Overmolding: Key Considerations When Selecting Materials and Molders

Overmolding is a value-added injection molding method for improving plastic and metal substrate performance and aesthetics. While seemingly simple, the process has a number of underlying complexities that must be carefully considered to ensure your overmolding project meets all goals and expectations.

What is overmolding?

In the simplest terms, overmolding refers to the injection molding process used to add a layer of thermoplastic elastomer (TPE) over a formed metal or plastic substrate for a soft touch, or to join rigid plastics and metals without the aid of glues or fasteners. The substrate provides structural support. The TPE overmold surrounds the substrate to accomplish specific project goals such as augmenting functionality, improving safety, or adding colors for identification and visual appeal. For example, overmolding on portable devices improves grip, increases visibility of buttons and gauges, and protects delicate internal electronics from vibration, moisture, and damage if the device is accidentally dropped.

how does overmolding benefit your project?

Overmolding is versatile, and when the process is done by an experienced overmolding molder, it enhances product designs in multiple ways:

• Safety/Performance: Overmolding alters the tactility of the surface to make gripping more secure in all environments, and also dampens vibration, absorbs sound, seals out moisture and dust, and provides electrical insulation.
• Comfort: Overmolded components and devices can be more flexible and generally easier for end users to manipulate, making repetitive or complex activities less taxing.
• Production: Overmolding  can provide all-in-one manufacturability, simplifying production line processes by eliminating the need for costly assembly processes and parts.
• Identity: Overmolding offers a convenient and functional way to brand a product or family of products using specific colors and patterns. Further, overmolded components may be colored for easy identification and quick use.

Which plastic is right for your overmolding project?

Identifying overmolding materials appropriate for a component or device is largely driven by the substrate:

• Plastic-over-metal substrates combine inherently compatible materials. There are few — if any — chemical formulations that limit the two from producing a component that consistently performs to its intended purpose.
• Plastic-over-plastic substrates provide exceptional versatility in component functionality, aesthetics, safety, and performance. The benefits are substantial but compared to plastic-over-metal substrates, the process presents a greater risk of materials incompatibility. The structure, chemical makeup, strength, and durability of the resins all factor into how well the plastics will interplay, and ultimately how the overmolded component will perform over time. Guidance from an experienced custom injection molder is essential in discerning how and which materials will best join and interlock mechanically so the parts remain physically held together.

To minimize missteps, molders also work closely with materials suppliers to understand and follow their guidelines during production. However, written documentation of potential compatibility issues is no guarantee of best-in-class results. There is simply no substitute for partnering with an experienced overmolding molder with extensive materials knowledge and a deep understanding of plastic behaviors — including flow, adhesion, and coloration — during molding and overmolding.

Learn more about overmolding principles and how the process contributes to project design, engineering, performance, and manufacturing efficiencies in our whitepaper, Overmolding Fundamentals. Click the button below to access your copy now!