Plastic Shrinkage Characteristics and Common Materials Used in Precision Injection Molding
The shrinkage behavior of plastics is one of the inherent properties of polymer materials, and it plays an important role in the dimensional stability and accuracy of plastic parts. Shrinkage characteristics include thermal shrinkage, elastic recovery, plastic deformation, post-molding shrinkage, and aging shrinkage. These effects are usually expressed in terms of linear shrinkage and volumetric shrinkage during molding and in later use, and they are critical factors in precision injection molding.
At present, four types of materials are commonly used in precision injection molding:
(1) POM and reinforced POM
POM, including carbon fiber reinforced or glass fiber reinforced grades, offers good creep resistance, fatigue resistance, weather resistance, dielectric performance, flame resistance, and good release behavior during molding. These properties make it suitable for precision parts that require dimensional stability and reliable mechanical performance.
(2) PA and glass fiber reinforced PA66
PA materials, especially glass fiber reinforced PA66, provide strong impact resistance, excellent wear resistance, and good flowability. They can be used to mold parts with relatively thin wall sections, such as 0.4 mm. Reinforced PA66 also has good heat resistance, with a melting point around 250°C. One important limitation is its moisture absorption, so humidity control after molding is often necessary.
(3) PBT reinforced polyester
PBT is known for its relatively short molding cycle and good processing efficiency. In terms of molding speed, the general comparison is: PBT ≤ POM ≈ PA66 ≤ PA6. Reinforced PBT is widely used when dimensional consistency and efficient production are both important.
(4) PC and glass fiber reinforced PC
PC and reinforced PC materials offer good wear resistance, increased rigidity, improved dimensional stability, weather resistance, flame resistance, and good moldability. These features make them suitable for precision molded components used in demanding structural or appearance-related applications.
In precision injection molding, material selection is closely linked to shrinkage control, dimensional accuracy, and long-term stability. Understanding the shrinkage behavior of different plastics and selecting the appropriate engineering material are both essential for producing high-precision plastic parts consistently.