber needed, thereby lowering the costs. However, a smaller frame may complicate the pouring process due to restricted space, potentially affecting the mold’s quality.
• Larger Frame Sizes: While a larger frame size can make the silicone pouring easier, it leads to wastage of material, increases the cost, and can reduce the flexibility of the silicone mold. This might complicate the demolding process, especially for intricate designs or delicate parts.

To optimize, the mold frame should be designed to have walls and a base around 20mm from the edges of the RP model, with side barriers that extend 90mm above the height of the model plus an additional 50mm clearance to prevent overflow during degassing.

2. Parting Line Selection

The choice of the parting line is pivotal for ease of demolding:

• Largest Projection Area: Typically, the parting line is selected along the largest projection area of the prototype to simplify the mold design and ensure even flow of silicone.
• Special Structures Consideration: Due to the high elasticity of silicone, rough handling during demolding is permissible, allowing for special structures like small protrusions on the sides to be ignored when choosing the parting line. This flexibility in handling reduces the risk of damage to both the mold and the parts.

3. Handling of High and Thin-Walled Parts

For high, thin-walled parts where dimensional accuracy is critical:

• Wall Positioning: It’s important to place the entire thin wall in the same half of the mold to minimize deformation caused by the mold closing or during the binding process, which could otherwise lead to inaccuracies in wall thickness.

4. Mold Frame Shape

While mold frames are typically rectangular or square, adapting the frame shape to match the specific geometry of the part can be more silicone-efficient and cost-effective:

• Custom Frame Shapes: Building a custom-shaped frame according to the part’s contour can reduce silicone usage and thus lower the overall mold cost.

5. Gating System and Air Vents

Proper placement of gates and air vents is essential to ensure quality casting:

• Gate Placement: For molds with a large planar surface, the gate should ideally be placed near the prototype’s center of gravity to facilitate even silicone flow and reduce air entrapment.
• Avoiding Air Traps: The orientation of the gating system should prevent large planar areas from being at the highest position in the mold cavity to avoid air pockets, which can lead to defects.

6. Cutting and Mold Opening

The technique used to cut open the mold affects the accuracy of mold alignment:

• Cutting Technique: Using a scalpel or similar tool, the incision should follow a straight line at the tip and a curved path at the tail to create an irregular parting line shape. This irregularity helps in precise alignment during subsequent mold closings, reducing errors due to misalignment.

Conclusion

Manufacturing silicone rubber molds involves careful consideration of various technical details that affect the mold’s cost, durability, and the precision of the final parts. By optimizing mold frame size, selecting appropriate parting lines, handling thin-walled parts delicately, customizing frame shapes, strategically placing gates, and employing precise cutting techniques, manufacturers can achieve high-quality outputs while maintaining cost-efficiency. These practices not only enhance the mold’s functionality but also extend its lifespan, making silicone rubber an invaluable material in the realm of rapid prototyping and specialized small-scale manufacturing.