Excessive internal stress in injection-molded products-a common issue in multi-material molding-can lead to quality defects such as cracking, warpage, dimensional deviation, and coating failure during subsequent processing. Comprehensive adjustments to the molding process, mold design, equipment, and post-processing can effectively reduce internal stress and enhance molding stability.
Reduce the injection speed: An excessively high injection speed disrupts laminar melt flow and causes compression and accumulation, leading to residual stress; using a staged, slow-speed injection process ensures uniform filling.
Reduce holding pressure and holding time: Excessive holding pressure can lead to forced compaction of the product and a concentration of internal compressive stress; parameters should be fine-tuned based on the product's wall thickness.
Increase material and mold temperatures: Appropriately raising the molding temperature enhances melt fluidity, reduces molecular tensile stress, and minimizes internal stress caused by uneven cooling.
Extend the cooling equalization time: prevent rapid surface solidification and uneven internal shrinkage, and reduce residual structural stress.
Optimize gate locations to prevent localized high-pressure buildup caused by single-point injection;
Widen gates and shorten runners to reduce flow resistance;
Optimize draft angles and wall thickness transitions to eliminate stress concentrations caused by right angles or abrupt changes in thickness.
Stabilize screw back pressure and plasticizing speed to ensure uniform plasticization and minimize melt density variations;
Avoid mass production using extreme parameters-such as high pressure and high speed-to reduce mechanical stress caused by forced filling.
For materials prone to cracking, stress-relief treatments-such as constant-temperature annealing or hot-air baking-can be employed to release internal residual stresses and enhance the product's stability during subsequent use.
Optimally balancing the process parameters-specifically reducing injection speed, increasing temperatures, and ensuring uniform cooling-represents the most direct and efficient mass-production strategy for mitigating internal stress in injection-molded parts.
