Why plastic mold injection parts will be underfilled? How can I remedy it?

Release time:2023-12-19
Why plastic mold injection parts will be underfilled? How can I remedy it?

Plastic mold injection molding parts filled with the reasons and their remedies
1. Characteristics of injection molded parts that are not injection molded properly
The injection process is incomplete because the mold cavity is not filled with plastic or the injection process is missing some details.
2.Possible causes of problems
(1). Insufficient injection speed.
(2). Shortage of plastic.
(3). Screw not leaving screw bedding at the end of its stroke.
(4). Variation in running time.
(5). Injection cylinder temperature too low.
(6). Insufficient injection pressure.
(7). Nozzle partially blocked.
(8). Heater outside of nozzle or injection cylinder not functioning.
(9). Injection time is too short.
(10). Plastic sticks to hopper throat wall.
(11). Injection molding machine capacity is too small (insufficient injection strength or plasticizing capacity).
(12). Mold temperature too low.
(13). Failure to clean the mold of rust preventive oil.
(14). Damaged stop ring with backflow of melt.

3. Remedies
(1). Increase the injection speed.
(2). Check the amount of plastic inside the hopper.
(3). Check if the injection stroke is set correctly and change it if necessary.
(4). Check that the non-return valve is not worn or cracked.
(5). Check for stable operation.
(6). Increase the melt temperature.
(7). Increase the back pressure.
(8). Increase the injection speed.
(9). Check the nozzle hole for foreign matter or unplasticized plastic.
(10). Check all heater outer layers for correct energy output with an ammeter.
(11). Increase screw forward time.
(12). Increase the amount of cooling in the throat area of the hopper or reduce the temperature in the rear area of the injection cylinder.
(13). Use a larger injection molding machine.
(14). Increase the mold temperature appropriately.
(15). Clean the rust inhibitor in the mold.
(16). Check or replace the stop ring.

Dimensional differences in injection molded parts
1. Characteristics of injection molded part defects
The variation of weight dimensions during the injection molding process exceeds the production capacity of the mold, injection molding machine, and plastic combination.
2. Possible causes of the problem
(1). Uneven plastic input into the injection cylinder.
(2). Temperature or fluctuation range of injection cylinder is too large.
(3). Injection molding machine capacity is too small.
(4). Unstable injection pressure.
(5). Unstable screw reset.
(6). Variation in operating time, inconsistent solution viscosity.
(7). Unstable injection speed (flow control).
(8). Use of plastic varieties that are not suitable for the mold.
(9). Consider the effect of mold temperature, injection pressure, speed, time and holding pressure on the product.
3. Remedies
(1). Check that there is sufficient cooling water flowing through the hopper throat to maintain the correct temperature.
(2). Check for poor quality or loose thermocouples.
(3). Check that the thermocouple used with the temperature controller is of the correct type.
(4). Check the injection volume and plasticizing capacity of the injection molding machine and compare it with the actual injection volume and the amount of plastic injected per hour.
(5). Check that there is a steady flow of molten hot material in every operation.
(6). Check the backflow preventer valve for leakage and replace it if necessary.
(7). Check for incorrect feed settings.
(8). Ensure that the screw's return position is stable,not more than 0.4mm change in each operation.
(9). Check for inconsistencies in operating time.
(10). Use back pressure.
(11). Check for proper hydraulic system operation and high or low oil temperature (25 to 60°C).
(12). Select the right type of plastic for the mold (mainly from shrinkage and mechanical strength considerations).
(13). Re-adjust the whole production process.
Shrink marks
1. Characteristics of injection molded part defects
Usually associated with surface marks, and is formed when the plastic shrinks away from the mold surface.
2. Possible causes of the problem
(1). Melt temperature is either too high or too low.
(2). Insufficient plastic in the mold cavity.
(3). Overheating of the surfaces in contact with the plastic during the cooling phase.
(4). Irrational flow channel, too small gate section.
(5). Whether the mold temperature is compatible with the characteristics of the plastic.
(6). The product structure is not reasonable.
(7). The cooling effect is not good, the product continues to shrink after demolding.
(1). Adjust the temperature of the injection cylinder.
(2). Adjust the screw speed to get the correct screw surface speed.
(3). Increase injection volume.
(4). Ensure that the correct bedding material is used, increase screw forward time:increase injection pressure:increase injection speed.
(5). Check that the stopcock is correctly installed, as abnormal operation can lead to pressure loss.
(6). Reduce the surface temperature of the mold.
(7). Correct the runner to avoid excessive pressure loss: Enlarge the cross-section according to the actual need.
(8). Control the mold temperature according to the characteristics of the plastic used and the structure of the product.
(9). Improvement of the product structure where possible.
(10). Try to allow sufficient cooling of the product.

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