Why wall thickness dominates
Cooling time rises rapidly as the thickest section increases. A thick boss, rib junction, or local mass can control ejection readiness even when most walls are thin. Keep nominal thickness as uniform as practical and inspect the complete geometry, not only a nominal drawing dimension.
What the simple estimate assumes
The calculator uses a one-dimensional flat-wall approximation with melt temperature, mold temperature, ejection temperature, and thermal diffusivity. It is best used to compare alternatives while holding assumptions constant.
t ≈ wall thickness² ÷ (π² × thermal diffusivity) × temperature term
What the estimate omits
- Actual cooling-channel distance, diameter, flow, corrosion, and temperature balance.
- Three-dimensional heat flow around ribs, corners, inserts, and thick transitions.
- Part stiffness, ejection friction, residual stress, warpage, and the required quality criterion.
- Grade-specific, temperature-dependent thermal properties and process variation.
How to validate before reducing cooling
Set an ejection-quality criterion first: no permanent distortion, unacceptable stress, sticking, or downstream dimensional drift. Then run controlled cooling-time trials while tracking part weight, dimensions, cosmetic quality, ejection force, and cycle stability. Moldflow or equivalent simulation is appropriate for complex or high-risk parts.
FAQ
Can a lower mold temperature always shorten cycle time?
It can shorten a thermal estimate, but it may compromise surface quality, stress, shrinkage, or dimensional behavior. Validate against the quality requirement.
Which wall thickness should I enter?
Use the controlling thick section for a first-pass estimate, then review local masses such as bosses and rib intersections.