Plastic Injection Molding

2K / Two-Shot Molding

Two-shot injection molding — also called 2K or double injection molding — molds two different plastics or two colors into one part in a single cycle. The first shot forms the substrate, the mold rotates or the core retracts, and the second shot is molded straight onto it while it is still warm.

What It Is

One part, two materials, no assembly.

Two-shot molding produces a single part with different plastic materials in different regions, or a single part with multiple independent colors. Because the second material is molded onto a hot substrate inside the same tool, the bond is stronger and the cycle faster than any two-step process. Applications range from power tools and toothbrushes to automotive buttons and medical devices.

The deciding factor is material compatibility — the two resins must be designed to bond and run at compatible cycle times. Many overmolding pairs are not suitable for two-shot, which is why we confirm the pairing in the DFM report before quoting the tool.

Process Types

Four Ways To Double-Inject a Part

Sequential (rotary) molding — the first shot is molded, the platen rotates 180°, and the second material is molded onto it. The standard method for two-color and soft-touch parts.
Core-back molding — a movable core retracts after the first shot to open a new cavity for the second material, without rotating the mold.
Co-injection molding — two materials injected through one nozzle, forming a skin and a core — used for parts with a soft skin over a rigid or recycled core.
Sandwich molding — two materials in the same cavity separated by a core material, for lightweight composite parts.

Tooling & Equipment

2K Molds Built and Run Under One Roof

A two-shot mold is really two molds in one: two cavity sets, two runner systems and a rotation or core-back mechanism that has to index perfectly every cycle. We design and build these tools in our own shop, then trial and run them on our parallel 2K injection machines and 90-degree double injection machines.