Plastic Shrinkage Rate and Its Influencing Factors

Understanding plastic shrinkage rates and their influencing factors is crucial for achieving accurate part dimensions. From part shape to molding conditions and mold structure, each aspect plays a significant role in determining the final dimensions of injection molded parts. Most importantly, attention must be paid to the following key aspects

Part Shape:

Thicker walls generally lead to greater shrinkage due to longer cooling times.Differences in dimensions along the flow (L) and transverse (W) directions can result in varying shrinkage rates.Areas with features like ribs, holes, or embossing typically exhibit lower shrinkage rates.

Mold Structure:

Gate design impacts shrinkage rates, with smaller gates leading to increased shrinkage.Proper cooling channel design prevents uneven cooling and subsequent size deviations or deformations, especially in thin-wall sections.

Molding Conditions:

• Barrel temperature affects shrinkage: higher temperatures reduce shrinkage but may not fully offset effects of small gates or thick walls.
• Minimize regrind usage to maintain stable part dimensions.
• Injection pressure significantly influences shrinkage, especially post-filling packing pressure.
• Injection speed has a minor impact, with faster speeds generally reducing shrinkage for thin-wall parts or reinforced materials.
• Mold temperature generally correlates with shrinkage, but high temperatures may reduce shrinkage for thin-wall parts by easing melt flow resistance.
• Cycle time indirectly affects shrinkage by altering temperatures; testing should align with production cycle parameters to ensure accuracy.

By addressing these critical aspects, manufacturers can optimize their molding processes and mold designs to minimize shrinkage-related issues and ensure consistent and precise part dimensions. This comprehensive understanding of shrinkage factors is essential for achieving high-quality injection molded parts that meet the stringent requirements of various industries.