There are two basic molding methods for PET bottles, one-step and two-step.
(1)In two step molding,
Two separate machines are used. The first machine injection molds the preform, which resembles a test tube, with the bottle-cap threads already molded into place. The body ofthe tube is significantly thicker, as it will be inflated into its final shape in the second step using stretch blow molding.
In one-step machines, the entire process from raw material to finished container is conducted within one machine, making it especially suitable for molding non-standard shapes (custom molding), including jars, flat oval, flask shapes, etc. Its greatest merit is the reduction in space, product handling and energy, and far higher visual quality than can be achieved by the two-step system.