There are mainly two ways to get injected parts made of dissimilar materials (by their nature and/or by their color): the so-called insert overmolding and the 2K molding (or 2 shot molding).
In the first rather common process, an “insert” whatever it is made of (metal, glass, plastic…) is placed into the mold before injecting the second material/color.
In 2K molding, the machine and the mold are a more complex in the sense that there are 2 injection units with the same mold which often rotates after the injection of the first material to allow the injection of the second material/color. There are some obvious advantages to use the 2K molding (the main drawback being the cost of the mold and the 2K machine) with respect to the insert overmolding:
- No (or much less) secondary operations and assembly steps
- Excellent or let’s say much better adhesion (provided similar shrinkage!)
- Low cycle time
- Cost when high production (less manual operation…)
- High reproducibility of the process
- Better dimensional tolerances
- Better long term performances