Plastic injection molding is an engineering technique that transforms a plastic material into a useful product that is able to retain its original features. The important process factors include injection molding temperature, injection pressure and corresponding effects that affect plasticizing and cooling.
1. Barrel temperature: The temperatures that need to be controlled during the plastic injection molding process include barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly influence the plasticization and activities of the plastic, and the last mainly influences the activities and cooling of the plastic. Each type of plastic has a different activity temperature, and the same plastic may have different activity and decomposition temperatures due to different sources or grades. This is caused by the difference in the average molecular mass and the molecular mass distribution. A plastic material features different plasticizing processes in different plastic injection molding machines, so the choice of barrel temperature is not the same.
2. Nozzle temperature: The nozzle temperature is usually slightly lower than the lowest temperature of the barrel. This is to avoid “drooling” of the melt that might occur in the straight-through nozzle. The nozzle temperature should not be too low, or it will cause premature condensation of the melt, which might block the nozzle, or may affect the function of the product due to the injection of pre-solidified material into the cavity.
3. Mold temperature: Mold temperature has a great influence on the intrinsic function and apparent quality of the product. The upper and lower temperature limits of the mold are determined by the crystallinity of the plastic, the size and structure of the product, functional requirements, as well as other process conditions (melt temperature, injection speed, injection pressure and molding cycle, etc.).
Injection molding temperature for common plastic as below:
| Plastic material | Injection Molding Temperature (C°) | Mold Temperature(C°) |
| ABS | 210-275 | 50-90 |
| PP | 250-270 | 50-75 |
| POM | 200-210 | >90 |
| LDPE | 160-260 | 50-70 |
| HDPE | 260-300 | 30-70 |
| PVC-soft | 170-200 | 15-50 |
| PVC-rigid | 180-210 | 30-50 |
| PS | 180-280 | 10-40 |
| PA6 | 240-260 | 70-120 |
| PA66 | 260-290 | 70-120 |
| PMMA | 210-240 | 50-70 |
| TPR | 120-250 | 50-70 |
| PC | 280-320 | 80-100 |
Note: Injection molding temperature include nozzle temperature and barrel temperature.