Underfill refers to the phenomenon that the injection material does not completely fill the cavity of the mold and result in incomplete parts, usually occurring in the thin-walled area or in the area away from the gate. For some internal short-circuiting that does not matter without affecting the beauty, no adjustment is needed. If it is adjusted, it may lead to the emergence of a front-facing fan.
The reasons for the lack of attention are many, mainly in the following situations:
1. Insufficient material or litter. Appropriately adjust until the parts are filled.
2. The barrel temperature is too low. When the material temperature is low, the viscosity of the molten material is large, and the resistance during filling is also large. If the material temperature is appropriately increased, the melt fluidity can be enhanced.
3. Injection pressure or speed is too low. The filling process of the molten material in the cavity lacks sufficient driving force to continue to flow remotely. Increase the injection pressure so that the molten material in the cavity is always replenished with sufficient pressure and material before condensing and hardening.
4. Insufficient injection time. It takes a certain amount of time to inject a certain weight of the part. If the time is not enough, it means that the injection volume is insufficient, and the injection time can be increased until the part is filled.
5. Improper holding pressure. The main reason is that the pressure is transferred too soon, that is, the pressure switching point is adjusted too much, and the remaining amount of material is supplemented by the holding pressure. It is inevitable that the weight of the workpiece is insufficient and the pressure is insufficient. The pressure conversion position should be readjusted to the optimal point. , Make the parts complete.
6. The mold temperature is too low. When the shape and thickness of the part change greatly, an excessively low mold temperature will consume too much injection pressure and increase the mold temperature or reset the mold water passage.
7. The nozzle and the mold gate have a bad fit. When the shot nozzle overflows during injection, part of the material is lost, and the mold is re-adjusted so that it fits well with the nozzle.