Direct Pin Sensor Placement and Dynamic Viscosity Control in Micro-Moulds
Direct pin pressure sensing in micro-moulds compensates for melt viscosity drift by dynamically adjusting injection speed to hold precise shear rates.
Dynamic Viscosity Control
Meaning
An automated process control methodology adjusts injection velocity or barrel temperature in real time to maintain a constant melt viscosity across sequential molding cycles. Molding machines utilize dynamic viscosity control to compensate for natural batch-to-batch variations in resin melt flow index or regrind ratio. By monitoring the relationship between injection speed and hydraulic pressure during the filling stage, the system calculates the flow resistance.
Velocity Adjustment
When the melt becomes more resistant to flow, the injection speed must be adjusted to ensure the cavity fills within the target time. The dynamic viscosity control system alters the hydraulic pressure or screw velocity profile dynamically during the stroke. This correction ensures that the melt front reaches the end of the cavity at the correct moment, preventing short shots or flash.
Temperature Regulation
Prolonged drift in raw material properties requires a shift in thermal energy to restore the target flow behavior. Barrel temperature zones are raised or lowered by the controller to affect the viscosity of the polymer chain network, keeping the material at a steady state. This secondary adjustment operates over a longer time horizon than the stroke-by-stroke speed adjustments.
The dual-loop system handles both instant shear variations and slow thermal drift, ensuring that the molding process is self-correcting over several shifts.
Yield Stabilization
Consistent viscosity guarantees that part weights and dimensions remain within tolerance throughout the production run. Recycled plastics and regrind materials exhibit wide variations in molecular weight distribution that disrupt standard molding setups. Integrating this automatic adjustment strategy allows the plant to use higher fractions of recycled material without increasing scrap rates.