Meaning
High-pressure injection moulding forces molten polymer into the cavity, which exerts asymmetric bending forces on slender tooling inserts. Analyzing core pin deflection mechanics is necessary to prevent dimension drift in hollow moulded parts. The calculation models the core pin as a cantilever beam subjected to a distributed fluid load during the filling phase.
Force Distribution
Molten plastic entering the gate can hit the pin from one side, creating a localized pressure peak. This uneven load pushes the pin away from its central axis. The magnitude of the force depends on melt viscosity, injection velocity and gate location.
Geometric Deformation
Deflection increases with the cube of the pin length, meaning long and thin features are highly susceptible. This movement changes the wall thickness of the plastic part, creating thin sections that might fail. In extreme cases, the pin bends permanently or breaks, stopping the production run completely.
Defect Prevention
Tooling designers decrease deflection by reducing the aspect ratio of the core pin or using tougher materials like tungsten carbide. Gating configurations are optimized to split the flow, balancing the pressure on both sides of the insert. Dynamic simulations during the design phase identify the maximum expected displacement before steel is cut.
By maintaining structural rigidity under load, these pin modifications ensure that wall thickness remains within specification throughout high-volume production cycles.
