Thermal Boundary Layer Instabilities and Viscoelastic Melt Degradation during High Throughput Molding
High throughput molding requires balancing injection velocity against viscous dissipation to prevent polymer chain scission and wall slip defects.
Flow Front Stability
Meaning
Rheological state describes the maintenance of a smooth and predictable interface between the advancing molten plastic and the air remaining in the cavity. Achieving flow front stability prevents air entrapment and ensures the material fills the tool in a uniform pattern. It is the metric for laminar behavior in high speed manufacturing environments.
Velocity Control
Variations in geometry cause the advancing polymer to accelerate or slow down based on the local cross section. If flow front stability is lost, the edge of the melt may break into irregular fingers that trap pockets of gas. Steady movement is essential for parts with complex internal features.
Interface Behavior
Tension between the mold wall and the melt determines the shape of the meniscus. Under conditions of flow front stability, the center of the melt flows through the skin layers to reach the front without turbulence. Uneven pressure across the width of the front causes drifting or hesitation.
Laminar Retention
High viscosity materials resist changes to their movement pattern better than low viscosity variants. Because flow front stability is sensitive to gate placement, designers use simulations to verify that the front remains cohesive throughout the fill. Chaotic fronts lead to surface defects known as jetting.