What Is the Injection Molding Part Cooling Time Calculator (Ballman Model)?
In-mold cooling time is the duration required for the molten polymer in the mold cavity to solidify and cool until the center plane reaches a safe ejection temperature.
Because plastics are poor thermal conductors, cooling time scales quadratically with wall thickness squared (t ∝ h²).
How Does the Injection Molding Part Cooling Time Calculator (Ballman Model) Work?
Molten plastic enters at Tmelt and freezes instantly upon contacting the cold mold metal walls at Tmold.
Heat conducts from the center plane outward via Fourier conduction; Ballman and Shusman (1959) solved the 1D transient slab equation to find the exact cooling duration to center solidification.
Injection Molding Part Cooling Time Calculator (Ballman Model) Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Exact Fourier transient heat conduction solution for the mid-plane of a flat plate bounded by constant mold surface temperatures.
How to Use the Injection Molding Part Cooling Time Calculator (Ballman Model)
- Input the maximum wall thickness of the part.
- Select material thermal diffusivity α and operating temperatures.
- Use the resulting cycle time to calculate hourly machine part output and piece cost.
Step-by-Step Example Calculation
2.5 mm Polypropylene Housing
Input Values:
Understanding Your Result
t_cool indicates the minimum hold time before opening the mold clamp.
Total cycle time adds typical dry-cycle mold open, close, and injection overhead (~3 to 5 seconds).
Factors That Affect the Result
- Wall thickness: Doubling part wall thickness quadruples cooling time (from 10 s to 40 s), heavily inflating piece cost.
- Mold temperature: Colder molds reduce cooling time but can cause high residual stresses, sink marks, or poor gloss.
When Should You Use This Calculator?
- Injection molding production quoting and cycle time optimization.
- Evaluating conformal cooling channel benefits in mold tooling design.
Assumptions & Limitations
- Assumes uniform 1D heat extraction through flat walls with constant thermal diffusivity.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard industry analytical cooling model (SPE / Ballman-Shusman).