Blow molding is a plastics process specific to hollow and dual-wall parts. Briefly, the process is as follows:
The tool/die of the molding machine extrudes molten plastic in the form of a hollow tube. This tube (called a parison) travels downward between the two halves of an open mold. When the parison reaches a specified length the mold closes, catching and holding the molten plastic. A rod-like blowpin or a series of needles is inserted into the mold, inflating the molten parison so that it fills the entire mold cavity. The mold cavity defines what shape the plastic will take. The formed parison cools within the mold for a period of one to four minutes depending on the size of the part. The mold then opens and ejects a formed part that is trimmed, finished, and packed by an employee.