Multi Cavity Mold Gate Shear Rate Evaluation Methods
Multi cavity mold gate shear rate evaluation requires Rabinowitsch-Mooney corrected velocity gradients matched against real micro-metrology tool dimensions.
Cavity Flow Balance
Meaning
Injection molding parameters measure the uniformity of polymer distribution among multiple cavities of a mold during the filling stage. Achieving cavity flow balance prevents structural discrepancies and weight variations between simultaneously molded plastic parts. This condition is monitored by measuring part weights and dimensions from a short-shot analysis.
The measurement is inapplicable to single-cavity tools or molds with independent hot runner controls.
Measurement Method
Short-shot tests, where the molding machine injects less than a full dose of polymer, reveal which cavities fill first under normal operating conditions. Calculating the percentage difference in fill levels or part weights provides a reliable assessment of flow variation. Technicians adjust gate sizing, runner geometry and runner temperature to minimize this discrepancy, ensuring each cavity fills under identical pressure.
This step is critical during the validation of high-volume production molds.
Quality Influence
Inconsistent filling leads to flash on early-filling cavities and sink marks or voids on late-filling ones. By optimizing cavity flow balance, manufacturers achieve uniform part densities and reduce scrap rates. The cost of running an unbalanced mold includes uneven tool wear and high rejection rates.
Dynamic Factor
Polymer viscosity shifts during high-speed injection, altering the flow distribution in unpredictable ways. While static runner designs attempt to balance flow, changes in melt temperature or material lot can disrupt the system. Operators must maintain precise process control to keep the balance stable.