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Key Design Points of Cooling Water Channel for Injection Mold

2026-04-30 11:33:16 Injection Mold
The cooling water channel is an indispensable core part of injection mold design, which directly determines the cooling speed of plastic parts, molding cycle, dimensional accuracy and appearance quality. Reasonable layout of cooling water channels can balance the temperature of each part of plastic parts, reduce shrinkage stress and warping deformation, shorten the injection molding cycle, and improve production efficiency and product yield. On the contrary, unreasonable design of water channels will lead to many molding defects such as local shrinkage, bubbles, weld lines and bending deformation, and also extend cooling time and increase production cost. Especially for thin-walled parts, annular parts, appearance precision parts and thick-walled ribbed plastic parts, the planning of cooling water channels is the key to mold success or failure. This paper systematically sorts out the key design points of injection mold cooling water channels from design principles, layout specifications, structural forms, process details and material installation control.

1. Overall Layout Design Principles of Cooling Water Channel

The design of cooling water channel firstly follows four major principles: uniform cooling, proximity and conformal arrangement, reasonable distance and smooth circulation. Firstly, it is necessary to ensure consistent cooling speed of each area of the mold cavity, minimize the temperature difference between thick and thin wall parts, and avoid shrinkage difference caused by uneven cooling, leading to warping, shrinkage and cracking. The water channel layout must be closely arranged along the product contour, away from dead corners of corners, covering the molding surface as much as possible without cooling blind areas. The distance between the water channel and the cavity surface and core surface should be kept standard and unified. The distance between conventional plastic mold water channel and cavity wall is controlled at 15～25mm. Too close will cause excessive temperature difference on mold surface and local stress; too far will lead to insufficient cooling efficiency and delayed cooling.

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At the same time, the trend of water channel should ensure smooth water circulation, avoid sharp bends, dead corners and reducing diameter structures, reduce water flow resistance and air blockage, ensure turbulent flow heat exchange of cooling water throughout the whole process, and improve heat dissipation efficiency. It is also necessary to take mold strength into account. Water channels shall not be arranged at stress key positions such as parting surface, insert splicing position, thimble hole and screw column, so as to prevent drilling from weakening mold structural strength and causing cracking, deformation and water leakage hidden dangers. In addition, the temperature difference between inlet and outlet water should be reasonable. The process of a single group of water channels should not be too long. Excessively long process will cause large temperature difference between the beginning and the end, inconsistent cooling effect before and after, and affect the overall setting stability of plastic parts.

2. Specifications of Water Channel Aperture, Spacing and Layout

Water channel aperture and spacing are key parameters affecting cooling effect, which should be reasonably selected according to product size, wall thickness and mold structure. The commonly used aperture of conventional small and medium-sized injection mold water channel is Φ8～Φ12mm, and Φ14～Φ16mm can be selected for large molds. Too small aperture leads to insufficient flow and slow heat dissipation; too large aperture makes drilling processing difficult and damages mold strength. The center distance between adjacent water channels is generally controlled at 3～5 times of the aperture to ensure overlapping heat dissipation coverage of adjacent water channels without leaving cooling blank areas. For thick-walled plastic parts, it is necessary to encrypt the spacing of water channels to strengthen centralized heat dissipation.

The cavity and core water channels should be symmetrical up and down and corresponding inside and outside to prevent unidirectional excessive cooling from causing plastic parts to bend inward or outward. For thickened areas such as ribs, columns and undercuts, separate insert water insulation or extended fine water channels must be arranged to make up for the cooling dead corners that ordinary water channels cannot cover. For deep cavity shell molds, the inner core preferentially adopts water insulation plate and fountain water channel structure to solve the problem of insufficient cooling in deep cavity. Flat thin-walled plastic parts adopt parallel straight-through water channels for uniform and rapid cooling; water channels at corner arc positions should make arc transition as far as possible to avoid water flow blockage and mold stress concentration caused by right-angle drilling.

3. Structural Form, Sealing and Installation Process Points of Water Channel

Common cooling water channel structures of injection molds include straight-through type, fold-back type, water insulation plate type, fountain type and spiral type, which should be selected according to product structure. Straight-through type is suitable for flat and shallow cavity plastic parts, with simple structure, convenient processing and smooth water flow; fold-back type is suitable for small and medium-sized shells, circulating and cooling around product contour; water insulation plate is mostly used for large deep cavity cores, separating water flow with water insulation plates to realize up and down circulating heat exchange; fountain type is aimed at slender cores and small inserts, fixed-point spray cooling from the inside to solve the problem of difficult heat dissipation of fine structures; spiral type is suitable for cylindrical and annular plastic parts, fitting circumferential uniform cooling to eliminate elliptical deformation.

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Water channel sealing and installation are equally important. Standard quick connectors are selected for water channel connectors, arranged on the non-operation side of the mold to facilitate pipe connection without affecting the safety spacing of injection molding machines. Water channel plugs and water stop bolts should be made of temperature and pressure resistant materials, sealed and leak-proof during assembly, to avoid mold corrosion by water leakage and affecting injection molding environment. All water channels must be filled with water and pressure tested after processing to check for leakage, blockage and poor water flow. 

Clean iron filings and impurities in water channels before production to prevent pipeline blockage from affecting long-term cooling effect. At the same time, mold water channels should be rust-proofed, and circulating cooling water should be equipped with filtering and softening devices to reduce scale deposition, avoiding narrowing of water channels and attenuation of heat dissipation efficiency due to scale accumulation in long-term use.

Summary

The design of injection mold cooling water channel is not a simple drilling layout, but a systematic design work combining product structure, plastic characteristics, molding process and mold strength. Grasp the four core key points of layout principle, aperture and spacing specification, structure selection and sealing installation, achieve conformal uniform cooling, smooth water circulation, undamaged mold structure and reinforced cooling for thick-walled dead corners. It can fundamentally reduce molding defects such as plastic part shrinkage, warping, deformation and weld lines, greatly shorten cooling cycle and improve mass production yield. Reasonable design of cooling water channel is not only the basis to ensure product size and appearance quality, but also an important guarantee for efficient energy saving and long-term stable mass production of molds.

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