When Is Overmolding Necessary?

Today’s manufacturers face a never-ending challenge—keeping costs low, maintaining consistently high product quality, keeping up with high order volume, and ensuring on-time delivery of time-critical components. Extended or missed delivery times reverberate throughout a supply chain, so many manufacturers are now partnering with plastic injection molding companies specializing in overmolding.

What Is Overmolding?

Overmolding is a multi-step plastic injection molding process where different materials, plastic resins, or rubbers are molded into a single finished product. A substrate (base material/base layer) is molded and allowed to cure before a second additional molded layer is added.

Each layer can be a combination of different materials or the same materials. However, for the most part, the materials are different for each layer. An ideal example might include a wrench where the wrench’s material (steel) has an overmolded layer of thermoplastic resin and rubber. The additional layers improve grip and provide better protection for the end-user. Ultimately, overmolding is commonly used to make handles or grips on products for various purposes.

Materials Used for Overmolding

In most applications, the base material (first layer) is a rigid, durable plastic, while the second molded layer is a premium rubber. While the number of material variations is endless with this overmolding, the most common materials used include polyetherimide (PEI), acrylonitrile butadiene styrene (ABS), polyetheretherketone (PEEK), polymethyl methacrylate (PMMA) and high-density polyethylene (HDPE).

PEI (Polyetherimide)

Polyetherimide is a high-performance, high-strength, semi-transparent thermoplastic that maintains rigidity at high temperatures. It has good electrical properties, and excellent creep and heat/flame resistance, making it an ideal replacement for certain metals in specific applications. 

ABS (Acrylonitrile Butadiene Styrene)

ABS is a low-melting-point thermoplastic with good abrasion resistance, excellent tensile strength and rigidity, and good machining characteristics. The material’s strong impact and corrosion resistance also make it ideal for producing lightweight, high-strength, and rigid components.

PEEK (Polyetheretherketone)

Polyetheretherketone, or PEEK, is another high-performance, high-strength thermoplastic. PEEK is known for its high tensile strength and strong chemical, abrasion, creep, wear, and fatigue resistance. This temperature-resistant material also has excellent electrical properties and is often the material of choice for extreme environments in the medical, aerospace, and automotive industries.  

PMMA (Polymethyl Methacrylate)

PMMA is a transparent thermoplastic with high hardness values, exceptional UV resistance, and strong rigidity. The material has superior optical qualities and strong weathering resistance, making it an ideal material replacement for glass. The material is also relatively inexpensive compared to other thermoplastics but is still durable and strong enough to be used for a wide range of medical implants and devices.

HDPE (High-Density Polyethylene)

High-density polyethylene, or HDPE, is a cost-effective translucent plastic commonly used in consumer products. This material is highly recyclable and has excellent weather, chemical, and general wear resistance. 

When Should You Use Overmolding?

Overmolding is ideal for any high-volume production run of multi-layered products or components requiring two or more materials with different colors and properties. The process is less labor-intensive than other manufacturing processes and helps reduce assembly times. 

Learn More About Overmolding From Silver Basis Engineering

Companies rely on Silver Basis Engineering to deliver time-critical plastic molded components and die castings to manufacturers worldwide. We hold multiple accreditations and certifications and are widely recognized for our 20 National Fine Model Awards and 511 patents. Visit our blog for more plastic injection molding resources, or contact us today to learn more about our manufacturing capabilities.