Improvement method of unstable injection volume in injection molding

In injection molding, there is often a bad phenomenon. After a period of time, the product is OK, but after a period of time, there will be various bad phenomena, such as lack of material, flash, pattern, shrinkage pit, etc. The reasons for this situation are the stability of materials and the difference of molding conditions. We call the instability of the molding product in size, appearance, weight and other aspects caused by the difference of molding conditions as the instability of injection volume.
Generally, the difference of molding conditions mainly includes the following four aspects: injection pressure, mold temperature, metering, and exhaust.
1. Injection pressure mainly refers to insufficient pressure. The general injection molding process is injection → pressure maintaining → cooling (metering). The injection-pressure holding stage should be the process of pressing the melted resin through pressure. When the pressure is low, the amount of resin pressed will easily become unstable. There are various reasons for this pressure shortage, as follows: the resin temperature is low; The mold temperature is low; The injection speed is slow; Low pressure holding; The holding time is too short; VP switch position too early; The channel parts of the main flow channel, diversion channel and gate are too thin, resulting in poor pressure transmission; The resin fluidity is poor, so the pressure loss is large; There are particularly thick parts in the thickness, etc.
2. The mold temperature control is unstable. When the mold temperature control is unstable, it is particularly easy to be associated with size eccentricity or deviation. According to the specific situation of the mold, it is sometimes difficult to adjust the local temperature of the plastic hole bolt, which aggravates the deviation.
3. The metering is not stable. If the metering is not stable, the amount of resin injected will also be unstable. In this way, the possibility of deviation between injections increases.
4. When the exhaust is poor, the exhaust port is weak, and the exhaust is not smooth, the filling volume sometimes becomes unstable.
Corresponding improvement measures.
1. Fully apply pressure maintaining
For some (even local) reason, the actual pressure retaining may be unstable. Therefore, the following countermeasures should be taken. Because the average size will be too large, it is necessary to set different standards for process management.
Molding conditions: increase the resin temperature; Increase the pressure retaining; Increase mold temperature; Extend the pressure holding time and accelerate the injection speed; Delay VP switching position.
Mold: expand the main runner, splitter, gate, etc; The wall thickness shall be homogenized as much as possible, and the thickness standard is 2-4t.
Materials: use materials with good fluidity.
2. Check mold temperature machine
During water temperature control, please check whether the temperature control channel near the problem location is unblocked. In particular, the temperature at the plastic hole plug is easy to rise, so it should be controlled as much as possible. If it is an electric heater, please check the position of the heater.
3. Keep the measurement stable
The unstable measurement is partly caused by the injection molding machine equipment, such as screw wear, sleeve wear, seal leakage, etc. The equipment needs to be overhauled, the causes found out, and repaired or replaced.
4. Improve exhaust conditions
Occasionally, the exhaust port is not smooth and the size is unstable. At this time, it is necessary to reduce the injection speed or strengthen the exhaust port to make the exhaust smooth.