Post-crystallization analysis improves warpage and deformation prediction
A part made of a semi-crystalline plastic was ejected without any warpage. However, one and a half hours later the part was measured and all geometrical tolerances were out of range. Why? The answer is post-crystallization. The cooling rates during injection were so high that crystallization process was impaired. However, after a certain amount of time, the molecules arranged themselves adjacent to each other and the plastic finally crystallized. As crystallization always means volume reduction, warpage takes place.
SIGMASOFT® predicted the influence of post-crystallization on shrinkage and warpage by calculating crystallization behavior automatically from the pvT data of the plastic material.
Figure 1 shows the crystallization rate just one minute after ejection. The crystallization in the core of the thick-walled areas starts later on, as the melt there takes longer to cool down. Figure 2 shows the corresponding warpage in z-direction. After approximately 1.5 h, the part has cooled down to room temperature and the crystallization of the molecular chains has increased, as seen in Figure 3. Due to crystallization related volume reduction, part warpage increases further (Figure 4).