Uneven cooling systems in injection molds can indeed cause both shrinkage and deformation of plastic parts, as well as reduced cooling efficiency. The core of this problem stems from the cooling system's role in ensuring uniform heat removal during injection molding. During the injection molding process, after hot, molten plastic is injected into the mold cavity, the heat must be removed by the coolant (e.g., water) in the cooling system, allowing the melt to gradually solidify and set. The uniformity of the cooling system directly determines the speed and consistency of heat removal. Any unevenness can directly impact the stability of the entire molding process and the quality of the plastic parts.
From the perspective of reduced cooling efficiency, an uneven cooling system means that heat removal capabilities vary across different areas of the mold cavity. For example, if the cooling circuit design is dense in some areas and the coolant flow is high, heat can be quickly removed, rapidly cooling the mold cavity and plastic part temperatures in those areas. Meanwhile, in other areas, the cooling circuit design is sparse, and coolant flow is poor (due to blockage or undersized pipes). Heat cannot be dissipated quickly, leading to localized "heat accumulation." This uneven heat distribution leads to asynchronous solidification of the entire part—faster cooling areas reach solidification temperature first, while slower cooling areas take longer to solidify. To ensure that all areas of the part are fully formed, the overall cooling cycle must be extended, leading to reduced production efficiency.
More importantly, the injection molds in areas of heat accumulation will also remain overheated. When the subsequent melt comes into contact with the injection molds, heat transfer efficiency is further reduced, creating a "vicious cycle" that makes it difficult to improve cooling efficiency and may even prevent some parts from fully solidifying due to insufficient cooling.
From the perspective of shrinkage deformation of plastic parts, plastics shrink in volume as they cool. This is an inherent characteristic of plastics, but the uniformity of this shrinkage directly determines the final shape accuracy of the part. When the cooling system is uneven, differences in cooling rates across different areas of a plastic part can lead to inconsistent shrinkage. In areas cooling faster, the plastic shrinks and sets first, maintaining a largely fixed volume and shape. In areas cooling slower, the plastic continues to shrink, but this shrinkage is restricted by the already-set areas, resulting in internal stresses.
This internal stress cannot be naturally released and ultimately manifests as shrinkage deformation within the part. For example, flat parts may warp toward the slower-cooling side. Complex parts with ribs and varying wall thicknesses may experience localized dents, sink marks, and even cracking due to stress concentration. Furthermore, if uneven cooling results in a significant difference in cooling rates between the surface and interior of a part, the surface can solidify first, followed by shrinkage within the interior. Internal shrinkage can pull on the surface, creating surface unevenness or internal bubbles, further damaging the part's appearance and structural integrity.
In actual production, this effect is exacerbated by the complexity of the plastic part structure. For example, for plastic parts with uneven wall thickness, if a reinforced cooling circuit is not designed for the thick-walled area, the cooling rate of the thick wall will be much slower than that of the thin wall. This will not only prolong the cooling time and reduce efficiency, but also easily cause severe shrinkage deformation at the junction of the thick and thin walls, causing the plastic part dimensions to exceed the tolerance range and necessitate rework or scrapping. Therefore, the uniformity of the injection molds cooling system is not a simple "design detail", but a core factor directly related to production efficiency and product quality. Only by ensuring that the cooling system can evenly remove heat from all parts of the cavity can the shrinkage and deformation of the plastic part be avoided, while maintaining stable cooling efficiency and ensuring the continuity and reliability of injection molding production.
