A reliable overmold interface is a system made from the silicone, rigid substrate, surface, geometry and molding process. Changing one element can change bond behavior.
Use geometry to support the interface
Through-holes, grooves, undercuts and wraparound features can add mechanical retention where the design allows. They should not create trapped air, weak rigid sections or impossible demolding.
Protect the shutoff
The mold must close against the insert without damaging it or allowing uncontrolled silicone flash onto critical surfaces. Insert tolerances and fixture repeatability therefore affect the silicone result.
Control contamination and surface condition
Oil, release agent, moisture, oxidation or inconsistent texture can interfere with bonding. The required cleaning, primer or self-bonding material route should be agreed for the actual substrate.
Test the load that matters
Pull, peel, torque, leak and thermal-cycle tests answer different questions. Select a method that represents the application, and define where failure is acceptable before comparing samples.