1. Dimensional shrinkage of plastic parts due to thermal expansion and contraction, elastic recovery during demolding, and plastic deformation can cause the parts to shrink after cooling to room temperature. Therefore, compensation must be considered in the mold design.

Synthetic high molecular materials. Alongside synthetic rubber and synthetic fibers, they form the three indispensable synthetic materials in today's daily life. Specifically, plastics are made primarily from synthetic resins, which can be molded into a specific shape under certain temperatures and pressures, and maintain that shape at room temperature.

2. During directional shaping, molecules align in the direction, resulting in anisotropic shaped parts. The shrinkage is greater and the strength higher along the flow direction (i.e., parallel direction), while it is smaller and the strength lower at the perpendicular direction (i.e., vertical direction) to the flow. Additionally, due to uneven density and filler distribution in different parts of the shaped parts during shaping, the shrinkage is also uneven. The resulting shrinkage differences can cause warping, deformation, and cracking in the shaped parts, particularly during extrusion and injection molding, where the directional effect is more pronounced. Therefore, mold design should consider the shrinkage directionality, selecting an appropriate shrinkage rate based on the shape of the shaped part and the flow direction.