Meaning
Unbalanced temperature distributions occur across opposing cavity surfaces when heat extraction rates differ between mold halves. Non-uniform mold wall cooling, known as thermal asymmetry, causes differential volumetric contraction across part wall thicknesses during solidification. Material datasheets report volumetric shrinkage values measured under isothermal cooling conditions that rarely exist in production tooling.
Tooling engineers adjust coolant flow rates and channel layouts to equalize surface temperatures and eliminate heat imbalances.
Heat Transfer
Non-isothermal heat exchange between hot polymer melt and tool steel depends on coolant flow rates, channel placement, and steel thermal conductivity. Core inserts often retain heat longer than outer cavity walls due to restricted coolant access in deep mold features. The resulting thermal gradient forces polymer on the cooler side to freeze faster and shrink sooner than polymer on the hotter side.
High melt temperatures worsen this imbalance by introducing extra heat that deep core channels struggle to extract effectively during fast cycles.
Warpage Development
Unequal shrinkage across wall sections induces bending moments that bow or twist cooled components. Correcting thermal asymmetry reduces internal stress concentration and prevents dimensional distortion in flat molded panels.
Cooling Balance
Independent temperature control units allow technicians to adjust coolant supply temperatures for individual mold plates. Adding recycled resin alters polymer thermal diffusivity, which modifies heat release during crystallization and accentuates surface thermal differences. Installing high-thermal-conductivity copper alloy inserts improves heat removal from hot core regions.
Achieving thermal equilibrium across cavity faces ensures molded parts maintain specified dimensional tolerances after ejection.
