Plastic Shrinkage Guide: Common Materials Compared
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<p>Understanding plastic shrinkage is critical for mold design. Incorrect shrinkage assumptions lead to out-of-tolerance parts and expensive mold rework.</p>
<p><strong>Shrinkage rates for common injection molding materials:</strong></p>
<p><strong>Crystalline materials:</strong></p>
<ul>
<li>POM (Acetal): 1.8-2.5 percent</li>
<li>PA6 (Nylon): 1.2-2.5 percent</li>
<li>PA66 (Nylon 66): 1.5-2.5 percent (glass-filled reduces to 0.3-0.7 percent)</li>
<li>PP (Polypropylene): 1.3-2.5 percent</li>
<li>HDPE: 1.5-3.0 percent (highest among common materials)</li>
<li>PBT: 1.5-2.5 percent</li>
</ul><p><strong>Amorphous materials:</strong></p>
<ul>
<li>ABS: 0.4-0.7 percent</li>
<li>PC (Polycarbonate): 0.5-0.7 percent</li>
<li>PMMA (Acrylic): 0.3-0.6 percent</li>
<li>PS (Polystyrene): 0.3-0.6 percent</li>
<li>PVC rigid: 0.2-0.5 percent</li>
<li>SAN: 0.4-0.7 percent</li>
</ul><p><strong>Semi-crystalline materials:</strong></p>
<ul>
<li>PET: 1.2-2.0 percent</li>
<li>PPS: 0.5-1.2 percent</li>
<li>LCP: 0.1-0.5 percent (very low)</li>
</ul><p><strong>Key factors affecting actual shrinkage:</strong></p>
<ol>
<li>Wall thickness: Thicker walls shrink more</li>
<li>Injection pressure: Higher pressure reduces shrinkage</li>
<li>Mold temperature: Higher mold temp increases crystallization and shrinkage</li>
<li>Hold time: Longer hold time reduces shrinkage</li>
<li>Glass fiber content: Each 10 percent glass fiber reduces shrinkage by roughly 0.2 percent</li>
</ol><p><strong>Rule of thumb:</strong> Design the cavity 0.5-1.0 percent larger than the nominal part dimension for amorphous materials, and 1.5-2.5 percent for crystalline materials.</p>
<p>Always validate shrinkage with mold flow simulation or test shots before cutting steel.</p>
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<p>各位师傅觉得这个方案怎么样？有更好的做法吗？</p>