Thermoplastic Elastomer Molding Guidelines:
Overmolding Design Considerations

Typical TPE Hardness Range Sprue Puller Type
>60 Shore A 60 to 90 Shore A
Z-type, Conventional Undercut, Pine Tree
Pine Tree Stem Puller/Sprue Puller

Gating Recommendations

  • Gate at thickest TPE wall cross section
  • Optimize gate type for part geometry and cosmetic component preferences
  • Gate orientation to component wall should be customized
  • Gates can be used in combination with added “flow” channels to insure minimal molded in stress
  • A perpendicular gate (at 90° angle) to the melt flow – can cause “jetting” surface effect
  • Need to consider exact gate location with respect to knit lines
  • Oversized TPE gate(s) – will reduce shear rate in molten TPE flow. Utilize “steel safe” practices by starting small followed by gradual increases

Gating to Avoid

  • Very long flow paths (greater than 200:1 L/T) should be avoided
  • Avoid gating into thin cross-section of components
  • Typically should not gate near core pins to minimize melt flow obstruction
Modified Fan Gate


  • The purpose of venting is to evacuate all entrapped air in the runner system and part cavities.
  • Adequate venting is most critical in complex and long length runner systems. Full peripheral venting is recommended – if not possible, vent at the end of fill directly opposite the gate.
  • Vent Depth: 0.0005 to 0.0010 in (0.0127-0.0254 mm) deep – 0.00075 in (0.1905 mm) optimum.
  • Land Length: Minimum 0.040 in (1.016 mm) where vent depth is cut.
  • Depth of land (vent run out): >0.060 in (>1.524 mm)