Meaning
Tooling design technique that alters the cavity profile of a gear mould to counteract polymer shrinkage. Implementing gear involute compensation ensures that the finished, shrunk plastic gear achieves the correct theoretical involute curve for quiet and efficient operation. Uncompensated cavities produce gears with deformed teeth that wear out quickly.
Shrinkage Adjustment
Volumetric shrinkage in semicrystalline polymers varies along the height and thickness of the gear tooth. The gear involute compensation method applies non-uniform scaling to the tooth profile on the tool. This correction is essential because simple isotropic scaling fails to account for the complex thermal contraction of the tooth geometry.
Profile Correction
Specialized software calculates the required profile offset based on the specific resin characteristics and processing conditions. Shrinkage is typically higher at the tooth tip than at the root due to differences in thickness and cooling rate. The resulting mould cavity has an exaggerated tooth profile that appears distorted until the cooled plastic shrinks into the correct shape, meaning the final gear operates with minimum friction and noise.
Tooling Implementation
Precision steel cutting with wire electro-discharge machining allows toolmakers to cut these complex shapes with micrometre accuracy. Correctly compensated tooling reduces the need for expensive post-moulding machining. Consistent process control keeps the gear within tolerance.
