Injection blow molding is a process used to manufacture small, precise, hollow plastic parts—typically bottles and containers with tight tolerances and smooth finishes. It combines elements of both injection molding and blow molding, producing parts in three main stages: injection, conditioning, and blow molding.
In the first stage, a thermoplastic material is injected into a mold cavity around a metal core pin to form a preform, sometimes called a parison. This preform looks like a thick-walled test tube with a fully formed neck and threads—features that are difficult to achieve with traditional extrusion blow molding. The core pin, which extends into the preform, serves not only to create the hollow section but also to allow easy transfer of the preform to the next stage without distortion.
After the preform has solidified just enough to retain its shape, it is transferred—still on the core pin—to a second station, typically by rotation of a multi-station indexing table. At this point, the preform is reheated to an ideal temperature for expansion, then enclosed within a blow mold. Compressed air is introduced through the core pin, causing the preform to expand and conform tightly to the interior surfaces of the blow mold cavity.
Once cooled, the mold opens and the finished part is ejected. The resulting component has a high-quality surface finish, precise dimensions, and a fully formed neck suitable for closures. Injection blow molding is commonly used for pharmaceutical bottles, cosmetics containers, and other applications where dimensional accuracy and appearance are critical. Unlike extrusion blow molding, this process generally produces less scrap, because there is little to no trimming required.