TPGOA Technical Insights
Optimizing Cooling Time in Injection Molding
Typically, 50% of the injection molding overall cycle time is used for cooling the part. As the part nominal wall section is increased, the cooling time must be increased as well. Several general guidelines exist for cooling time, which may or may not be applicable to your part and tool design. For amorphous resins such as PC, ABS, and PS, the calculation is 200 times the thickest part wall section. Assuming a nominal wall of 0.150", the cooling time would then become 200 x 0.150" = 30 seconds.
For semi-crystalline resins such as PP, PE, Nylon, and Polyester, the calculation is 175 times the thickest nominal wall section. Assuming a nominal wall section
of 0.150" once again, the cooling time would then become 175 x 0.150" = 26.25 seconds.
If the water lines in the injection mold were designed properly and in sufficient number, heat removal will be facilitated, thus reducing cooling time. I would approach the challenge of optimizing cooling time in the following fashion:
Set up and line out your molding machine with the resin manufacturers guidelines in the middle of the recommended range.
Use Scientific Molding methodology to optimize fill times and pressures for that press and tool.
Start to reduce mold temperature settings in 5 degree increments until ejector pin push is visible on the part. When pin push is observed, start to increase mold temperature in 2 degree increments until it goes away.
Remember, time is money, especially in injection molding. Any excess cooling time in the cycle will reduce output and increase overall part costs. This will reduce your profit margins.
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