There is no universal TPE injection-molding recipe. Start with the exact grade’s technical data sheet, establish a stable fill and pack sequence, then change one factor at a time while measuring part weight, dimensions, appearance and function.
Record the material and machine before changing settings
- supplier, full grade, color and lot;
- drying method and moisture result where the grade is hygroscopic;
- machine shot capacity, screw design and estimated residence time;
- actual melt temperature, not only barrel setpoints;
- mold temperature, coolant stability and cavity balance;
- fill time, transfer position, peak pressure and cushion; and
- part weight by cavity and conditioned dimensions.
Avient’s TPE injection-molding guide provides general starting principles but directs processors to the individual product data for specific conditions.
Build a stable process in sequence
- Material preparation: follow the grade’s drying and handling requirements; protect opened material from contamination.
- Temperature profile: use the supplier’s range and verify a homogeneous melt without excessive residence time.
- Velocity-controlled fill: establish a repeatable fill profile and transfer before the cavity is overpacked.
- Hold study: determine gate freeze by increasing hold time and tracking part weight until it no longer changes.
- Cooling study: reduce cooling only until ejection remains dimensionally stable and mark-free.
- Process window: test practical high/low limits for critical variables and confirm all cavities.
Troubleshooting table
| Defect | Confirm first | Possible corrections and side effects |
|---|---|---|
| Short shot | Feed, venting, frozen gate, actual melt and pressure limit | Improve vent/gate or raise speed/temperature within grade limits; watch flash and degradation |
| Flash | Parting-line condition, clamp, transfer point and trapped gas | Repair steel/stabilize clamp before simply lowering pressure, which may create shorts |
| Burn mark | End-of-fill location, blocked vent, speed and residence time | Improve venting/decrease local shear; too-slow fill may worsen hesitation |
| Sink or void | Section thickness, gate freeze, hold and cooling | Reduce thick section or improve pack path; excess hold can flash or stress the part |
| Flow line/poor gloss | Gate, velocity transition, mold finish and temperature | Stabilize flow front and temperature; do not use heat to mask an undersized gate |
| Sticking/deformation | Draft, texture, undercut, cooling and ejector area | Add draft/ejection support or cooling; excess cooling increases cycle |
| Weak overmold bond | Material pair, contamination, substrate temperature and flow path | Correct compatibility and interface before changing pressure alone |
Separate a material problem from a tool problem
If a defect repeats in one cavity or location, inspect gates, vents, temperature, steel dimensions and ejection before blaming the resin. If the defect follows a material lot, color or dryer condition across cavities, investigate handling and material. Short-shot studies and cavity-by-cavity part weights help distinguish flow imbalance from global settings.
Control residence time and shutdown
A machine that is too large for the shot can hold material at temperature for excessive time. Symptoms may include odor, color change, gas, viscosity shift or black specks. Follow the supplier’s purge and shutdown instructions for the exact chemistry; do not assume all TPEs can be purged or left hot the same way.
What a production setup sheet should contain
- approved material/lot and preparation;
- machine and mold identification;
- barrel, nozzle and mold-temperature windows;
- fill profile, transfer, hold and cooling limits;
- cushion, part-weight and critical-dimension limits;
- start-up, interruption and shutdown instructions; and
- reaction plan for drift or cavity-specific defects.
For a TPE part with recurring defects, send the CAD, exact grade, mold layout, defect photos by cavity and the current process record. CKMOLD can review the tool and flow path through DFM analysis and mold testing and validation. Use request a quote for a tooling or production review.