Injection molding · Process validation
Injection Molding Pressure Drop Study Calculator
Separate cumulative plastic-pressure measurements into nozzle, runner, gate and cavity increments.
Formula and method
Incremental pressure drop at each stage = cumulative pressure at that stage − cumulative pressure at the prior stage. The nozzle air shot is the first increment.
Inputs and units
Enter plastic pressure—not unconverted hydraulic pressure—for nozzle air shot, through sprue/runner, through gate and fill-only part.
Worked example
Cumulative values of 15, 45, 78 and 110 MPa produce increments of 15, 30, 33 and 32 MPa; the largest is 33 MPa.
When to use the study
Use during controlled progressive short-shot stages to localize measured pressure demand.
How to interpret the result
The largest increment identifies where measured demand increased most in this study. It does not prescribe a geometry change.
Assumptions and limitations
Pressure readings depend on machine dynamics, material, melt temperature, injection rate and stage definition. Follow site safety procedures for any air shot.
Validation guidance
Preserve machine, mold, material lot, melt/mold temperature, cycle state, units, instrument and sample order with the result. Repeat after any material, machine or tooling change.
FAQ
Does the largest pressure increment identify the required mold change?
No. It localizes measured demand for inspection; geometry, material, temperature, rate and machine response still need engineering review.
Related workflow
Process Validation & Stability hub · Scientific molding validation workflow · Weight measurement guide · Gate seal and pressure-drop setup
Sources
PlasticsToday: Scientific Molding, Part 1 · M. Holland: Monitoring Pressure Loss · BASF: Injection-Molding Problems · NIST: Measures of Scale · NIST: Coefficient of Variation · PMC: Filling Imbalance in Multi-cavity Molds · Hingtung: Cavity Balance Study
