Reference Target Placement for Flexible Plastic Parts
Position reference targets on flexible plastic parts at high-stiffness rib intersections using explicit 3-2-1 restraint forces to eliminate gravity sag and inspection disputes.
Residual Stress Warp
Meaning
Dimensional deformation occurs in molded plastic parts when internal stresses from uneven cooling relax after the part is ejected. The defect known as residual stress warp causes flat surfaces to twist or bow out of their intended shapes. It is particularly common in thin-walled parts made from semi-crystalline polymers.
Thermal Cause
Uneven cooling across different regions of a mold causes localized differences in polymer solidification rates. When these regions contract at different times, they lock in internal forces that cause residual stress warp upon ejection from the tool. Adjusting cooling line layouts and mold surface temperatures helps balance this cooling, ensuring that the part solidifies at a uniform rate.
Processing Remedy
Moulders can reduce internal stresses by optimizing the packing phase of the injection cycle. Increasing pack pressure and time ensures that more material enters the mold to compensate for shrinkage, which reduces residual stress warp. This modification improves the dimensional stability of the component.
Material Role
Polymers with high crystallinity are more prone to this type of deformation due to their high volumetric shrinkage during phase change. Sourcing amorphous resin grades can minimize warping issues when part geometry prevents uniform cooling. This material substitution solves difficult design challenges.