Liquid Silicone Rubber (LSR) exhibits unique thermal properties that demand special attention during mold design. Unlike thermoplastics, LSR undergoes significant volumetric shrinkage—typically 1-3%—as it cures and cools. This must be precisely calculated and compensated for in cavity dimensions to achieve accurate final part geometry.
Thermal expansion coefficients of both the cured LSR part and the mold steel differ substantially. During the molding cycle, the mold expands while the part contracts upon ejection. Accounting for these opposing forces prevents warpage, dimensional instability, and fit issues in assemblies. Accurate simulation tools aid in predicting these behaviors.
Gate location is critical; it influences flow patterns and localized heating which affect shrinkage distribution across the part. Uniform wall thickness should be maintained wherever possible to minimize differential shrinkage. Strategic placement of ribs and bosses with proper draft angles also mitigates stress concentration points prone to distortion.
Collaboration between mold designers and material engineers ensures optimal mold construction. Using proven design databases and past project data enhances prediction accuracy. Regular mold trials validate assumptions and allow fine-tuning before full production launch, reducing costly post-production modifications.
