1. The dimensional shrinkage of plastic parts due to thermal expansion and contraction, elastic recovery upon demolding, and plastic deformation causes the parts to shrink after cooling to room temperature. Therefore, compensation must be considered during the mold design to account for this.

Synthetic high polymer materials. They, along with synthetic rubber and synthetic fibers, form the three indispensable synthetic materials in today's daily life. Specifically, plastics are materials mainly composed of synthetic resins, which can be molded into a specific shape under certain conditions of temperature and pressure, and maintain their shape at room temperature.

2. During directional forming, the molecules align in the direction, resulting in anisotropic plastic parts. Along the flow direction (i.e., parallel direction), there is greater shrinkage and higher strength, whereas at the perpendicular direction (i.e., vertical direction), shrinkage is smaller and strength is lower. Additionally, due to uneven density and filler distribution across different parts of the plastic part during forming, shrinkage is also uneven. This uneven shrinkage can lead to warping, deformation, and cracking in the parts, especially during extrusion and injection molding, where directional effects are more pronounced. Therefore, mold design should consider the shrinkage directionality, selecting an appropriate shrinkage rate based on the shape of the part and the flow direction.