Injection molding

In the injection molding industry, people often say, "This part is warping — just add some cooling channels." So what exactly does that mean?

"Cooling channels" is the industry term for the water lines inside a mold. During injection molding, plastic is injected into the mold at high temperature and then needs to cool and solidify. The speed and uniformity of cooling directly determine the dimensional accuracy, surface quality, and degree of deformation of the part. The cooling channels in a mold are the pipes through which cooling water flows. Cold water enters from one end and warm water exits from the other, carrying heat away from the mold steel and allowing the part to cool evenly.

Plastic has a characteristic: it shrinks as it cools, and if the shrinkage is not uniform, the part deforms. If different areas of the mold cool at different rates, the faster-cooling areas shrink first while the slower-cooling areas shrink later. This creates internal stress inside the part, which leads to warping and deformation after ejection. The core function of cooling channels is to allow all areas of the mold to cool in sync, reducing differences in shrinkage.

Adding cooling channels means creating new cooling passages in addition to the mold's existing cooling system. This is usually done in the following situations: an area has thick walls and cools slowly, causing sink marks or deformation; a corner or deep slot has no cooling channels and heat cannot escape; or after trial molding, uneven cooling is found and additional cooling is needed. The purpose is clear — to speed up cooling in the slow areas and make the overall cooling more uniform.

One thing must be made very clear: adding cooling channels is a mold modification, not a machine adjustment. Cooling channels are cut into the mold steel. To add them, the mold must be disassembled, holes must be drilled in the cavity insert or the insert block to create new water lines, piping and fittings must be reconnected, and then the mold must be reassembled for trial molding. This is a real mold modification — it requires machine work, cutting into steel, and several days of time. It is not something that can be solved by adjusting machine parameters. Adjusting packing pressure, by contrast, is a machine adjustment — it changes parameters on the injection molding machine and can be done in minutes. The two are completely different in nature.

There are several common ways to add cooling channels. The most common is to drill directly into the cavity insert or insert block to form new water lines. If the slow-cooling area is relatively localized, it can be made into an insert with cooling channels machined inside, then installed back into the mold. For deep holes or slender areas, baffles or bubbler cooling can be used to guide cooling water into the depths. For dead corners where cooling channels truly cannot be added, beryllium copper inserts with excellent thermal conductivity can be used to draw heat away quickly.

After adding cooling channels, the usual benefits are reduced warping and deformation, reduced sink marks, shorter cycle times, and improved dimensional stability. But adding cooling channels is not a cure-all. If the main cause of deformation is flow orientation or the product structure itself, cooling channels alone are not enough — gate changes and process adjustments are also needed.

In the injection molding industry, adding cooling channels and adjusting packing pressure are the most common combination. Adding cooling channels addresses the root cause, while adjusting packing pressure optimizes the process. Only when the two work together can warping and sink marks be brought under control.