Injection Mold Cooling and Cycle Time
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An injection molding cycle is mostly waiting. Filling takes a second or two; then the part has to cool enough to eject without warping. Cooling is usually the longest step in the cycle, often more than half of it, so that's where most of the savings are.
Wall thickness rules it
Cooling time grows with the square of wall thickness. Double the wall and cooling takes roughly four times as long. Going from 3 mm to 2 mm cuts it to about 45 percent. That's why uniform, thin walls do more for cycle time than any mold feature, and why one thick boss can set the cycle for the whole part.
Cooling channel layout
- Keep channels close to the cavity surface, evenly spaced and following the part's shape.
- Cool the core as well as the cavity. Cores are surrounded by hot plastic and trap heat. Baffles and bubblers get water into deep cores, and inserts in highly conductive copper alloys help in thin ones.
- Make the flow turbulent. Turbulent water removes heat far better than slow, smooth flow, so check flow rates, not just that the water is connected.
- Keep the difference between inlet and outlet temperature small, a few degrees, so the whole mold runs evenly.
- Treat the water. Scale inside the channels insulates them and slowly stretches the cycle.
Conformal cooling
Drilled channels run in straight lines. Inserts made by metal 3D printing can have channels that follow the part's shape at a constant distance from the surface. For parts with deep cores or uneven geometry, conformal cooling can shorten the cycle and reduce warp. It costs more, so it's usually reserved for the inserts that set the cycle.
Uneven cooling causes warp
Cycle time isn't the only reason to care. If one side of a part cools faster than the other, it shrinks unevenly and warps. Warp that looks like a material problem is often a cooling problem.
Ask for a cooling layout and analysis with your mold quote, and see injection molding design rules for wall thickness guidance.