Injection compression molding (ICM) is a hybrid manufacturing process that combines elements of injection molding and compression molding. It is used to produce high-precision plastic parts with excellent surface finish, dimensional accuracy, and minimal residual stress. This process is particularly well-suited for manufacturing large, thin-walled parts, optical lenses, and components requiring tight tolerances. Here’s a detailed explanation of how injection compression molding works:

1. Mold Preparation

Mold Design: The mold is designed with a slightly larger cavity than the final part dimensions. It consists of two halves: a stationary mold (cavity) and a movable mold (core).

Mold Heating: The mold is heated to a specific temperature to ensure proper flow and curing of the plastic material.

2. Material Preparation

Plastic Material: Thermoplastic or thermosetting materials are used, depending on the application.

Melting: The plastic pellets are fed into an injection unit, where they are melted and homogenized.

3. Injection Phase

Partial Mold Closure: The mold is partially closed, leaving a small gap between the core and cavity.

Injection: The molten plastic is injected into the partially open mold cavity under low pressure. The low pressure reduces shear stress and minimizes material degradation.

4. Compression Phase

Mold Compression: After the molten plastic is injected, the mold is fully closed, compressing the material and forcing it to fill the entire cavity.

Pressure Application: The compression force ensures uniform distribution of the material, reducing warpage and improving part quality.

Key Point: The combination of injection and compression allows for better control over material flow and part formation.

5. Cooling and Solidification

Cooling: The mold is cooled to solidify the plastic material. Cooling channels within the mold help maintain consistent temperatures.

Solidification: The plastic takes the shape of the mold cavity and hardens into the final part.

6. Ejection

Mold Opening: Once the part has cooled and solidified, the mold opens.

Part Ejection: The finished part is ejected from the mold using ejector pins or plates.

Key Features of Injection Compression Molding:

Improved Surface Quality: The compression step results in a better surface finish with fewer defects such as voids, air pockets, and rough textures. This is particularly important in industries like automotive and consumer electronics, where surface aesthetics matter.

Reduced Material Waste: The compression of the material helps minimize waste by filling the mold more efficiently. The material is compacted into tight spaces and small features of the mold, allowing for better use of the raw material.

Precision: Because the compression phase ensures better filling and material distribution, parts produced using injection compression molding tend to have higher precision and better dimensional accuracy compared to standard injection molding, particularly for complex shapes.

Better Strength: The combination of injection and compression processes allows the material to flow more uniformly into the mold, resulting in parts that have improved structural integrity.

Reduced Cycle Time: While the cycle time in injection compression molding can be slightly longer than traditional injection molding, it often requires fewer steps and less material preparation, leading to a more efficient process overall.

Applications of Injection Compression Molding

Optical Components:

Lenses, light guides, and prisms.

Automotive:

Large panels, interior trim, and light covers.

Consumer Electronics:

Display screens, touch panels, and housings.

Medical Devices:

Transparent components and precision parts.

Packaging:

Thin-walled containers and lids.