Overmolding: Key Considerations When Selecting Materials and Molders

    Posted by Al Timm on Jan 18, 2017 9:19:00 AM
    Al Timm

    overmolding-med-device.jpgOvermolding 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 which 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 substrate for a soft touch, or to join rigid plastics and metals without the aid of glues or fasteners. The substrate provides structural support and comes in many forms: a machined metal or molded plastic part, or separately purchased components like screws, tools, push buttons and washers. The overmold surrounds the substrate to accomplish specific project goals like augmenting functionality, improving safety or adding colors for identification and visual appeal. For example, overmolding on a hand-held medical device to improve grip and allow the addition of a red stop button that’s easy to find, yet won’t get pressed accidentally in the heat of an emergency.

    Which plastic is right for your overmolding project?

    The overmolding material appropriate for a component or device is largely driven by the substrate:

    • Plastic over a metal substrate provides great versatility since the materials are inherently compatible and there are few — if any — chemical formulations that would limit the two from producing a component that consistently performs to its intended purpose.
    • Plastic over plastic substrates presents a greater risk for materials incompatibility, which is why it’s crucial to work with a complex injection molder with deep plastics engineering support. 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.

    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 a complex injection molding partner with materials knowledge, experience and a deep understanding of plastic behaviors — including flow, adhesion and coloration — during molding and overmolding. An experienced molder will also be able to identify how materials will best join and interlock mechanically so the parts remain physically held together.

    Why overmold?

    Overmolding is versatile, and when the process is done by an experienced 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 and provides water resistance and 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 yet functional way to brand a product or family a product line with specific colors and patterns. Further, overmolded components may be colored for easy identification and quick use.

    Your overmolding project can be dynamic and cost-effective when you partner with an expert complex injection molder, as demonstrated in the recent Kaysun case study Why Molder Experience Matters in Critical-Use Applications. Click the button below to download your free copy.

    Molder Experience Case Study

    Topics: Overmolding