• How to calculate mould shrinkage

    Thermoplastics shrink as they cool and solidify during the plastic injection molding process and after part ejection.   The plastic injection mold cavity is machined larger than the final desired molded plastic part size in order to compensate for part shrinkage as the part cools.   Mold shrinkage data for the specific plastic material can be used to calculate the amount of mold expansion needed.     Shrinkage in mould units are expressed as length-per unit-length, or as a percentage, and is calculated using the following mould shrinkage calculation formula :     (mold dimension – part size) / mold dimension  = Mold Making Shrink Factor   We could alse use a simplied formula as below.   S={(D-M)/D}×100%(1)   Shrinkage; D-Mold Size; M-Molded part size   However, since the actual shrinkage is influenced by many factors, only the approximate value can be used,When building the mould, the cavity should be machined according to the lower deviation while the core be machined according to the upper deviation to leave…

    Injection molding process February 29, 2020
  • What is Mould Shrinkage?

    Shrinkage is a characteristic of resin which occurs during plastic injection molding process. Different resins have different mold shrinkages. Crystalline and semi-crystalline materials exhibit higher shrinkage than amorphous materials. Unreinforced plastics have higher shrinkage than reinforced grades. It is important that the grade of material be selected before the injection mold tooling is constructed and that the proper mold shrinkage be specified.   Mold shrinkage rate can vary with part and tool design: thick walls will have higher shrinkage rates than thin, variation in section thickness can cause differential shrinkage and warpage;flow direction will effect shrinkage,particularly with glass fiber-reinforced grades       Shrinkage in mould is also influenced by process conditions. As cavity pressure increases,shrinkage typically will decrease. The plastic injection mold and melt temperature will also influence shrinkage. Cooler molds will reduce shrinkage while hotter melt temperatures will increase shrinkage especially with semi-crystalline materials.   Contact HS Mold Company for shrinkage recommendations on any of plastic injection molded products. We…

    Mold making February 27, 2020
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