Overmolding Injection Molding: Integrating Multiple Materials in a Single Product

From soft‑touch grips on toothbrushes to waterproof electronic housings, overmolding has become a game‑changing process in modern manufacturing. By injecting two (or more) materials in succession, engineers create cohesive, multi‑function parts that add durability, ergonomics, and style—while eliminating secondary assembly. This article explains how overmolding injection molding works, key design guidelines, and the benefits of partnering with INTERTECH (taiwanmoldmaker.com) to bring multi‑material ideas to life.

1 What Is Overmolding?

Overmolding is an injection‑molding technique in which a base substrate (hard plastic, metal, or even a pre‑molded plastic part) is partially or fully covered by a second material during the same molding cycle. The second shot may provide:

Soft‑touch feel (TPE, TPU)
Sealing or vibration damping
Colour contrast or branding
Mechanical reinforcement
Electrical insulation or EMI shielding

Common Overmolding Methods:

Two‑Shot (Two‑Component) Molding – A rotary platen or transfer operation injects two polymers in one press.
Insert Overmolding – A pre‑molded or machined insert is loaded into the mold and encapsulated by a second material.
Multi‑K Molding – Three or more materials molded in sequential or simultaneous shots.

2 Advantages of Multi‑Material Integration

Benefit	Example Application
Ergonomic Comfort	Soft TPU grips on power‑tool housings
Waterproofing & Sealing	TPE gaskets over PC/ABS sensor covers
Assembly Reduction	Single‑piece syringe plungers—no post assembly
Enhanced Aesthetics	Dual‑colour cosmetic packaging
Weight Saving vs. Mechanical Fasteners	Integrated hinge pins or seals

3 Design Guidelines for Successful Overmolding

Material Compatibility – Choose polymers with good chemical or mechanical bonding (e.g., TPE→PP, PC→ABS). INTERTECH works with resin suppliers to confirm adhesion data.
Undercuts & Mechanical Keys – Add ribs or through‑holes for extra grip when adhesion alone is insufficient.
Gate Placement – Gate directly onto the overmolded area to improve flow and minimise knit lines.
Vent & Cool – Ensure proper venting to avoid air traps; balance cooling circuits for both materials.
Draft Angles – Increase draft on softer overmolded material (2–4°) to aid ejection.

4 Material Choices and Adhesion Matrix

Substrate	Over‑Mold	Bonding Level*
PP	TPE (SEBS)	★★★
PC/ABS	TPU	★★
Nylon 6 + GF	TPE‑E	★★ + mechanical lock
Metal (Al, Cu)	PA 6/6 + GF	Mechanical only

*★★★ = excellent chemical bond; ★★ = good bond; ★ = limited.

5 Process Control Essentials at INTERTECH

Rotary two‑shot presses (up to 350 t)
Cavity pressure sensors for each shot to verify packing & adhesion
Mold‑flow simulation (2K modules) prior to steel cut
Automated insert loading for consistent cycle times

6 Industries Leveraging Overmolding

Consumer Electronics – Protective bumpers on phone cases
Medical Devices – Autoinjector soft grips and color-coded dosage rings
Automotive – Nylon brackets with rubber bushings molded in
Industrial Tools – Dual‑material handles for vibration isolation

7 Why Choose INTERTECH?

In‑House 2K Tooling: Design, CNC, EDM, and conformal cooling for complex shut‑offs
Material Expertise: Partnerships with Avient™, RTP, and Sabic™ for adhesion‑ready grades
ISO 9001 & ISO 13485 Quality Systems: Documentation and traceability for automotive & medical
Rapid Prototyping: Aluminum pilot tools for validation in < 3 weeks

Visit our custom molding page or arrange a free DFM review.

Conclusion

Overmolding unlocks robust, value‑added, multi‑material products without extra assembly steps. With advanced two‑shot presses, simulation‑driven tooling, and material‑science expertise, INTERTECH turns complex designs into high‑volume reality—on time, on budget, and to exacting quality standards.

Ready to integrate multiple materials in a single product? Contact INTERTECH for a feasibility analysis and quotation.