Plastic Injection Parts Shortage

A fundamental tenet of plastic injection parts shortage

Plastic Injection Parts Shortage, also known as under injection, short shot, insufficient filling, etc, describes the situation where the plastic melt enters the cavity of the mold but does not fill every.

Plastic injection parts shortage: Causes of flaws and techniques for improvement

• Incorrect equipment choice:

The maximum injection volume of the injection molding machine must be more than the weight of the plastic parts when choosing injection molding equipment. During the inspection, the overall injection volume (including plastic components and runner condensate) cannot be greater than 85% of the injection machine’s plasticizing volume. Otherwise, the products that are opened are extremely prone to plastic injection parts shortage.

• Insufficient feeding:

That is, there may be a “bridge” phenomenon at the bottom of the injection molding machine’s hopper’s feeding port. The solution is to appropriately increase the injection stroke of the screw to increase the feeding amount.

• Poor flow performance of raw materials:

Trying to improve the stagnation defect of the mold gating system, such as setting the position of the runner reasonably, expanding the size of the gate, the runner, etc, and using a larger nozzle. At the same time, an appropriate amount of additives can be added to the raw material formula to improve the flow properties of plastics.

• An excessive amount of lubricant:

Reduced the amount of lubricant or adjust the gap between the barrel and the screw.

• Impurities in the cold material block the runner:

The nozzle should be disassembled to clean up or expand the cross-section of the cold material cavity and runner.

• The gating system’s design is illogical:

It should be noted that when designing the gating system, the weight of the inner plastic part that balances the gate is proportional to its size to ensure that each cavity is filled during repair, the gate position should be chosen at the thick-walled part, or the design scheme of balanced arrangement of runners is adopted.

The pressure loss of the melt throughout the flow process will be extremely high if the gate or runner is small, thin, and long. This will make it simple to stop the flow and cause the phenomena of poor filling. The runner cross-section and gate area should be increased to address this problem, and multi-point feeding can be employed if necessary.

• Poor mold exhaust:

Trapped air causes body flow to be blocked. Check for cold slug pockets or the correct location of the cold slug pockets. For molds with a deep cavity, additional vent grooves or vent holes can be added. On a reasonable parting surface, vent grooves with a depth of 0.02~0.04mm and a width of 5~10mm can be set up. The vent holes should be set in the mold. final filling of the cavity.

In addition, a large amount of gas will be generated when using raw materials with excessive moisture and volatile content, resulting in the poor exhaust of the mold. At this time, the raw materials should be dried to remove the volatile substances. In terms of the injection molding process, auxiliary measures such as increasing the mold temperature, reducing the injection speed, and reducing the flow resistance of the gating system can be used to reduce the clamping force and increase the mold gap to improve the poor exhaust phenomenon.

• Mold temperature is too low:

The mold must be preheated to the temperature required by the process before starting the machine. When the machine is just turned on, 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.

• The nozzle temperature is too low:

the nozzle should be separated from the mold when the mold is opened to reduce the influence of the mold on the nozzle temperature and keep the temperature at the nozzle within the range required by the process.

• Insufficient injection pressure or holding pressure:

The injection pressure and the filling process are close to a proportional relationship. If the injection pressure is too small, the filling process will be shortened, resulting in insufficient filling of the cavity. In this regard, the injection pressure can be increased by reducing the forward speed of the screw and appropriately extending the injection time.

• The rate of injection is too slow:

The melt-filling speed is directly correlated with the injection speed, therefore, the injection speed is too sluggish. Slow melt filling results from excessively slow injection speed. The melt flow performance is further decreased, leading to Plastic injection parts shortage issues, because the melt flowing at a low speed is simple to cool. In this regard, the injection speed needs to be increased suitably.

• The structural design of the plastic part is unreasonable:

When the ratio of the width of the plastic part to its thickness is too large or the shape is very complex and the molding area is large, the melt is easily blocked at the entrance of the thin-walled part of the plastic part, making it difficult to fill the cavity and resulting Plastic injection parts shortage.  Therefore, when designing the shape and structure of the plastic part, attention should be paid to the relationship between the thickness of the plastic part and the limited filling length of the melt.

Experience shows that the wall thickness of injection-molded plastic parts is mostly 1~3mm, the wall thickness of large plastic parts is 3~6mm, and the thickness of plastic parts exceeds 8 mm or is less than 0.5 mm, which is not good for injection molding and should be avoided in the design of parts of this thickness.

What are the reasons for the Plastic Injection parts shortage?

1. The melt temperature is too low.

2. The injection pressure is too low or the oil temperature is too high.

3. Insufficient melt amount (insufficient injection amount).

4. The injection time is too short or the pressure holding switch is too early.

5. The injection speed is too slow.

6. Uneven mold temperature.

7. The mold temperature is low.

8. Poor mold exhaust (trapped air).

9. The nozzle is blocked or leaking glue (or the heating ring is burned out).

10. The number and position of gates are not suitable, and the glue feeding is uneven.

11. The runner, the gate is too small or the runner is too long.

12. There is insufficient lubricant in the raw material.

13. Wear of screw check ring (over the apron).

14. The machine capacity is not enough, or the plastic in the hopper is not cut.

15. The wall thickness of the finished product is unreasonable or too thin.

16. Poor melt flow (low FMI).

Plastic Injection parts shortage: The improvement method is as follows

1.Increase the barrel temperature.
2. Increase the injection pressure or clean the condenser.
3. Increase the metering stroke.
4. Increase injection time or delay. switching holding pressure.
5. Speed up the injection speed.
6. Reopen the molded waterway.
7. Increase the mold temperature.
8. Add venting grooves or venting. needles at appropriate locations.
9. Remove, clean, or realign the nozzle.
10. Reset the gate and adjust the balance.
11. Increase the size of the runner, or gate or shorten the runner.
12. Add lubricant as appropriate (to improve fluidity).
13. Remove the check ring and repair or replace it.
14. Replace larger machines or check and improve the blanking situation.
15. Improve the thickness of the glue or thicken the thin position.
16. Switch to plastic with better fluidity.