Two-shot, also referred to as dual-shot, double-shot, multi-shot and overmolding, is a plastic molding process in which two different plastic resins are molded together in a single machining cycle, as illustrated below.
There are two phases of the two-shot molding process. The first is similar to traditional injection molding: A shot of resin is injected into a mold and cooled to form a solid part. In the second phase, the just-molded part is transferred to a second mold via a rotating platen or a robotic arm, and receives the second shot of resin – in, through or around certain parts of the first molded part, depending on the design. The two plastic resins then form a molecular bond and the multi-resin molded part is cooled and ejected.
The process isn’t difficult to understand, but it’s highly difficult to master. It requires high levels of technical expertise and attention to detail, and even the smallest mistakes can cost big money, especially in high-volume production scenarios.
That’s why it’s critical to find a highly capable supplier. Look for excellent supplier quality scorecards, defined processes to mitigate against flash, flow lines, and short-shots, and contingency plans to expand capacity as your business and your two-shot molding needs grow.
Once you find a supplier, involve them early on in the design phase of your part. They can identify potential problem areas and engineer value into your product.