During injection moulding manufacturing process, mold temperature not only directly governs polymer melt flow behavior and final product quality, but also critically determines cycle time and production efficiency. Therefore, the cooling system design must adhere to the core principle of achieving uniform cooling throughout the mold structure. Essentially, Temperature control in plastic injection molding tools is fundamentally achieved through precision-engineered cooling channel designs combined with strategic media selection, where the cooling medium – whether room-temperature water, chilled water (for rapid cooling), temperature-controlled hot water, or thermostatic oil (for high-precision regulation) – is systematically chosen based on specific thermal management needs and polymer solidification requirements.

To acieve these objectives, the following design principles should be prioritized when developing an effective mold cooling system:

1. Heat Concentration Analysis

- Identify high-heat areas (e.g., thick sections, gate regions) to prioritize targeted cooling.

2. Cooling System Design Principles

The cornerstone principle in mold cooling system design lies in achieving uniform cooling, which requires strict adherence to two critical guidelines:

(1) Strategic Channel Placement: Cooling channels must be positioned in close proximity to high heat flux zones to maximize heat extraction efficiency.

(2) Thermal Zone Isolation: Simultaneously maintain sufficient isolation from low thermal load areas to prevent uneven cooling effects.

This dual-approach methodology establishes optimized thermal gradients and enhances cooling efficiency throughout the mold structure.

3. Cooling Channel Specifications

Standard cooling channel diameters are 6.0 mm, 8.0 mm, 10.0 mm, and 12.0 mm, with 8.0 mm and 10.0 mm being the preferred selections for optimal thermal conductivity and pressure drop balance. The corresponding pipe thread specifications are as follows:

Ø6.0/8.0 mm channels: 1/8" NPT (National Pipe Thread)

Ø10.0 mm channels: 1/4" NPT

Ø12.0 mm channels: 3/8" NPT

For oil-temperature controlled cooling systems, counterboring operations are exempted from coolant connector installations.

4. Cooling Channel Clearance Standards

Theoretical Design: Maintain 15–20 mm clearance between cooling channels and cavity surfaces

Practical Implementation: Standard clearance of 10–12 mm (absolute minimum 8 mm).

Hardened Materials Requirement: ≥20 mm clearance mandatory for quenched tool steels (e.g., DIN 1.2344).

Edge Proximity Specifications:

Optimal Distance: >12 mm from core edges.

Minimum Allowance: 10 mm (critical threshold) to facilitate copper plug sealing (ISO 4032) or threaded plug installation (NPT standards).

5. Cooling Channel Clearance Requirements

- Minimum clearance between cooling channels and screw clearance holes: 5 mm

- Minimum clearance from ejector pin clearance holes: 4 mm

- Water seal (O-ring) distance from ejector pin hole edges: ≥2.5 mm

6. Cooling Channel Spacing Design Principles

Conventional Channel Spacing

The center-to-center distance between adjacent cooling channels should be **3–5 times the channel diameter (e.g., 30–50 mm for a φ10 mm channel).

This spacing range ensures uniform heat dissipation, reduces mold thermal stress, and balances cooling efficiency with structural integrity, preventing localized overheating or machining deformation due to insufficient spacing.

Crossing Channel Spacing

Minimum Planar Crossing Clearance:

-Short channels (≤150 mm length): ≥3 mm (to ensure machining feasibility).

- Long channels (>150 mm length): ≥5 mm.

To accommodate the recessed installation of water pipe fittings within the mold base, a minimum clearance of 26 mm must be maintained between adjacent cooling channels.

7. Cooling Channel Layout Constraints

Directional Changes: Each independent cooling channel should not exceed 15 turns (each baffle counts as 4 turns).

- Temperature Differential:

- For large/medium-sized molds: Optimal inlet-outlet temperature difference ≤5°C.

- For precision molds: Temperature difference ≤2–3°C.

-Channel Length: Keep cooling channels below 1.2–1.5 meters whenever possible.

8. Cooling Line Connection Priorities

Priority Sequence for Water Line Connections: Non-operator side > Operator side > Floor side > Top side.

Why avoid the top side?

Concerns about water leakage causing corrosion of the mold core.

Potential interference with robotic arm movements during automated production.

Why avoid the floor side?

Risk of crushing connections during mold hoisting if water pipes are not disconnected.

Possibility of products catching on water pipes during automated ejection.

From safety and production efficiency perspectives, non-operator side takes priority over operator side. Export molds are required to have water connections strictly on the non-operator side, while domestic molds have no such specification.

9. Common Cooling Line Configuration for Mold Components

①Perimeter Cooling (Serpentine Channels): Used in core/cavity plates.

②Central Cooling Channel: For multi-cavity small parts (adds a central well within a serpentine layout).

③Contoured Channels: Follow part geometry (requires angled drilling).

④ Multi-Tiered Cooling: For tall parts with height variations (dual-layer channels).

⑤Reservoir Cooling ("Water Ponds"): For deep cores (interconnected reservoirs).

⑥ Slender Cores: Use cooling tubes or heat-dissipation pins.

⑦ Cylindrical Inserts: Concentric or spiral cooling channels.

⑧Large Cylindrical Inserts: External/internal spiral channels.

⑨ Cooling in Angled Lifters: Large angled lifters require integrated cooling channels.

⑩ Cooling Design in Sliders: Cooling channels should be prioritized in sliders where feasible.

10. Methods for Connecting Cooling Channels in Mold Bases

①Angled Machining: Requires tilting the mold base during processing, commonly used for small molds.

② Reverse-side Machining: Processed from the back side, suitable for small/medium-sized molds.

③ Water Transfer Inserts: Additional cooling inserts added (requires more complex machining), recommended for large molds.

11. Sealing Methods for Cooling Channels

① O-ring Specifications & Groove Dimensions

O-rings require 0.4 mm pre-compression (standard).

Installation principle: O-rings should be mounted on stationary components for ease of assembly/disassembly.

② Sealing with Plugs:

Use cooling channel plugs (threaded or press-fit) for localized sealing.

③ Copper Bar Sealing:

Seal channels by driving copper bars into designated positions.

Additional Design Guidelines:

① Cooling for Flat or Elongated Parts:

Prioritize uniformly distributed straight cooling channels over multi-loop configurations to minimize warpage and dimensional instability.

② Runner Plate Cooling:

Incorporate two independent cooling circuits in the runner plate for thin-gate systems.

③ Hot Runner Cooling:

Integrate coolant channels into nozzle sleeves within hot runner systems whenever possible.