LSR's high coefficient of thermal expansion means parts shrink significantly during cooling. Mold temperature uniformity is crucial to prevent differential shrinkage that causes warpage. Material batch variations in viscosity and cure rate also affect dimensions. Part geometry, especially varying wall thicknesses, creates internal stress concentrations that lead to distortion if not properly managed.
Uniform cooling channels and balanced heating systems minimize thermal gradients across the mold. Proper gate sizing and location reduce internal stresses from injection forces. Ejection pin placement avoids witness marks that could affect critical dimensions. Core and cavity materials with matched thermal expansion coefficients prevent mold component movement that would transfer to part tolerances.
Precise temperature control maintains consistent cure conditions throughout production runs. Holding pressure compensates for LSR shrinkage during the curing phase. Multi-zone mold controllers adjust local temperatures to balance shrinkage rates in complex geometries. Statistical process control tracks key dimensions and alerts operators to trends indicating process drift.
Some LSR parts undergo post-cure treatments in ovens to complete cross-linking reactions and stabilize dimensions. This step is particularly important for parts with tight tolerances or those subject to significant temperature variations in service. Secondary operations like machining or grinding may be required for critical features, though these add cost and complexity to the manufacturing process.
