Amortizing Multi Cavitation Tooling Assets across Volatile Component Demand Curves
Structure high-cavitation tooling capital through modular inserts and explicit true-up clauses to eliminate unamortized debt exposure during demand swings.
POM Shrinkage
Meaning
Reduction in physical dimensions that occurs as polyoxymethylene resin cools and crystallizes after molding. This material is known for a high and predictable contraction rate, which must be accounted for during the design of the mold cavity. POM shrinkage is influenced by the degree of crystallinity achieved, which is a function of both the cooling rate and the mold temperature.
Crystalline Structure
Rapid cooling prevents the molecules from organizing into an ordered state, resulting in lower initial contraction. However, if the part is later exposed to heat, it may undergo post-molding POM shrinkage as the crystals continue to grow. To prevent this, molders often use high mold temperatures to ensure crystallization is complete before the part is ejected.
Dimensional Precision
Tooling designers typically add between 1.5 percent and 2.5 percent to the cavity dimensions to compensate for the expected change. Because POM shrinkage is not perfectly uniform, sections with different wall thicknesses will contract at different rates. This can lead to internal stresses or warping if the part geometry is not carefully balanced.
Process Variables
Injection pressure and hold time also play a role in how much the material pulls away from the walls. Increasing the pack pressure forces more material into the cavity, which can slightly reduce the final POM shrinkage. A stable process is the only way to hold the tight tolerances required for the precision gears and clips usually made from this resin.