Quantifying Melt Viscosity Drift under Dynamic Feedstock Sourcing in Injection Molding
Melt flow rate fails to catch high-shear viscosity drift in dynamic feedstocks, requiring capillary rheology and inline pressure monitoring to control scrap.
Flash Formation
Meaning
A moulding defect occurs when pressurized liquid polymer escapes the intended cavity space into thin gaps along parting lines or ejector pin clearances. High cavity pressure exceeding clamp force triggers flash formation during the injection moulding packing phase. The phenomenon generates thin unwanted plastic fins attached to part edges, requiring manual trimming or automated deflashing operations.
Boundary limits of the condition cover flow into clearances down to five micrometres, beyond which melt viscosity prevents resin penetration.
Mould Clearance
Tooling wear along core and cavity shut-off surfaces widens mating gaps over extended production runs. Melted resin under high packing pressure enters open gaps between mating steel blocks. Worn ejector pin bushings and damaged venting channels allow polymer melt to leak outside part boundaries.
Proper mould maintenance restores tight surface contact and eliminates micro-clearances that promote thin resin fins.
Viscosity Impact
Polymer melt viscosity drops sharply when barrel temperatures exceed recommended processing windows. Thin, highly fluid polymer melt penetrates narrow parting line gaps much faster than viscous resin streams.
Clamping Requirement
Machine clamping force must counteract hydraulic opening forces generated by melt pressure inside the cavity. Insufficient tonnage allows cavity plates to separate micro-inches during peak packing pressure. Reducing peak hold pressure or transferring to hold phase earlier limits cavity pressure spikes.
Adjusting injection speed profiles controls melt front velocity and reduces localized pressure surges near gate locations.