Shrinkage Warpage

The part shrinks in size or deforms after demolding. Warpage deformation has various manifestations: flat parts show bowl-shaped or saddle-shaped bending, long strip parts show bowing or twisting, and box-shaped parts show opening dimension changes. The directionality and severity of the deformation depend on the distribution pattern of uneven cooling and the symmetry of molecular orientation. Warpage has a hysteresis — it may not be obvious right after ejection, and only gradually appears after storage for several hours to several days, which brings challenges to production process quality control.

1. Cooling factors: large curing shrinkage, uneven cooling, uneven part wall thickness, post-curing shrinkage. 2. Mixing quality factors: in the RIM process, the mixing uniformity of the two components is the foundation of all quality; the Reynolds number of the mixing head, the impingement mixing energy, and the residence time distribution are the key engineering parameters determining mixing quality. 3. Temperature control factors: raw material temperature affects component viscosity and reaction rate, mold temperature affects the curing process and part surface quality, and both need to be precisely controlled within a narrow window.

1. Process parameter optimization and adjustment: select low-shrinkage formulations, cool uniformly, optimize wall thickness design, control post-curing conditions. 2. Systematic troubleshooting method: RIM problem troubleshooting follows the order of "formulation -> mixing -> temperature control -> equipment". First check the two-component ratio and catalyst dosage, then check the mixing head and self-cleaning function, then check the raw material and mold temperature control, and finally check the accuracy of the metering pump and hydraulic system. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluation. For recurring problems, use fishbone diagram or 5Why analysis to trace the root cause, and fix the countermeasures as PFMEA control points.

Warpage is macroscopic bending caused by inconsistent shrinkage of various parts of the part. The solution ideas are: achieve uniform cooling of all parts during the cooling stage (cooling water channel optimization), adopt symmetrical layout and isotropic design in structural design (wall thickness and gate position optimization), and reduce shrinkage anisotropy in material selection.