The cooling system of a tool is an extremely important factor in the performance of the tool. Incorrect cooling can lead to both longer than necessary cycle times and to less than optimum product properties. The objective of good cooling is to maintain a constant temperature throughout the tool.
 
Properties affected by tool temperature include surface finish, dimensions (shrinkage and warpage) and mechanical performance (moulded in stresses). For PA66, the optimal tool temperature ranges from 80 °C to 120 °C.
 
Positioning of cooling channels is the key to good cooling. This positioning must be considered from the start when making a tool design. Too often, it is left too late in the design process, and channels are placed wherever there is room.
 
Some design tips for achieving good cooling:

• Take care in corners. Concave areas have a lower cooling rate than convex areas. It may be necessary to place an insert of a highly conductive material (e.g. Copper Berylium) on the inside of a corner, or to put more cooling capacity on the inside.
  
• Ensure the flow in the cooling channels is turbulent, as this will give a 3 to 5 times better heat transfer than laminar flow. Channel diameters of 6 to 12 mm recommended.
• Ensure enough flow of the cooling medium to ensure the difference between the flow into the tool and the flow out of the tool is less than 2°C.
• Put cooling channels close enough together to minimize temperature fluctuation (usually 10 to 25 mm centre distance).
• Put cooling channels close to the cavity surface (15-25 mm from centre distance of the channel).
• Avoid long thin cores, which will be difficult to cool and will heat up during the moulding process. Ensure that cores are cooled by using heat pipes or spiral channels.
• Avoid hot spots in the product design