Common plastic shrinkage for mold making

Common plastic shrinkage for Mold making.

Plastic shrinkage or Mold shrinkage is an important consideration for Mold design before Molding.

Mold shrinkage refers to the dimensional change of the injection Molded object as it cools, while plastic shrinkage can be used to refer to the characteristics of a specific plastic. Designers must take into account the shrinkage and contraction rate of the injected material and how that will affect the shape of the part.  

For example, if the length of an ABS plastic product is 100mm and the length after cooling is 98mm, the shrinkage rate of the product is 2%.

For Mold design processing, the shrinkage will be different for different plastic material, while the parts structures will be also influenced the shrinkage for different direction of one part.

Normally, there is reference of Mold shrinkage on material data sheet for different material, here is some common plastic material shrinkage for reference.

ABS: 0.5% (Range 0.4~0.7%)

PC: 0.5% (Range 0.5~0.7%)

HIPS: 0.5%(Range 0.4~0.6)

PMMA:0.5%(Range 0.5~0.7%)

PC/ABS: 0.6%(Range 0.5%~0.7%)

POM:2%(Range 1.8~2%)

PP:1.5% (Range 1~3%)

PBT+30%GF:0.75%

PA6: 1.5~1.7%(Range 0.7~2.2%)

PA66: 1.8~2.0% (Range 1~2.5%)

TPU:2%

NL66+GF20 0.5%
POM+GF25 0.6%

If the material with a shrinkage rate of about 6% is added with glass fiber, the shrinkage rate is as follows;

+GF10 3.5-4.5‰

+GF15 3.0-4.0‰

+GF20 2.5-3.5‰

+GF30 1.5-2.5‰

+GF40 1.0-2.0‰

>GF40 0.5-1.5‰

In actual production, the size of the Mold can be adjusted according to the shrinkage rate to ensure the dimensional accuracy of the product. In addition, it is also necessary to set the temperature, pressure, cooling time and other parameters of the Mold reasonably according to the characteristics of the plastic material and the Molding process to ensure the quality and performance of the products.