The layout of the cooling system in a precision injection mold is crucial for reducing product warpage. Its core lies in achieving a uniform temperature distribution within the mold through scientific design, thereby reducing internal stress caused by uneven cooling in the plastic part. Uneven cooling is a direct cause of warpage. When the temperature difference between the cavity or core surfaces of the precision injection mold is too large, the shrinkage rate of different areas of the plastic part will be inconsistent, leading to deformation. Therefore, the cooling system layout must revolve around the core objective of "uniform cooling."
In layout design, the principle of "close to high-heat areas and away from low-heat areas" must be followed. The area near the gate is the initial location where the melt enters the cavity, and its temperature is the highest. Cooling water inlets should be preferentially located in this area so that low-temperature water directly cools the hottest spot, avoiding heat accumulation. For plastic parts with uneven wall thickness, thick-walled areas require denser water channels due to concentrated heat, or even the use of baffles to divert water flow, to ensure cooling efficiency; while thin-walled areas can have a reduced water channel density to prevent over-cooling and subsequent cracking. For example, when producing curved, irregularly shaped parts such as car door handles, using traditional straight-through cooling channels can easily cause warping at the edges of the plastic part due to insufficient cooling. However, using 3D-printed conformal cooling channels to fit the curved surface significantly reduces warping.
The arrangement of the cooling channels must be highly compatible with the shape of the plastic part. For flat plastic parts, the distance between the cooling channels and the surface should be equal everywhere. A uniformly distributed straight-through channel is typically used to avoid adjustment difficulties caused by multiple circulations. For deep-cavity parts, such as cups or buckets, ordinary straight-through channels are insufficient to cool to the bottom; a "well-type" channel is required, extending the cooling pipes 3-5mm from the bottom to eliminate stagnant areas. For irregularly shaped parts, such as curved automotive interior parts, conformal cooling channels can conform to the contours, ensuring consistent cooling speeds across all areas. Furthermore, the spacing between the cooling channels and the surface distance must be set in a multiple relationship. Generally, the spacing is 3-5 times the diameter of the cooling channel, and the surface distance is 1.5-2.5 times the diameter, ensuring cooling efficiency while preventing mold surface concavity.
The design of the inlet and outlet water systems is equally crucial. Series water channels cause the cooling water to heat up as it flows, resulting in uneven cooling of the molded parts in different cavities. Therefore, multi-channel systems must use a parallel layout; if space is limited and series connection is necessary, the total length of the water channels should not exceed 1.5m. The inlet should be aligned with the "hot spots" of the molded part, such as thick-walled sections and near the gate, while the outlet should be placed in the low-temperature zone, forming a "water-material parallel" cooling path. Simultaneously, an vent plug should be installed at the highest point of the water channel to prevent air bubbles from causing insufficient cooling in certain areas and leading to shrinkage marks.
For special scenarios, customized cooling solutions are required. For thick-walled molded parts, cooling rods can be inserted in the center of the thick wall or spiral cooling pipes can be used to shorten the heat transfer path. For small, precision molded parts, such as electronic connectors, a dense layout of 4-6mm thin water channels is required, ensuring the distance between the water channels and ejector pins is ≥3mm to prevent ejector pin deformation due to heat. For sliders or inserts, sliders can use rotary joints to connect the water channels, while inserts can use 3-5mm thin water channels or heat pipes for cooling, solving space constraints.
The selection and temperature control of the cooling medium are also crucial. Under normal circumstances, clean industrial cooling water is the preferred choice due to its low cost and high specific heat capacity. For low-temperature applications, a 20%-30% ethylene glycol aqueous solution should be added to prevent freezing. For high-temperature applications, such as PA66 molding, hot water at 80-90℃ should be circulated to prevent the molded parts from cracking. The chiller should be equipped with PID temperature control to keep water temperature fluctuations within ±1℃. Simultaneously, the mold temperature is typically 5-10℃ higher than the water temperature to prevent condensation on the precision injection mold surface.
Finally, design verification is a critical step in ensuring the effectiveness of the cooling system. Using software such as Moldflow to simulate the temperature field distribution, special attention should be paid to identifying "hot spots." If areas with temperature differences >5℃ are found, the water channels need to be densified or the layout adjusted. Simultaneously, cooling time and warpage should be simulated to optimize the design in advance. During the trial molding stage, it is necessary to observe the defects of the plastic parts. If shrinkage marks appear, the water channels in the corresponding area should be densified or the cooling time should be shortened. If warping occurs, the uniformity of the water channels should be adjusted. If one side cools faster, the diameter of the water channel on that side should be increased. Flow detection should ensure that the flow deviation of each branch is ≤10%. Otherwise, the diverter valve should be replaced.
