1 Use plastics with low viscosity and sound fluidity or adjust prescription of plastics and reduce viscosity of melt;

2 Improve barrel temperature, increase injection pressure, raise melt temperature to reduce erection degree, and improve plastication quality;

3 Improve mold temperature and uniformity thereof, raise nozzle temperature and properly set cold-slug well ;

4 Increase dimension of the runner and gate and properly set gate position to avoid overlong flow during filling and overlarge loss of pressure when the melt enters cavity;

5 Properly design mold exhausting scheme and change number of position of gate as well as position of parting line when necessary to achieve sound exhausting effect;

6 Select proper injection machine and correctly adjust screw injection stroke to ensure sufficient actual quantity of injection; meanwhile, it should be ensured that the melt stored in the plastication room at the front of the screw can perfectly transmit pressure. Check the plastic raw material in the hopper of injection machine in due course to see whether it is sufficient;

7 Increase injection pressure, injection rate and the filling power of melt; meanwhile, check whether the non-return valve on the screw is damaged to avoid pressure caused by the counterflow of melt as well as loss of melt during injection;

8 Improve structure of plastic parts and design of wall thickness, reduce complication of structure, improve uniformity of wall thickness and properly design wall thickness to reduce structural resistance during the melt filling stroke.

Injection molding is not enough, referring to the phenomenon of partial incompleteness at the end of the injection plastic flow or a part of a mold cavity is not filled, especially the thin-walled area or the end area of the flow path. It is manifested that the melt condenses without filling the cavity, and the melt is not completely filled after entering the cavity, resulting in the lack of material in the product.

What causes injection molding is not enough?
The main reason for short injection is that the flow resistance is too large, causing the melt can not continue to flow. Factors affecting the melt flow length include: wall thickness of the part, mold temperature, injection pressure, melt temperature and material composition. These factors can cause short injection if not handled properly.

Hysteresis effect: also called stagnant flow, if there is a relatively thin structure, usually reinforcement bars, etc., at a location closer to the gate, or at a location perpendicular to the flow direction, then during the injection process, the melt will encounter a relatively large forward resistance when passing through the location, and in the flow direction of its main body, due to the smooth flow, no flow pressure can be formed, and only when the melt is filled in the main body direction, or enters the holding pressure will sufficient pressure be formed to fill the stagnant part, and at this time, because the position is very thin, and the melt does not flow without heat replenishment, it has been cured, thus causing under-injection.

How to solve the injection molding underfill?
1.Under-injection defect elimination methods.
–Material

Increase the fluidity of the melt

Reduce the addition of recycled materials

Reduce the decomposition of gas in raw materials

–Mold design

The location of the gate is designed to ensure that it fills the thick wall first to avoid stagnation, which can lead to premature hardening of the polymer melt.

Increase the number of gates to reduce the flow ratio.

Increase the runner size to reduce the flow resistance.

Proper location of the venting port to avoid poor venting (see if the under-injection area is burnt).

Increase the number and size of exhaust port.

Increase the design of cold material well to discharge cold material.

The distribution of cooling water channel should be reasonable to avoid causing the local temperature of the mold to be low.

–Injection molding machine

Check whether the non-return valve and the inner wall of the barrel are seriously worn, the above wear will lead to serious loss of injection pressure and injection volume.

Check whether there is material at the filling port or whether it is bridged

Check whether the capacity of the injection molding machine can reach the required capacity of the molding

–Process conditions

Increase the injection pressure

Increase the injection speed and enhance the shear heat

Increase the injection volume

Increase the barrel temperature and mold temperature

Increase the melt length of the injection molding machine

Decrease the buffer volume of the injection molding machine

–Extend the injection time

Reasonably adjust the position of each section of injection and the speed and pressure of injection.

–Part design

The wall thickness of the part is too thin.

There are reinforcement bars in the part that cause stagnation.

Large differences in the thickness of the part, causing stagnation in the local appearance, can not be avoided by mold design.

2. Measures to solve the problem of stall under-injection.
(1) Increase the thickness of the stagnant part, the thickness difference of the parts should not be too big, the disadvantage is that it is easy to cause shrinkage.

(2) change the location of the gate to the end of the filling, so that the location to form pressure.

(3) reduce the speed and pressure of injection molding, so that the early stage of filling on the front of the material flow to form a thicker curing layer, that increase the melt pressure, this method is our common measures.

(4) The use of materials with good flowability.

Material Viscosity
Material viscosity plays a vital role in short shot injection molding. Highly viscous materials can cause flow problems as it may not fill the mold cavities swiftly before the cooling phase sets in. If the raw material is very thick or viscous, it will need more force (pressure or heat) to fill the mold. Short shot defects can occur if the material’s viscosity isn’t taken into account during the process setup. The solution here lies in fine-tuning the material’s melt temperature or even choosing a material with lower viscosity, suitable for the specific molding process and part design.

Improper Venting
Improper venting poses a significant problem for successful injection molding. Without proper venting, air gets trapped in the mold cavities and impedes the plastic material flow. The result is a short shot, with voids or incomplete areas in the final part. To overcome this, you should ensure the mold design includes vents to allow air and other gases to escape from the mold cavities during the injection process—poor venting translates to poor quality products.

Material Variations
Material variations can significantly impact the injection molding process, leading to short shots. If the plastic material’s properties are inconsistent, it can affect the flow and filling of the mold. For instance, variations in the material’s moisture content, temperature, or composition can alter its behavior during the molding process. The solution is to ensure a consistent supply of material, properly dried and stored to maintain its properties. Regular checks and quality control measures can help identify and rectify any material inconsistencies.

Improper Machine Settings
Improper machine settings are a common cause of short shot injection molding. If the settings on the injection molding machine are incorrect, it can lead to incomplete filling of the mold. This includes incorrect injection pressure, speed, or temperature settings. Regular maintenance and calibration of the injection molding machine are crucial to ensure that it operates under the right conditions. It’s also important to train operators to understand the machine settings and adjust them appropriately for different materials and molds.

Low Fill Volume
Low fill volume is another factor that can lead to short shots. If there isn’t enough material injected during the first stage of the molding process, the mold may not fill completely. This can be due to an insufficient injection volume or a problem with the machine’s feed system. The solution is to ensure that the fill volume is set correctly according to the part’s size and complexity, and the machine’s feed system is functioning properly.

Insufficient Pack and Hold Pressure
Insufficient pack and hold pressure can also cause short shots. After the initial injection of plastic into the mold, additional pressure is applied to pack more material into the mold and compensate for shrinkage as the plastic cools. If the pack and hold pressure is too low, the mold may not fill completely, leading to a short shot. The solution is to adjust the pack and hold pressure settings on the injection molding machine to ensure that they are high enough to fully pack the mold.

Low Melt Temperature
Low melt temperature can prevent the plastic material from flowing properly, leading to short shots. If the melt temperature is too low, the plastic may not be fluid enough to fill the mold completely before it starts to solidify. The solution is to increase the melt temperature to improve the material’s flow properties. However, care must be taken not to set the temperature too high, as this can degrade the plastic and affect the part’s properties.

Low Mold Temperature
Similarly, if the mold temperature is too low, the plastic may start to solidify before it has fully filled the mold, leading to a short shot. The solution is to increase the mold temperature to slow down the cooling rate of the plastic, giving it more time to fill the mold. However, the mold temperature must be carefully controlled to prevent the plastic from overheating and degrading.

Slow Injection Speed
Slow injection speed can also lead to short shot injection molding. If the speed at which the molten plastic is injected into the mold is too slow, the material may begin to cool and solidify before the mold is completely filled. This can result in a short shot, where part of the mold cavity remains unfilled. To solve this issue, the injection speed should be increased to ensure that the mold is filled before the plastic has a chance to cool. However, the speed should not be so high that it causes excessive pressure or stress on the mold and machine.

Inappropriate Mold Design
Inappropriate mold design is another significant cause of short shot injection molding. If the mold design has flow restrictions, poor venting, or complex geometries that are hard to fill, it can lead to short shots. The solution to this problem often involves a redesign of the mold to improve the flow of plastic, enhance venting, and simplify the part geometry if possible. Using simulation software can help identify potential issues in the mold design before it’s manufactured.

Inconsistent Production Cycle
An inconsistent production cycle can also lead to short shot injection molding. If the machine is frequently stopped and started, or if the cycle times vary significantly, it can affect the consistency of the molded parts. This can lead to variations in the material’s temperature and flow properties, which can cause short shots. The solution is to maintain a consistent production cycle, with regular checks and adjustments to ensure that the machine is operating smoothly and consistently.

Foreign Material Contamination
Foreign material contamination is another cause of short shot injection molding. If foreign materials get into the plastic or the mold, they can block the flow of plastic and prevent the mold from filling completely. This can be caused by poor material handling practices or a lack of cleanliness in the molding area. The solution is to implement strict material handling and cleanliness procedures to prevent contamination. Regular checks of the material and the mold can also help identify and remove any foreign materials.