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.
Thin Wall Injection
Meaning
High-pressure molding process focuses on creating parts with extremely low thickness relative to their overall surface area. Execution of thin wall injection requires machines with fast response times and high injection speeds to fill the cavity before the polymer freezes. It is common in the production of light-weight packaging and cell phone cases.
Filling Speed
Molten resin cools almost instantly when it touches the metal of a thin cavity. Because thin wall injection relies on overcoming this heat loss, hydraulic accumulators are used to fire the material into the tool in fractions of a second. Delays of even a millisecond can cause the part to fail.
Pressure Demand
Forcing plastic through small gaps takes significantly more energy than filling a standard part. Inside a thin wall injection system, internal pressures can exceed twenty-thousand pounds per square inch. The mold must be built with extreme rigidity to prevent the plates from separating under this load.
Part Geometry
Successful designs include gentle transitions and avoid sharp corners that increase flow resistance. By utilizing thin wall injection, designers save on material costs and reduce the weight of finished shipments. Strength is maintained through careful ribbing rather than bulk material.