Cooling Time in Injection Molding: Maximize Quality, Minimize Cycle Time

Cooling time begins at the end of the packing phase and ends when the part reaches its ejection temperature, typically just below the resin’s Heat Deflection Temperature (HDT). Effective cooling allows heat to dissipate uniformly from the part’s core to the mold walls and ultimately to the coolant system.

 

Condition	Result	Possible Defects
Insufficient Cooling	Ejection before full solidification	Warpage, sink marks, stress cracking
Excessive Cooling	No added benefit, only longer cycles	Reduced productivity, higher energy cost

Further reading： Common‌ Injection Molding Defects: Causes, Types, and Solutions

 

 

Proper calculation of cooling time enables data-driven cycle time prediction and mold validation, avoiding guesswork.

 

 

• ：Cooling time (seconds)
• ：Maximum wall thickness of the part (mm)
• ：Thermal diffusivity of the material (mm²/s)
• ：Melt temperature (°C)
• ：Mold temperature (°C)
• ：Ejection temperature (°C), typically near HDT

Wall thickness has the greatest impact—cooling time scales with the square of its thickness. Minor increases in thickness lead to significant cycle delays.

Further reading： Injection Molding Cycle Time: The Key to Faster and Smarter Manufacturing

 

 

 

• Uniform Wall Thickness： Thicker sections take longer to cool. Designing parts with uniform thickness helps minimize uneven cooling and deformation.
• Ribs & Bosses： These localized thick sections act as heat sinks, prolonging the cooling process.

 

• Injection molding materials with low thermal conductivity (e.g., ABS) require longer cooling； plastics with high thermal conductivity (e.g., PA6) cool more rapidly.
• Crystalline plastics (e.g., POM, PP) must cool below their crystallization point for ejection, extending the cooling time.
• Amorphous plastics (e.g,. PC, PS) only need to cool below HDT, requiring less time.

 

• Cooling Channel Layout： Cooling lines should closely follow the mold cavity contour, be symmetrically arranged, and ensure adequate flow rate and pressure differential.
• Thermal Insulation Components： Reduce heat transfer back into the mold structure, helping maintain consistent mold temperatures.

 

• Melt Temperature: Excessive melt temperatures prolong cooling; settings should follow the material supplier's recommendations.
• Mold Temperature： Higher mold temperatures increase cooling time, while overly low temperatures may cause weld lines or surface defects； balance is key.
• Separation of Dwelling (Holding) and Cooling Phases： Properly defining the end of packing and the beginning of cooling ensures accurate time management and process control.

Further reading: Injection Molding: Processes, Benefits, Applications, and Future Trends

 

 

 

• Conformal Cooling (3D-Printed Channels): Matches cavity geometry and shortens cycle time by 20–40%.
• Microcellular Foaming: Reduces material density and internal heat retention, enabling faster cooling and fewer sink marks.
• Anti-Condensation Systems: Essential when the mold temperature is lower than the dew point, preventing water-related defects.
• Dry Coolers & Closed Loop Chillers: Stable water temperature and less scaling improve heat removal consistency.

Further reading： Microcellular Foaming – Revolutionizing Lightweight Injection Molding]

 

 

• Filtration & Softening: Prevents mineral scale from blocking channels.
• Low-pressure Air-Water Cleaning: Maintains flow without chemical corrosion risk.

 

 

 

Symptom	Probable Cause	Suggested Action
Warpage	Uneven or insufficient cooling	Adjust water flow; balance channel design
Short shots / deformation	Mold opened too early	Extend cooling time; verify ejection temperature
Surface whitening or cracking	Overcooling or internal stress	Reduce cooling time; lower holding pressure
Cycle time too long	Excessive cooling for safety margin	Re-evaluate material and cavity temperature zones

 

 

Feature	Traditional Straight Channels	Conformal Cooling (3D)
Heat Extraction Efficiency	Medium	High
Cooling Time (Example Part)	20 sec	12–14 sec (up to -40%)
Tooling Cost	Low	High (initial)
Long-Term Energy Savings	Limited	Significant

 

 

Efficient cooling isn’t only about the mold—it must match the machine’s capabilities and cycle timing strategy:

• Screw Fly (Simultaneous Plasticizing & Ejection): Reduces dead time post-cooling.
• Ejector Fly (Simultaneous Mold Open & Ejection): Further shrinks cycle time window.
• Injection/Plasticizing Separation: Allows higher flexibility in cooling duration setting without affecting plasticizing rhythm.
• Servo Hydraulic System: Enables precise control of clamp force and water-cooling timing, ensuring no overcooling or premature ejection.

 

To further enhance synchronization with the cooling phase, we recommend upgrading to a Direct Drive Material Storage System. This design eliminates the need for gear reducers, delivering more stable torque and longer-lasting servo performance.
Compared to conventional storage systems, this solution reduces energy consumption by up to 26% during the plasticizing process. It operates independently, enabling material storage to occur concurrently with cooling and mold opening, effectively shortening the molding cycle and boosting productivity.

Further reading: Energy-Efficient Direct Drive Material Storage Motor
 

 

Look for signs like warpage, short shots, or cracking at ejection. You can also measure mold surface and part temperature right before ejection.

 

No. Overcooling adds unnecessary time without improving the product and increases energy usage.

 

It depends on the part complexity and volume. For multi-cavity, thin-wall, or high-precision molds, conformal cooling often justifies the higher tooling cost.

 

This depends on the water quality, but many factories clean their channels every 3–6 months. Water softening systems can reduce the frequency of these occurrences.

 

 

In the world of injection molding, optimizing the cooling phase is key to enhancing product quality, reducing cycle time, and lowering energy consumption. By engineering the cooling process, manufacturers not only improve part consistency but also reduce the total cost of ownership. Advanced cooling strategies now play a critical role in sustainable manufacturing.

 

 

Cooling time in injection molding is not merely a passive phase—it is a controllable, data-driven lever that defines the success of any molding process. From part design and resin selection to tool layout and cooling circuit optimization, every element contributes to how heat is dissipated and how quickly production can continue.

• Group Name: Huarong Group
• Brand: Huarong, Yuhdak, Nanrong
• Service Offerings: Injection Molding Machine, Vertical Injection Molding Machine, Injection Molding Automation
• Tel: +886-6-7956777
• Address: No.21-6, Zhongzhou, Chin An Vil., Xigang Dist., Tainan City 72351, Taiwan
• Official Website: https://www.huarong.com.tw/