Closed Loop Piezoelectric Core Compensation for Polymer Thermal Shrinkage
Dynamic piezoelectric core compensation applies localized physical packing during cooling to eliminate shrink voids and hold DIN 16742 TG3 tolerances.
Volumetric Phase Change
Meaning
Specific volume contractions occurring as a polymer transitions from a melt to a solid govern the shrink rate of molded parts. This volumetric phase change is set during the cooling stage as molecular chains pack together.
Molecular Packing
Semicrystalline polymers exhibit a more pronounced volume contraction than amorphous materials because their molecular chains organize into dense crystalline lattices as they cool. The density increase during this volumetric phase change can cause up to twenty percent contraction in volume. Amorphous resins, which cool into a disordered state, experience much less contraction, making them easier to mold to tight dimensional tolerances.
Shrinkage Compensation
Process engineers adjust the packing stage of the injection molding cycle to feed extra material into the cavity to offset the shrink. This compensation must occur before the gate freezes, after which no more material can enter the cavity. If the gate freezes too early, the volumetric phase change will proceed without extra material, resulting in internal voids or sink marks.
Part Stability
Achieving consistent part dimensions requires a stable cooling rate across the mold face. Inconsistent cooling rates cause uneven volumetric phase change, leading to internal residual stresses that cause the part to warp after ejection. Mold temperature controllers are used to maintain a uniform temperature profile across the cavity, minimizing the internal stress and ensuring the part remains within the required dimensional tolerance during shipping and final assembly.
This ensures that the molded components assemble correctly without requiring mechanical adjustments or manual rework.