Meaning
Variation in the reduction of part dimensions across different regions of a moulded component results from uneven cooling and pressure distribution. This volumetric shrinkage spread indicates the risk of internal stresses and warp in the finished product. It represents the difference between the maximum and minimum contraction values within a single geometry.
Geometry Influence
Thicker sections of a part naturally retain heat longer and shrink more than thin ribs or walls. A wide volumetric shrinkage spread often leads to sink marks or bowing as the different regions pull against each other during solidification. Design engineers aim to minimize this delta by maintaining uniform wall thicknesses.
Process Optimization
Packing pressure must be applied consistently to compensate for the natural contraction of the cooling polymer. If the gate freezes too early, the volumetric shrinkage spread increases because the areas furthest from the gate cannot receive additional melt. This results in poor dimensional stability.
Tolerance Management
Precision components for automotive or medical applications require a tight control over how much the material moves. When the volumetric shrinkage spread is high, the part may fall outside of the specified tolerances even if the average shrinkage is correct. Consistent processing is the only way to hold these limits.
