how to solve the insufficient filling injection parts

how to solve the insufficient filling injection parts

The first mock exam is short shot, insufficient filling and dissatisfactory parts. It is commonly known as under injection, which means that some incomplete phenomena at the end of the material flow, or a part of the cavity filled with a few dissatisfied parts, especially the end area of the thin wall area or the flow path. It shows that the melt condenses without filling the mold cavity, and the molten material does not fill completely after entering the mold receiving cavity, resulting in the lack of material in the product.

The main reason for short injection is that the flow resistance is too large, which makes the melt unable to continue to flow. The factors influencing the melt flow length include: the wall thickness of the part, mold temperature, injection pressure, melt temperature and material composition. If these factors are not handled well, it will cause short injection.
1. Improper equipment selection
When using the equipment, the maximum injection volume of the injection molding machine must be greater than the total weight of the plastic part and nozzle, and the total injection weight cannot exceed 85% of the plastic volume of the injection molding machine.
2. Insufficient supply
At present, the commonly used method to control the feeding is the constant volume feeding method. Whether the roller material quantity is uniform with the fruit grain diameter of the raw material, and whether there is a "bridge" phenomenon at the bottom of the feeding port. If the temperature at the feeding port is too high, it will also cause poor blanking. In this regard, the feeding port should be dredged and cooled.
3. Poor material fluidity
When the fluidity of raw materials is poor, the structure parameters of the die are the main reason for the under injection. Therefore, it is necessary to improve the stagnant flow defects of the mold pouring system, such as setting the sprue position reasonably, enlarging the sprue, the runner and the size of the sprue, and using a larger nozzle. At the same time, some additives can be added to the raw material formula to improve the flow performance of the resin. In addition, it is also necessary to check whether the amount of raw material is excessive and reduce the amount properly.
4. Excessive lubricant
If there is too much lubricant in the raw material formula, and the wear clearance between the feed screw check ring and the barrel is large, the refluxing of the melt in the barrel will cause the shortage of feed and the lack of injection. Therefore, it is necessary to reduce the amount of lubricant, adjust the gap between the barrel and the injection screw and the check ring, and repair the equipment.
5. Cold material impurities block the material channel
When the impurities in the molten material block the nozzle or the cold material block
When gate and runner, the nozzle should be folded down to clean or expand the cold cavity and runner section of the mold.
6. Unreasonable design of pouring system
When the first mock exam is multi chamber, the appearance defects of plastic parts often result from unreasonable design of gate and runner balance. When designing the gating system, we should pay attention to the balance of the gates. The weight of the plastic parts in each cavity should be proportional to the size of the gates, so that the cavities can be filled at the same time. The gate location should be at the thick wall, or the design scheme of balanced layout of the shunt channel can be adopted.
If the gate or runner is small, thin and long, the pressure loss of molten material along the flow process is too large, the flow is blocked, and it is easy to produce poor filling. For this reason, the runner section and gate area should be enlarged, and the method of multi-point feeding can be adopted if necessary.
7. Poor mold exhaust
When a large amount of residual gas in the mold due to poor exhaust is squeezed by the flow material, which produces a high pressure greater than the injection pressure, it will prevent the melt from filling the mold cavity and cause under injection. In this regard, it is necessary to check whether there is a cold material hole or its position is correct. For the mold with a deep cavity, an exhaust groove or exhaust hole should be added at the under injected part;
On the die closing surface, an air vent with a depth of 0.02-0.04mm and a width of 5-10 mm can be set. The air vent shall be set at the final filling position of the cavity.
When using raw materials with excessive moisture and volatile content, a lot of gas will be produced, which will lead to poor exhaust of the mold. At this time, the raw materials shall be dried and volatile substances shall be removed.
In addition, in the process operation of the mold system, the poor exhaust can be improved by improving the mold temperature, reducing the injection speed, reducing the flow power of the gating system, reducing the mold closing force, increasing the mold gap and other auxiliary measures.
8. Mold temperature too low
When the melt enters the low temperature mold cavity, it will not be able to fill every corner of the mold cavity because of the fast cooling. Therefore, it is necessary to preheat the mold to the temperature required by the process before starting the machine. When starting the machine, the amount of cooling water in the mold should be properly controlled. If the mold temperature cannot rise, check whether the design of the mold cooling system is reasonable
9. Melt temperature too low
Generally, in the range suitable for molding, the material temperature and filling length are close to a positive proportion, and the flow performance of low-temperature melt is decreased, which makes the filling length shorter. When the material temperature is lower than the temperature required by the process, it is necessary to check whether the barrel feeder is in good condition and try to increase the barrel temperature.
When the machine is just started, the temperature of the barrel is lower than that indicated by the instrument of the barrel heater. It should be noted that it will take a while for the barrel to start after it is heated to the temperature of the instrument. If the injection at low temperature is necessary to prevent the decomposition of the melt, the injection cycle time can be appropriately prolonged to overcome the under injection. For screw injection molding machine, the temperature of the front section of the barrel can be increased properly.
10. Nozzle temperature too low
In the process of injection, the nozzle is in contact with the mold. Because the mold temperature is generally lower than the nozzle temperature, and the temperature difference is large, the frequent contact between the two will reduce the nozzle temperature, resulting in the freezing of molten materials at the nozzle.
If there is no cold cavity in the mold structure, the cold material will solidify immediately after entering the cavity, so that the hot melt material behind the plug can not fill the cavity. Therefore, the nozzle should be separated from the mold when opening the mold, so as to reduce the influence of mold temperature on the nozzle temperature and keep the temperature at the nozzle within the range required by the process.

If the nozzle temperature is very low and cannot be raised, check whether the nozzle heater is damaged, and try to raise the nozzle temperature, otherwise, the pressure loss of the flow material will cause under injection.

11. Insufficient injection pressure or pressure maintaining
The relationship between injection pressure and filling length is close to positive proportion. The injection pressure is too small, the filling length is short, and the cavity is not filled. In this regard, the injection pressure can be increased by slowing down the injection forward speed and prolonging the injection time appropriately. When the injection pressure can not be further improved, it can be remedied by increasing the material temperature, reducing the viscosity of the melt and improving the melt flow performance. It should be noted that too high material temperature will make the melt decompose and affect the performance of plastic parts.
In addition, if the holding time is too short, it will also lead to insufficient filling. Therefore, the pressure holding time should be controlled within the appropriate range, but it should be noted that too long pressure holding time will cause other faults, and the molding should be adjusted according to the specific situation of the plastic parts.
12. Injection speed is too slow
The injection speed is directly related to the filling speed. If the injection speed is too slow, the mold filling of the melt is slow, and the melt with low speed flow is easy to cool, which further reduces its flow performance and results in under injection.
Therefore, the injection speed should be increased properly. However, it should be noted that if the injection speed is too fast, it is easy to cause other molding failures.
13. Unreasonable plastic structure design
When the thickness and length of the plastic part are not in proportion, the shape is very complex and the forming area is large, the molten material flow is easily blocked at the entrance of the thin-walled part of the plastic part, which makes the cavity difficult to be filled. Therefore, when designing the shape and structure of the plastic part, it should be noted that the thickness of the plastic part is related to the limit flow length of the molten material when filling the mold.
In addition, in the process of forming complex structural plastic parts, necessary measures should also be taken, such as reasonable determination of gate position, proper adjustment of flow channel layout, improvement of injection speed or adoption of rapid injection. Improve mold temperature or select resin with better flow performance.
resolvent
Improper control of process conditions. It should be adjusted properly.
The injection capacity of injection molding machine is less than the weight of plastic parts. The injection molding machine with larger specifications should be replaced.
Runner and gate sections are too small. It should be increased appropriately.
The flow distance of the molten material in the mold cavity is too long or there is a thin-walled part. Cold pockets shall be provided.
The mold exhaust is bad, and the residual air in the cavity leads to under injection. The exhaust system of the mould should be improved.
The fluidity of raw materials is too poor. The resin with better fluidity should be used instead.
Under injection can also be caused by too low barrel temperature, insufficient injection pressure or too short injection time for replenishment. The control quantity of relevant process parameters should be increased accordingly.