The basic principles of HDPE (High-Density Polyethylene) plastic injection molding align with those of other thermoplastics; however, process parameters must be adjusted to accommodate the specific material characteristics of HDPE. The core process can be summarized as follows:
Feeding and Plasticization
HDPE granules are fed from the hopper into the injection molding machine's barrel, where, under the combined action of heating bands and shear heat generated by the screw, they melt into a uniform, viscous fluid state.
Injection and Mold Filling
The screw or plunger injects the melt-at high pressure (typically 50–200 MPa) and high velocity-through the nozzle and gating system into the cavity of a closed mold.
Holding Pressure and Shrinkage Compensation
After mold filling, pressure is continuously applied to compensate for the volumetric shrinkage of HDPE during the cooling process, thereby preventing defects such as sinkholes and depressions.
Cooling and Solidification
The melt cools within the mold until it achieves sufficient rigidity. This stage accounts for 70% to 80% of the entire molding cycle and is critical for the dimensional accuracy and deformation control of the molded product.
Mold Opening and Ejection
The mold opens, and the ejection mechanism pushes out the cured HDPE product.
Essentially, HDPE granules are heated and melted, then injected under high pressure into a closed mold cavity; after cooling and solidifying, a product is obtained that precisely matches the shape of the mold cavity.
HDPE injection molding is a process in which HDPE granules are heated to a molten state, injected into a mold, and subsequently cooled and solidified to produce a product of the desired shape. This process relies on HDPE's excellent thermoplasticity-specifically, its ability to soften and flow when heated, and to solidify and retain its shape when cooled. This characteristic enables HDPE to readily adapt to molds of various complex geometries, resulting in the production of products characterized by high precision and consistent quality.
