Thermoplastic Elastomer Molding Guidelines:
Overmolding Design Considerations

The required adhesion is dependent on the end-use application and environment. Not all overmold grades bond to all substrates. The substrate type determines which RTP Company TPE overmolding grade must be used to achieve the best bond. The end-use environment also influences which grade to select. The expected service life of the product should be considered when establishing adhesion requirements. Initial material selection is the first step.

Shear and peel forces that the product encounters should be considered. Mechanical interlocks and use of undercuts and ribs will create a higher surface area and improve product performance.

  • Proper material selection is key to good bonding.
  • Do not use only melt temperature to arrive at the optimum set of molding process conditions.
  • Avoid condensation of mold steel surface (caused by too low water temperature)
  • Shear rate is very important to optimum TPE overmolding.
  • Do not oversize the gate(s) – start “steel safe” and slowly increase gate size as required.

Material Flow Behavior

TPE compounds have relatively low viscosity. They are shear responsive and their viscosity is reduced when they are processed at high shear rates. This helps them flow into and fill thin walled sections commonly encountered in TPE overmolding.