plastic injection mold setup

Two-Shot Injection Molding Versus Overmolding

Plastic injection molding is a versatile manufacturing process that helps produce thousands of products for industries such as food and beverage packaging, medical, domestic goods, automotive, computers, and electronics. While there is a wide range of plastic injection molding techniques, this blog post will cover two of the most common methods: two-shot injection molding and overmolding.

What Is Two-Shot Injection Molding?

Two-shot injection molding is used to create multi-layered or multi-colored components with different geometries, such as a hard plastic tool with a soft plastic grip handle. Two-shot injection molding eliminates the need for an additional assembly step because the two substrates are molded together in a single process.

The two-shot injection molding process is heavily used in the automotive and aerospace industries to reduce the use of metal, resulting in a lighter vehicle or aircraft. Seals, gaskets, soft-grip handles, and any consumer products that benefit from better tactile, sound absorption, vibration dampening, ergonomics, and aesthetics are good candidates for two-shot injection molding.

What Is Overmolding?

The overmolding process involves joining a base component with a second layer molded on top of the previous thermoplastic part. Overmolding takes advantage of the strength of hard plastic while adding a softer, flexible, consumer-friendly overlay.

Overmolding can also help lower manufacturing costs because the multiple substrates are joined in one process.

How Two-Shot Injection Molding Differs From Overmolding

Both plastic injection mold processes are multi-stage methods and can be used interchangeably. However, overmolding is best suited for low-volume runs, while two-shot injection molding is more economical for mass-producing a wider range of plastic parts. 

Manufacturers often use two-shot injection molding to produce components that feature more complex geometries. Generally, the two-shot injection molding process yields parts that are adequately bonded, have excellent durability, and have a long service life. 

Comparatively, overmolding has more imitations and disadvantages; the process requires two different molds (tools), which increases development, production, and labor costs. The process is also slower and requires specialized equipment.

How to Choose the Right Molding Technique for Your Project

The right molding process you select will depend on the production volume, product geometry, materials you are using, and if the product aesthetics and precision are critical to product performance or marketing. 

Two-shot molding should be considered for larger runs and/or to produce parts with better precision and excellent mechanical properties. The unit cost per molded part will be less with two-shot molding because there are fewer production steps. This method will also save production time by combining previous assembly steps into one molding process.

Overmold designs are typically simpler and easier to produce on a wider range of standard plastic injection molding machines. But, the designs must adhere to basic principles, including avoiding thin edges, accounting for shrinkage, and maintaining an overall uniform thickness. Overmolding material selections will also be limited to certain plastics such as polycarbonate, ABS (Acrylonitrile Butadiene Styrene), polystyrene, and nylons.

Find the Best Solution for Your Project

Silver Basis Engineering is an award-winning global plastics manufacturer delivering strong and reliable solutions to clients in many markets, including automotive, aerospace, medical, renewable energy, and consumer goods.

Please view our blog for additional plastic injection molding resources, or contact us today to learn more about our manufacturing capabilities.