Underfill is a phenomenon that occurs when the injection material does not fill the mold cavity, resulting in an incomplete part, usually in thin-walled areas or areas away from the gate. For some underfill that is not important internally and do not affect the aesthetics, no adjustment can be made, but if it is, it may lead to the appearance of phi.
The causes of underfill are manifold, the main ones are as follows.
1. the amount of material or bedding material is not enough. Moderate adjustment until the part is filled. 2.
2. The barrel temperature is too low. When the material temperature is low, the viscosity of the melt is larger, and the resistance when filling the mold is also large, appropriate to increase the material temperature, which can enhance the fluidity of the melt.
3. Injection pressure or speed is too low. The melt in the cavity filling process, the lack of sufficient driving force to continue to remote flow. Increase the injection pressure so that they melt in the cavity always gets sufficient pressure and material volume replenishment before condensation and hardening.
4. Insufficient injection time. To inject a certain weight of the complete part requires a certain amount of time, if the time is not enough that means the injection volume is not enough, increasing the injection time to fill the mold complete parts can be.
5. Improper pressure-holding. Mainly premature pressure transfer, that is, the pressure-holding switching point adjustment is too large, the remaining more material volume by pressure-holding to supplement the weight of the part is bound to be insufficient and under-injection, you should readjust the pressure-holding conversion position to the best point, so that the part is complete.
6. Mold temperature is too low. When the shape and thickness of the parts change greatly, too low mold temperature will consume too much injection pressure, raise the mold temperature or reset the molded waterway.
7. Poor fit between nozzle and mold gate. The injection nozzle overflows during injection and loses part of the material volume. Readjust the mold to make it fit well with the injection nozzle.
8. The nozzle hole is damaged or partially blocked. When choosing the seatback production, the injection nozzle and mold due to a long time of continuous impact, easy to make the injection hole by the small, that is, the material flow channel becomes small, the area of the material strip than the capacity increases, will make the cold material block the injection nozzle hole or consume too much injection pressure. The injection nozzle should be removed to repair or clean up, properly reset the forward termination position of the injection seat, and reduce the impact force to a reasonable value.
9. Wear the over-glue ring. The wear gap between the stop ring and the thrust ring on the screw head is large, and the injection cannot be effectively cut off, so that the front end of the melt that has been measured produces a backflow and a loss of injection fraction, resulting in incomplete parts.
Verify the wearing method of the over glue ring: After the last cycle of injection is completed, switch to manual operation mode, and adjust the injection pressure and speed at a lower value, and then execute the storage material to complete. At this time, observe the degree of obstruction to the advance of the screw position indicator scale when manually executing the injection, which is also to check the degree of leakage of the over-glue ring. The less obstruction, the greater the degree of leakage.
The large degree of wear and tear over the rubber ring should be replaced as soon as possible, otherwise, barely carrying out production, product quality can not be guaranteed.
10. Poor mold exhaust. In the injection process
, the air in the mold cavity is too late to discharge from the parting surface or the ejector gap so that the last melt entering the mold cavity is constantly compressed by the high air pressure blocked, leaving a defect at the end of the material flow blocked and can not be fused.
In the parting face should be blocked air position to open a moderate exhaust channel. If the air blocking position is not in the parting surface, you can use the original sleeve or ejector pin to change the internal exhaust can also be used, or re-select the location of the gate, so that the air is discharged according to the expected location.
11. The rib position of the part is too thin or too deep. These are the dead ends where air can be easily stored, and they are also the places where it is difficult to fill the mold, so thicken the ribs or increase the rounded angle of the root.
12. uneven manifold or sprue channel. Due to the continuous improvement of mold manufacturing technology and design level, the majority of runner designs for single-headed mold rubber are reasonable and meet the molding requirements. Here refers to the distribution of multi-cavity runners, often there is a small difference in each gate, which will lead to uneven injection into the cavities of the material flow fraction so that some cavities filled, some cavities are still under-injection.