Injection Mould Wall Thickness Design Rules and Flow Ratios
Melt flow length scales with cavity thickness raised to the third power while cycle time increases quadratically, forcing tight nominal wall control.
Thin Wall Moulding
Meaning
Injection moulding of components with a wall thickness below one millimeter requires specific control of flow length to wall thickness ratios. High pressure injection and rapid cycle times define this thin wall moulding process. Molten resin must travel across the mould cavity before solidification occurs at the extremity.
Shear heating within the thin channels compensates for the rapid cooling of the polymer melt.
Processing Velocity
Precise synchronization of injection speed and clamp tonnage prevents flash or short shots during high speed filling. The moulder adjusts injection rate to ensure the melt front reaches the end of the cavity before the polymer reaches its freezing point. Excessive injection pressure leads to thermal degradation of the material at the gate.
Consistent velocity control maintains the mechanical integrity of the final part.
Material Specification
Choice of resin with high melt flow index remains necessary to fill constrained volumes without excessive clamp force. Low viscosity polymers allow for lower temperature profiles during production runs. Virgin material typically provides more stability than regrind during high shear flow.
Variability in resin rheology causes shifts in wall thickness consistency across the moulded surface.
Production Outcome
Improper cooling rates or uneven wall dimensions lead to warping and structural failure under load. Precise regulation of the packing stage minimizes sink marks on surfaces adjacent to ribs. Surface defects appear when the melt front meets resistance from trapped gases or cold runners.
Dimensional stability depends upon the equilibrium between thermal contraction and the holding pressure applied during the cycle.