A stack mold, also known as a stack injection mold or a multi-level mold, is a specialized type of injection mold used to increase production output by allowing multiple parts to be molded simultaneously in a single molding cycle. Stack molds consist of multiple mold layers or levels, each containing separate cavities for molding identical or different parts.

Here's how a stack mold typically works:

1. Mold design: A stack mold is designed with multiple levels or layers, each containing a set of cavities for molding parts. The cavities in each level are aligned vertically to allow for simultaneous molding of multiple parts in a single molding cycle. The number of levels and cavities per level can vary depending on the specific application and production requirements.

2. Injection molding process: During the injection molding process, molten plastic resin is injected into the mold cavity under high pressure. In a stack mold, the injection molding machine delivers the molten resin to each level of the mold simultaneously, filling all cavities in each level with plastic material.

3. Mold closing and cooling: Once the mold cavities are filled with plastic resin, the mold closes, and the plastic material is allowed to cool and solidify. Cooling channels within the mold help to dissipate heat and speed up the solidification process. The mold may remain closed for a predetermined period to ensure proper cooling of the molded parts.

4. Mold opening and ejection: After the cooling cycle is complete, the mold opens, and the molded parts are ejected from the cavities using ejector pins or plates. The molded parts may then undergo additional finishing processes, such as trimming, deburring, or assembly, as needed.

Stack molds offer several advantages over traditional single-level molds, including:

- Increased production output: Stack molds allow for the simultaneous molding of multiple parts in a single molding cycle, effectively doubling or tripling production output compared to single-level molds.
- Reduced cycle time: By molding multiple parts simultaneously, stack molds can significantly reduce cycle times and increase overall production efficiency.
- Cost savings: Despite their higher initial cost, stack molds can provide cost savings over time by reducing production time, labor costs, and energy consumption per part.
- Space efficiency: Stack molds occupy less floor space than multiple single-level molds running simultaneously, making them ideal for facilities with limited space.

Stack molds are commonly used in high-volume production applications where increased production output and efficiency are critical, such as consumer goods, packaging, automotive components, and medical devices. However, they require careful design, engineering, and maintenance to ensure proper alignment, cooling, and ejection of molded parts.