"Mastering TPE Shrinkage: Optimizing Mold Design and Processing for Precision Manufacturing"
Time of issue:2025-04-28
Don’t Overlook TPE Shrinkage in Product Processing: Key Impacts and Considerations
When processing TPE materials, understanding shrinkage (or contraction behavior) is critical. How does TPE shrinkage affect manufacturing?
1. Shrinkage Fundamentals
As TPE cools from a molten state, molecular alignment causes dimensional contraction. While typically minimal (thousandths of an inch), this shrinkage significantly impacts molding, ejection, and finished part aesthetics. Uneven shrinkage can warp or distort flat components, and unexpected dimensional changes may compromise assembly precision in tight-tolerance applications. Shrinkage must be factored into production workflows.
2. Ejection Challenges
For parts with cores or hollow sections, shrinkage can lock the component onto mold features, complicating demolding. Mold design, surface finishes, and processing parameters can mitigate these effects, sometimes enabling automated ejection.
3. Processing Influences
Molding conditions drastically affect shrinkage magnitude and behavior. Rapid stress transitions (e.g., high-to-low stress) amplify contraction. Cooling rate, injection speed, and pressure also influence shrinkage outcomes.
4. Design Adaptations
To compensate for shrinkage, molds must be slightly oversized relative to final part dimensions. Actual shrinkage values often emerge only during trial molding. Like other TPE properties, shrinkage is anisotropic—varying with polymer flow direction. Gate placement determines melt flow orientation and thus directional shrinkage. Some TPEs exhibit greater anisotropy, contracting more in one axis than others. This directional bias must inform mold design.
Shrinkage rates vary by TPE base resin: non-polar SBS/SEBS-based TPEs typically show minimal water absorption and predictable shrinkage, while polar polyester/polyether-based TPUs may swell (not shrink) in moisture, with shrinkage rates ranging 1.5–3% depending on formulation.
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