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Multi durometer molding

Multi durometer injection molding

What Is multi durometer molding?

Multi-durometer injection molding is a specialized injection molding technique that allows for the simultaneous or sequential molding of materials with different hardness (or durometer) values into a single part. 

Essentially, it’s a variation of overmolding but focuses on the specific characteristic of material hardness.

Durometer is a measure of the hardness of a material, particularly for polymers, elastomers, and rubbers. A lower durometer indicates a softer material, while a higher durometer signifies a harder material. The process and purpose of multi-durometer injection molding can be understood as follows:

1. Process

Initial Molding: Similar to the overmolding process, the initial part, often made from a harder plastic, is molded first.

Once the initial part has cooled or semi-cooled, it’s placed in another mold or remains in the same mold (depending on the mold’s design) for the secondary injection. The secondary material, which can be softer or harder depending on the design requirements, is then injected. This second material will form around or alongside the initial part, adhering to it. After cooling, the two materials, having different hardness values, become one integrated part.

2. Advantages

Allows for parts with varying hardness to be produced in a single step, reducing assembly processes.

Gives designers more flexibility in part design, allowing for a balance between rigidity and flexibility in specific areas of a part.

The ability to combine hard and soft materials can improve the overall functionality and user experience of a product.

3. Applications

Commonly found in tool handles, medical devices, or consumer electronics, where one part needs to be rigid (hard) for structural purposes and another part soft for comfort.

In cases where a part needs a rigid structure but also requires an integrated soft seal.

Like those on flip-top caps, where a rigid cap might have a flexible hinge made from a softer material.

4. Challenges

It’s crucial to ensure that the materials selected bond well with each other during the molding process.

Designing molds and processes for multi-durometer molding can be more complex than for single material parts.

As with overmolding, ensuring a strong bond between materials of different hardness requires precision in temperature, pressure, and other process parameters.

Summary

In summary, multi-durometer injection molding provides an effective way to create parts that combine the properties of both hard and soft materials, expanding design possibilities and improving product functionality.
 

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