Shrinkage & Warpage Due to Thermal Distribution

Trial Mold Successful - Production Mold Failed

A typical situation. A prototype mold was constructed and tested, all problems were solved. However, during the mold trial a series of production issues arise and you have some shrinkage and warpage. We all know this happens all too often!

The temperature distribution in the mold advances the formation of warpage. It can significantly differ from the temperature distribution of the prototype mold, especially when the production mold contains more cavities than the prototype mold. Suddenly one becomes aware that cooling is not sufficient and that the ejectors become too hot, etc.

SIGMASOFT^® can calculate the temperature distribution before the mold is constructed. The locally different temperatures at the cavity wall cause the temperatures to vary in the part. These differences in temperature facilitate shrinkage and warpage. The Young's modulus of a certain plastic in the temperature interval between solidification and room temperature can differ by factor 10. This results in different stiffnesses in those areas of the part that are either well cooled or poorly cooled; the further consequence is warpage.
If you understand the way your part cools down, then you will also understand the reasons for shrinkage and warpage - and you can take the appropriate actions.

Figure 1 shows a core with insufficient cooling. Figure 2 additionally shows the part. The lower temperatures are obviously at the outer surface, caused by a well cooled mold half.

Due to the high temperatures of the core, the part shrinks after ejection causing the formation of a dished surface (see Figure 3, shrinkage exaggerated by factor 7).