1. Two-Step Injection Molding
This process involves injecting a first material (the substrate) into a mold, then transferring it manually or robotically to a second mold to inject a second material.
Key steps include:
– Substrate Injection: Performed in the first mold, similar to traditional injection molding.
– Cooling and Transfer: The substrate is demolded and placed into a second mold for overmolding.
– Second Material Injection: An elastomeric material (e.g., TPE) is injected onto the substrate to form a homogeneous dual-material part.
– Applications: Ergonomic grips, technical parts combining rigidity and flexibility.
2. Insert Overmolding
Insert overmolding refers to the process of covering an existing component (called a substrate or insert) with another material—usually a polymer—to create a composite part. The overmolding material can differ from the substrate, enhancing the final part’s properties such as strength, flexibility, or appearance.
Common uses include:
– Metal insert encapsulation (e.g., screws, connectors) as well as shafts, steel plates.
– Mechanical reinforcement: Improves vibration resistance and pull-out strength.
– Examples:
– Toothbrush handles, tools, or utensils with soft-touch areas for comfort.
– Electronic components with inserts for conductivity or fastening.
3. Two-Shot Molding (2K)
Two-shot molding uses a special machine equipped with two injection units to create a part in a single cycle, with no manual transfer:
– Simultaneous or Sequential Injection: Both materials are injected into the same mold, using a rotating mold section (rotary table or rotating core).
– Chemical or Mechanical Bonding: The materials must be compatible to avoid delamination.
– Applications: Keypads (soft keys on rigid base), automotive bumpers.
Comparative Advantages Table
Process | Advantages | Disadvantages / Limitations |
|---|---|---|
Sequential Overmolding | – Uses standard machines – Low investment – Ideal for prototyping or small batches | – Longer cycle time – Risk of poor adhesion if the substrate cools too much |
Insert Overmolding | – Functional integration (e.g., connections, anchoring) – Better mechanical performance | – Manual or automated placement is more complex – Mold cost may be higher |
Two-Shot Molding (2K) | – Fast single cycle – Optimized bonding quality – High repeatability | – Requires expensive dedicated machines – Material compatibility is essential |
Practical Tip: Which Process Should You Choose?
The choice of overmolding process depends on production context and technical requirements.
Situation | Recommended Process |
|---|---|
Prototypes, small batches, material trials | Two-Step Sequential Overmolding |
Metal/plastic integration, technical inserts | Insert Overmolding |
Large series, high speed, high repeatability | Two-Shot Molding (2K) |
Overmolding transforms simple plastic injection into a multifunctional solution: more comfort, better performance, and greater durability.
Material Combinations:
Two-shot overmolding process with 180° mold rotation
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