Blow molding is a manufacturing process used to produce hollow plastic parts or containers. In blow molding, plastic material is melted and formed into a hollow tube (called a parison) which is then inflated or blown into a mold cavity to take the shape of the desired part.

There are three main types of blow molding processes:

1. Extrusion blow molding: In extrusion blow molding, a molten tube of plastic (parison) is extruded through a die and clamped into a mold cavity. The mold cavity is then closed, and pressurized air is injected into the parison, causing it to expand and take the shape of the mold. Once the part has cooled and solidified, the mold is opened, and the finished part is ejected.

2. Injection blow molding: Injection blow molding is similar to extrusion blow molding, but with an additional step. A preform is first injection molded from molten plastic resin. The preform is then transferred to a blow molding machine, where it is heated and blown into the desired shape using pressurized air. Injection blow molding is commonly used for producing small, high-precision parts such as bottles and containers.

3. Stretch blow molding: Stretch blow molding is a variation of injection blow molding used to produce bottles and containers with thin walls and precise dimensions. In stretch blow molding, a preform is first injection molded and then heated and stretched axially and radially to orient the polymer molecules and improve mechanical properties. Finally, pressurized air is used to blow the preform into the shape of the mold cavity.

Blow molding is widely used in various industries to produce plastic containers, bottles, tanks, drums, automotive components, and other hollow parts. It offers several advantages, including high production efficiency, low tooling costs, lightweight construction, and the ability to produce complex shapes with minimal post-processing. However, blow molding is typically limited to producing hollow parts with relatively simple geometries and uniform wall thicknesses.